添加表面活性剂两步沉淀法制备甲醇催化剂

At present, the most catalysts studied for methanol synthesis are on the basis of Cu/ZnO/Al2O3 catalyst. It was believed that the particle size and surface composition of Cu in Cu/ZnO/Al2O3 catalyst are important factors to the catalytic process. In recent years, various methods, such as sol-gel method, micro-emulsions, coprecipitation with adding surfactant, two-step precipitation etc, have been developed to prepare Cu/ZnO/Al2O3 catalysts with fine particle size or (and) high relative surface composition of Cu. In this paper, a novel method by the two-step precipitation combined with addition of surfactant method was proposed to prepare a ultrafine Cu/ZnO/Al2O3 catalyst. The particle size and surface composition of Cu and catalytic activity of the catalysts were studied. Four kinds of Cu/ZnO/Al2O3 catalysts for methanol synthesis were prepared by conventional coprecipitation, two-step precipitation without addition of surfactant, coprecipitation adding surfactant and two-step precipitation combined with addition of surfactant, labeled as Cat 1, Cat 2, Cat 3 and Cat 4 separately. These catalysts were tested in a micro-reactor using a feed gas of H2/CO/CO2/N2 (vol ratio)=66/27/3/4.The reaction conditions were 483 K～543 K, 3 MPa and 7 500 h-1. The properties and structure of the catalysts were characterized by means of SEM, XRD and XPS. The space-time yield (STY) of methanol is in the order of STYCat 4>STYCat 3>STYCat 2 >STYCat 1. The optimal temperature for all four catalysts is 523 K. Under the reaction condition of 523 K, 3 MPa and 7 500 h-1, the STY of Cat 4 reaches to 0.494 g·g-1·h-1, which is 47.9%, 16.8% and 9.3%higher than that of Cat 1, Cat 2 and Cat 3 respectively, From results of SEM and XRD, it can be found that the particle size of catalysts are in the order of Cat 1>Cat 2>Cat 3>Cat 4. The XPS results show that the relative surface Cu contents are in the order of Cat 4>Cat 3>Cat 2>Cat 1. SEM, XRD and XPS results all suggest that Cat 4 has high methanol synthesis activity because of its fine particle size and high relative surface Cu content. Based on the study, two-step precipitation combined with addition of surfactant is a good method to prepare an ultrafine and high surface Cu content catalyst with high methanol synthesis activity.