Production of hydrogen from methanol over Cu/ZnO and Cu/ZnO/Al2O3 catalysts prepared by homogeneous precipitation : Steam reforming and oxidative steam reforming

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Two series of Cu/ZnO and Cu/ZnO/Al2O3 catalysts with varying Cu/Zn ratio have been prepared by the homogeneous precipitation (hp) method using urea hydrolysis. Steam reforming and oxidative steam reforming of methanol were performed using the hp-Cu/Zn-based catalysts for catalytic production of hydrogen. The hp-Cu/ZnO/Al2O3 catalyst showed a higher activity than the hp-Cu/ZnO catalysts. In both cases, the catalytic activity was well correlated with the surface area of Cu metal, and the maximum activity was obtained on the hp-Cu/ZnO/Al2O3 catalyst with the Cu/Zn ratio of 1/1. Although a large amount of Cu+ was detected on the surface of the Cu/Zn-based catalysts after the reduction at 260 °C, no obvious correlation was observed between the activity and the surface amount of Cu+. The hp-Cu/ZnO/Al2O3 catalyst showed a high and stable activity not only for steam reforming but also for oxidative steam reforming of methanol, and the latter reaction effectively produced H2 with a low CO selectivity at a low temperature around 200 °C. It was confirmed by the temperature-programmed desorption experiments that CH3OH was first dehydrogenated to HCHO, which then underwent a nucleophilic attack of H2O to form HCOOH, followed by the decomposition to H2 and CO2 on the hp-Cu/Zn-based catalysts.
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