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Boehmite (γ-AlOOH) nanorods and nanoplates were hydrothermally fabricated with the aid of tetrapropylammonium bromide (TPABr) by modifying the pH values of solutions. Under acidic conditions, the adsorption of anions such as Br− or NO3− on (001) and (100) surfaces may promote the heterogeneous nucleation of boehmite, leading to rod-like boehmite. While under basic solutions, the adsorption of TPA+ cation on the (010) surface inhibits the growth of boehmite along the [010] direction and generates nanosheets. The as-synthesized γ-AlOOH precursors were calcined at 873 K and transformed into γ-Al2O3 nanorods and nanosheets. The obtained γ-Al2O3 samples presented a clear morphology-depended effect for ethanol dehydration; nanorods gave the improved selectivity of C2H4 due to the exposure of {100} facets. [ABSTRACT FROM AUTHOR]

Abstracts A Cu/SiO 2 catalyst with a core-shell structure was found to be highly active and stable for the hydrogenation of methyl acetate to ethanol during 96 h reaction test at 523 K; MA conversion reached at 95% while the selectivity towards the major products (ethanol and methanol) approached ∼95%. Structural analysis revealed that most copper particles in the hydrogen-reduced Cu/SiO 2 catalyst had sizes of 3–7 nm and were coated with a thin layer of silica, forming a core-shell structure. The average size of copper particles and the core-shell structure kept unchanged in the spent catalyst, but the Cu + /(Cu 0 + Cu + ) ratio increased during the course of reaction, probably because of the electronic interaction between copper surface and methyl acetate under the reaction conditions. Mechanistic and kinetic studies have identified that ethyl acetate was formed through trans -esterification of initially produced ethanol with methyl acetate, while the subsequent hydrogenation of ethyl acetate to ethanol proceeded much faster. The Cu + /(Cu 0 + Cu + ) ratio played a crucial role in reaction network; MA could adsorb equally on Cu 0 and Cu + sites while the activation of molecular hydrogen occurs only on the Cu 0 site. Therefore, a rather stable performance could be attained with the increase in the Cu + /(Cu 0 + Cu + ) ratio during the course of reaction as long as the reaction is kinetically controlled by MA adsorption. The outstanding stability of the Cu/SiO 2 catalyst was ascribed to a combination of geometric and electronic effect. [ABSTRACT FROM AUTHOR]

This work presents a kinetic analysis of ethanol steam reforming (ESR) over a performing Ir/CeO 2 catalyst based on a bi-functional mechanism. A first conventional power-law based kinetic study was carried out by varying the main operating parameters (temperature, steam/ethanol molar ratio and partial pressure of products). A limited fit was achieved between the experimental data and the data calculated from this model based on a single type of site, demonstrating the need of a kinetic analysis integrating more closely the demonstrated bi-functional mechanism of the reaction. A kinetic model considering two distinct adsorption sites, on ceria support and on iridium particles, was then considered and only reactions involving the two types of sites, i.e. occurring at the ceria/metal interface, were used to build that model. A good agreement between the experimental data and the model was obtained, without systematic deviations. The central role of the metal-support interface was also consistent with the deactivation of this catalyst upon sintering, related to both changes in metal and support dispersion with time on stream. [ABSTRACT FROM AUTHOR]

Abstract: The ageing processes of a model Ir/CeO2 catalyst during ethanol steam reforming was investigated. Various causes of deactivation were identified, depending on reaction temperature and time on stream. The initial, fast and but rather limited deactivation process was ascribed essentially to a loss of ceria surface (smoothing by loss of microporosity and/or roughness in the presence of steam), coinciding with an active phase build-up formed by a monolayer of carbonaceous reacting intermediates. In addition, a progressive and long-term deactivation was found to superimpose, originating from structural changes at the ceria/Ir interface linked to the Ir particles sintering and the ceria restructuring. The continuous build-up of an encapsulating layer of carbon at moderate temperature, coming from C2 intermediate polymerization, was found not to contribute significantly to the catalyst deactivation, at least under the operating conditions investigated in this study. [Copyright &y& Elsevier]

Abstract: A series of Ir/CeO2 catalysts of different oxide and metallic phase dispersions was investigated by XRD, TPR, HRTEM, CO2 TPD/calorimetry, in situ DRIFT spectroscopy, and oxygen isotopic exchange techniques in order to elucidate the specific influence of catalyst morphology and structure on the oxidative steam reforming (OSR) of ethanol. Structure/texture sensitivity is demonstrated on the basis of the OSR mechanism, which involves, in order: (i) ethanol adsorption on the ceria surface, (ii) partial oxidation to acetate and surface migration of the C2 intermediates along the ceria support toward the Ir particles, (iii) cracking and further oxidation into Ir carbonyls and ceria carbonates, and (iv) hydrogen and carbon monoxide desorption from the Ir particles. Structure sensitivity is established by considering two types of sites: the ceria surface sites, which are essentially pairs of oxygen vacancies and basic OH groups, as well as interfacial sites between Ir and ceria phases, involving pairs of Ir coordinately unsaturated sites (CUSs) and the aforementioned peripheral ceria sites. This structure sensitivity is revealed by TOF calculations based on these two types of sites, which correspond to the two main rate controlling steps of the ethanol OSR mechanism, namely steps (ii) and (iii). The materials considered display activity, selectivity, and resistance to aging (manifested by coke deposition and sintering) that are closely related to their initial structure and texture. Two domains in terms of iridium and ceria particle size are identified, leading either to stable and selective catalysts or to unstable and unselective catalysts. Such an original and quantified structure sensitivity analysis should prove useful for further process development. [Copyright &y& Elsevier]

Abstract: We studied ethanol steam reforming over Ir/Ce0.9Pr0.1O2 and Ir/CeO2 catalysts comparatively with respect to activity and stability. We found that PrOx-doping have significantly promoted the oxygen storage capacity and thermal stability of the catalysts by incorporation into the ceria lattice. Ethanol was readily converted to hydrogen, methane and carbon oxides at 773 K over the Ir/Ce0.9Pr0.1O2 catalyst, and this is 100 K lower than that found for the Ir/CeO2 catalyst. Moreover, the PrOx-doped catalyst was stable toward ethanol steam reforming at 923 K for 300 h without an apparent variation in ethanol conversion and product distribution. However, the severe aggregation of ceria particles and heavy coke deposition were observed on the Ir/CeO2 catalyst, resulting in remarkable deactivation under the same reaction conditions. [Copyright &y& Elsevier]

Abstract: ZrO2-doped manganese–cerium oxide catalyzed ethanol oxidation effectively and ethanol was fully oxidized to CO2 at 453K. The catalyst also showed quite promising stability for 120h on-stream without obvious loss in ethanol conversion. Structural analyses have revealed that ZrO2-doping enhanced the oxygen storage capacity of ceria by generating more oxygen vacancies, and at the same time promoted the thermal stability through the formation of solid solution. [Copyright &y& Elsevier]

Abstract: A Mn0.6Ce0.4O2 mixed oxide exhibited rather high activity and stability for ethanol oxidation. Complete conversion of ethanol to CO2 was obtained at a temperature as low as 463K and the activity maintained for 120h on-stream without obvious deactivation. The Mn0.6Ce0.4O2 catalyst showed higher ethanol oxidation rate and better selectivity to CO2 which was even superior to a Pt/Al2O3 catalyst. Temperature-programmed surface reaction and spectroscopic studies have revealed that ethoxy species were formed immediately upon ethanol adsorption on the catalyst at room temperature. These intermediates were further oxidized to acetate and carbonate species, and finally converted to CO2 at elevated temperatures. The effective activation of molecule oxygen over the Mn0.6Ce0.4O2 solid solution plays an essential role in determining the catalytic performance. Oxygen transfer from molecular oxygen to MnO2 active sites through CeO2 in the solid solution realized the effective activation of molecular oxygen. At lower temperatures, the oxidation of ethanol mainly produced acetaldehyde, and the direct oxidation of ethanol to CO2 became the major route at higher temperatures, depending on the activation of molecular oxygen. [Copyright &y& Elsevier]

Abstract: Steam reforming of ethanol over unsupported Ni and Ni–Cu catalysts was investigated. Ethanol and the reaction intermediates like acetaldehyde and acetone are entirely converted into hydrogen and C1 products at 400°C, while methane steam reforming and reversible water gas shift are the major reactions at higher temperatures. The Ni–Cu catalyst exhibited stable performance during 40h on-stream at 650°C without apparent deactivation, but the Ni catalyst showed severe deactivation only after 12h on-stream due to heavy coke deposition. Filament carbon was mainly produced on the Ni catalyst through the Boudouard reaction, whereas condensed carbon was formed on the Ni–Cu catalyst by methane decomposition. [Copyright &y& Elsevier]

Abstract: Hydrogen production from ethanol by autothermal reforming over an Rh/CeO2 catalyst was investigated with a stoichiometric feed composition. Ethanol as well as the reaction intermediates like acetaldehyde and acetone was entirely converted to hydrogen and C1 products at 673K, and methane steam reforming and reverse water gas shift were the major reactions above 823K. The Rh/CeO2 catalyst exhibited stable activity and selectivity during 70h on-stream operation at 823–923K without obvious deactivation evidenced by the constant effluent gas composition. Structural analysis of the used catalyst revealed that CeO2 prevented effectively the highly dispersed Rh particles with sizes of 1–3nm from sintering and thus maintained sufficient Rh–CeO2 interfacial areas, which facilitated coke gasification through the high oxygen storage-release capacity. [Copyright &y& Elsevier]

Abstract: Steam reforming of ethanol over an Ir/CeO2 catalyst has been studied with regard to the reaction mechanism and the stability of the catalyst. It was found that ethanol dehydrogenation to acetaldehyde was the primary reaction, and acetaldehyde was then decomposed to methane and CO and/or converted to acetone at low temperatures. Methane was further reformed to H2 and CO, and acetone was directly converted into H2 and CO2. Addition of CO, CO2, and CH4 to the water/ethanol mixture proved that steam reforming of methane and the water gas shift were the major reactions at high temperatures. The Ir/CeO2 catalyst displayed rather stable performance in the steam reforming of ethanol at 650°C even with a stoichiometric feed composition of water/ethanol, and the effluent gas composition remained constant for 300h on-stream. The CeO2 in the catalyst prevented the highly dispersed Ir particles from sintering and facilitated coke gasification through strong Ir–CeO2 interaction. [Copyright &y& Elsevier]

Steam reforming, partial oxidation, and oxidative steam reforming of ethanol over Ir/CeO2 catalysts were studied to elucidate the reaction pathway and determine catalytic stability. Temperature-programmed desorption and surface reaction revealed that ethoxy species were immediately formed on ethanol adsorption at room temperature, and were mainly further oxidized to acetate and carbonate species that finally decomposed into CH4/CO and CO2, respectively. Under reaction conditions, acetaldehyde was the primary product below 673 K, which decomposed mainly to methane and carbon monoxide at higher temperatures, whereas methane reforming and the water–gas shift were the major reactions above 773 K. The Ir/CeO2 catalyst demonstrated rather high stability for the reactions at 823 and 923 K with no apparent deactivation for 60 h on stream; the mean size of Ir particles was stable at around 2–3 nm, but the ceria particles sintered significantly from 6–8 to 14–27 nm. CeO2 likely prevented the highly dispersed Ir particles from sintering and inhibited coke deposition through strong Ir–CeO2 interactions. [Copyright &y& Elsevier]

Abstract: Oxidative steam reforming of ethanol over an Ir/CeO2 catalyst was investigated. Ethanol dehydrogenation to acetaldehyde and decomposition to methane and carbon monoxide were the primary reactions at low temperatures, and complete reforming of ethanol was achieved at 773K with hydrogen, carbon oxides and methane as the only products in the outlet stream. More importantly, stability test revealed that the Ir/CeO2 catalyst could show rather stable catalytic performance for 60h time-on-stream without deactivation. The improvement was attributed to the effective prevention of the sintering of the highly dispersed Ir particles through the strong interaction between Ir and CeO2 and to the significant resistance to coke deposition due to the higher oxygen storage-release capacity of ceria. [Copyright &y& Elsevier]

Hydrogen production from the steam reforming reactions of ethanol and glycerol has been studied over ceria-supported Ir, Co and Ni catalysts with respect to the nature of the active metals and the reaction pathways. For ethanol steam reforming, ethanol dehydrogenation to acetaldehyde and ethanol decomposition to methane and carbon monoxide were the primary reactions at low temperatures, depending on the active metals. At higher temperatures where all the ethanol and the intermediate compounds, like acetaldehyde and acetone, were completely converted into hydrogen, carbon oxides and methane, steam reforming of methane and water gas shift became the major reactions. The Ir/CeO2 catalyst was significantly more active and selective toward hydrogen production, and the superior catalytic performance was interpreted in terms of the intimated contact between Ir particles and ceria based on the ceria-mediated redox process. Additionally, hydrogen production from steam reforming of glycerol was also examined over these ceria-supported metal catalysts, and the Ir/CeO2 catalyst again showed quite promising catalytic performance with hydrogen selectivity of more than 85% and 100% glycerol conversion at . [Copyright &y& Elsevier]

Membrane-assisted steam reforming of ethanol is an intriguing option for on-site H 2 production from biomass in refueling stations for automotive fuel cells. The energy consumption for H 2 compression and thus fuel costs can be significantly reduced if this process could deliver H 2 at elevated pressures. Thermodynamic analyses show that reforming temperatures above 823 K are needed for attaining H 2 partial pressures that will enable operation without sweep gas and allow appreciable compression energy savings. Reforming of a 6:1 steam/ethanol mixture was practically driven to completion at 873 K and 1.3 MPa employing thin, supported Pd and PdCu membranes without sweep gas. Both H 2 yield and H 2 recovery factor remained stable during 10 day continuous testing of these membranes. The H 2 yield reached nearly 94% with ca. 92% H 2 separated by the PdCu membrane, for example. However, purity of the permeated H 2 declined from about 97% to nearly 91% in the Pd membrane reformer whereas it remained steady at 98% when using the PdCu membrane. In addition, the twice as high single gas H 2 permeation rate of the Pd membrane was reduced by ca. 85% during reforming due to inhibition by unstable carbon compounds while that of the PdCu membrane was diminished by less than 60%. Hence, the relative H 2 permeability of the two membranes was virtually inverted under reforming conditions. In consequence, PdCu membranes are clearly the better option for integration into high-temperature ethanol steam reformers. • Thermodynamics require reforming above 823 K for H 2 production at elevated pressure. • Marginal impact of intrinsic H 2 permeance on membrane reformer efficiency. • PdCu membrane stability superior to that of Pd membrane during reforming at 873 K. • PdCu membrane inhibition substantially weaker under reforming conditions. [ABSTRACT FROM AUTHOR]