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用TPD-MS,XPS,ESR,脉冲反应技术和活性测定等研究了CuO-ZnO-Al_2O_3催化剂上CO_2的加氢行为。结果表明,CO_2加氢的反应动力学行为与CO加氢有明显不同,反应产物只有CH_3OH和CO,完全没有烃类产生,也没有出现结炭失活现象。反应时,CO_2先与OH作用生成HCO_3和CO_3,再进一步加氢生成HCOO和HCO等中间物种。HCOO有多种吸附状态,只有一部份HCOO能进一步加氢,而HCO则很容易加氢生成CH_3OH。还原过程中,各中间物种的吸附位不尽相同,进一步反应需要的H的状态可能也不同。CO_2,CO和CH_3OH可能通过中间物种HCOO相互转化。催化剂的活性和选择性与Cu(Ⅰ)和Zn(Ⅰ)的数量密切相关。
The hydrogenation behavior of CO_2 on CuO-ZnO-Al_2O_3 catalysts was investigated by TPD-MS, XPS, ESR, pulsed reaction and activity measurement. The results show that the reaction kinetics of CO_2 hydrogenation is obviously different from that of CO hydrogenation. The reaction products have only CH_3OH and CO. There is no hydrocarbon generation at all, and no deactivation of the carbon occurs. During the reaction, CO 2 first interacts with OH to form HCO 3 and CO 3, and further hydrogenates to form intermediate species such as HCOO and HCO. HCOO has a variety of adsorption state, only part of HCOO hydrogenation can be further, and HCO is easy to hydrogenation CH_3OH. In the process of reduction, the adsorption sites of each intermediate species are different, and the state of H needed for further reaction may be different. CO 2, CO and CH 3 OH may interconvert with intermediate species HCOO. The activity and selectivity of the catalyst are closely related to the amount of Cu (I) and Zn (I).