预处理条件对用于CO_2加氢的超细CuO－ZnO－SiO_2催化剂性能的影响

采用ＸＲＤ、ＢＥＴ、ＴＰＲ手段，研究了焙烧和还原温度对超细ＣｕＯ－ＺｎＯ－ＳｉＯ２催化剂的性质及其ＣＯ２加氢反应催化活性的影响．胶体在５７３－７７３Ｋ范围内焙烧生成ＣｕＯ、Ｃｕ２Ｏ、ＺｎＯ晶相，随着焙烧温度继续升高，ＣｕＯ和ＺｎＯ晶粒逐渐变大，但催化剂的比表面积和孔容变化很小．在９７３Ｋ焙烧后出现Ｚｎ２ＳｉＯ４晶相，使催化剂比表积和孔容变小，导致催化剂活性降低．焙烧温度对催化剂活性的影响大于对ＣＯ２加氢产物分布的影响．在５４８－６４８Ｋ范围内，催化剂还原温度对其催化活性影响不大．７０３Ｋ高温还原后，可能由于Ｃｕ０晶粒的出现，使得催化剂的活性下降．ＴＰＲ研究结果进一步表明，焙烧温度影响ＣｕＯ同ＺｎＯ、ＳｉＯ２之间的相互作用和催化剂的还原行为．

Effect of Pretreatment Conditions on the Properties and Activities of Ultrafine CuO ZnO SiO 2 Catalysts for Hydrogenation of Carbon Dioxide

The effects of ruduction and calcination temperature on the properties and activities of ultrafine CuO ZnO SiO 2 catalysts prepared by sol gel method for hydrogenation of carbon dioxide were investigated by XRD, BET and TPR techniques. When calcination temperatures were in the range of 573-773 K, CuO, Cu 2O and ZnO crystallites were detected, and CuO and ZnO diffraction peak intensities and their crystalline sizes increased with the increase of calcination temperature, while Cu 2O crystalline might turn into CuO gradually. In the range of 573-873 K, calcination temperature had little influence on the specific surface area and pore volume of ultrafine CuO ZnO SiO 2 catalysts, but crystalline Zn 2SiO 4 appeared after calcination at 973 K, which caused remarkable decrease of the specific surface area and pore volume of catalysts and led to decrease of the activity of catalysts. Calcination temperature showed much greater influence on the activity of catalysts than on the product distribution of hydrgenation of carbon dioxide; the selectivity to methanol increased with the increase calcination temperature, while selectivity to CO decreased, and calcination at 773 K was favorable for methanol synthesis from hydrogenation of carbon dioxide over ultrafine CuO ZnO SiO 2 catalysts. TPR results as well as XRD patterns further confirmed the influences of calcination temperature on the interaction between CuO and ZnO, SiO 2, such as the formation of crystalline Zn 2SiO 4 and moreover on the reduction behaviour and activity of catalysts. Reduction temperature in the range of 548-648 K had little influence on the catalytic activity, but after reduction at 703 K Cu 0 might be formed and accounted for the decrease of catalytic activity.