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Journal Cover Catalysis Today
  [SJR: 1.378]   [H-I: 142]   [5 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0920-5861
   Published by Elsevier Homepage  [2805 journals]
  • Spatio-temporal features of the sequential NOx storage and reduction and
           selective catalytic reduction reactor system
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Mengmeng Li, Vencon G. Easterling, Michael P. Harold
      Combined NOx storage and reduction (NSR) and selective catalytic reduction (SCR) were conducted in a sequential reactor system containing a Pt/Rh/BaO/Al2O3 Lean NOx Trap (LNT) catalyst and Cu-SSZ-13 SCR catalyst. Spatially-resolved mass spectrometry (SpaciMS) was used to construct temporal concentration profiles spanning the two monolith catalysts. The effects of feed gas temperature, gas hourly space velocity (GHSV) and carrier gas water were examined with propylene as the reductant. The working concept of the sequential LNT+SCR is evident in both the transient and cycle-averaged concentration profiles. During the rich phase NH3 is generated in the upstream LNT and trapped in the downstream SCR where it reacts with NOx that slips from the LNT during the subsequent lean phase. The instantaneous profiles provide insight into the storage and reduction dynamics and the mass coupling between the LNT and SCR catalysts. Axial gradients in the NOx storage and release during the lean and rich phases confirm classical LNT cyclic behavior. The spatio-temporal temperature measurements reveal a large exotherm caused by the propylene oxidation, manifested as a propagating temperature front. The cycle-averaged concentration profiles help to pinpoint the LNT length that gives a product mixture having a NH3/NOx ratio approaching unity, the desired stoichiometry for promoting NOx reduction in the SCR. The generation of NH3 and conversion of NOx is enhanced by water, suggesting an important role of the water gas shift chemistry. Propylene consumption and breakthrough from the LNT reveals its role in contributing to the overall NOx reduction. A non-NH3 SCR reaction pathway is identified that has an increasing contribution down the length of Cu-SSZ-13 SCR catalyst. The generation of formaldehyde over the Cu-SSZ-13 SCR catalyst suggests a pathway resulting from breakthrough of propylene from the LNT, followed by its oxidation to acrolein and followed in turn by reverse aldol condensation.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Spectroscopic investigation of sulfur-resistant Pt/K2O/ZrO2/TiO2/Al2O3
           NSR/LNT catalysts
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Z. Say, M. Tohumeken, E. Ozensoy
      An alternative ternary support oxide material and its K2O and Pt functionalized counterparts in the form of Pt/K2O/Al2O3/ZrO2/TiO2 with different K2O loadings were synthesized. Structural and morphological properties of the catalysts were characterized via XRD and BET techniques in comparison to a conventional Pt/20Ba/Al benchmark NSR/LNT catalyst. Comprehensive in-situ FTIR and TPD analysis revealed that increasing the K2O loading in the Pt/K2O/AZT system leads to an increase in NO x Storage Capacity (NSC) at the expense of the formation of bulk-like sulfates requiring higher temperature for complete sulfur elimination with H2(g). Observed delicate trade-off between NSC and sulfur poisoning tendencies of the currently investigated family of AZT-based NSR/LNT catalysts implies that Pt/5.4K2O/AZT is a promising catalyst revealing comparable NSC within the temperature range of 473–673K to that of the conventional Pt/20Ba/Al benchmark catalyst, while exhibiting superior sulfur tolerance and regeneration characteristics.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Chemical deSOx: An effective way to recover Cu-zeolite SCR catalysts from
           sulfur poisoning
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Ashok Kumar, Michael A. Smith, Krishna Kamasamudram, Neal W. Currier, Aleksey Yezerets
      Despite the recent remarkable advances in the development of Cu-zeolite materials for selective catalytic reduction (SCR) of NOx with NH3, their performance is not immune to the poisoning by sulfur oxide species SO2 and SO3, commonly referred as SOx. Periodic removal of SOx, i.e. deSOx, is needed to maintain high NOx conversion efficiency of these catalysts even when ultra-low sulfur diesel (ULSD) fuel is used. Such deSOx events require high temperatures, typically in excess of 550°C, which can be detrimental to the durability of the SCR catalysts and other aftertreatment components, and may also result in a fuel penalty. In this work, a recently discovered method, herein referred to as chemical deSOx, was found to be effective for removal of sulfur and for recovery of NOx conversion at substantially lower temperatures. The method relies on the use of low concentrations of reductants under net oxidizing conditions, arguably by inducing a locally reducing environment on the catalyst surface through different chemical mechanisms. Reductants such as NOx+NH3, NH3, C3H6 and n-C12H26 were demonstrated to achieve the removal of sulfur species without resorting to high temperatures. It is proposed that the change of the oxidation state of Cu sites in response to these exposures, achieved through different chemical mechanisms depending on the reductant, was responsible for facilitating the removal of sulfur from the catalyst.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • The catalytic behavior of precisely synthesized Pt–Pd bimetallic
           catalysts for use as diesel oxidation catalysts
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Andrew P. Wong, Eleni A. Kyriakidou, Todd J. Toops, John R. Regalbuto
      The demands of stricter diesel engine emission regulations have created challenges for current exhaust systems. With advances in low-temperature internal combustion engines and their operations, advances must also be made in vehicle exhaust catalysts. Most current diesel oxidation catalysts use heavy amounts of precious group metals (PGMs) for hydrocarbon (HC), CO, and NO oxidation. These catalysts are expensive and are most often synthesized with poor bimetallic interaction and dispersion. The goal of this work was to study the effect of aging on diesel emission abatement of Pt–Pd bimetallic nanoparticles precisely prepared with different morphologies: well dispersed core–shell vs. well dispersed homogeneously alloyed vs. poorly dispersed, poorly alloyed particles. Alumina and silica supports were studied. Particle morphology and dispersion were analyzed before and after hydrothermal treatments by XRD, EDX, and STEM. Reactivity as a function of aging was measured in simulated diesel engine exhaust. While carefully controlled bimetallic catalyst nanoparticle structure has a profound influence on initial or low temperature catalytic activity, the differences in behavior disappear with higher temperature aging as thermodynamic equilibrium is achieved. The metallic character of Pt-rich alumina-supported catalysts is such that behavior rather closely follows the Pt–Pd metal phase diagram. Nanoparticles disparately composed as well-dispersed core–shell (via seq-SEA), well-dispersed homogeneously alloyed (via co-SEA), and poorly dispersed, poorly alloyed (via co-DI) end up as well alloyed, large particles of almost the same size and activity. With Pd-rich systems, the oxidation of Pd also figures into the equilibrium, such that Pd-rich oxide phases appear in the high temperature forms along with alloyed metal cores. The small differences in activity after high temperature aging can be attributed to the synthesis methods, sequential SEA and co-DI which give rise, after aging, to a bimetallic surface enriched in Pd.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Spatially resolving CO and C3H6 oxidation reactions in a Pt/Al2O3 model
           oxidation catalyst
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Melanie J. Hazlett, William S. Epling
      Spatially resolved Fourier transform infrared spectroscopy (Spaci-IR) was used to measure gas-phase concentration profiles during CO and C3H6 oxidation reactions over a Pt/Al2O3 monolith-supported catalyst. The reaction conditions were selected as representative of certain low temperature combustion (LTC) engine exhaust conditions, where in this study higher concentrations of CO and C3H6 and lower concentrations of NO X were used relative to standard engine exhaust. CO and C3H6 oxidation and NO X reduction reactions were examined individually and in combination via temperature programmed oxidation (TPO) experiments. Significant NO X reduction occurred right at CO and C3H6 light off, and NO oxidation only occurred after the oxidation of CO and C3H6. C3H6 oxidation was not observed until after most of the CO oxidized, as CO was more strongly adsorbed to the active site surface at low temperature. During the TPO of CO and C3H6, the conversion versus temperature profiles did not monotonically increase; two inflections were observed where the rate of conversion change as a function of temperature slowed over a small temperature range before again accelerating with temperature. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used in order to characterize intermediates that were present on the surface at the temperatures where these steps were noted. Surface ethylene and formate species were present during the first step, with acetate and formate in the second step. The inhibition steps were therefore attributed to the partial oxidation of propylene to ethylene, and then the subsequent partial oxidation of ethylene to acetate.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Selective oxidation of ammonia to nitrogen on bi-functional
           Cu–SSZ-13 and Pt/Al2O3 monolith catalyst
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Sachi Shrestha, Michael P. Harold, Krishna Kamasamudram, Ashok Kumar, Louise Olsson, Kirsten Leistner
      The selective oxidation of NH3 to N2 on bi-functional mixed and dual-layer Cu–SSZ-13 and Pt/Al2O3 washcoated monolith catalysts is investigated under several reaction conditions to probe the effects of the added mass transfer barrier, in terms of the SCR loading (layer thickness), on the activity and selectivity of the catalyst. The combination of Cu–SSZ-13, itself shown to have high activity in reducing NO x to N2 with NH3, and Pt/Al2O3 is effective in converting the NO x produced by the very active but poorly selective precious metal catalyst. The data reveal a trade-off between NH3 conversion and N2 selectivity due to the mass transport barrier afforded by the added Cu–SSZ-13 top-layer: NH3 conversion decreases while N2 selectivity increases as Cu–SSZ-13 loading is increased. In the presence of feed NO, the NO x conversion of the dual-layer catalyst increases with an increase in the Cu–SSZ-13 washcoat loading. In the absence of feed NO, the dual-layer catalyst has a high selectivity to N2 due to the selective reaction in the Cu–SSZ-13 layer between NH3 from the bulk and counter-diffusing NO x formed in the underlying Pt/Al2O3. For the same catalyst loadings, the mixed washcoat catalyst gives a higher NH3 conversion at high space velocity than the dual-layer catalyst. This is attributed to NH3 conversion on Pt/Al2O3 sites not impeded by a SCR catalyst top-layer. In the presence of feed NO, the dual-layer catalyst shows a high NO x to N2 conversion as a result of the high SCR activity of the Cu–SSZ-13 top-layer. The mixed catalyst is more selective to NO x because the Pt catalyst in proximity to the SCR catalyst leads to the oxidation of NH3 back to NO x . Finally, we demonstrate that a hybrid catalyst having dual-layer and mixed catalyst attributes exhibits good performance by exploiting the beneficial effects of both catalyst types.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Simultaneous removal of soot and NOx over K- and Ba-doped ruthenium
           supported catalysts
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Roberto Matarrese, Eleonora Aneggi, Lidia Castoldi, Jordi Llorca, Alessandro Trovarelli, Luca Lietti
      Ruthenium-based materials are investigated for the simultaneous removal of soot and NO x and their behavior is compared with that of model Pt-Ba/Al2O3 and Pt-K/Al2O3 catalysts. The materials, 1%wt Ru–10%wt AM/MO (AM=Ba or K; MO=Ce0.8Zr0.2O2, ZrO2, Al2O3), have been prepared by incipient wetness impregnation and characterized by BET, XRD, HRTEM and TPR experiments. The catalytic activity for diesel soot combustion is studied under loose contact conditions by means of TPO (Temperature Programmed Oxidation) while the reactivity in the NO x removal is investigated by Isothermal Concentration Step Change experiments. All the ruthenium-based formulations are active in the combustion of diesel soot, particularly potassium-doped materials that show low onset temperatures, near 230°C. The catalytic activity in the simultaneous removal of soot and NO x shows that Ru-based catalysts are very efficient in the oxidation of soot also under isothermal conditions and that their NO x removal capacity (i.e. storage capacity) is almost comparable to that of traditional Pt-based LNT systems. However, the NO x reduction efficiency of the Ru-containing catalysts is lower than that of traditional LNT Pt-based catalysts.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Experimental study of the interaction between soot combustion and NH3-SCR
           reactivity over a Cu–Zeolite SDPF catalyst
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Fabio Marchitti, Isabella Nova, Enrico Tronconi
      The interplay between the NH3 SCR reactions and the oxidation of particulate matter (PM) is systematically investigated in view of the development of SDPF systems, which consist of a Selective Catalytic Reduction (SCR) catalyst coated on a diesel particulate filter (DPF). Both steady state and dynamic catalytic activity runs are performed on a commercial Cu-promoted zeolite catalyst supported on a SiC DPF crushed to powders and mixed with synthetic soot (Printex U). Three main effects are addressed, namely: (i) the influence of NO and/or NO2 on soot combustion, (ii) the influence of the co-presence of NH3 and NOx on soot combustion, and (iii) the influence of soot on the SCR reactions. It is found that NO2 oxidizes soot to COx at much lower temperatures than O2, but the co-presence of NH3 strongly reduces such a downshift of the soot combustion light-off. In fact, our results clearly point out that the NH3-SCR reactions successfully compete with soot combustion for NO2 usage, the reactivity with NH3 being the NO2 preferred reaction pathway at low temperature. In addition, the Standard and the Fast SCR reactions (NO2/NOx ≤1/2) are slightly but negatively affected by the presence of soot, while in case of NO2 excess (NO2/NOx >1/2) the SCR deNOx activity benefits from the soot/NO2 interaction.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • An assessment of Pt and Pd model catalysts for low temperature NOx
           adsorption
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Joseph R. Theis
      Low temperature NO x adsorbers (LTNA) are being developed to adsorb the cold start NOx emissions from diesel engines and release the NO x when the urea/SCR system is operational. To assess the contributions of the precious metal and washcoat, model catalysts with 0.43g/L (26 gpcf) of platinum (Pt) or palladium (Pd) on washcoats of alumina (Al2O3) or ceria/zirconia (CZO) were evaluated for lean NO storage and release with and without C2H4 and H2O. The degreened samples were evaluated on a reactor-based transient test that partially simulated the exhaust temperatures during the first two phases of the light-duty Federal Test Procedure (FTP) followed by a Supplemental FTP (US06) test. After oxidation, the Pd/CZO catalyst stored NO at the lowest temperatures of the test (∼90°C) without C2H4 and H2O, and the NO storage was enhanced by the presence of C2H4 but inhibited by H2O at bed temperature under 100°C. Most of the NO x emissions during the FTP simulation were in the form of NO, and the catalyst produced low N2O levels on tests with C2H4. The oxidized Pd/Al2O3 sample exhibited poor NO storage with or without C2H4 and H2O, suggesting that cerium is important for NO x storage when the catalyst is oxidized. Both Pd technologies stored more NO when the samples were reduced, indicating that metallic Pd is effective for storing NO. The Pt/Al2O3 sample exhibited high NO storage efficiency between 90 & 120°C without H2O & C2H4 but lower efficiency with these species. Above 120°C, the catalyst produced high NO2 levels and high N2O levels on the tests with C2H4. The Pt/CZO sample performed similarly to the Pd/CZO sample except for higher NO2 and N2O levels. The Pd/CZO catalyst provided the best combination of NO storage with C2H4 and H2O above 100°C, essentially complete NO x release at the maximum bed temperature of the US06 simulation (400°C), low NO2 and N2O formation, and cost effectiveness.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Hydrocarbon-Water Adsorption and Simulation of Catalyzed Hydrocarbon Traps
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Manish Sharma, Michael Shane
      Catalyzed hydrocarbon traps (HC traps) are being developed to provide HC control during the cold start. HC traps are made up of an adsorbent material, such as a zeolite, and a three way catalyst (precious metal based) present on the same monolith to provide trapping and oxidation functions. Traps are typically formulated with a multi-layer washcoat structure with the catalyst layer on top, and the trapping material placed under. The HC traps operate by storing (trapping) the unburned hydrocarbon molecules in the adsorbent material at a lower temperature when adsorption is favored and oxidation does not occur, and subsequently releasing these trapped HCs when the catalyst has heated sufficiently to convert the HCs to carbon dioxide and water. This paper presents the results of a modeling, laboratory and vehicle study on the performance of HC traps. First we present procedure to evaluate trap performance in the laboratory that provides the kinetic parameters for HC adsorption. A mathematical model is presented that can be used to simulate the HC trap. The feedgas to the zeolite trap on vehicle contains both HCs and water, present in the vehicle exhaust. The various HC species and water compete for adsorption on the zeolites. Lab experiments conducted on zeolites to study the competitive adsorption of various HCs and water is presented. Experiments have been conducted where different HCs and water are sequentially adsorbed on the zeolite, and TPD conducted. For modeling, Langmuir isotherm is assumed to represent the adsorption phenomena on the zeolite sites. Exothermic effects of water adsorption on acidic zeolites have been presented. Details on the experiments done to estimate the heat of adsorption of water on zeolites, and the modeling results of water adsorption on zeolites have also been provided.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • Characterization of the active species in the silver/alumina system for
           lean NOx reduction with methanol
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Marika Männikkö, Xueting Wang, Magnus Skoglundh, Hanna Härelind
      Low-temperature activity and selectivity for lean NO x reduction over silver/alumina is strongly dependent on the composition of surface silver species. This motivates the present investigation of the role of the supported silver species for the lean NO x reduction with methanol. The catalyst samples, with different composition of silver species, are characterized by temperature programmed desorption of ammonia (NH3-TPD), temperature programmed reduction with hydrogen (H2-TPR) and temperature programmed desorption with NO (NO-TPD) in oxygen excess. The small differences in acidity do not significantly influence the lean NO x reduction with methanol. However, comparison of results from H2-TPR experiments with previous characterization by UV–vis spectroscopy shows that fairly small silver species are reduced by hydrogen, possibly small silver clusters. These small silver species are likely, in addition to others, involved in the lean NO x reduction reactions. NO-TPD experiments, in the presence of oxygen and hydrogen, reveal a shift in temperature for one of the desorption peaks from the different samples. This peak is likely related to the shift in temperature for NO x reduction during methanol-SCR conditions for the compared samples.
      Graphical abstract image

      PubDate: 2016-04-20T07:33:39Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267




      PubDate: 2016-04-20T07:33:39Z
       
  • Contents list
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267




      PubDate: 2016-04-20T07:33:39Z
       
  • Advances in Automobile Emissions Control Catalysis
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Di Wang, Bill Epling, Isabella Nova, Janos Szanyi



      PubDate: 2016-04-20T07:33:39Z
       
  • Identification of two types of Cu sites in Cu/SSZ-13 and their unique
           responses to hydrothermal aging and sulfur poisoning
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Jinyong Luo, Di Wang, Ashok Kumar, Junhui Li, Krishna Kamasamudram, Neal Currier, Aleksey Yezerets
      Cu/SSZ-13 has been widely used in industry as catalyst for selective catalytic reduction of NOx with NH3. For real-world application, hydrothermal aging and sulfur poisoning have been considered as two key mechanistic routes responsible for performance degradation, due to their direct impact on the active sites. In this study, exchanged Cu sites, the major active sites in Cu/SSZ-13, were characterized using DRIFTS, and their unique responses to hydrothermal aging and sulfur poisoning were revealed. Two types of exchanged Cu sites were identified, based on the perturbed zeolite TOT bond vibration, one at 900cm−1 and the other one at 950cm−1. Upon hydrothermal aging from 550°C to 700°C or 800°C, exchanged Cu ions at 950cm−1 transformed into the one type of Cu ions at 900cm−1; upon sulfur exposure (SO3/H2SO4), both types of exchanged Cu species decreased significantly in the population, as a result of interaction of Cu ions with sulfur species. Surprisingly, Cu species at 950cm−1 disappeared upon sulfur exposure. The unique responses of exchange Cu sites to different aging routes depend on the relative stability of Cu species, and could be explained by their interaction with zeolite framework. Meanwhile, since the relative population of exchanged Cu sites could be tuned by hydrothermal aging and sulfur exposure, the correlation of each Cu species with the performance could be well-resolved. It was found that both types of Cu species were active for SCR reactions, while only one type of Cu ions (950cm−1) appeared to be active for oxidation functions such as NO oxidation and NH3 oxidation.
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      PubDate: 2016-04-20T07:33:39Z
       
  • Ammonia formation over Pd/Al2O3 modified with cerium and barium
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Emma Catherine Adams, Magnus Skoglundh, Pär Gabrielsson, Mats Laurell, Per-Anders Carlsson
      We report experimental results for ammonia formation from nitric oxide and either a direct source of hydrogen or from a mixture of carbon monoxide and water over palladium based catalysts. Specifically, the addition of barium or cerium into an alumina supported palladium sample was studied. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation. Modification of Pd/Al2O3 with cerium proved to be beneficial for the activity due mainly to its enhancement of the water-gas-shift reaction, thus providing a higher availability of hydrogen for ammonia formation, but also because it remains active in the presence of slightly oxidizing global conditions when hydrogen is provided directly to the feed. Although the modification of Pd/Al2O3 with barium did not affect the ammonia formation during static conditions, the activity during lean/rich cycling increased. This is important for applications of passive selective catalytic reduction.
      Graphical abstract image Highlights

      PubDate: 2016-04-20T07:33:39Z
       
  • Passive SCR for lean gasoline NOX control: Engine-based strategies to
           minimize fuel penalty associated with catalytic NH3 generation
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Vitaly Y. Prikhodko, James E. Parks, Josh A. Pihl, Todd J. Toops
      Lean gasoline engines offer greater fuel economy than common stoichiometric gasoline engines. However, excess oxygen prevents the use of the current three-way catalyst (TWC) to control nitrogen oxide (NOX) emissions in lean exhaust. A passive SCR concept, introduced by General Motors Global R&D, makes use of a TWC that is already onboard to generate NH3 under slightly rich conditions, which is stored on the downstream SCR. The stored NH3 is then used to reduce NOX emissions when the engine switches to lean operation. In this work, the effect of engine parameters, such as air-fuel equivalence ratio and spark timing, on NH3 generation over a commercial Pd-only TWC with no dedicated oxygen storage component was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine. NOX reduction, NH3 formation, and reductant utilization processes were evaluated, and fuel efficiency was assessed and compared to the stoichiometric engine operation case. Air-fuel equivalence ratio was found to be one of the most important parameters in controlling the NH3 production; however, the rich operation necessary for NH3 production results in a fuel consumption penalty. The fuel penalty can be minimized by adjusting spark timing to increase rich-phase engine out NOX emissions and, thereby, NH3 levels. Additionally, higher engine out NOX during engine load increase to simulate acceleration resulted in additional fuel savings. A 10% fuel consumption benefit was achieved with the passive SCR approach by optimizing rich air-fuel equivalence ratio and spark timing while also utilizing acceleration load conditions.
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      PubDate: 2016-04-20T07:33:39Z
       
  • Rapid propylene pulsing for enhanced low temperature NOx conversion on
           combined LNT-SCR catalysts
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Yang Zheng, Mengmeng Li, Di Wang, Michael P. Harold, Dan Luss
      Lean reduction of NO x (NO+NO2) was conducted over combined LNT-SCR dual-layer and zoned monolithic catalysts using rapid propylene periodic pulsing into a lean feed. We investigated the effects of cycling frequency, reaction exotherm, hydrocarbon (HC) intermediates, top-layer material, LNT ceria content and catalyst configuration on the performance of dual-layer catalysts under fast propylene pulsing. High frequency propylene injection expands the operating temperature window of a conventional NO x storage and reduction (NSR) system in both low and high-temperature regions. The combination of rapid propylene pulsing and the dual-layer catalyst architecture achieves a low-temperature NO x conversion of up to 80% at a feed temperature of ca. 200°C and relevant space velocities (∼70kh−1). The working mechanisms of rapid propylene pulsing on both LNT and LNT-SCR catalysts are discussed. Fast cycling facilitates the generation of partially oxidized hydrocarbon intermediates over the LNT that can then either directly react with NO x or act as oxygen scavenger to maintain Pt in a reduced state for direct NO decomposition. The SCR top-layer traps partially oxygenated species that desorb from the LNT layer, enabling further production of N2 through a LNT-assisted HC-SCR pathway. Optimization of ceria content, top-layer material and catalyst configuration like SCR and PGM zoning can improve system performance at lower cost.
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      PubDate: 2016-04-20T07:33:39Z
       
  • The selective catalytic reduction of NOx over Ag/Al2O3 with isobutanol as
           the reductant
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): D. William Brookshear, Josh A. Pihl, Todd J. Toops, Brian West, Vitaly Prikhodko
      This study investigates the potential of isobutanol (iBuOH) as a reductant for the selective catalytic reduction (SCR) of NO x over 2wt% Ag/Al2O3 between 150 and 550°C and gas hourly space velocities (GHSV) between 10,000 and 35,000h−1. The feed gas consists of 500ppm NO, 5% H2O, 10% O2, and 375–1500ppm iBuOH (C1:N ratios of 3–12); additionally, blends of 24 and 48% v/v iBuOH in gasoline are evaluated. Over 90% NO x conversion is achieved between 300 and 400°C using pure iBuOH, including a 40% peak selectivity toward NH3 that could be utilized in a dual HC/NH3-SCR configuration. The iBuOH/gasoline blends are only able to achieve greater than 90% NO x conversion when operated at a GHSV of 10,000h−1 and employing a C1:N ratio of 12. Iso-butyraldehyde and NO2 appear to function as intermediates in the iBuOH-SCR mechanism, which mirrors the mechanism observed for EtOH-SCR. In general, the performance of iBuOH in the SCR of NO x over a Ag/Al2O3 catalyst is comparable with that of EtOH, although EtOH/gasoline blends display higher NO x reduction than iBuOH/gasoline blends. The key parameter in employing alcohols in SCR appears to be the COH:N ratio rather than the C1:N ratio.
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      PubDate: 2016-04-20T07:33:39Z
       
  • In situ FTIR spectroscopy of highly dispersed FeOx catalysts for NO
           reduction: Role of Na promoter
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Charles A. Roberts, Louisa Savereide, David J. Childers, Torin C. Peck, Justin M. Notestein
      The effect of Na on highly dispersed FeOx impregnated onto CeO2 via the unique precursor Na/Fe-ethylenediaminetetraacetate (NaFeEDTA) was investigated by comparison to a series of well-defined catalysts synthesized by the traditional precursor Fe(NO3)3 both with and without Na addition. Catalysts were evaluated for steady-state NO reduction by CO and activities varied based on synthesis method and Fe:Na ratio. Na contributed a promoter effect when added at a stoichiometric ratio (Fe:Na=1), providing an explanation for the higher activity of NaFeEDTA/CeO2 for NO reduction by CO. Activity decreased when excess Na was present in Fe(NO3)3 catalysts, but the stoichiometric promoter effect persisted up to ∼4.0Fe/nm2. In situ Fourier transform infrared (FTIR) spectroscopy during NO adsorption revealed the presence of unique NO adsorption species (1460cm−1) on the NaFeEDTA/CeO2, suggesting enhanced NO adsorption due to Na. At reaction temperature, FTIR bands of bulk nitrates on CeO2 were quantitatively shown to more rapidly undergo NO reduction catalytic transformations over NaFeEDTA/CeO2. These results increase understanding of mechanistic effects of Na on NO reduction over FeOx/CeO2 catalysts and serve to guide future design of oxide-based emission control catalysts that are free of Pt-group metals.
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      PubDate: 2016-04-20T07:33:39Z
       
  • Effect of lean-oxygen treatment on the adsorption and activity of
           zirconium phosphate @ Ce0.75Z0.25O2 for NH3-SCR deNOx
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Jun Yu, Zhichun Si, Xuankun Li, Lei Chen, Xiaodong Wu, Duan Weng
      As oxygen is one of the essential reactants in the standard SCR reactions, the ability of restoring and releasing oxygen is an important factor to determine the SCR activity of the catalyst. Ceria catalysts present an innate prospect in SCR reaction because of the facilitated redox cycles from Ce4+ to Ce3+. In the present study, zirconium phosphate @ Ce0.75Z0.25O2 (ZP/CZ) catalysts were pre-treated by O2, N2 and H2 to study the effects of lean-oxygen teatment on the structure, NH3/NO x adsorption and activity of catalysts. The catalysts were characterized by activity test, H2-TPR, XPS, DRIFT, NO x -TPD and kinetics study. The results showed that H2 treatment led to deeply reduced catalyst surface, resulting in mainly nitrites instead of nitrates adsorbed on catalyst in NO+O2 reaction and reduced Brønsted acidity of catalyst, which were responsible for the lowered deNO x activity of H2 treated catalyst. N2 treatment had only negligible influence on catalyst compared to O2 treated catalyst. Ammonium nitrate route was consolidated as possible NH3-SCR reaction mechanism over ZP/CZ catalyst by kinetics study.
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      PubDate: 2016-04-20T07:33:39Z
       
  • The impact of finite temperature on the coordination of Cu cations in the
           zeolite SSZ-13
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Florian Göltl, Philippe Sautet, Ive Hermans
      Understanding the fundamental properties of the Cu-exchanged zeolite SSZ-13, a catalyst for the selective catalytic reduction of nitrous oxides in the presence of ammonia, is a major challenge. Recent results for vibrational spectroscopy show that the active Cu centers are not static at room temperature, but change their coordination regularly when probe molecules are adsorbed. In this work we model the movement of bare Cu cations in SSZ-13 at room temperature (300K) using ab-initio molecular dynamics simulations. We find that Cu cations also change their coordination without adsorbent. We identify different coordinations for different oxidation states and analyze their distribution in dependence on the local Al position. The results in this work show that this thermal motion of the cation is a general feature, which probably influences the interpretation of various characterization methods as well as reaction path analysis. In the future it will be interesting to see which conditions have to be fulfilled that similar phenomena can also be observed for other systems.
      Graphical abstract image Highlights

      PubDate: 2016-04-20T07:33:39Z
       
  • Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu
           exchange sites under different conditions
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Renqin Zhang, Kathy Helling, Jean-Sabin McEwen
      Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal stability in the selective catalytic reduction (SCR) of NO x by using NH3 as a reductant. We find that the 6-membered ring (6MR) site is the most energetically favorable for a Cu+ ion while the 8-membered ring (8MR) sites are less favorable by about 0.5eV with respect to the 6MR site in Cu-SAPO-34. Upon adsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MR sites decreases and almost disappears. Further, a thermodynamic phase diagram study shows that a Cu+ ion bound to a single H2O molecule is the most stable species at low oxygen potential values while a Cu2+ ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. By comparing Cu K-edge XANES between Cu-SSZ-13 and Cu-SAPO-34 with Cu in different oxidation states, we conclude that it is difficult to differentiate the simulated XANES of Cu in these structures at a given oxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in the presence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidation state and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained under standard SCR conditions.
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      PubDate: 2016-04-20T07:33:39Z
       
  • NO oxidation on zeolite supported Cu catalysts: Formation and reactivity
           of surface nitrates
    • Abstract: Publication date: 1 June 2016
      Source:Catalysis Today, Volume 267
      Author(s): Hai-Ying Chen, Zhehao Wei, Marton Kollar, Feng Gao, Yilin Wang, Janos Szanyi, Charles H.F. Peden
      The comparative activities of a small-pore Cu-CHA and a large-pore Cu-BEA catalyst for the selective catalytic reduction (SCR) of NOx with NH3, and for the oxidation of NO to NO2 and the subsequent formation of surface nitrates were investigated. Although both catalysts are highly active in SCR reactions, they exhibit very low NO oxidation activity. Furthermore, Cu-CHA is even less active than Cu-BEA in catalyzing NO oxidation but is clearly more active for SCR reactions. Temperature-programed desorption (TPD) experiments following the adsorption of (NO2 +NO+O2) with different NO2:NO ratios reveal that the poor NO oxidation activity of the two catalysts is not due to the formation of stable surface nitrates. On the contrary, NO is found to reduce and decompose the surface nitrates on both catalysts. To monitor the reaction pathways, isotope exchange experiments were conducted by using 15NO to react with 14N-nitrate covered catalyst surfaces. The evolution of FTIR spectra during the isotope exchange process demonstrates that 14N-nitrates are simply displaced with no formation of 15N-nitrates on the Cu-CHA sample, which is clearly different from that observed on the Cu-BEA sample where formation of 15N-nitrates is apparent. The results suggest that the formal oxidation state of N during the NO oxidation on Cu-CHA mainly proceeds from its original +2 to a +3 oxidation state, whereas reaching a higher oxidation state for N, such as +4 or +5, is possible on Cu-BEA.
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      PubDate: 2016-04-20T07:33:39Z
       
  • Bimetallic carbon nanocatalysts for methanol steam reforming in
           conventional and membrane reactors
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Aleksandra A. Lytkina, Natalia V. Orekhova, Margarita M. Ermilova, Sergey V. Belenov, Vladimir E. Guterman, Mikhail N. Efimov, Andrey B. Yaroslavtsev
      In this paper we report the results obtained by a comparative study of catalytic activity of bimetallic (Ru–Rh, Ni–Cu) catalysts synthesized on a surface of different carbon supports: detonation nanodiamonds (DND), infrared pyrolyzed polyacrylonitrile, carbon black Vulcan-XC-72, in steam reforming of methanol (MSR) for hydrogen production. All obtained catalysts were characterized by N2 physisorption, SEM, TEM, FTIR spectroscopy, X-ray diffraction. It was shown, that activity of catalysts and products distribution depends on metal type, support material and the specific surface area. Support effect was investigated for Ru–Rh system. DND showed the best properties as a catalyst support. Ru–Rh system is more active than Cu–Ni as it is shown on the example of DND supported catalysts. Comparative study between conventional (CR) and membrane (MR) reactors was carried out. MR represented a flow system with a plane Pd-containing membrane. The effect of different catalysts on the MR performances as well as a general comparison of the experimental results was considered. Obtained results demonstrate the ability of the membrane to increase the reaction conversion. The hydrogen stream produced from the MR is ultra pure: especially, it is CO-free and thus suitable to be directly fed to a polymer electrolyte membrane fuel cell.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Towards a new membrane micro reactor system for direct synthesis of
           hydrogen peroxide
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Manuel Selinsek, Marcius Bohrer, Bhanu Kiran Vankayala, Katja Haas-Santo, Manfred Kraut, Roland Dittmeyer
      The approach of producing hydrogen peroxide (H2O2) by direct catalyzed reaction of H2 and O2 has been extensively studied over the past decades. The process offers the potential to establish a “green” alternative to the conventional large-scale anthraquinone process. However, the implementation of this reaction still faces major hurdles including safety, selectivity and productivity of the reaction. In this work, we report results on the development of a novel intensified suspension-flow membrane micro reactor system for direct synthesis of hydrogen peroxide as well as on a related flexible micro reactor system for transfer hydrogenation which served as a starting point. In the new reactor system for H2O2 direct synthesis safety issues are greatly reduced by the introduction of a membrane to separate the gaseous reactants. Furthermore productivity is maximized by increased mass transfer in micro channels and constant reactant feeding over the length of the reactor. Finally, the selectivity can be optimized by controlling the reactant distribution in the liquid phase. A rigorous two-dimensional single-phase model based on ANSYS Fluent was adopted to study the influence of the design on the reaction. This model had already been validated in a previous study. By expanding the model to describe the multiphase phenomena we were able to get further insight on the behavior of the overall system.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Vapor phase esterification using a CHA type of zeolite membrane
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Naotsugu Itoh, Jun Ishida, Takafumi Sato, Yasuhisa Hasegawa
      Vapor phase esterification in a chabazite (CHA) zeolite membrane reactor was attempted not only to improve the productivity but also to avoid the use of liquid strong acid. CHA zeolite membrane was successfully prepared on a porous alumina tube by hydrothermal synthesis, showing a water permeance of ca. 2×10−7mol/(m2·s·Pa) and a selectivity of 2850 for H2O/EtOH at 130°C. As the alternate of the liquid acid, proton exchanged mordenite (H-MOR) was selected as a solid catalyst, where the esterification was found to be explained according to the Eley-Rideal mechanism. When vapor-phase esterification was carried out in a double tube type membrane reactor, some equilibrium shift was observed; this was achieved by continuous and selective water removal along the reactor length. Further, it was demonstrated that a simulation model for the membrane reactor, established on the assumption that the ideal conditions could be applied, described the reactor performance well.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Electrochemically assisted synthesis of fuels by CO2 hydrogenation over Fe
           in a bench scale solid electrolyte membrane reactor
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Esperanza Ruiz, Pedro J. Martínez, Ángel Morales, Gema San Vicente, Gonzalo de Diego, José María Sánchez
      The electrochemically assisted synthesis of fuels by CO2 hydrogenation was studied over a cheap, widespread and non-precious Fe catalyst in a bench scale oxygen ion conducting membrane (YSZ) reactor. The studies were performed under conditions representative of potential practical application i.e., under atmospheric pressure, at relatively low temperatures and high gas flow rates, with varying H2/CO2 ratios and using gas compositions typical for postcombustion CO2 capture exit streams and easily scalable catalyst-electrode configurations. The Fe-TiO2 catalyst film was deposited by “dip-coating” and characterised both after pre-reduction and after testing. CO2 conversion and selectivities to CH3OH and C2H6O can be enhanced up to 4, 50 and 1.7 times, respectively, by electrochemically controlled migration of O2− promoting ions to or from the catalyst surface. The optimum temperature for the process was 325°C. Lower gas flow rates favoured the synthesis of CH3OH and C2H6O. CO2 conversion and selectivities to CH3OH and C2H6O showed a maximum for a stoichiometric H2/CO2 ratio of 3. Formation of C3H6 and CO is strongly favoured for a H2/CO2 ratio of 4 and 2, respectively, as a result of the increased and decreased hydrogen availability in the reaction system.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Catalytic membrane reactor for the production of biofuels
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Dalia Liuzzi, Francisco José Pérez-Alonso, José Luis G. Fierro, Sergio Rojas, Frank L. van Wijk, Ivo Roghair, Martin van Sint Annaland, Ekain Fernandez, Jose Luis Viviente, D.A. Pacheco Tanaka
      The H2-distributed feeding concept using Pd/Ag-based membranes and an Ru-based catalyst in a Packed Bed Membrane Reactor (H2-PBMR) for the synthesis of biofuels via the so-called Fischer–Tropsch Synthesis has been demonstrated. The most successful approach resulted when H2-poor syngas (H2/CO=1) typically obtained from the gasification of biomass was fed directly through the reaction chamber, i.e., to the catalyst bed, whereas the H2 needed to reach the proper stoichiometry for the FTS (H2/CO=2) was admitted, and properly distributed, into the catalyst bed through the Pd/Ag-based membrane by flowing H2/He mixtures at the retentate side of the membrane. Under the optimum reaction conditions, the CO conversion measured with the H2-distributed feeding concept is lower than that obtained in a conventional Packed Bed Reactor with H2/CO=2 (37.9 vs 50.7%), but significantly higher than that obtained in a conventional reactor with H2/CO=1 (14.1%). Remarkably, the productivity towards high-molecular hydrocarbons increases by almost 70% and the methane production decreases by one order of magnitude when using the H2-distributed feeding concept in a Packed Bed Membrane Reactor.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Experimental and exergy evaluation of ethanol catalytic steam reforming in
           a membrane reactor
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Ali Hedayati, Olivier Le Corre, Bruno Lacarrière, Jordi Llorca
      The application of exergy analysis in the evaluation of the ethanol steam reforming (ESR) process in a catalytic membrane reactor (CMR) was presented. ESR experiments were performed at T =873–923K and P =4–12bar in a CMR containing Pd–Ag membranes sandwiched by Pd–Rh/CeO2 catalyst, aiming to produce fuel cell grade pure hydrogen. The effect of the operating conditions on the pure hydrogen production rate, hydrogen yield and recovery, exergy efficiency, and thermodynamic losses was investigated. Total hydrogen yield of 3.5mol H2 permeated per mol ethanol in feed with maximum hydrogen recuperation of 90% was measured at 923K and 12bar. The highest amount of exergy was destructed via heat losses and the retentate gas stream. Exergy efficiency up to around 50% was reached in the case of the insulated reactor at 12bar and 923K. Exergy efficiency placed between 70–90% in the case of recovery of the retentate gas in an insulated reactor. It was concluded that operating at the highest pressure, the lowest S/C ratio, and 923K gives the best exergy efficiency.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Aqueous phase hydrogenation of levulinic acid using a porous catalytic
           membrane reactor
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): John P. Stanford, Michelle C. Soto, Peter H. Pfromm, Mary E. Rezac
      Membrane reactors offer an alternative approach for conducting three-phase heterogeneous chemical reactions. The membrane acts as a liquid/gas phase contactor, while also serving as the support for a solid catalyst. A significant benefit from this approach is circumvention of gas phase dissolution and diffusion in the liquid phase to reach catalytic sites. This method of gas phase mass transfer allows a significant reduction in operating pressure compared to traditional three-phase reactors that often require higher gas pressures due to low gas solubility and diffusivity in the liquid phase. The membrane reactor in this work consists of a porous expanded polytetrafluoroethylene (ePTFE) membrane with deposited Ru catalyst particles. The reaction studied is the aqueous phase hydrogenation of levulinic acid to produce γ-valerolactone. The highly hydrophobic PTFE material provides an almost impermeable barrier to the liquid phase while allowing hydrogen gas to freely transport through the pores to reach catalytic sites located at the liquid/membrane interface. The reaction kinetics displayed by the membrane reactor favorably compare to those of a packed bed reactor (PBR). In terms of hydrogen pressure the maximum catalytic benefit in comparison to the PBR is obtained at pressures greater than 0.7bar, and a more pronounced and continuously increasing catalytic benefit is obtained with increasing temperature.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Catalytic activity of LiZr2(PO4)3 nasicon-type phosphates in ethanol
           conversion process in conventional and membrane reactors
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Andrey B. Ilin, Natalia V. Orekhova, Margarita M. Ermilova, Andrey B. Yaroslavtsev
      In this paper synthesis and catalytic properties of new catalysts based on double lithium-zirconium phosphate (LiZr2(PO4)3) with monoclinic NASICON-type structure, doped by indium, niobium and molybdenum are discussed. The obtained samples with particle size of 50–300nm were characterized by X-ray diffraction, scanning electron microscopy and X-ray microanalysis. The synthesized samples exhibit catalytic activity in the dehydration and dehydrogenation reactions of ethanol conversion. The main products were acetaldehyde, diethyl ether, hydrogen, C2- and C4-hydrocarbons. Indium- and molibdenum-doped samples were characterized by high activity in dehydrogenation processes, while niobium-doped was more active in dehydration processes. The highest selectivity in diethyl ether formation was achieved for LiZr2(PO4)3 and Nb-doped samples (90 and 60% at 300°C). The highest hydrogen yield (up to 60%) was obtained with the use of In-doped catalyst. LiZr2(PO4)3 and Mo-doped samples are also noticeable for high C4-hydrocarbons formation, selectivity to which reaches 60% at 390°C. Use of a 100% hydrogen selective palladium-ruthenium alloy membrane increases hydrogen yield by 20%.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Hydrogen production from energy carriers by silica-based catalytic
           membrane reactors
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Lie Meng, Toshinori Tsuru
      Catalytic membrane reactors equipped with a microporous inorganic membrane have attracted a considerable amount of research interest as an alternative to the current industrial processes for hydrogen production. The present article focuses on the state of the art in the development of silica-based catalytic membrane reactors for hydrogen production from energy carriers. Highly promising energy carriers for the storage and transportation of hydrogen are illustrated. Recent advances in high-performance silica-based microporous membranes for use in hydrogen separation are highlighted. Experimental and theoretical investigations into the application of silica-based catalytic membrane reactors for the dehydrogenation of energy carriers including ammonia, cyclohexane and methylcyclohexane are discussed.
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      PubDate: 2016-04-16T03:02:18Z
       
  • Composite catalytic tubular membranes for selective hydrogenation in
           three-phase systems
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Michael D. Wales, Logan B. Joos, Wade A. Traylor, Peter Pfromm, Mary Rezac
      Catalytic membrane contact reactors (CMCRs) were evaluated for the selective three-phase hydrogenation of the model reaction, the partial hydrogenation of soybean oil (PHSO). PHSO produces copious amounts of trans-fats when carried out in a batch slurry reactor due to hydrogen starvation at the catalyst, caused by inherent mass transfer limitations of the system. In this study composite ceramic/polymer membranes were rendered catalytically active by depositing a polymer-palladium complex, (poly(N-vinyl-2-pryyolidone) (PVP)-palladium (Pd)), onto the selective skin of the membrane. Hydrogen gas was supplied to the support side of the membrane, the hydrogen gas permeated from the support side to the skin side of the membrane, where it dissociated onto the catalyst surface. Liquid reactant was circulated over the skin side of the membrane, allowing the three components to come into contact and react. Our system is shown to be nearly zero order in hydrogen, indicating that the catalyst surface maintains high hydrogen coverage throughout. CMCRs produced 50% less trans-fat at equivalent levels of hydrogenation compared to slurry reactors. It was further demonstrated that an increase in temperature had minimal effects on trans-fat formation, while significantly increasing hydrogenation rates; allowing the system to capture higher reaction rates without adversely affecting product quality.
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      PubDate: 2016-04-16T03:02:18Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268




      PubDate: 2016-04-16T03:02:18Z
       
  • Contents list
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268




      PubDate: 2016-04-16T03:02:18Z
       
  • Preface
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Sylwia Mozia, Angelo Basile, José M. Sousa



      PubDate: 2016-04-16T03:02:18Z
       
  • Effect of Re addition on the WGS activity and stability of
           Pt/CeO2–TiO2 catalyst for membrane reactor applications
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): V. del Villar, L. Barrio, Arash Helmi, M. Van Sint Annaland, F. Gallucci, J.L.G. Fierro, R.M. Navarro
      The catalytic performance of RePt/CeO2–TiO2 catalysts for the WGS reaction under conditions compatible with membrane reactor was investigated. The WGS activity and stability of the Pt/CeO2–TiO2 catalyst was significantly influenced by the addition of rhenium. The intrinsic WGS activity per atom of platinum improves with the addition of Re to Pt/CeO2–TiO2 catalyst. The addition of rhenium also has a beneficial effect on its stability under WGS conditions compatible with membrane reactor use. The improvement in WGS activity and stability is proposed to be associated with the improvement in the reduction behavior of the highly dispersed CeO2 and ReO x species present in the bimetallic RePt catalyst respect to the monometallic Pt/CeTi counterpart and to the presence of rhenium species in close contact with Pt that could introduce an additional redox activity sites stable under WGS conditions and/or prevent the sintering of Pt crystallites under WGS conditions.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Theoretical and experimental study of methane partial oxidation to syngas
           in catalytic membrane reactor with asymmetric oxygen-permeable membrane
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): E. Shelepova, A. Vedyagin, V. Sadykov, N. Mezentseva, Y. Fedorova, O. Smorygo, O. Klenov, I. Mishakov
      This paper presents results of theoretical and experimental research concerning synthesis of multilayer asymmetric oxygen-permeable membrane and its application for partial oxidation of methane. The membrane is based on macroporous Ni-Al foam substrate with three layers of perovskite-fluorite nanocomposites with graded (meso-micro) porosity, thin dense MnFe2O4–Ce0.9Gd0.1O2 layer and porous layer of LaNi0.9Pt0.1O3/Pr0.3Ce0.35Zr0.35O2-x catalyst. Testing of membrane in methane partial oxidation process demonstrates a good and stable performance. The mathematical modeling of the methane partial oxidation process in the catalytic membrane reactor has been provided. The developed model was applied to find the process (temperature, gas flow rates, etc.) and membrane (pore diameter of porous layer, thickness of porous layer) parameters corresponding to highest methane conversion and syngas selectivity.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Fe/EuroPh catalysts for limonene oxidation to 1,2-epoxylimonene, its diol,
           carveol, carvone and perillyl alcohol
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Jacek Młodzik, Agnieszka Wróblewska, Edyta Makuch, Rafał J. Wróbel, Beata Michalkiewicz
      The catalysts in the form of an activated carbon EuroPh supported Fe were prepared and characterized structurally and chemically by XRD, nitrogen sorption, FESEM, EDX, and ICP-AES methods. The active phase was magnetite Fe3O4. The concentration of Fe in the catalysts was equal to 0.68, 1.32, 2.64wt%. The catalytic activity of the obtained catalysts was examined in limonene oxidation with hydrogen peroxide and tert-butyl hydroperoxide as oxidants. The studies were carried out in a batch reactor. The catalytic activity of the recovered catalysts was also tested. The research showed that all from the studied catalysts were active in the limonene oxidation. As a result of limonene oxidation the following products were mainly obtained: 1,2-epoxylimonene diol, carveol, carvone and perillyl alcohol – products with a great importance. The reused catalysts were characterized by considerably lover activity in the limonene oxidation than in the first run, especially when the oxidation was performed with t-butyl hydroperoxide.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • The studies on the limonene oxidation over the microporous TS-1 catalyst
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Agnieszka Wróblewska, Edyta Makuch, Piotr Miądlicki
      The studies on the oxidation of limonene with 60wt% hydrogen peroxide over the titanium silicalite TS-1 catalyst were carried out. The influence of the following parameters was examined: the temperature 0–120°C, the molar ratio of limonene/H2O2 =1:2–5:1, methanol concentration 60–95wt%, TS-1 content 0.25–8wt% and the reaction time 15min to 11 days. The studies showed that the most beneficial conditions for the obtaining of high selectivity of 1,2-epoxylimonene, at simultaneously high values of the conversion of reactants and the efficiency of hydrogen peroxide, are as follows: the temperature 80°C, the molar ratio of limonene/H2O2 =1:1, the methanol concentration 80wt%, the TS-1 content 3wt% and the reaction time 10 days. Moreover, the research showed that the process of limonene oxidation is very complicated, because during this process also other very useful oxygenated derivatives of limonene can be obtained, for example: perillyl alcohol, carveol, carvone and 1,2-epoxylimonene diol. The studies on the reuse of the TS-1 catalyst showed that it is very stable catalyst at the studied conditions and it can be recycled to the oxidation process at least three times.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Flow-through catalytic membrane reactors for the destruction of a chemical
           warfare simulant: Dynamic performance aspects
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): M.M. Yousef Motamedhashemi, Fokion Egolfopoulos, Theodore Tsotsis
      A model was developed to describe the dynamic performance of a flow-through catalytic membrane reactor (FTCMR) used for the destruction of a chemical warfare agent (CWA) simulant, specifically dimethyl methylphosphonate (DMMP). For such a reactor, after a certain time period during which it provides full protection, its performance begins to decline, as manifested by a gradual decline in the thermocatalytic destruction rate of the DMMP and discernible changes in the membrane's throughput. The model ascribes these phenomena to changes in the catalytically active membrane surface area and in the accessible membrane pore volume, which are brought upon by the deposition of phosphorous-containing by-products of the DMMP's thermocatalytic decomposition reaction. Such a hypothesis is supported by experimental data for both fresh and aged membranes that substantiate significant losses in surface area and pore volume, and indicate the presence of phosphorous in the aged membranes. The model was used to fit the experimental data from a FTCMR operating under a total flow-through (100% stage-cut) mode of operation, and was shown to describe well the experimental data. In addition, the model was utilized in a predictive mode to describe the performance of a FTCMR employing another membrane from the same batch and catalytically activated under the same procedure, but operating under different operating conditions (0% stage-cut). The model was shown to provide an adequate fit to the experimental data. Following such validation, the model has been used to gain further insight into the impact of the various reactor parameters on FTCMR performance. Its use has, subsequently, led to the development of a novel reactor configuration that significantly expands the operating performance window of the FTCMR for the thermocatalytic CWA destruction.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Cu SSZ-13 zeolite catalyst on metallic foam support for SCR of NOx with
           ammonia: Catalyst layering and characterisation of active sites
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): J. Kryca, P.J. Jodłowski, M. Iwaniszyn, B. Gil, M. Sitarz, A. Kołodziej, T. Łojewska, J. Łojewska
      A particular aim of this work was to develop a method of catalyst layering on the surface of metallic catalyst carriers used in structured reactors. The CuSSZ-13 catalyst was chosen as a prospective catalyst for SCR of NO x converter for exhaust from biogas engines. For the first time in the literature the method of in situ synthesis CuSSZ-13 catalyst was elaborated and tested for precalcined Kanthal foam. The CuSSZ-13 catalyst prepared in such a way demonstrated very high activity in NH3-SCR of NO with ammonia and high hydrothermal stability in comparison with analogically prepared CuZSM-5 used as a reference catalyst. The active centres working during SCR at various temperatures were investigated by in situ FTIR experiments with NH3 and CO probe molecules. The structure-activity relationships found for catalyst working at high temperature show that the Lewis acidic Cu+ sites are available exclusively for NO and Brønsted acidic sites for NH3 sorption above 400°C. Furthermore, high hydrothermal stability of the CuSSZ-13 catalyst is correlated to the favourable location of Al atoms in the zeolite lattice which prevents dealumination and also to the resulted from this stabilization of copper Cu+ active sites.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Removal of trichloroethylene from water in the catalytic membrane reactor
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Inna V. Petrova, Tatyana S. Anokhina, Roman S. Borisov, Vladimir V. Volkov, Andrey B. Yaroslavtsev
      This work describes a single-stage method for the removal of chlorine-containing species from water using a catalytic membrane reactor based on Pd-loaded porous polypropylene hollow fiber membranes. The kinetics of this process is characterized. The degree of water purification is shown to be not less than 98%.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Ethanol production from whey in a bioreactor coupled with direct contact
           membrane distillation
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Maria Tomaszewska, Lidia Białończyk
      The ethanol production from whey in a bioreactor integrated with direct contact membrane distillation (MDBR) was investigated. Fermentation was studied using concentrated whey and deproteinized whey enriched with lactose or sucrose. Whey lactose was prehydrolyzed in an enzymatic process using β-galactosidase into a mixture of glucose and galactose. The fermentation process was performed using Saccharomyces cerevisiae yeasts species. It was found that MDBR can be successfully applied for ethanol production from whey. A continuous removal of produced ethanol and other volatile compounds from a fermenting broth by membrane distillation resulted in a high efficiency of sugar conversion into ethanol. The efficiency of ethanol production in MDBR in the fermentation of deproteinized whey enriched with sucrose was close to the theoretical value and 1.9× higher than that in the process carried out in a bioreactor without MD. It was found that salt present in the concentrated whey decreased the process efficiency.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • Application of nanofiltration for production of 1,3-propanediol in
           membrane bioreactor
    • Abstract: Publication date: 15 June 2016
      Source:Catalysis Today, Volume 268
      Author(s): Marta Waszak, Agata Markowska-Szczupak, Marek Gryta
      Biodiesel production from rapeseed oil generates various by-products, for example crude glycerol. Glycerol can be utilized by microbial conversion to 1,3-propanediol (1,3-PD), which can be used as a raw material for the synthesis of polyesters and polyurethanes. The results of studies on the synthesis of 1,3-PD from glycerol by use of Citrobacter freundii bacteria were presented. A biosynthesis cost is generally determined based on the costs of nutrients used for culture medium preparation and the costs of broth separation by integrated downstream processes. In this work nanofiltration (NF) was used as a pre-treatment stage for 1,3-PD separation from the broth. Additionally, the NF retentate was reused for the preparation of culture medium, resulting in a change of the initial composition of broth. The catalytic activity of enzymes is strongly affected by broth composition. However, the efficiency of batch fermentations based on the commercial media and NF retentate was similar. Thus, the application of NF process enables a cheaper production of 1,3-PD by biosynthesis. The influence of some broth ingredients, such as carboxylic acids, on variations of biocatalytic properties of used bacteria was discussed.
      Graphical abstract image

      PubDate: 2016-04-16T03:02:18Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 15 May 2016
      Source:Catalysis Today, Volume 266




      PubDate: 2016-03-22T02:25:13Z
       
  • Contents list
    • Abstract: Publication date: 15 May 2016
      Source:Catalysis Today, Volume 266




      PubDate: 2016-03-22T02:25:13Z
       
  • Novel nanomaterials for photocatalysis, photochemistry, and photobiology
    • Abstract: Publication date: 15 May 2016
      Source:Catalysis Today, Volume 266
      Author(s): Vicente Rodríguez-González, Agileo Hernandez-Gordillo, Yun Hang Hu



      PubDate: 2016-03-22T02:25:13Z
       
  • Renewable hydrogen harvest process by hydrazine as scavenging electron
           donor using gold TiO2 photocatalysts
    • Abstract: Publication date: 15 May 2016
      Source:Catalysis Today, Volume 266
      Author(s): Mariana Hinojosa-Reyes, Agileo Hernández-Gordillo, Rodolfo Zanella, Vicente Rodríguez-González
      The photocatalytic activity of well-known gold photocatalysts is investigated in the water splitting reaction by using either the ethanol or the hydrazine molecule as a scavenging agent in order to generate a renewable hydrogen harvest process. Gold photocatalysts are prepared by the deposition–precipitation method on sol–gel TiO2 and using P25 as reference. These photocatalysts are surface and structurally characterized by N2 physisorption, UV–vis and XPS spectroscopies, X-ray diffraction, H2-TPR, and STEM-HAADF microscopy. The Au/TiO2 photocatalysts exhibit the highest H2 generation in the presence of either a high concentration of ethanol (3.5M) or a low hydrazine concentration (20mM). Stability tests for the Au/TiO2 photocatalysts are carried out in several cycles using the same water–hydrazine solution, showing a hydrogen production enhancement followed by a steady state reaction. The stability of the production process is corroborated by both photocatalysts and the scavenging solution, which suggest either a slow concentration decrement or a dosage process of the hydrazine molecule. Hydrazine acts as a scavenging dosing agent which maintains the stability of the more photoactive catalysts for 50h.Keywords: Gold TiO2; Water splitting; Water–hydrazine; Hydrogen production
      Graphical abstract image

      PubDate: 2016-03-22T02:25:13Z
       
 
 
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