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Publisher: Elsevier   (Total: 2812 journals)

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Telematics and Informatics     Hybrid Journal   (Followers: 5, SJR: 0.412, h-index: 26)
Terrestrial Ecology     Full-text available via subscription   (Followers: 2)
Tetrahedron     Hybrid Journal   (Followers: 35, SJR: 1.141, h-index: 171)
Tetrahedron Letters     Hybrid Journal   (Followers: 24, SJR: 0.933, h-index: 130)
Tetrahedron Organic Chemistry Series     Full-text available via subscription   (Followers: 10)
Tetrahedron: Asymmetry     Hybrid Journal   (Followers: 7)
Textile Science and Technology     Full-text available via subscription   (Followers: 5)
The Alkaloids: Chemistry and Biology     Full-text available via subscription   (Followers: 1, SJR: 0.348, h-index: 20)
The American J. of Cardiology     Hybrid Journal   (Followers: 27, SJR: 2.315, h-index: 169)
The American J. of Emergency Medicine     Hybrid Journal   (Followers: 23)
The American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 2, SJR: 1.322, h-index: 36)
The American J. of Medicine     Hybrid Journal   (Followers: 40, SJR: 1.847, h-index: 168)
The American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
The American J. of Surgery     Hybrid Journal   (Followers: 23, SJR: 1.328, h-index: 114)
The Arts in Psychotherapy     Hybrid Journal   (Followers: 7)
The Breast     Hybrid Journal   (Followers: 6)
The British Accounting Review     Hybrid Journal   (Followers: 6, SJR: 0.634, h-index: 34)
The Chemical Physics of Solid Surfaces     Full-text available via subscription  
The Cytoskeleton: A Multi-Volume Treatise     Full-text available via subscription  
The Electricity J.     Partially Free   (Followers: 3, SJR: 0.517, h-index: 25)
The Enzymes     Full-text available via subscription   (Followers: 1, SJR: 0.339, h-index: 7)
The Extractive Industries and Society     Hybrid Journal  
The Foot     Hybrid Journal   (Followers: 8)
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The History of Neuroscience in Autobiography     Full-text available via subscription   (Followers: 1)
The Internet and Higher Education     Hybrid Journal   (Followers: 69, SJR: 2.565, h-index: 40)
The Intl. J. of Accounting     Hybrid Journal   (Followers: 1)
The Intl. J. of Biochemistry & Cell Biology     Hybrid Journal   (Followers: 4, SJR: 2.423, h-index: 128)
The J. for Nurse Practitioners     Hybrid Journal   (Followers: 4, SJR: 0.136, h-index: 7)
The J. of Arthroplasty     Hybrid Journal   (Followers: 36)
The J. of Chemical Thermodynamics     Hybrid Journal   (Followers: 2, SJR: 1.292, h-index: 52)
The J. of Foot and Ankle Surgery     Full-text available via subscription   (Followers: 11)
The J. of Hand Surgery     Full-text available via subscription   (Followers: 28)
The J. of Heart and Lung Transplantation     Hybrid Journal   (Followers: 5, SJR: 2.881, h-index: 86)
The J. of High Technology Management Research     Hybrid Journal   (Followers: 1, SJR: 0.245, h-index: 26)
The J. of Logic and Algebraic Programming     Hybrid Journal   (Followers: 2, SJR: 0.647, h-index: 38)
The J. of Mathematical Behavior     Hybrid Journal   (Followers: 1, SJR: 0.766, h-index: 24)
The J. of Molecular Diagnostics     Hybrid Journal   (Followers: 1, SJR: 1.974, h-index: 57)
The J. of Nutritional Biochemistry     Hybrid Journal   (Followers: 1, SJR: 1.627, h-index: 88)
The J. of Pain     Hybrid Journal   (Followers: 9)
The J. of Pediatrics     Hybrid Journal   (Followers: 70)
The J. of Prosthetic Dentistry     Full-text available via subscription   (Followers: 2)
The J. of Socio-Economics     Hybrid Journal   (Followers: 4, SJR: 0.356, h-index: 29)
The J. of Strategic Information Systems     Hybrid Journal   (Followers: 15, SJR: 2.903, h-index: 50)
The J. of Supercritical Fluids     Hybrid Journal   (Followers: 3, SJR: 1.141, h-index: 69)
The J. of the American College of Certified Wound Specialists     Hybrid Journal   (Followers: 1, SJR: 0.14, h-index: 3)
The J. of Thoracic and Cardiovascular Surgery     Hybrid Journal   (Followers: 7, SJR: 2.268, h-index: 143)
The J. of Urology     Full-text available via subscription   (Followers: 57)
The Kaohsiung J. of Medical Sciences     Full-text available via subscription  
The Knee     Hybrid Journal   (Followers: 13, SJR: 1.137, h-index: 44)
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The Lancet Diabetes and Endocrinology     Full-text available via subscription   (Followers: 17)
The Lancet Global Health     Open Access   (Followers: 20)
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The Lancet Psychiatry     Full-text available via subscription   (Followers: 6)
The Lancet Respiratory Medicine     Full-text available via subscription   (Followers: 9)
The Leadership Quarterly     Hybrid Journal   (Followers: 39, SJR: 2.069, h-index: 76)
The North American J. of Economics and Finance     Hybrid Journal   (Followers: 1, SJR: 0.667, h-index: 20)
The Quarterly Review of Economics and Finance     Hybrid Journal   (Followers: 12, SJR: 0.565, h-index: 26)
The Social Science J.     Hybrid Journal   (Followers: 4, SJR: 0.255, h-index: 18)
The Spine J.     Hybrid Journal   (Followers: 13, SJR: 1.493, h-index: 62)
The Surgeon     Hybrid Journal   (Followers: 1, SJR: 0.784, h-index: 25)
The Veterinary J.     Hybrid Journal   (Followers: 10, SJR: 1.005, h-index: 63)
Theoretical and Applied Fracture Mechanics     Hybrid Journal   (Followers: 6, SJR: 1.179, h-index: 35)
Theoretical and Computational Chemistry     Full-text available via subscription   (Followers: 7)
Theoretical Computer Science     Hybrid Journal   (Followers: 4, SJR: 0.932, h-index: 74)
Theoretical Ecology Series     Full-text available via subscription   (Followers: 1)
Theoretical Population Biology     Hybrid Journal   (Followers: 11, SJR: 0.973, h-index: 61)
Theriogenology     Hybrid Journal   (Followers: 2, SJR: 1.059, h-index: 89)
Thermochimica Acta     Hybrid Journal   (Followers: 16, SJR: 0.645, h-index: 77)
Thin Films and Nanostructures     Full-text available via subscription   (Followers: 4)
Thin Solid Films     Hybrid Journal   (Followers: 10, SJR: 0.884, h-index: 130)
Thin-Walled Structures     Hybrid Journal   (Followers: 1, SJR: 1.786, h-index: 38)
Thinking Skills and Creativity     Hybrid Journal   (Followers: 11, SJR: 0.709, h-index: 15)
Thoracic Surgery Clinics     Full-text available via subscription   (Followers: 1, SJR: 0.311, h-index: 35)
Thrombosis Research     Hybrid Journal   (Followers: 24, SJR: 1.098, h-index: 80)
Ticks and Tick-borne Diseases     Hybrid Journal   (Followers: 5, SJR: 0.943, h-index: 12)
Tissue and Cell     Hybrid Journal   (Followers: 2, SJR: 0.464, h-index: 35)
Topics in Companion Animal Medicine     Hybrid Journal   (Followers: 1, SJR: 0.521, h-index: 28)
Topics in Inorganic and General Chemistry     Full-text available via subscription  
Topology     Full-text available via subscription  
Topology and its Applications     Full-text available via subscription   (SJR: 0.663, h-index: 28)
Tourism Management     Hybrid Journal   (Followers: 9, SJR: 1.961, h-index: 80)
Tourism Management Perspectives     Hybrid Journal   (Followers: 1, SJR: 0.476, h-index: 4)
Toxicologie Analytique et Clinique     Full-text available via subscription  
Toxicology     Hybrid Journal   (Followers: 13, SJR: 1.196, h-index: 105)
Toxicology and Applied Pharmacology     Hybrid Journal   (Followers: 12, SJR: 1.429, h-index: 117)
Toxicology in Vitro     Hybrid Journal   (Followers: 7, SJR: 0.923, h-index: 63)
Toxicology Letters     Hybrid Journal   (Followers: 8, SJR: 1.098, h-index: 101)
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Toxicon     Hybrid Journal   (Followers: 3, SJR: 1.008, h-index: 88)
TrAC Trends in Analytical Chemistry     Full-text available via subscription   (Followers: 20, SJR: 2.325, h-index: 103)
Trace Metals and other Contaminants in the Environment     Full-text available via subscription   (Followers: 2, SJR: 0.101, h-index: 5)
Trace Metals in the Environment     Full-text available via subscription   (Followers: 2)
Transactions of Nonferrous Metals Society of China     Hybrid Journal   (Followers: 8, SJR: 0.893, h-index: 27)
Transfusion and Apheresis Science     Hybrid Journal   (SJR: 0.56, h-index: 37)

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Journal Cover   Catalysis Today
  [SJR: 1.378]   [H-I: 142]   [6 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0920-5861
   Published by Elsevier Homepage  [2812 journals]
  • The non-innocent role of cerium oxide in heterogeneous catalysis: A
           theoretical perspective
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): M. Verónica Ganduglia-Pirovano
      Ceria (CeO2) is the most significant of the oxides of rare-earth elements in industrial catalysis with its reducibility being essential to its functionality in catalytic applications. The complexity of real (powder) catalysts hinders the fundamental understanding of how they work. Specifically, the role of ceria in the catalytic activity of ceria-based systems is still not fully understood. To elucidate it, well-defined ceria-based model catalysts are prepared experimentally or created theoretically and studied. The purpose of this brief review is to discuss recent results on model ceria-based catalysts using CeO2(111), VO x /CeO2(111), and Ni/CeO2(111) as examples of catalysts for partial alkyne hydrogenation, oxidative dehydrogenation, and hydrogen production, respectively. The emphasis is here put on theoretical studies and special attention is given to the effects of ceria as catalyst support.
      Graphical abstract image Highlights

      PubDate: 2015-06-24T06:56:26Z
       
  • Dynamic redox properties of vanadium and copper in microporous supports
           during the selective oxidation of propene
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Katrine Lie Bøyesen , Tina Kristiansen , Karina Mathisen
      Vanadium(V) and copper(II) were co-deposited into the microporous neutral AlPO-5 and the acidic ZSM-5, obtaining VCu:AlPO-5 and VCu:ZSM-5. In this study we seek to investigate the effect of feed gas composition for the selective oxidation of propene applying C3H6/O2 ratios from 4 to 0.25 over VCu:AlPO-5 and VCu:ZSM-5. The results from catalytic measurements were correlated with in situ X-ray Absorption Spectroscopy (XAS) to monitor metal speciation for different feeds. VCu:AlPO-5 produces acrolein over the whole feed composition range, reaching maximum yield (1.5%) for C3H6/O2 =0.5. In situ XAS reveal that when the major valence fractions present are the Cu(I)/Cu(II) and V(III)/VIV) redox pairs, the selectivity and activity is improved over VCu:AlPO-5. By comparison, VCu:ZSM-5 produce acrolein for C3H6/O2 =1 and 0.5 only, but with significantly lower yields (0.1% and 0.2%, respectively). At these conditions copper is mainly present as Cu(0), whereas vanadium exists as V(III)/V(IV). We believe activity is governed by the presence of available oxygen associated with a binuclear Cu/V complex in VCu:AlPO-5, not formed in the zeolite. Also, the activity is independent of copper valence state, indicating a possible Cu0/VO x interface is present in VCu:AlPO-5.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Total oxidation of propane in vanadia-promoted platinum-alumina catalysts:
           Influence of the order of impregnation
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Tomas Garcia , Said Agouram , Stuart H. Taylor , David Morgan , Ana Dejoz , Isabel Vázquez , Benjamin Solsona
      Differently prepared vanadium promoted Pt/alumina catalysts have been prepared, characterized and tested for propane total oxidation. V-promoted Pt/Al2O3 catalysts have shown remarkably higher catalytic activity than V-free Pt/Al2O3 catalyst. Among V-promoted Pt catalysts that prepared by coimpregnation gave the highest alkane conversions in the whole range of reaction temperatures studied. Factors such as Pt particle size or the oxidation state of platinum do not seem to be the responsible for the enhanced performance. Modification of the redox properties of the catalyst (i.e. high reducibility of vanadium species) likely provoked by the close contact between platinum particles and vanadium species and the partial introduction of vanadium in the platinum particles can be related to the improved reactivity of the PtV catalysts.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Impact of cerium-based support oxides in catalytic wet air oxidation:
           Conflicting role of redox and acid–base properties
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Gwendoline Lafaye , Jacques Barbier Jr. , Daniel Duprez
      High surface area ceria is an excellent support of metals (Ru, Pt, etc.) for catalytic wet air oxidation reactions (CWAO). Due to the low solubility of oxygen in water, the rate of transfer of O2 from the gas phase toward the catalyst has a decisive impact on the whole oxidation process. The role of the ceria support would be to facilitate this oxygen transfer. Redox properties of ceria (generally measured by the oxygen storage capacity, OSC) have a great impact on this step. Attempts were made to modulate the redox properties of ceria by using mixed oxides: CeO2–ZrO2, CeO2–PrO2–ZrO2 or CeO2–TiO2. In doing so, acid–base properties of the supports are also modified. The role of the redox and acid–base properties on CWAO reactions (acetic acid, aniline and phenol) are reviewed. In most cases, acid–base properties can have a great impact on the catalyst stability (deactivation by carbonates or polymer deposit). Increasing the redox properties may have an adverse effect on the catalytic performances when acid–base properties bias the whole process. In some cases (phenol over CeO2–TiO2 supported catalysts), an adequate Lewis acidity is preferable to a high OSC of the catalyst.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Formation of BaMnO3 in Ba/MnOx–CeO2 catalyst upon the hydrothermal
           ageing and its effects on oxide sintering and soot oxidation activity
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Yuxi Gao , Xiaodong Wu , Shuang Liu , Duan Weng , Hongwei Zhang , Rui Ran
      MnO x –CeO2 mixed oxides were synthesized using a sol–gel method and the barium-loaded catalyst was prepared by a wet impregnation. Both catalysts were hydrothermally aged at 800°C for 10h. The fresh and aged catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), high-resolution transmission electron microscopy (HRTEM), H2 temperature-programmed reduction (H2-TPR), NO temperature-programmed oxidation (NO-TPO) and soot temperature-programmed oxidation (soot-TPO). Compared with MnO x –CeO2, the Ba-modified mixed oxides show a much higher hydrothermal stability. Barium exists in the form of orthorhombic carbonate and cubic nitrate on the fresh sample. BaMnO3 nanoparticles are identified to form at the interface of CeO2 crystallites upon the hydrothermal ageing. The formation of the perovskites prohibits the sintering of ceria significantly, and consequently maintains the redox property of the aged mixed oxides to a great degree. Additionally, the nanoscaled perovskites themselves also contribute to the catalytic activity of the aged oxides catalyst.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Effect of the CeZrNd mixed oxide synthesis method in the catalytic
           combustion of soot
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Jorge González Mira , Verónica Rico Pérez , Agustín Bueno-López
      Ce0.64Zr0.27Nd0.09O δ mixed oxides have been prepared by three different methods (nitrates calcination, coprecipitation and microemulsion), characterized by N2 adsorption, XRD, H2-TPR, Raman spectroscopy and XPS, and tested for soot combustion in NO x /O2. The catalyst prepared by microemulsion method is the most active one, which is related to its high surface area (147m2/g) and low crystallite size (6nm), and the lowest activity was obtained with the catalyst prepared by coprecipitation (74m2/g; 9nm). The catalyst prepared by nitrates precursors calcination is slightly less active to that prepared by microemulsion, but the synthesis procedure is very straightforward and surfactants or other chemicals are not required, being very convenient for scaling up and practical utilization. The high activity of the catalyst prepared by nitrates calcination can be attributed to the better introduction of Nd cations into the parent ceria framework than on catalysts prepared by coprecipitation and microemulsion, which promotes the creation of more oxygen vacancies.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Reactivity and reaction intermediates for acetic acid adsorbed on
           CeO2(111)
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Florencia C. Calaza , Tsung-Liang Chen , David R. Mullins , Ye Xu , Steven H. Overbury
      Adsorption and reaction of acetic acid on a CeO2(111) surface was studied by a combination of ultra-high vacuum based methods including temperature desorption spectroscopy (TPD), soft X-ray photoelectron spectroscopy (sXPS), near edge X-ray absorption spectroscopy (NEXAFS) and reflection absorption IR spectroscopy (RAIRS), together with density functional theory (DFT) calculations. TPD shows that the desorption products are strongly dependent upon the initial oxidation state of the CeO2 surface, including selectivity between acetone and acetaldehyde products. The combination of sXPS and NEXAFS demonstrate that acetate forms upon adsorption at low temperature and is stable to above 500K, above which point ketene, acetone and acetic acid desorb. DFT and RAIRS show that below 500K, bridge bonded acetate coexists with a moiety formed by adsorption of an acetate at an oxygen vacancy, formed by water desorption.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Influence of isovalent and aliovalent dopants on the reactivity of cerium
           oxide for catalytic applications
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): T. Vinodkumar , Bolla Govinda Rao , Benjaram M. Reddy
      The influence of dopant size and valence state on the reduction properties, oxygen defects, and lattice strain in doped ceria has been studied fastidiously. This is of particular importance in environmental application, such as soot and CO oxidation. Herein, isovalent (Zr4+) and aliovalent (La3+, Eu3+, and Sm3+) metal ions doped ceria catalysts were synthesized by coprecipitation method with aqueous ammonia as the precipitant. The interplay of dopant size and valence in the ceria lattice is experimentally analysed in detail at the structural and electronic level by XRD, BET, TEM, Raman, TPR, and XPS techniques, and finally evaluated for soot and CO oxidation reactions. According to the analysis results, the size or the valence of the dopant or both together positively influence the ceria properties. The isovalent substituent (Zr4+), which is different in size with respect to ceria, enhanced the ceria intrinsic activity by decreasing its reduction temperature and oxygen vacancy formation energy, thereby increased the activity. Whereas, aliovalent dopants (La3+, Eu3+, and Sm3+) having different in size and valence compared to pure ceria further improved the structural and catalytic properties of bare ceria by inducing additional oxygen vacancies. The observed activity of doped materials towards soot and CO oxidation reactions is as follows: aliovalent doped ceria>isovalent doped ceria>ceria. The marked influence of isovalent and aliovalent dopants on the ceria properties are highlighted in this study.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Noble metal ion substituted CeO2 catalysts: Electronic interaction between
           noble metal ions and CeO2 lattice
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): M.S. Hegde , Parthasarathi Bera
      In last 40 years, CeO2 has been found to play a major role in the area of auto exhaust catalysis due to its unique redox properties. Catalytic activity is enhanced when CeO2 is added to the noble metals supported Al2O3 catalysts. Reason for increase in catalytic activity is due to higher dispersion of noble metals in the form of ions in CeO2. This has led to the idea of substitution of noble metal ions in CeO2 lattice acting as adsorption sites instead of nanocrystalline noble metal particles on CeO2. In this article, a brief review of synthesis, structure and catalytic properties of noble metal ions dispersed on CeO2 resulting in noble metal ionic catalysts (NMIC) like Ce1−x M x O2−δ , Ce1−x−y Ti x M y O2−δ , Ce1−x−y Zr x M y O2−δ , Ce1−x−y Sn x M y O2−δ and Ce1−x−y Fe x M y O2−δ (M=Pt, Pd, Rh and Ru) are presented. Substitution of Ti, Zr, Sn and Fe in CeO2 increases oxygen storage capacities (OSC) due to structural distortion, whereas dispersion of noble metal ions in Ti, Zr, Sn and Fe substituted CeO2 supports increase both OSC and catalytic activities. Electronic interaction between noble metal ions and CeO2 in NMICs responsible for higher OSC and higher catalytic activities is discussed.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Local structure in CeO2 and CeO2–ZrO2 nanoparticles probed by Eu
           luminescence
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Vasile I. Parvulescu , Carmen Tiseanu
      We report on the local structure properties of trivalent lanthanide-doped CeO2 based nanoparticles by using Eu luminescence as a structural probe. To this aim, we investigate Eu doped CeO2 and CeO2–ZrO2 (Ce/Zr=1) by use of site-selective time-resolved luminescence spectroscopy, in situ/ex situ X-ray diffraction (XRD) and in situ/ex situ Raman spectroscopy. The CeO2 nanoparticles were synthesized by oil in water microemulsion as well as citric acid method and investigated in the as-synthesized state or after calcination in air at 500, 750 and 1000°C. For the as-synthesized Eu–CeO2 nanoparticles by oil-in-water microemusion method, the analysis of the emission/excitation spectra and emission decays of Eu suggest that only surface doping was achieved. In general, the emission of Eu in CeO2 indicates the co-existence of two main Eu centers differentiated by the mode of interaction with the oxygen vacancy. The addition of 10% Eu via wet impregnation onto pre-formed CeO2–ZrO2 followed by calcination induces a remarkable homogenous solid solution of pseudo-cubic phase. The analysis of in situ XRD, in situ Raman and in situ luminescence data evidences for the defect reconfiguration in Eu doped CeO2 during the heating/cooling cycles (30–500 at 30°C). Finally, it is suggested that the structural data inferred from luminescence complements significantly the structural information indicated by X-ray diffraction and Raman spectroscopy, such as the phase content and homogeneity and the presence of defects.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Preface
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): M. Olga Guerrero-Pérez , José Rodríguez-Mirasol , Tomás Cordero



      PubDate: 2015-06-24T06:56:26Z
       
  • Role of surface vanadium oxide coverage support on titania for the
           simultaneous removal of o-dichlorobenzene and NOx from waste incinerator
           flue gas
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): M. Gallastegi-Villa , A. Aranzabal , Z. Boukha , J.A. González-Marcos , J.R. González-Velasco , M.V. Martínez-Huerta , M.A. Bañares
      The catalytic activity of VO x species supported on TiO2 was investigated in the simultaneous destruction of NO and 1,2-dichlorobenzene (o-DCB), as typical pollutants molecules in the off-gases from municipal waste incinerator (MWI) plants. Catalysts with different vanadium loading were prepared in order to obtain different VO x species and characterized by ICP-AES, XPS, N2 adsorption at −196°C, XRD, H2-TPR, Raman and UV–vis–NIR DRS spectroscopy. The characterization results show that molecularly dispersed isolated and polymeric vanadia species form below the dispersion limit loading (“monolayer coverage”), while crystalline species form above it. We used moderate HNO3 treatment to partially leach vanadium oxide species, creating a series of catalysts with variable vanadia loading. The catalytic activity of the VO x /TiO2 catalyst shows that it is able to catalyze the destruction of both pollutants, although higher temperature is required for o-DCB oxidation than for NO reduction. Surface vanadia coverage has a clear effect on TOF and activation energy values, which underline that isolated vanadia species are more efficient for o-DCB oxidation, while the polymeric ones are more efficient for NO reduction.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Re-dispersion of Pd on Ce0.5Zr0.5O2 upon cooling in the presence of oxygen
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Jie Wan , Rui Ran , Xiaodong Wu , Yidan Cao , Min Li , Duan Weng , Kaisheng Huang
      Pd/Ce0.5Zr0.5O2 catalyst was prepared by impregnation method and subjected to different cooling procedures (rapid cooling vs. slow cooling in O2 or in He) after pretreated at 950°C for 30min. The obtained catalysts were characterized by CO chemisorption, transmission electron microscope (TEM), CO temperature-programmed oxidation (CO-TPO), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The results revealed that Pd species on Ce0.5Zr0.5O2 (CZ) suffered severe sintering during high-temperature calcination, but the Pd dispersion increased remarkably after slow cooling in O2. Further investigations ascribed this phenomenon to the Pd re-dispersion process, which needed three essential factors, i.e. sufficient cooling time, oxidizing atmosphere and active support which had strong interaction with Pd species. The re-dispersion process was proved to be mainly due to both the re-oxidization of the sintered Pd particles and the slow migration of the PdO x under the driving of the interaction between Pd and CZ.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253




      PubDate: 2015-06-24T06:56:26Z
       
  • Contents list
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253




      PubDate: 2015-06-24T06:56:26Z
       
  • Catalysis by ceria
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Paolo Fornasiero , Alessandro Trovarelli



      PubDate: 2015-06-24T06:56:26Z
       
  • Invited Review: Some recent developments in the atomic-scale
           characterization of structural and transport properties of ceria-based
           catalysts and ionic conductors
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Masatomo Yashima
      Ceria-based materials are utilized as automotive exhaust catalysts for the removal of noxious compounds, as catalysts for reforming ethanol and methane to produce hydrogen in fuel cells, as materials for solar-energy-to-fuel conversion, and as cathode, anode, and electrolyte materials in solid oxide fuel cells (SOFCs). The present paper is a critical review on the atomic-scale characterization of oxide-ion diffusion pathway, the existing phases, the phase transformations, “metastable” and stable phase diagrams, and oxygen storage capacity (OSC) of ceria-based materials. “Metastable,” compositionally (x) homogeneous t′- and t″-ceria–zirconia Ce x Zr1–x O2 solid solutions (0.2< x <0.9) are key materials to obtain a high OSC, leading to high catalytic activity. Here, the t′- and t″-forms are unstable compared to the two-phase mixture of stable ZrO2-rich tetragonal and CeO2-rich cubic (or t″) phases, but are stable in the partitionless, compositionally homogeneous phases. The axial ratio, c/a F where the subscript F represents the pseudo-fluorite lattice, of the t′-form is larger than unity, while the c/a F ratio of the t″-form equals unity. Formation of the t′- and t″-Ce x Zr1–x O2 is depicted in the “metastable” phase diagram consisting of allotropic phase boundaries in the CeO2–ZrO2 system and is explained using the schematic Gibbs energy–composition (G–x) diagram. The composition (CeO2 content x)-induced t′–t″ transition in Ce x Zr1–x O2 is discrete and of first order. The c–t″ phase transition of Ce x Zr1–x O2 is induced by the oxygen displacement from the regular fluorite position 1/4,1/4,1/4 along the c-axis. The c–t″ transition is continuous and might be of higher order. The c–t″ phase boundary at room temperature is located at around x =0.85–0.9 in both bulk and nanocrystalline Ce x Zr1–x O2. The tetragonal symmetry of compositionally homogeneous nano-sized Ce0.5Zr0.5O2 in air is retained up to 1176K. The c/a F ratio, and the oxygen displacement are smaller in the nanocrystalline Ce0.5Zr0.5O2 than in bulk Ce0.5Zr0.5O2. Bulk oxide-ion diffusion is an important step of oxygen storage and release in ceria-based catalysts, and the oxide-ion diffusivity is essential for high OSC and efficiency of the SOFCs and the solar-energy-to-fuel conversion. The present paper reviews the atomic-scale characterization of ion diffusion in ceria-based catalysts and fluorite-type ionic conductors and discusses the correlation between their bulk ion diffusivity and structural properties. The spatial distributions of neutron scattering length density, bond valence sum (BVS), and bond-valence-based energy (BVE) in the unit cell of tetragonal ceria–zirconia compounds, cubic fluorite-type ceria-based materials, and other fluorite-structured compounds such as Ce0.5Zr0.5O2, CeO2, ceria–yttria Ce0.97Y0.07O1.96, bismuth oxide solid solution δ-Bi1.4Yb0.6O3, and copper iodide α-CuI indicate the three-dimensional network of curved 〈100〉F ion diffusion pathways and anisotropic 〈111〉F thermal vibration of mobile ions, which are responsible for the bulk ion diffusion and conduction. Here, the subscript F denotes the pseudo-fluorite lattice. The BVE distributions of Ce0.5Zr0.5O2 and CeO2 indicate lower activation energy and higher mobility of oxide ions in Ce0.5Zr0.5O2 compared with CeO2.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Biofuel steam reforming catalyst for fuel cell application
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): P. Kowalik , K. Antoniak-Jurak , M. Błesznowski , M.C. Herrera , M.A. Larrubia , L.J. Alemany , I.S. Pieta
      Within the ongoing project, related to fuels and energy production from biomass, agricultural and other wastes, the technology based on SOFC stack and steam reforming is under development. The project aims to present an efficient technology for biogas reforming and continuous supply of reformate fuel to the working SOFC stack. The decision, concerning reforming unit and the stack separation, has been made after detailed analysis of advantages and disadvantages of internal reforming. The set of Ni-based catalysts was prepared and investigated for the external biogas steam reforming. To determine the optimal condition of the reforming process the effect of reaction temperature (RT–773K) for steam to carbon (S/C) molar ratio of 2.5 in the feedstock was investigated. Conversions rates and H2/CO ratios in the produced syngas were influenced by the feedstock composition and catalyst used. The increase in the catalyst activity can be attributed to the specific catalyst–promoter interactions such as the redox capacity of V2O5 and its influence on surface Ni-species.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Synthesis, characterisation and photocatalytic activity of N-doped
           TiO2–Nb2O5 mixed oxides
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): A.M. Ferrari-Lima , R.G. Marques , M.L. Gimenes , N.R.C. Fernandes-Machado
      Nitrogen-doped TiO2 and TiO2–Nb2O5 catalysts were prepared by sol–gel technique using titanium isopropoxide (TIP) and potassium niobate. The obtained samples were subsequently calcined at 380 and 500°C. Undoped TiO2 and TiO2–Nb2O5 samples were also prepared by way of comparison. The photocatalytic activities of the synthesised catalysts were evaluated on the photodegradation of benzene, toluene and xylenes (BTX) solution under UVA and visible light. The level of nitrogen incorporated on N-doped TiO2–Nb2O5 catalyst was found to be 0.49 at%. Concentrations of BTX were analysed by gas chromatography applying the headspace technique. The N-doped TiO2–Nb2O5 catalyst calcined at 500°C led to reductions of benzene, toluene and xylenes greater than 65wt% after 150min of irradiation. The photocatalytic reactions followed the first order kinetics.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Esterification processes based on functionalized mesoporous solids
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Maciej Trejda , Beata Pokora , Maria Ziolek
      The abilities of niobium and manganese to enhance oxidation of thiol groups in (3-mercaptopropyl)trimethoxysilane (MPTMS) used for functionalization of SBA-15 and MCF materials, by hydrogen peroxide in order to form catalysts with acidic properties were evaluated. Materials obtained were characterized by: N2 adsorption, XRD, XRF, elemental and thermal analyses and titration of acid sites. The highest concentration of acidic sites was found for SBA-15 structure modified with niobium. The catalytic activities of materials obtained were examined in esterification of acetic acid with ethanol and 2-propanol. Both niobium containing samples (MP-NbSBA-15 and MP-NbMCF) showed high yields of ethyl and 2-propyl acetate. The amount of 2-propyl acetate formed was found to linearly depend on the number of acid sites on the catalyst surface. The reuse tests proved that the drop in the catalyst activity in consecutive catalytic cycles is not too high, which suggests possible application of the materials obtained after further optimization.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Mesostructured cellular foams modified by niobium or tantalum and
           functionalized with (3-mercaptopropyl)trimethoxysilane – Raman
           inspired reduction of synthesis time
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Katarzyna Stawicka , Vanesa Calvino-Casilda , Maciej Trejda , Miguel A. Bañares , Maria Ziolek
      The synthesis of mesostructured cellular foams (MCF) modified by niobium or tantalum source and functionalized with MPTMS (3-mercaptopropyl)trimethoxysilane was monitored in situ by Raman spectroscopy. The results from Raman monitoring prompted us to check for a possibility of shorter time synthesis of mesostructured cellular foams. A series of MCFs materials prepared using different times of gel mixing (5h and standard 20h) were synthesized. The samples obtained were characterized by N2 adsorption/desorption, XRD, TEM, XRF, elemental analysis, UV–Vis, FTIR and amperometric titration. The effects of niobium and tantalum on the rate and efficiency of thiol oxidation as well as on the time of silica formation were explored. The most important outcome of the study is the evidence of the formation of MCFs materials having strong Brønsted acidic centers in a shorter preparation time. SO3H groups form faster than in MP-MCF material in the presence of niobium or tantalum in the synthesis gel. The extension of synthesis time for silica and tantalosilicate samples leads to more efficient oxidation of thiol species. This feature does not depend on the synthesis time of niobiosilicate materials.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Influence of preparation methods and structure of niobium oxide-based
           catalysts in the epoxidation reaction
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Rosa Turco , Antonio Aronne , Paolo Carniti , Antonella Gervasini , Luciana Minieri , Pasquale Pernice , Riccardo Tesser , Rosa Vitiello , Martino Di Serio
      The catalytic activity of niobium oxide-based materials, containing the same amount of Nb2O5 (∼15wt%) and prepared by different methods, with that of pure Nb2O5 in the epoxidation of methyl oleate with hydrogen peroxide was compared. The catalytic performances of the catalyst prepared by impregnation do not differ substantially from the ones of Nb2O5. The performances of Nb-supported catalysts prepared by sol–gel can be modulated by controlling the process parameters. The high dispersion of the active NbO x species obtained by this preparation method gives very higher selectivity than in the case of pure Nb2O5. Morphologic and structural characterization of the catalysts helped justifying the obtained catalytic results in terms of activity and selectivity.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Amphiphilic property of niobium oxyhydroxide for waste glycerol conversion
           to produce solketal
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Talita E. Souza , Izabela D. Padula , Mariana M.G. Teodoro , Poliane Chagas , Jarbas M. Resende , Patterson P. Souza , Luiz C.A. Oliveira
      Amphiphilic catalysts are synthesized using NbCl5 in the presence of the CTAB (cetyltrimethylammonium bromide) to generate partial hydrophobicity to the catalysts. The partial hydrophobicity of the niobium oxyhydroxides improved the acetalization reaction of a residual glycerol from biodiesel production by decreasing the interaction between the water molecules and the acid sites of the catalyst. A waste glycerol conversion of 73% with a selectivity to solketal (2,2-dimethyl-[1,3]dioxolan-4-yl)methanol of 95% was obtained. Many reuses of the catalysts showed glycerol conversions between 70 and 80%.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Exploitment of niobium oxide effective acidity for xylose dehydration to
           furfural
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Maria José Campos Molina , Manuel López Granados , Antonella Gervasini , Paolo Carniti
      Xylose together with other pentose and hexose sugars can be dehydrated to produce interesting platform chemical compounds, like 5-hydroxyfurfural (HMF) and furfural. This study continues our investigation on the niobium oxide based catalysts in connection with the research of adequate solvents systems to minimize catalyst deactivation and increase catalyst stability and durability during the dehydration of sugars. Silica-zirconia supported niobia samples (10wt.% of Nb) prepared by impregnation or sol–gel in comparison with pure niobic acid are here presented for xylose dehydration. The reactions have been studied at different temperatures (130–180°C) in batch or fixed bed continuous catalytic reactors in various solvents. Green solvents soluble in the aqueous solution of xylose or biphasic systems have been taken into account: water, water–isopropanol mixtures, water-γ-valerolactone, and water-cyclopentylmethyl ether. The surface acidities of the catalysts have been measured in cyclohexane (intrinsic acidity) and also in water to determine the effective catalyst acidity. The continuous tests and batch-recycling tests showed that the supported Nb-catalysts, even if initially less active, are more stable than niobic acid. The presence of isopropanol in water improves both the activity and stability of the catalysts in comparison with water and the use of cyclopentylmethyl ether gave the most interesting selectivity to furfural preserving the catalyst stability.
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      PubDate: 2015-06-24T06:56:26Z
       
  • TiO2/SiO2 supported vanadia catalysts for the ODH of propane
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Soumik Chakraborty , Sudhir C. Nayak , Goutam Deo
      Supported vanadia catalysts were prepared on two TiO2/SiO2 supports, which contained 70% and 90% TiO2. The supports were thermally stable up to 1023K and surface vanadia species were formed on them. The supported catalysts were characterized by Raman and FTIR spectroscopy, XRD and TPR. The surface area of the catalysts was also determined. The supported vanadia catalysts were active for the propane oxidative dehydrogenation (ODH) reaction and the most active and selective catalyst contained 6% vanadia, which appeared to be the monolayer limit on these supports. Furthermore, the catalyst formed with 70% TiO2 in the support was more active than the catalyst containing 90% TiO2. The kinetic parameters were determined and were able to explain the variations in conversion at iso-contact time and selectivity at iso-conversion for the different catalysts.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Au–Cu on Nb2O5 and Nb/MCF supports – Surface properties and
           catalytic activity in glycerol and methanol oxidation
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Izabela Sobczak , Łukasz Wolski
      Nb2O5 and Nb/MCF were used as supports for gold and copper (Au–Cu system). The activity of these catalysts in the oxidation of glycerol in the liquid phase and methanol in the gas phase was compared with that of monometallic gold catalysts. The oxidation states of metals in the samples prepared were characterised by XRD, TEM, UV–Vis, XPS and H2-TPR. It was found that gold was present in metallic form, whereas copper in the form of CuO, oligonuclear [Cu δ+⋯O δ−⋯Cu δ+] n clusters and isolated cations. The introduction of copper changed the electronic state of gold in Au–Nb2O5 and Au–Nb/MCF and the reduction of copper was found easier in bimetallic AuCu catalysts, which was interpreted as a result of the interaction between gold and copper. Nb2O5 supported catalysts were active in the glycerol oxidation. Monometallic catalysts show high selectivity to glyceric acid, whereas an increase in the selectivity to glycolic acid was found over bimetallic samples due to the presence of copper species active in the oxidative dehydrogenation of glyceric acid. Au–Cu catalysts exhibit very high activity in methanol oxidation towards CO2 as a result of the presence of basic oxygen from CuO-like species on the catalyst surface. Superior performance of bimetallic catalysts in oxidation reactions is due to the synergy between gold and copper.
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      PubDate: 2015-06-24T06:56:26Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 1 September 2015
      Source:Catalysis Today, Volume 252




      PubDate: 2015-06-24T06:56:26Z
       
  • Contents list
    • Abstract: Publication date: 1 September 2015
      Source:Catalysis Today, Volume 252




      PubDate: 2015-06-24T06:56:26Z
       
  • Selected contributions of the “8th European Meeting on Solar
           Chemistry and Photocatalysis: Environmental Applications”
    • Abstract: Publication date: 1 September 2015
      Source:Catalysis Today, Volume 252
      Author(s): Sixto Malato , Pilar Fernández-Ibáñez , Ioannis Poulios , Dionissios Mantzavinos



      PubDate: 2015-06-24T06:56:26Z
       
  • Deposition of BiOBr thin films by thermal evaporation and evaluation of
           its photocatalytic activity
    • Abstract: Publication date: 1 September 2015
      Source:Catalysis Today, Volume 252
      Author(s): E. López Cuellar , A. Martínez-de la Cruz , N. Chávez Torres , J. Olivares Cortez
      Thin films of BiOBr were prepared by a sequential evaporation process in a thermal evaporation system (TES) starting from BiOBr powders previously synthesized by co-precipitation. The deposition rate was fixed at 1.2Ås−1 to get a controlled evaporation of the material using glass slides as substrate. BiOBr thin films with a thickness of 300nm were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The analysis by XRD of the thin film deposited confirmed the formation of BiOBr, showing a high degree of specific crystal orientation in {001} planes. In the same way, SEM analysis showed that the deposition of oxide took place by formation of plates and small particles with shape of flowers. The photocatalytic activity of BiOBr thin films was evaluated in the degradation reaction of rhodamine B (RhB) in aqueous solution under sun-like irradiation. BiOBr thin films were able to bleach a solution of RhB (5mgL−1) in 99% after 24h, and to mineralize a solution of RhB (50mgL−1) in 38% after 96h.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Electrospun ceria-based nanofibers for the facile assessment of catalyst
           morphological stability under harsh HCl oxidation reaction conditions
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Maren Möller , Herbert Over , Bernd Smarsly , Nikolay Tarabanko , Sven Urban
      Long-term stability is a major issue in the development of new catalysts and in the improvement of existing catalysts. In general, high-surface-area materials in catalysis are not well suited as model materials for testing catalyst stability, because changes in the morphology are difficult to recognize with electron microscopy. Therefore, we developed a new type of model catalyst in the form of nanofibers for assessing structural changes of CeO2-based catalysts under highly corrosive Deacon reaction conditions. In the Deacon process, chlorine is recycled by heterogeneously catalyzed gas-phase oxidation of HCl, using metal oxide catalysts. The Deacon process generally suffers from degradation of the catalyst due to in-depth chlorination. One-dimensional CeO2-based nanofibers with a well-defined morphology and surface enable direct visualization of structural changes before and after the Deacon reaction, simply employing scanning electron microscopy supported by X-ray diffraction and physisorption measurements. Preparing solid solutions of CeO2 and ZrO2 has shown to improve both the chemical stability and the activity of the catalyst.
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      PubDate: 2015-06-24T06:56:26Z
       
  • MnOx-CeO2 catalysts synthesized by solution combustion synthesis for the
           low-temperature NH3-SCR
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): S. Andreoli , F.A. Deorsola , R. Pirone
      MnO x -CeO2 catalysts with different compositions have been investigated as catalysts for low temperature SCR by preparing a series of samples by the solution combustion synthesis (SCS) method. Variable amounts of two different organic fuels (glycine and citric acid) with respect to the stoichiometry of synthesis were investigated. The samples were characterized by XRD, BET, H2-TPR, XPS, FESEM and their catalytic activity tested for NO x abatement in the range of temperature of interest (120–350°C). By varying the synthesis parameters it was possible to obtain catalysts different in terms of structure, morphology, specific surface area, Mn average oxidation state as well as superficial content of Mn, Ce and O atoms. These features were correlated with the resulting catalytic performances in the SCR reaction and compared to pure MnO x phases obtained through the same synthesis method. All the developed catalysts were considerably active in the temperature range investigated and could be considered suitable for the low-temperature SCR process. The sample with the higher content of manganese oxide obtained with glycine in below-stoichiometric amount showed the best performance in terms of NO x conversion and N2 yield, likely due to the high reducibility as well as the presence of the Mn3O4 phase.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Comparative study of the catalytic performance and final surface structure
           of Co3O4/La-CeO2 washcoated ceramic and metallic honeycomb monoliths
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Juan Carlos Hernández-Garrido , Diana Gaona , Diana María Gómez , José Manuel Gatica , Hilario Vidal , Oihane Sanz , José Manuel Rebled , Francisca Peiró , José Juan Calvino
      Co3O4/La-modified-CeO2/Al2O3 powders washcoated onto ceramic and metallic monolithic catalysts have been compared in order to evaluate the contribution of both the type of substrate and the total washcoat loading on the actual surface structure of the corresponding monolithic devices. Detailed structural and chemical characterization studies have been performed combining FIB (Focused Ion Beam) and STEM (Scanning Transmission Electron Microscopy). Atomic scale STEM data recorded on the electron-transparent lamellae prepared by FIB were complemented with those coming from micron scale analysis performed by different SEM (Scanning Electron Microscopy) techniques combined with digital image analysis. X-Ray Energy Dispersive Spectroscopy (X-EDS) elemental maps, acquired from the FIB lamellae, revealed the occurrence of an unexpected surface structure with large ceria aggregates constituted by crystallites with an average size 5nm and Co3O4 nanocrystallites with two layered structure underneath of some of these aggregates. The existence of this particular structure has been observed for all the samples analyzed here, and seems to be independent of either the nature of the support (ceramic or metallic) and/or the total amount of deposited material. All the investigated monolithic catalysts show high activity and selectivity to total oxidation of model VOCs (Volatile Organic Compounds) such as toluene and ethyl acetate. The present study highlights the key role of the combination of the FIB sample preparation and STEM to monitor the influence of the preparation method on the actual surface of catalytic monolithic devices, confirming the occurrence of microstructural features driven by physical processes involved in the multistep procedure of the washcoating technique followed to prepare the final monolithic device.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Performance of platinum and gold catalysts supported on
           ceria–zirconia mixed oxide in the oxidation of chlorobenzene
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Pavel Topka , Romain Delaigle , Luděk Kaluža , Eric M. Gaigneaux
      Monometallic noble metal catalysts supported on ceria–zirconia mixed oxide were prepared by impregnation and tested in the oxidation of chlorobenzene (100ppm in air). With the pure ceria–zirconia support, 27% conversion was achieved at 400°C and only incomplete oxidation to carbon monoxide was evidenced. The introduction of gold and especially platinum significantly improved the efficiency of the catalyst. The catalytic performance increased with increasing noble metal content. The catalyst with 1wt.% of Pt achieved 97% conversion of chlorobenzene already at 350°C and complete oxidation to CO2 with only traces of by-products was detected. Platinum catalysts were more efficient than gold ones, which was ascribed to their superior redox properties. On the other hand, the lower acidity of platinum catalysts was not detrimental for their catalytic performance.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Ru-modified Au catalysts supported on ceria–zirconia for the
           selective oxidation of glycerol
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Lidia E. Chinchilla , Carol M. Olmos , Alberto Villa , Anna Carlsson , Laura Prati , Xiaowei Chen , Ginesa Blanco , José J. Calvino , Ana B. Hungría
      In the present work, a series of supported gold–ruthenium bimetallic catalysts of varying Au:Ru molar ratios were prepared onto ceria–zirconium mixed oxide (Ce0.62Zr0.38O2) using sequentially deposition-precipitation and impregnation techniques to add gold and ruthenium, respectively. A combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analyses and different transmission electron microscopy techniques as high-resolution transmission electron microscopy (HRTEM), high-angle annular field imaging (HAADF-STEM) and X-ray energy-dispersive spectroscopy (XEDS) were used to characterize the bimetallic catalysts, being their catalytic behaviour tested in the selective oxidation of glycerol to glyceric acid. The analytical electron microscopy results of the bimetallic catalysts are consistent with the low miscibility gap reported between gold and ruthenium in the bulk state. Nevertheless, detailed STEM-XEDS analyses of individual particles provided evidence that both metals display certain tendency to form bimetallic particles. For the glycerol oxidation, the Au:Ru molar ratio is a key parameter to achieve optimal catalytic performance, i.e. the supported bimetallic catalyst with 1Au:0.5Ru ratio was found to be several times more active than monometallic gold and ruthenium catalysts. Furthermore, studies on bimetallic catalyst reduced at increasing temperatures confirm that the presence of small amounts of ruthenium prevents the aggregation of gold particles. These structural findings strongly suggest that if this increased stability is kept under reaction conditions, this could be one of the key factors to explain its exceptional activity.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Room temperature oxidation of formaldehyde on Pt-based catalysts: A
           comparison between ceria and other supports (TiO2, Al2O3 and ZrO2)
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Sara Colussi , Marta Boaro , Loredana de Rogatis , Alfonsina Pappacena , Carla de Leitenburg , Jordi Llorca , Alessandro Trovarelli
      Platinum-based catalysts for the room temperature removal of formaldehyde are prepared on ceria and other supports (TiO2, Al2O3 and ZrO2) for comparison, starting from chloride and nitrate precursors. The behaviour towards formaldehyde adsorption and oxidation is evaluated by means of temperature-programmed desorption (TPD), temperature-programmed oxidation (TPO) and catalytic tests. The results indicate that the catalytic performances are affected by Pt oxidation state, which, in turn, strongly depends on the properties of the support. In order to obtain high HCHO conversions, the support should guarantee the accessibility to metal active sites as well as affinity for water. Moreover, to avoid Pt partial oxidation, non-reducible oxides are preferable to reducible ones.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Boosting the activity of a Au/CeO2/Al2O3 catalyst for the WGS reaction
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): T.R. Reina , S. Ivanova , M.A. Centeno , J.A. Odriozola
      Herein a strategy to design highly efficient Au/CeO2/Al2O3 based WGS catalysts is proposed. The inclusion of transition metals, namely Fe, Cu and Zn as CeO2 dopant is considered. All the promoters successfully increased the WGS performance of the undoped sample. The activity improvement can be correlated to structural and/or redox features induced by the dopants. The comparative characterization of the doped samples by means of XRD, Raman spectroscopy and OSC evaluation permits an accurate understanding of the boosted WGS activity arising from the Ce-promoter interaction. This study establishes distinction among both, structural and redox sources of promotion and provides a useful strategy to develop highly active Au/CeO2 based catalysts for the WGS reaction.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Biogas to syngas conversion without carbonaceous deposits via the dry
           reforming reaction using transition metal catalysts
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Petar Djinović , Ilja Gasan Osojnik Črnivec , Albin Pintar
      This study investigates how morphology, active metal content and oxygen storage capacity of various bimetallic NiCo/CeZrO2 materials influence their catalytic activity and stability in the methane dry reforming reaction. Catalyst preparation procedure and chemical composition were steered to finally obtain materials, which do not accumulate carbon during the CH4/CO2 reforming reaction. Oxygen storage capacity of the CeZrO2 catalyst support was identified to play a vital role in retarding carbon accumulation over the tested NiCo/CeZrO2 materials. This property can be fully developed when a nanocrystalline solid solution of CeO2 and ZrO2 is formed. Secondly, a high dispersion of nickel and cobalt is crucial for two reasons: (i) catalysts which contain larger NiCo bimetallic particles (for example with 12–18wt.% active metal loading) exhibit a low metal-support interphase that results in enhanced coke formation rates; (ii) additionally, only a marginal gain in methane reforming rates are achieved at higher loadings, compared to catalysts with a 3–6wt.% active metal content. We demonstrated that a NiCo/CeZrO2 catalyst under relevant operating conditions after 400h TOS maintains 79 and 84% conversion of CH4 and CO2, with negligible coke accumulation.
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      PubDate: 2015-06-24T06:56:26Z
       
  • Improved activity and stability of Pd@CeO2 core–shell catalysts
           hybridized with multi-walled carbon nanotubes in the water gas shift
           reaction
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): A. Beltram , M. Melchionna , T. Montini , L. Nasi , R.J. Gorte , M. Prato , P. Fornasiero
      An efficient method is presented for preparing hierarchical catalysts composed of multi-walled carbon nanotubes (MWCNTs) and Pd@CeO2 core–shell nanoparticles. These materials were then examined for the water gas shift reaction (WGSR), which demonstrated intimate contact between the constituent parts. The integration of the carbonaceous support improves the stability of the nanoparticles by ordering the dispersion of the inorganic phase and increases the activity by suppressing the deactivation of the active phase that is commonly observed in conventional Pd–CeO2 under reducing conditions, e.g. WGSR conditions. An optimum MWCNTs:Pd@CeO2 ratio exists that affords totally homogeneous structures and provides the best catalytic properties.
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      PubDate: 2015-06-24T06:56:26Z
       
  • A comparison of hierarchical Pt@CeO2/Si–Al2O3 and
           Pd@CeO2/Si–Al2O3
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Lisandra Arroyo-Ramírez , Chen Chen , Matteo Cargnello , Christopher B. Murray , Raymond J. Gorte
      A comparison of catalytic and adsorption properties for Pt@CeO2/Si–Al2O3 (1-wt% Pt and 9-wt% CeO2) and Pd@CeO2/Si–Al2O3 (1-wt% Pd and 9-wt% CeO2) core–shell catalysts indicates that the CeO2 shell is stable for Pd but not for Pt. Following calcination at 773K, Pt@CeO2/Si–Al2O3 exhibits water–gas-shift (WGS) rates in 3% H2O and CO that are similar to rates found on conventional Pt/CeO2, implying that there is good contact between the Pt and CeO2 phases, even at the relatively low CeO2 loading. WGS rates on Pt@CeO2/Si–Al2O3 were also reasonably stable with time and unaffected by pre-reduction of the catalyst. By comparison, WGS rates over Pd@CeO2/Si–Al2O3 declined rapidly due to reduction of CeO2 and were suppressed by pre-reduction of CeO2. After calcination to 1073K, large metal particles were observed with Pt@CeO2/Si–Al2O3, but not on Pd@CeO2/Si–Al2O3. Coulometric titration measurements on these two materials suggest stronger interactions between CeO2 and Pd and these are likely responsible for the higher stability of the core–shell structure in Pd@CeO2 compared to Pd@CeO2.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • A first-principles modeling of glycerol and ammonia interactions on the
           cation-deficient VSbO4(110) surface
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): Ignacio M. Alliati , Beatriz L. Irigoyen
      Glycerol, a major by-product of biodiesel production, is usually involved in reactions of low selectivity. Recently, it has been reported that new reaction of glycerol ammoxidation on vanadium antimonate led to very promising results in terms of conversion and selectivity to acrylonitrile, a valuable monomer for the chemical industry. Therefore, in this work we performed theoretical calculations based on the density functional theory (DFT), in order to study glycerol and ammonia interactions on the cation-deficient VSbO4(110) surface. Our results show that glycerol and ammonia interactions on Brønsted acid sites are rather weak, reaching adsorption energy values of −0.72eV and −0.67eV, respectively. However, the interactions of those molecules on Lewis acid sites are more favorable. Glycerol adsorption mainly involves V sites (−2.83eV); while the most stable interaction of ammonia (−2.08eV) leads to a new NSb bond, suggesting the participation of Sb sites in CN bonds formation.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • V and V–P containing Zr-SBA-15 catalysts for dehydration of glycerol
           to acrolein
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): J.A. Cecilia , C. García-Sancho , J.M. Mérida-Robles , J. Santamaría-González , R. Moreno-Tost , P. Maireles-Torres
      A series of solid acid catalysts based on vanadium and vanadium–phosphorous supported on a zirconium doped mesoporous SBA-15 silica has been synthesized, characterized by using XRD, N2 sorption, NH3–TPD, FT-IR spectroscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy, and evaluated in the gas-phase dehydration of glycerol. Under the operating conditions used, all materials are active in the glycerol dehydration, being acrolein the main product in all cases. Although higher values of conversion are obtained in the presence of vanadium oxide based catalysts, acrolein yield improves after the treatment with phosphoric acid, attaining a value of 42% after 2h of reaction at 325°C with the 12VP0.2 catalyst, which contains 12wt.% of V2O5 and a V/P molar ratio of 0.2. However, the incorporation of phosphorous to the catalytic system partially destroys the mesoporous structure. Allyl alcohol has been also detected using vanadium based catalysts, due to a partial reduction of V2O5 species during the reaction, increasing its yield with the vanadium oxide loading. All catalysts suffer from deactivation by coke deposition on the catalyst surface, being the carbon content considerably higher for catalysts without phosphorous.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • The influence of promoters (Zr, La, Tb, Pr) on the catalytic performance
           of CuO-CeO2 systems for the preferential oxidation of CO in the presence
           of CO2 and H2O
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Juan Antonio Cecilia , Ana Arango-Díaz , Verónica Rico-Pérez , Agustín Bueno-López , Enrique Rodríguez-Castellón
      CuO supported on CeO2 and Ce0.9X0.1O2, where X is Zr, La, Tb or Pr, were synthesized using nitrate precursors, giving rise ceria based materials with a small particle size which interact with CuO species generating a high amount of interfacial sites. The incorporation of cations to the ceria framework modifies the CeO2 lattice parameter, improving the redox behavior of the catalytic system. The catalysts were characterized by X-ray fluorescence spectrometry (XRFS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, thermoprogrammed reduction with H2 (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts were tested in the preferential oxidation of CO under a H2-rich stream (CO-PROX), reaching conversion values higher than 95% between 115 and 140°C and being the catalyst with 6wt.% of Cu supported on Ce0.9Zr0.1O2 (sample 6CUZRCE) the most active catalyst. The influence of the presence of CO2 and H2O was also studied simulating a PROX unit, taking place a decrease of the catalytic activity due to the inhibitor effect both CO2 and H2O.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • CuO-CeO2 supported on montmorillonite-derived porous clay heterostructures
           (PCH) for preferential CO oxidation in H2-rich stream
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): J.A. Cecilia , A. Arango-Díaz , F. Franco , J. Jiménez-Jiménez , L. Storaro , E. Moretti , E. Rodríguez-Castellón
      This study reports on the preparation and characterization of porous clay heterostructures (PCH) as a high-surface-area support for CuO–CeO2 based catalysts for the preferential oxidation of CO in excess of H2 (CO-PROX). After pillaring the montmorillonite clay with silica (Si-PCH) and silica-zirconia (SiZr-PCH), the Cu-Ce active phase was loaded by incipient wet impregnation setting the cerium amount constant (20wt%) and investigating three different copper loadings (3, 6 and 12wt%). The use of pillars of silica or silica-zirconia inserted in the interlayer space of a natural clay provides a high surface area support that can favor the dispersion of both CuO and CeO2 active phases, leading to the formation of a high amount of copper-ceria interfacial sites, responsible for a very high catalytic activity in the CO-PROX reaction. The results obtained from characterization of the materials by XRD, N2 physisorption, H2-TPR, XPS and CO2-TPD suggest that this synthesis method gives rise to catalysts with copper species highly active and selective for the CO-PROX reaction. The catalysts exhibit high CO conversion values and the sample with 6wt% of copper on Si-PCH displays very good performances, comparable to those based on precious metal catalysts, even at low temperatures. The system reducibility was found modified by the incorporation of zirconium in the support, with a slight decrement of the CO conversion value, compared to the same material without Zr. The influence of the presence of CO2 and H2O in the gas feed was also studied in order to simulate the real operating conditions of a PEMFC feed stream. Correlations between catalytic performances and physicochemical properties of the materials have been made.


      PubDate: 2015-06-24T06:56:26Z
       
  • The influence of nano-architectured CeOx supports in RhPd/CeO2 for the
           catalytic ethanol steam reforming reaction
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): N.J. Divins , A. Casanovas , W. Xu , S.D. Senanayake , D. Wiater , A. Trovarelli , J. Llorca
      The ethanol steam reforming (ESR) reaction has been tested over RhPd supported on polycrystalline ceria in comparison to structured supports composed of nanoshaped CeO2 cubes and CeO2 rods tailored toward the production of hydrogen. At 650–700K the hydrogen yield follows the trend RhPd/CeO2-cubes>RhPd/CeO2-rods>RhPd/CeO2-polycrystalline, whereas at temperatures higher than 800K the catalytic performance of all samples is similar and close to the thermodynamic equilibrium. The improved performance of RhPd/CeO2-cubes and RhPd/CeO2-rods for ESR at low temperature is mainly ascribed to higher water–gas shift activity and a strong interaction between the bimetallic–oxide support interaction. STEM analysis shows the existence of RhPd alloyed nanoparticles in all samples, with no apparent relationship between ESR performance and RhPd particle size. X-ray diffraction under operating conditions shows metal reorganization on {100} and {110} ceria crystallographic planes during catalyst activation and ESR, but not on {111} ceria crystallographic planes. The RhPd reconstructing and tuned activation over ceria nanocubes and nanorods is considered the main reason for better catalytic activity with respect to conventional catalysts based on polycrystalline ceria.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Trends in the CO oxidation and PROX performances of the platinum-group
           metals supported on ceria
    • Abstract: Publication date: 15 September 2015
      Source:Catalysis Today, Volume 253
      Author(s): Thanh-Son Nguyen , Franck Morfin , Mimoun Aouine , Françoise Bosselet , Jean-Luc Rousset , Laurent Piccolo
      PGM–CeO2 (PGM=Pt, Pd, Ir, Rh, Ru) catalysts were prepared by one-step solution combustion synthesis (SCS) and characterized by elemental analysis, N2 volumetry, aberration-corrected HRTEM, X-ray diffraction, and CO-DRIFTS. The samples, consisting of 2–6nm metal nanoparticles supported on mesoporous ceria, were tested in CO oxidation in absence and presence of hydrogen (PROX). To our knowledge, this work presents the first comparison of all the platinum-group metals (except Os) for these reactions in the same conditions. The as-prepared SCS catalysts are active in CO oxidation and a reducing treatment has no significant effect on their performances. While the best catalyst in H2-free CO oxidation is Rh–CeO2, the addition of a high hydrogen excess decreases the Rh catalyst activity but enhances the CO oxidation rate on all other systems, including alumina-supported metals employed as reference catalysts. The resulting PROX turnover frequencies (Pt>Pd>Rh>Ir>Ru) follow the trends predicted by published density-functional-theory calculations considering the COad +Oad elementary reaction as the rate-determining step. Pt–CeO2 is not only the most active but also the most selective catalyst, reaching near 100% CO2 at low temperature (ca. 100°C). The alumina-supported catalysts appeared less active than their ceria-supported counterparts in both reactions. The effect of heating/cooling cycles on the reaction kinetics was also investigated. Whereas the Pt, Pd and Ir ceria-supported catalysts were stable throughout PROX cycles, Rh and Ru ones exhibited apparently chaotic behaviors above ca. 200°C, which are proposed to be induced by favorable CO dissociation and methanation pathways and/or variable metal oxidation states.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Vanadium oxide supported on porous clay heterostructure for the partial
           oxidation of hydrogen sulphide to sulfur
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): M.D. Soriano , J.A. Cecilia , A. Natoli , J. Jiménez-Jiménez , J.M. López Nieto , E. Rodríguez-Castellón
      Vanadium oxide supported on porous clay heterostructures (PCH) catalysts have been synthesized, characterized and evaluated in the selective oxidation of H2S to elemental sulfur. The catalysts were characterized by XRD, adsorption–desorption of N2 at −196°C, diffuse reflectance UV–vis, H2-TPR, Raman spectroscopy and XPS. The catalysts with higher vanadium content are more active and selective, exhibiting a H2S conversion close to 70% after 360h on stream with a high selectivity toward elemental sulfur and a low formation of undesired SO2. The catalysts with V2O5 crystallites have shown a higher activity and resistance to the deactivation. The analysis of the spent catalyst has revealed the formation of V4O9 crystals during the catalytic test, which has been reported as the active phase in the selective oxidation of the H2S.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • Mesostructured vanadia–alumina catalysts for the synthesis of
           vitamin K3
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254
      Author(s): M. Florea , R.S. Marin , F.M. Pălăşanu , F. Neaţu , V.I. Pârvulescu
      Liquid-phase selective oxidation of 2-methylnaphtalene to the vitamin K3 was investigated on a series of mesostructured vanadia–alumina catalysts with different V/Al ratios (0.1–1). They were prepared by the co-precipitation of ammonium metavanadate and aluminum nitrate at pH 5 and characterized by XRD, Raman, TG–DTA, elemental analysis and adsorption-desorption isotherms of nitrogen at −196°C. The influence of the catalyst composition and calcination temperature upon the physico-chemical properties were closely investigated in relation with the catalytic performances. The result of this investigation indicated the catalysts containing a higher vanadium loading and calcined at 300°C as the most active. Thus, the VAl07 catalyst led to a selectivity in vitamin K3 of 54% for a conversion of 2-methylnaphtalene of 76%. Such an activity corresponded to mixtures where metavanadate (Raman line at 940cm−1) and decavanadate (Raman line at 990cm−1) species were the most abundant. No lines of V2O5 (around 705cm−1) were detected in the catalysts calcined below 600°C.
      Graphical abstract image

      PubDate: 2015-06-24T06:56:26Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254




      PubDate: 2015-06-24T06:56:26Z
       
  • Contents list
    • Abstract: Publication date: 1 October 2015
      Source:Catalysis Today, Volume 254




      PubDate: 2015-06-24T06:56:26Z
       
 
 
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