Efficient hydrogen production using Cu-based catalysts prepared via homogeneous precipitation

Abstract

We report here preparation of multi-composition Cu/ZnO/Al₂O₃ (CZA) catalyst by homogeneous precipitation (HP) method using urea treatment. Compared to the conventional co-precipitation (CP) method, the HP method used here improves the uniformity of metal mixing through homogeneous generation of hydroxide ions as a result of hydrolysis of urea in the solution. In this study, optimization of the conditions to prepare CZA catalyst was achieved by adjusting the urea concentration, amount of water, reaction temperature and reaction time; to control the pH value. The HP-derived CZA particles exhibited a characteristic flower-like morphology with a higher surface area, typically 78.5 m²/g as measured by the BET analysis, as compared to the CP-derived CZA catalysts. Induction coupled plasma and energy dispersive spectroscopy mapping results further confirmed the homogeneity of HP-CZA components and highly uniform dispersion of the active metal. Significantly lowering and a narrower range of the reduction temperature for HP-CZA is observed. An improved performance in methanol reforming reaction, in terms of methanol conversion, yield of hydrogen production, and higher carbon dioxide selectivity, has been achieved. Furthermore, the concentration of carbon monoxide can be further reduced by employing CeO₂ and ZrO₂ to modify the support, which also results in reduced reduction temperature and improved performance. Among the modified catalysts, HP-CZCZ catalyst showed the highest methanol conversion and rate of hydrogen production, simultaneously with reduced concentration of CO. Moreover, only 20 mg of catalyst loading yielded 98% methanol conversion rate under more than 8500 h⁻¹ GHSV. In future, not only can this method be used to synthesize other multi-composition materials with high homogeneity, but also our approach presents opportunity for production of a highly active catalyst for efficient generation of hydrogen for fuel cell applications.