Zn/SiO_2气相催化裂解1,1,2-三氯乙烷脱HCl:酸性与失活

用浸渍法制备了一系列SiO_2负载的过渡金属催化剂M/SiO_2(M为第Ⅳ周期过渡金属),用于气相催化裂解1,1,2-三氯乙烷(TCE)脱HCl的反应。研究发现,在M/SiO_2催化剂中,Zn/SiO_2催化性能最好,TCE转化率能达到98%,顺-1,2-二氯乙烯(cis-DCE)的选择性为82%。随着Zn负载量的增加,Zn/SiO_2催化剂上TCE转化率逐渐增加,与催化剂上总酸量变化一致。将总酸量以Zn负载量归一化得到比酸量,则比酸量越大,Zn/SiO_2催化剂比活性越高,表明Zn/SiO_2催化剂表面酸性中心是TCE脱氯反应的活性中心。Zn/SiO_2催化剂在TCE脱HCl反应中存在一定的失活现象,归因于反应过程中催化剂表面积炭。低Zn负载量催化剂上会产生较多积炭,归因于其具有较多强酸性中心,表明催化剂表面强酸中心是导致催化剂积炭和失活的主要原因。

Gas Phase Dehydrochlorination of 1, 1, 2-Trichloroethane over Zn/SiO2 Catalysts: Acidity and Deactivation

A series of SiO₂-supported fourth period transition metal catalysts (M/SiO₂) was prepared by a wetness impregnation method for the dehydrochlorination of 1, 1, 2-trichloroethane (TCE) in the gas phase. Among these M/SiO₂ catalysts, Zn/SiO₂ had the best catalytic activity with the highest TCE conversion (~98%) and excellent selectivity for cis-1, 2-dichloroethylene (82%). By increasing the zinc loading, the conversion of TCE using the Zn/SiO₂ catalyst was gradually improved, in agreement with the total acidity in the Zn/SiO₂ catalyst. Associating the specific activity and specific acidity of the Zn/SiO₂ catalyst with different Zn loadings, it was found that higher specific acidity contributed to higher specific activity, indicating that the acid center of Zn/SiO₂ was the catalytic active site for the dehydrochlorination of TCE. In the process of dehydrochlorination, the Zn/SiO₂ catalyst could be deactivated, mainly due to coke deposition on the catalyst surface. Catalysts with low Zn loading had stronger acid sites, which resulted in more coke formation on the catalyst. The results showed that strong acid sites on the catalyst surface were responsible for the deposition of coke and deactivation of the catalyst.