Influence Of Support Material Research Articles

Influence of support materials on the electroactive behavior, structure and gene expression of wild type and GSU1771-deficient mutant of Geobacter sulfurreducens biofilms.

Geobacter sulfurreducens DL1 is a metal-reducing dissimilatory bacterium frequently used to produce electricity in bioelectrochemical systems (BES). The biofilm formed on electrodes is one of the most important factors for efficient electron transfer; this is possible due to the production of type IV pili and c-type cytochromes that allow it to carry out extracellular electron transfer (EET) to final acceptors. In this study, we analyzed the biofilm formed on different support materials (glass, hematite (Fe2O3) on glass, fluorine-doped tin oxide (FTO) semiconductor glass, Fe2O3 on FTO, graphite, and stainless steel) by G. sulfurreducens DL1 (WT) and GSU1771-deficient strain mutant (Δgsu1771). GSU1771 is a transcriptional regulator that controls the expression of several genes involved in electron transfer. Different approaches and experimental tests were carried out with the biofilms grown on the different support materials including structure analysis by confocal laser scanning microscopy (CLSM), characterization of electrochemical activity, and quantification of relative gene expression by RT-qPCR. The gene expression of selected genes involved in EET was analyzed, observing an overexpression of pgcA, omcS, omcM, and omcF from Δgsu1771 biofilms compared to those from WT, also the overexpression of the epsH gene, which is involved in exopolysaccharide synthesis. Although we observed that for the Δgsu1771 mutant strain, the associated redox processes are similar to the WT strain, and more current is produced, we think that this could be associated with a higher relative expression of certain genes involved in EET and in the production of exopolysaccharides despite the chemical environment where the biofilm develops. This study supports that G. sulfurreducens is capable of adapting to the electrochemical environment where it grows.

Density functional theory study on Support-Promoted CH4 reforming in Ni-Based oxygen carriers for chemical-looping conversion

Metal oxides play a pivotal role in the conversion of carbonaceous fuels. Nickel-based oxides, due to their affordability and high C–H activation activity, are regarded as promising oxygen carriers (OCs) for CH4 chemical looping technologies. Additives like Al2O3, ZrO2, and MgAl2O4 are used to boost the reactivity of OCs and mitigate agglomeration of OC particles at elevated temperatures. Despite extensive experimental studies on support selection, the influence of support materials on CH4 conversion remains unclearly. This research analyzed and compared the kinetic pathways of CH4 conversion on the supported and unsupported nickel-based OCs, utilizing the Density Functional Theory (DFT) model, to determine the rate limiting step (RLS) in the chemical looping process. The most promising support, NiAl2O4, weakens the Ni-C bond due to pronounced interaction between the OCs and supports, thereby leading to a reduced activation energy barrier for CH4 dehydrogenation. By probing the relationships between reaction kinetic barriers and critical electronic properties of OCs, a screening strategy is proposed to accelerate the development and optimization of novel OC/support materials for CH4 chemical looping conversion.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) provides the combined benefit of reducing anthropogenic CO2 emissions while supplying a wide variety of valuable chemical feedstock chemicals.[1] While many transition metals are CO2RR active catalysts, only copper can form products requiring more than two electrons in the electrochemical conversion of CO2. This includes a multitude of high-value-added products such as ethylene, ethanol, or propanol.[1-3] The selectivity of the CO2RR is strongly influenced by the structure and morphology of the copper catalysts. Consequently, structural properties such as copper nanoparticle size, display an influence on CO2RR product selectivity.[4] This creates a substantial problem as copper is highly susceptible to reorganization during the electrochemical CO2RR, which inhibits the retention of apparently favorable surface structures during the CO2RR.[5] As a consequence, structure-selectivity relations can neither be reliably described nor completely understood. This problem is exacerbated by a lack of understanding of the underlying reasons that drive reorganization and therefore degradation of the catalyst. At reductive potentials, as used in the electrochemical CO2RR, coalescence and subsequent agglomeration are assumed to be the dominant degradation mechanism, while oxidative potentials generally trigger support corrosion and dissolution. Strategies for stabilization to retain activity and selectivity are therefore essential. Nevertheless their importance in the electrochemical CO2RR, stabilization methods are largely missing. For other reactions, such as the oxygen reduction reaction, various studies showed an increase in overall stability by containing the catalysts in a confined space.[6-8] This work presents the stabilizing effect of three different carbon support materials with unique morphologies on copper nanoparticles (CuNPs). Through the use of a non-porous Vulcan, a Ketjenblack with a diverse pore size distribution and highly defined mesoporous graphitic spheres (MGS) with a unimodal pore size distribution, the influence on structural characteristics of the carbon material on the stabilization of the CuNPs can be presented. The representative copper catalysts were prepared by colloidal synthesis or incipient wetness impregnation and evaluated through micro-flow cell measurements with online gas chromatography (GC) analytics and pre-/post catalytic high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), visualizing changes in the catalyst structure and morphology after the reaction. We demonstrate the successful stabilization of CuNPs by pore confinement against particle coalescence and subsequent agglomeration for up to 20 h of electrochemical CO2RR conditions, with GC analysis providing great insight into the influence of particle size, morphology, and location of the CuNPs on CO2RR product selectivity. Intriguingly, a high share of CO2RR products was observed for stabilized < 4 nm CuNPs putting the established particle size effect for the CO2RR, where the hydrogen evolution reaction was predominantly observed on nanoparticles below 15 nm, into question.[4] These results present new ways of stabilizing CuNPs and highlight the need for post-catalytic evaluation of the catalysts' morphological state to precisely derive performance-structure indicators.Work accepted and soon to be published in ChemElectroChemdoi.org/10.1002/celc.202200924Literature:[1] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramollo, I. Chorkendorff, Chem Rev. 2019, 119, 7610–7672.[2] Y. Hori, Modern Aspects of Electrochemistry No. 42, Springer, 2008.[3] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ. Sci. 2012, 5, 7050–7059.[4] R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. 2014, 136, 6978–6986.[5] W. T. Osowiecki, J. J. Nussbaum, G. A. Kamat, G. Katsoukis, M. Ledendecker, H. Frei, A. T. Bell, A. P. Alivisatos, ACS Appl. Energy Mater. 2019, 2, 7744–7749.[6] Y. Li, F. Cui, M. B. Ross, D. Kim, Y. Sun, P. Yang, Nano Lett. 2017, 1312–1317.[7] Y. T. Guntern, J. R. Pankhurst, J. Vavra, M. Mensi, V. Mantella, P. Schouwink, R. Buonsanti, Angew. Chem. 2019, 131, 12762–12769.[8] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc. 2012, 134, 20457 – 20465. Figure 1

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

AbstractThe copper‐catalyzed electrochemical CO2 reduction reaction represents an elegant pathway to reduce CO2 emissions while producing a wide range of valuable hydrocarbons. The selectivity for these products depends strongly on the structure and morphology of the copper catalyst. However, continued deactivation during catalysis alters the obtained product spectrum. In this work, we report on the stabilizing effect of three different carbon supports with unique pore structures. The influence of pore structure on stability and selectivity was examined by high‐angle annular dark field scanning transmission electron microscopy and gas chromatography measurements in a micro‐flow cell. Supporting particles into confined space was found to increase the barrier for particle agglomeration during 20 h of chronopotentiometry measurements at 100 mA cm−2 resembling long‐term CO2 reduction conditions. We propose a catalyst design preventing coalescence and agglomeration in harsh electrochemical reaction conditions, exemplarily demonstrated for the electrocatalytic CO2 reduction. With this work, we provide important insights into the design of stable CO2 electrocatalysts that can potentially be applied to a wide range of applications.

The Influence of Support Materials on The Photo-Fenton-like Degradation of Azo Dye Using Continuous Nanoparticles Fixed-bed Column

This study used a continuous photo-Fenton-like method to remediate textile effluent containing azo dyes especially direct blue 15 dye (DB15). A Eucalyptus leaf extract was used to create iron/copper nanoparticles supported on bentonite for use as catalysts (E@B-Fe/Cu-NPs). Two fixed-bed configurations were studied and compared. The first one involved mixing granular bentonite with E@B-Fe/Cu-NPs (GB- E@B-Fe/Cu-NPs), and the other examined the mixing of E@B-Fe/Cu-NPs with glass beads (glass beads-E@B-Fe/Cu-NPs) and filled to the fixed-bed column. Scanning electron microscopy (SEM), zeta potential, and atomic forces spectroscopy (AFM) techniques were used to characterize the obtained particles (NPs). The effect of flow rate and DB15 concentration on the photo-Fenton-like degradation of DB15 in continuous fixed-bed systems was investigated. To optimize both studied systems, the response surface methodology using the central composite design (CCD) was used. The analysis shows that the removal efficiency for GB-E@B-Fe/Cu-NPs was 81% and for glass beads-E@B-Fe/NPs was 62.6%.

High-value products from ex-situ catalytic pyrolysis of polypropylene waste using iron-based catalysts: the influence of support materials.

Catalytic pyrolysis is considered a promising strategy for the utilisation of plastic waste from the economic and environmental perspectives. As such, the supporting materials play a critical role in the properties of the catalyst. This study clarified this influence on the dispersion of the iron (Fe) within an experimental context. Four different types of typical supports with different physical structures were introduced and explored in a two-stage fixed-bed reactor; these included metallic oxides (Al2O3, TiO2), a non-metallic oxide (SiO2), and molecular sieves (ZSM-5). The results show that the liquid products were converted into carbon deposits and lighter gaseous products, such as hydrogen. The Al2O3-supported catalyst with a relatively moderate specific surface areas and average pore diameter exhibited improved metal distribution with higher catalytic activity. In comparison, the relatively low specific surface areas of TiO2 and small average pore diameters of ZSM-5 had a negative impact on metal distribution and the subsequent catalytic reformation process; this was because of the inadequate reaction during the catalytic process. The Fe/Al2O3 catalyst produced a higher yield of carbon deposits (30.2wt%), including over 65% high-value carbon nanotubes (CNTs) and hydrogen content (58.7vol%). Additionally, more dispersive and uniform CNTs were obtained from the Fe/SiO2 catalyst. The Fe/TiO2 catalyst promoted the formation of carbon fibre twisted like fried dough twist. Notably, there was interesting correspondence between the size of the reduced Fe nanoparticles and the product distribution. Within certain limits, the smaller Fe particle size facilitates the catalytic activity. The smaller and better dispersed Fe particles over the support materials were observed to be essential for hydrocarbon cracking and the subsequent formation of carbon deposits. The findings from this study may provide specific guidance for the preparation of different forms of carbon materials.

Ru nanoparticles supported on amorphous ZrO2for CO2methanation

The influence of support materials and preparation methods on CO2methanation activity was investigated using Ru nanoparticles supported on amorphous ZrO2(am-ZrO2), crystalline ZrO2(cr-ZrO2), and SiO2.

The influence of support materials on the structural and electronic properties of gold nanoparticles - a DFT study.

Supported gold nanoparticles are used for a wide range of catalytic processes. In this work, we use dispersion corrected density functional theory (DFT-D) to study the effect of commonly used support materials (MgO, C, CeO2) on small gold particles with up to 19 atoms. Our results show that the preferred cluster shape and morphology is highly dependent on the support material due to different adsorption strength and structural mismatch between the cluster and the surface material. We developed an algorithm to measure the mismatch between the cluster interface and the support surface. Moreover, depending on the support material, the gold clusters exhibit a positive or negative polarisation, which ultimately has strong implications on the catalytic activity of such particles. This behaviour is rationalised by an analysis of the electronic structure of the metal particles and support materials.

Influence of support material on the electrocatalytic activity of nickel oxide nanoparticles for urea electro-oxidation reaction

Nickel oxide nanoparticles were deposited on different carbon supports including activated Vulcan XC-72R carbon black (NiO/AC), multi-walled carbon nanotubes (NiO/MWCNTs), graphene (NiO/Gr) and graphite (NiO/Gt) through precipitation step followed by calcination at 400 °C. To determine the crystalline structure and morphology of prepared electrocatalysts, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed. The electrocatalytic activity of NiO/carbon support electrocatalysts was investigated towards urea electro-oxidation reaction in NaOH solution using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Urea oxidation peak current density was increased in the following order: NiO/AC < NiO/MWCNTs < NiO/Gr < NiO/Gt. Chronoamperometry test also showed an increased steady state oxidation current density for NiO/Gt in comparison to other electrocatalysts. The increased activity and stability of NiO/Gt electrocatalyst encourage the application of graphite as an efficient and cost-saving support to carry metal nanoparticles for urea electro-oxidation reaction.

Influence of support materials on continuous hydrogen production in anaerobic packed-bed reactor with immobilized hydrogen producing bacteria at acidic conditions.

This study assesses the impact of different support materials (Mutag BioChip™, expanded clay and activated carbon) on microbial hydrogen production in an anaerobic packed-bed reactor (APBR) treating synthetic waste water containing glucose as the main carbon source at low pH value. The APBRs were inoculated with acid pretreated anaerobic sludge and operated at pH value of 4±0.2 and hydraulic retention time (HRT) of 3h. The maximum hydrogen yield of 1.80mol H2/mol glucose was achieved for the APBR packed with Mutag BioChip™ (R1), followed by expanded clay (R2, 1.74mol H2/mol glucose) and activated carbon (R3, 1.46mol H2/mol glucose). It was observed that the investigated support materials influenced the immobilization of hydrogen producing bacteria and consequently hydrogen production performance as well as composition of soluble metabolites. The main metabolic products were acetic acid and butyric acid accompanied with a smaller content of ethanol. The data indicated that in reactors with higher hydrogen yield (R1 and R2), acetate/butyrate (HAc/HBu) ratios were 1.7 and 1.6, respectively, while in the reactor with the lowest hydrogen yield (R3) the obtained HAc/HBu ratio was 4.8. Finally, stable hydrogen and organic acids production throughout the steady-state operation period at low pH values was achieved in all reactors.

Selective oxidation of ethanol over vanadia-based catalysts: The influence of support material and reaction mechanism

The catalytic performance of vanadia supported on silica, alumina, zirconia, and titania was investigated in the selective oxidation of ethanol. It was shown that the activity and product distribution strongly depend on the support material, which determines the structure of supported vanadia species. On silica and alumina, low-active V2O5 crystallites were mainly formed regardless of the vanadium content. These catalysts demonstrated high selectivity toward only acetaldehyde. In contrast, monomeric surface vanadia species and polymeric surface vanadia species were mainly formed over TiO2 when the vanadium content did not exceed what is necessary for the ideal monolayer. Over zirconia, both the surface vanadia species and the V2O5 crystallites existed regardless of the vanadium content. It was found that the surface vanadia species are more active in the selective oxidation of ethanol than the V2O5 crystallites. The highest activity was observed for the polymeric vanadia species and, correspondingly, the best catalytic performance was achieved on the monolayer V2O5/TiO2 catalyst. At low temperatures between 110 and 150°C, this catalyst demonstrated high activity in the oxidation of ethanol to acetaldehyde with the selectivity ranging between 80% and 100%. At temperature near 200°C, the same catalyst was active in the oxidation of ethanol to acetic acid with the selectivity of approximately 65%. The surface intermediates and the catalyst state were also studied in situ by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was shown that under reaction conditions near 100°C, non-dissociatively adsorbed molecules of ethanol, ethoxide species, and adsorbed acetaldehyde exist on the catalyst surface, while at higher temperatures, V2O5/TiO2 is mainly covered with acetate species. Titanium cations remained in the Ti4+ state, whereas V5+ cations underwent a reversible reduction under reaction conditions. On the basis of the in situ data complemented by the results of kinetic measurements, a reaction mechanism for the selective oxidation of ethanol to acetaldehyde and acetic acid over the monolayer catalysts was proposed.

The heat and mass transfer of vacuum membrane distillation: Effect of active layer morphology with and without support material

Abstract The aim of this research was the analysis of heat and mass transfer in vacuum membrane distillation (VMD), specifically for a dead-end feed set-up. The influence of support material on the supported membranes VMD performance was identified. A mathematical model was proposed to evaluate the membrane/feed interface temperature, membrane tortuosity, membrane mass transfer coefficient, and temperature polarization coefficient (TPC). The model was solved by an excel solver based on experimental results of feed temperature, system pressure and the evaporative fluxes. The SEM images showed that the thickness of unsupported membrane was reduced by 42% after the VMD test. Pore shrinkage and tortuosity increase were also expected during this pore collapsing process. On the other hand, the cross-sectional views of the supported membranes did not show significant changes. These results show that the support material can help prevent the membrane pore channel structure from collapsing during the VMD experiment. TPC is close to unity at low feed temperatures. However, it decreases with an increase in evaporation flux as the feed temperature increases, or when a high flux supported membrane is applied.

Influence of Support Material on the Activity and Selectivity of Pt–Ir Catalysts for Ring Opening Reactions

The influence of the supports (Al2O3, TiO2 and SiO2) on the activity and selectivity of Pt–Ir catalysts for the ring opening (RO) of decalin was studied. It was found that the properties of the supports strongly influence the distribution, size and Pt–Ir interaction of the metal particles. They therefore also influence the catalytic activity for reactions like dehydrogenation and hydrogenolysis, but also specifically the activity for RO reactions of naphthenes. Via their acid sites the supports influence RO reactions although the effect is not very marked on conversion because the acidity differences are not very significant among them. The results show that the highest decalin conversion for three different supports, alumina, silica and titania, is obtained with the catalysts of highest metal loading. The best selectivity to RO products is obtained with Pt–Ir(1.0)/Al2O3 catalyst. Moreover this catalyst shows the highest performance for MCP RO. .

Structure and Catalytic Performance of Pt–Cu Bimetallic Catalysts Synthesized by a Radiation-Induced Reduction Method in the Aqueous Phase: Influence of Support Material and Sulfate Ion in the Precursor

The structure of bimetallic nanoparticles has a great impact on catalytic performance. By radiation-induced reduction of metal ions in the aqueous phase, supported bimetallic Pt–Cu catalysts were synthesized with various Cu loadings, support materials, and copper sources. These parameters had a great impact on the structural properties of Pt–Cu nanoparticles. On carbon black, Pt–Cu alloy nanoparticles were readily formed with little oxide phase. On CeO2 support, Pt–Cu was highly oxidized for the low-Cu region (Cu/Pt 1). The structure of CeO2-supported catalysts obtained from two different copper sources (CuSO4 and CuCl2) suggested that such a drastic change in oxidation state is the result of two competing effects, CeO2 to oxygenate metals and the sulfate ion to stabilize them in the metallic state. The reaction characteristics in preferential CO oxidation reflected the Pt–Cu structure (oxidation state) dete...

Growth and Analysis of C Nanotubes on Ceramic Polymer-Additives

C nanotubes are synthesized by catalytic route on ceramic supports (Al2O3, MgO and CaO), usually utilized for polymer reinforcing/flame-retardancy, aiming at nanotube-based hybrid preparation. Chemical vapor deposition is carried out in i-C4H10+H2 atmosphere over 17 wt% Fe-catalysts upon different conditions. In order to clarify the influence of support material, calcination (450 degrees C or 750 degrees C) and reduction temperature (500 degrees C or 600 degrees C) of the catalysts, and synthesis temperature (600 degrees C or 700 degrees C), catalysts utilized and nanotubes obtained are systematically investigated by the use of several analysis techniques (electron microscopy, X-ray diffraction, thermo-gravimetry and Raman spectroscopy). The results obtained show that, in the considered range of variation, support material is the most influential parameter. The most catalytically active alumina supports allow achieving higher yields, but involve larger metallic inclusions and lower crystalline quality. Remaining supports behave oppositely. The reasons for such differences are discussed in the light of the current assessments on the nanotube growth and the results obtained are compared with those available in literature for similar catalysts.

Effect of support on the catalytic activity of manganese oxide catalyts for toluene combustion

The aim of this work was to study combustion of toluene (1000ppm) over MnO2 modified with different supports. α-Al2O3 and γ-Al2O3 obtained from Boehmite, γ-Al2O3 (commercial), SiO2, TiO2 and ZrO2 were used as commercial support materials. In view of potential interest of this process, the influence of support material on the catalytic performance was discussed. The deposition of 9.5MnO2 was performed by impregnation over support. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction and oxidation (TPR/TPO) and thermogravimetric analysis (TGA). The catalytic tests were carried out at atmospheric pressure in a fixed-bed flow reactor. 9.5MnO2/α-Al2O3(B) (synthesized from Boehmite) catalyst exhibits the highest catalytic activity, over which the toluene conversion was up to 90% at a temperature of 289°C. Considering all the characterization and reaction data reported in this study, it was concluded that the manganese state and oxygen species played an important role in the catalytic activity.

Bimetallic catalysts performance during ethanol steam reforming: Influence of support materials

Abstract Ni–Cu catalysts supported on different materials were tested in ethanol steam reforming reaction for hydrogen production. These catalysts were evaluated at reaction temperature of 400 °C under atmospheric pressure. The reagents, with a water/ethanol molar ratio equal to 10, were fed at 70 dm3/(h gcat) (after vaporization). Analysis of the ethanol conversion, as well as evaluation and quantification of the reaction products, indicated the catalyst 10% Ni–1% Cu/Ce0.6Zr0.4O2 as the most appropriate for the ethanol steam reforming under investigated reaction conditions, among the studied catalysts. During 8 h of reaction this catalyst presented an average ethanol conversion of 43%, producing a high amount of H2 by steam reforming and by ethanol decomposition and dehydrogenation parallel reactions. Steam reforming, among the observed reactions, was quantified by the presence of carbon dioxide. About 60% of the hydrogen was produced from ethanol steam reforming and 40% from parallel reactions.

Influence of support material on the immobilization of biomass for the degradation of linear alkylbenzene sulfonate in anaerobic reactors

Two horizontal-flow anaerobic immobilized biomass reactors (HAIB) were used to study the degradation of the LAS surfactant: one filled with charcoal (HAIB1) and the other with a mixed bed of expanded clay and polyurethane foam (HAIB2). The reactors were fed with synthetic substrate supplemented with 14 mg l −1of LAS, kept at 30 ± 2 °C and operated with a hydraulic retention time (HRT) of 12 h. The surfactant was quantified by HPLC. Spatial variation analyses were done to quantify organic matter and LAS consumption along the reactor length. The presence of the surfactant in the load did not affect the removal of organic matter (COD), which was close to 90% in both reactors for an influent COD of 550 mg l −1. The results of a mass balance indicated that 28% of all LAS added to HAIB1 was removed by degradation. HAIB2 presented 27% degradation. Molecular biology techniques revealed microorganisms belonging the uncultured Holophaga sp., uncultured delta Proteobacterium, uncultured Verrucomicrobium sp., Bacteroides sp. and uncultured gamma Proteobacterium sp. The reactor with biomass immobilized on charcoal presented lower adsorption and a higher kinetic degradation coefficient. So, it was the most suitable support for LAS anaerobic treatment.

Steam reforming of methanol over copper-containing catalysts: Influence of support material on microkinetics

Steam reforming of methanol (SRM) was investigated over copper-containing catalysts supported on four different oxides and mixed oxides: Cu/ZnO/Al 2O 3, Cu/ZrO 2/CeO 2, Cu/SiO 2, and Cu/Cr 2O 3/Fe 2O 3. After observing slight differences in the way of catalyst aging and experimental exclusion of mass transport limitation effects, a detailed kinetic study was carried out at 493 K. The dependence of the reaction rate on the molar ratio of methanol and water was determined, as was the influence of addition of inert nitrogen and the main reaction products hydrogen and carbon dioxide to the reactant mixture. Although there were remarkable differences in the catalytic activity of the samples, the main mechanistic steps reflected in the rate law were similar for all catalysts. The reaction rate is determined mainly by the methanol partial pressure, whereas water is not involved in the rate-determining step, except over Cu/Cr 2O 3/Fe 2O 3, where several differences in the chemistry were observed. Hydrogen and carbon dioxide were found to inhibit the reaction. These results were confirmed by a DRIFT study at 493 K using an equimolar reactant mixture and an excess of 4:1 of water and methanol, respectively. The same surface species could be identified on each catalyst, but neither kinetic modeling nor the DRIFT spectra could clearly indicate whether the reaction pathway occurs via a dioxomethylene species or a methyl formate species as intermediate. Similar activation energies of SRM confirm the assumption that the surface chemistry of SRM over copper-based systems is independent of the catalyst support material.

Influence of Support Materials and Aging on NO Oxidation Performance of Pt Catalysts under an Oxidative Atmosphere at Low Temperature

The predominant factor in catalytic low-temperature NO oxidation under an oxidative condition over supported Pt, Pd and Rh catalysts was investigated and discussed using a thermodynamic calculation, XPS analysis, CO adsorption, and reaction evaluation. New insights were gained as follows; the resistance to metal oxide formation of these metals is important for NO oxidation activity under an excess oxygen condition. In the fresh catalysts, the oxidation status of Pt was affected by the electronegativity of the support cation, and the Pt supported on a more acidic support has a higher NO oxidation activity. After aging treatment, the oxidation status of Pt on each support was almost the same, and a large amount of surface metallic Pt favors Pt catalysts to have high activity. The analysis of the NO oxidation kinetics revealed that the affinity of Pt for NO molecules was improved with the aging treatment. It could be concluded that a suitable combination of Pt and the support facilitates high dispersion of the metallic Pt, even after the aging treatment, which is favorable for the NO oxidation in the presence of excess oxygen at low temperature.