CuO/ZnO/Al₂O₃ Catalysts For Hydrogen Production Via Steam Reforming Of Methanol:Preparation, Structure-Performance Relationship And Reaction Kinetics

Steam reforming of methanol is an important reaction for hydrogen production that is applied in the polymer electrolyte membrane fuel cell. How to reduce the CO concentration in product gas is one of the most significant issues for the catalyst development. In this study, a series of Cu-based catalysts were prepared by a coprecipition method and applied to steam reforming of methanol. The effects of some critical factors on the structure and performance of catalyst were investigated, including the CuO/ZnO mass ratio and the introduction of ZrO2 and CeO2. The structure of catalyst was characterized in detail by various techniques and its catalytic performance in the steam reforming of methanol was evaluated. The results showed that the catalyst activity depended greatly on the catalyst reducibility and the specific surface area of Cu. The optimal compositon of CuO/ZnO mass ratio was 50/40, when the Al2O3 was fixed at 10 wt%. Compared to CuO/ZnO/Al2O3, the ZrO2-doped CuO/ZnO/Al2O3 exhibited higher activity and selectivity to CO, while the CeO2-doped catalyst displayed lower activity and selectivity. An intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO2/Al2O3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the Langmuir-Hinshelwood-type kinetic model-derived effluent concentrations of CO (CO2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO2/Al2O3 were 93.1,85.1 and 116.5 kJ·mol-1, respectively. In addition, a mathematical model composed of the diffusion-reaction model on the catalyst scale and the one-dimensional model on the reactor scale was developed, which can describe very well the performance of the steam methanol reforming reactor. Finally, the effect of adding Ga2O3 into the Cu-based catalysts on the catalyst activity and selectity was explored, and it was found that the catalyst with a CuO/ZnO/Ga2O3 mass ratio of 40/50/10 had the highest activity among all the Ga2O3-doped catalysts investigated. Compared to CuO/ZnO/CeO2/Al2O3, CuO/ZnO/Ga2O3 showed a lower CO selectivity, which was mainly ascribed to the better reducibility and higher specific surface area of Cu of CuO/ZnO/Ga2O3.