添加表面活性剂两步沉淀法制备甲醇催化剂

采用添加表面活性剂两步沉淀法制备了具有高表面铜相对浓度的超细甲醇合成催化剂。以组成为H2/CO/CO2/N2=66/27/3/4(体积比）的原料气对催化剂进行了活性评价。结果表明，该催化剂比传统并流沉淀法制备的铜基催化剂活性提高47.9%，比两步沉淀法和添加表面活性剂并流沉淀法制备的铜基催化剂活性分别提高9.3%和16.8%。利用SEM、XRD及XPS方法对催化剂的结构、形貌和表面金属组成进行了表征。

Methanol synthesis catalyst prepared by two-step precipitation combined with addition of surfactant

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.