The preparation and properties of coprecipitated Cu-Zr-Y and Cu-Zr-La catalysts used for the steam reforming of methanol

A series of Cu-zirconia catalysts containing various additives (Y2O3, La2O3, Al2O3 and CeO2) have been prepared by coprecipitation and their activities and stabilities under operating conditions have been obtained for the steam reforming of methanol. It has been found that an yttria-promoted catalyst containing 30 mol% Cu and 20 mol% of Y2O3 is not only very active but is also very stable under reaction conditions. The yttria appears to stabilise a high copper surface area and may also have a slight promotional effect on the copper. The results obtained with this material compare very favourably with data for the best catalysts reported in the literature. (C) 2007 Published by Elsevier B.V.

Steam reforming of model compounds and fast pyrolysis bio-oil on supported noble metal catalysts

The production of hydrogen by steam reforming of bio-oils obtained from the fast pyrolysis of biomass requires the development of efficient catalysts able to cope with the complex chemical nature of the reactant. The present work focuses on the use of noble metal-based catalysts for the steam reforming of a few model compounds and that of an actual bio-oil. The steam reforming of the model compounds was investigated in the temperature range 650-950 degrees C over Pt, Pd and Rh supported on alumina and a ceria-zirconia sample. The model compounds used were acetic acid, phenol, acetone and ethanol. The nature of the support appeared to play a significant role in the activity of these catalysts. The use of ceria-zirconia, a redox mixed oxide, lead to higher H-2 yields as compared to the case of the alumina-supported catalysts. The supported Rh and Pt catalysts were the most active for the steam reforming of these compounds, while Pd-based catalysts poorly performed. The activity of the promising Pt and Rh catalysts was also investigated for the steam reforming of a bio-oil obtained from beech wood fast pyrolysis. Temperatures close to, or higher than, 800 degrees C were required to achieve significant conversions to COx and H-2 (e.g., H-2 yields around 70%). The ceria-zirconia materials showed a higher activity than the corresponding alumina samples. A Pt/ceria-zirconia sample used for over 9 h showed essentially constant activity, while extensive carbonaceous deposits were observed on the quartz reactor walls from early time on stream. In the present case, no benefit was observed by adding a small amount of O-2 to the steam/bio-oil feed (autothermal reforming, ATR), probably partly due to the already high concentration of oxygen in the bio-oil composition. (c) 2005 Elsevier B.V. All rights reserved.

Steam reforming of ethanol over Co3O4–Fe2O3 mixed oxides

Co3O4, Fe2O3 and a mixture of the two oxides Co–Fe (molar ratio of Co3O4/Fe2O3 = 0.67 and atomic ratio of Co/Fe = 1) were prepared by the calcination of cobalt oxalate and/or iron oxalate salts at 500 °C for 2 h in static air using water as a solvent/dispersing agent. The catalysts were studied in the steam reforming of ethanol to investigate the effect of the partial substitution of Co3O4 with Fe2O3 on the catalytic behaviour. The reforming activity over Fe2O3, while initially high, underwent fast deactivation. In comparison, over the Co–Fe catalyst both the H2 yield and stability were higher than that found over the pure Co3O4 or Fe2O3 catalysts. DRIFTS-MS studies under the reaction feed highlighted that the Co–Fe catalyst had increased amounts of adsorbed OH/water; similar to Fe2O3. Increasing the amount of reactive species (water/OH species) adsorbed on the Co–Fe catalyst surface is proposed to facilitate the steam reforming reaction rather than decomposition reactions reducing by-product formation and providing a higher H2 yield.

Ethanol Steam Reforming on Rh Catalysts: Theoretical and Experimental Understanding

Through combined theoretical and experimental efforts, the reaction mechanism of ethanol steam reforming on Rh catalysts was studied. The results suggest that acetaldehyde (CH3CHO) is an important reaction intermediate in the reaction on nanosized Rh catalyst. Our theoretical work suggests that the H-bond effect significantly modifies the ethanol decomposition pathway. The possible reaction pathway on Rh (211) surface is suggested as CH3CH2OH -> CH3CH2O -> CH3CHO -> CH3CO -> CH3 + CO -> CH2 + CO -> CH + CO -> C + CO, followed by the water gas shift reaction to yield H-2 and CO2. In addition, we found that the water-gas shift reaction, not the ethanol decomposition, is the bottleneck for the overall ethanol steam reforming process. The CO + OH association is considered the key step, with a sizable energy barrier of 1.31 eV. The present work first discusses the mechanisms and the water effect in ethanol steam reforming reactions on Rh catalyst from both theoretical and experimental standpoints, which may shed light on designing improved catalysts.

Theoretical and experimental understanding on ethanol steam reforming for H-2 production

H2 is considered to be a potential alternative fuel due to its high energy density by weight and working with pollution free. Currently, ethanol conversion to hydrogen has drawn much attention because it provides a viable way for H2 production from renewable resources. In this work, we combined theoretical and experimental efforts to study the reaction mechanism of ethanol steam reforming on Rh catalysts. The results suggest that acetaldehyde (CH3CHO) is an important reaction intermediate in the reaction on nano-sized Rh catalyst. Our theoretical work suggests that the H-bond effect significantly modifies the ethanol decomposition pathway. The possible reaction pathway on Rh (211) surface is suggested as: CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3+CO → CH2+CO → CH+CO → C+CO, followed by the water gas shift reaction to yield H2 and CO2. It was found that that the water gas shift reaction is paramount in the ethanol steam reforming process.

Continuous flow gas phase photoreforming of methanol at elevated reaction temperatures sensitised by Pt/TiO2

Gas phase photoreforming of methanol using a Pt/TiO2 photocatalyst has been performed under flow conditions at elevated temperatures. Comparing the activity of the reforming process as a function of temperature under dark and irradiated conditions shows a significant enhancement in the rate of H2 production using the photo-assisted conditions at temperatures between 100-140 °C. At higher temperatures, the effect of irradiation is small with the process dominated by the thermal process. Deactivation of the catalyst was observed under irradiation but the catalyst was easily regenerated using an oxygen treatment at 120 °C. Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) showed that the activity of the catalyst could be correlated with the presence of the photogenerated trapped electrons. In addition, lower amounts of CO adsorbed on Pt, compared to those observed in the dark reaction, were found for the UV-irradiated systems. It is proposed that CO and adsorbed intermediates, such as formate, can act as inhibitors in the photoreforming process and this is further supported by the observation that, before and after the regeneration process in O2, the CO and surface adsorbed organic intermediate products are removed and the activity is recovered.

A first principles study of methanol decomposition on Pd(111): Mechanisms for O-H bond scission and C-O bond scission

There is some dispute as to whether methanol decomposition occurs by O-H bond scission or C-O bond scission. By carrying out density functional theory calculations, we investigate both scenario of the reaction pathways of methanol decomposition on a Pd(111) surface. It is shown that the O-H bond scission pathway is much more energetically favorable than the C-O bond scission pathway. The high reaction barrier in the latter case is found to be due to the poor bonding abilities of CH3 and OH with the surface at the reaction sites. (C) 2001 American Institute of Physics.

Effect of precursor on the performance of alumina for the dehydration of methanol to dimethyl ether

Dimethyl ether (DME) is amongst one of the most promising alternative, renewable and clean fuels being considered as a future energy carrier. In this study, the comparative catalytic performance of γ-Al2O3 prepared from two common precursors (aluminum nitrate (AN) and aluminum chloride (AC)) is presented. The impact of calcination temperature was evaluated in order to optimize both the precursor and pre-treatment conditions for the production of DME from methanol in a fixed bed reactor. The catalysts were characterized by TGA, XRD, BET and TPD-pyridine. Under reaction conditions where the temperature ranged from 180 °C to 300 °C with a WHSV = 12.1 h−1 it was found that all the catalysts prepared from AN(η-Al2O3) showed higher activity, at all calcination temperatures, than those prepared from AC(γ-Al2O3). In this study the optimum catalyst was produced from AN and calcined at 550 °C. This catalyst showed a high degree of stability and had double the activity of the commercial γ-Al2O3 or 87% of the activity of commercial ZSM-5(80) at 250 °C.

On-line FTIR spectroscopic investigations of methanol oxidation in a direct methanol fuel cell

A real-time Fourier transform infrared spectroscopy (FTIRS) analysis of the products of methanol oxidation in a prototype direct-methanol fuel cell operating at high temperatures (150 to 185°C) is reported here. The methanol oxidation products on platinum black and platinum-ruthenium catalyst surfaces were determined as a function of the fuel cell operating temperature, current density, and methanol/water mole ratio. Neither formaldehyde nor formic acid was detected in anode exhaust gas at all cell operating conditions. The product distributions of methanol oxidation obtained by on-line FTIRS are consistent with our previous results obtained by on-line mass spectroscopy under similar conditions. With pure methanol in anode feed, methanaldimethylacetal was found to be the main product, methyl formate and CO were also found. However, when water was present in the anode feed, the main product was CO , and the formation of methanaldimethylacetal and methyl formate decreased significantly with increase of the water/methanol mole ratio. Increase of cell operating temperature enhanced the formation of CO and decreased the formation of methanaldimethylacetal and methyl formate. Pt/Ru catalyst is more active for methanol oxidation and has a higher selectivity toward CO formation than Pt-black. Nearly complete methanol oxidation, i.e., the product was almost exclusively CO , was achieved using a Pt/Ru catalyst and a water/methanol mole ratio of 2 or higher in the anode feed at a temperature of 185°C or above.