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- Agrell, J., et al.
(author)
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Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation
- 2003
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In: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 253:1, s. 201-211
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Journal article (peer-reviewed)abstract
- Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.
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| 2. |
- Agrell, J., et al.
(author)
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Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O3
- 2003
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In: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 219:2, s. 389-403
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Journal article (peer-reviewed)abstract
- Production of H-2 from methanol by steam reforming, partial oxidation, or a combination thereof was studied over Cu/ZnO-based catalysts. The catalysts were characterized by a variety of techniques, including N2O chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction/oxidation. The influence of feed composition, reaction temperature, and catalyst formulation on H-2 production rate, product distribution, and catalyst lifetime was investigated. Distinct differences between the processes were observed with respect to catalyst behavior. ZrO2-containing catalysts, especially Cu/ZnO/ZrO2/Al2O3, exhibit the best performance in the steam reforming reaction. During partial oxidation, however, a binary Cu/ZnO catalyst exhibits the lowest light-off temperature and the lowest level of CO by-product. The redox properties of the catalyst appear to play a key role in determining the pathway for H-2 production. In particular. the extent of methanol and/or H-2 combustion at differential O-2 conversion is strongly dependent on the ease of copper oxidation in the catalyst.
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