La掺杂对Cr2O3催化剂气相氟化四氯乙烯反应性能的影响

Effects of doped La on the performance of Cr_2O_3 catalysts in vapor phase hydrofluorination of tetrachloroethylene

采用共沉淀法制备了LaF3-Cr2O3催化剂,并考察了催化剂对气相氟化四氯乙烯(PCE)反应性能的影响。结果表明,随着La掺杂量的增加,LaF3-Cr2O3催化剂上PCE的转化率不断升高,而有效产物(HCFC-123+HCFC-124+HFC-125)总选择性出现先升高后下降。当La掺杂为1%时,1LaF3-Cr2O3催化剂的气相氟化四氯乙烯(PCE)反应性能最佳,PCE的转化率和有效产物总选择性分别达到92.8%和90.1%。NH3程序升温脱附结果表明,随着La掺杂量的增加,LaF3-Cr2O3催化剂弱酸中心减少,催化剂酸强度和强酸中心数目增加。这是由于催化剂中LaF3和CrF3含量的增加所致,催化剂表面相对酸量的增加不利于有效产物(HCFC-123+HCFC-124+HFC-125)的生成。

LaF3-Cr2O3 catalysts were prepared by a precipitation method,and their effects on the catalytic performance in vapor phase hydrofluorination of tetrachloroethylene were studied. With increasing La content,the tetrachloroethylene conversion over LaF3-Cr2O3 catalyst increases,while the total selectivity to effective products（HCFC-123 ＋ HCFC-124 ＋ HFC-125） first increases and then decreases. When the addition content of La is 1%,1LaF3-Cr2O3 catalyst exhibits the highest catalytic performance;the tetrachloroethylene conversion and the selectivity to effective products reach 92.8% and 90.1%,respectively. Results of NH3 temperature-programmed desorption indicate that the amount of weak acid sites of LaF3-Cr2 O3 catalysts decreases with the increase of La content,while both the acid intensity and the amount of strong acid sites increase. It may be attributed to the increase in the content of LaF3 and amorphous CrF3 in the catalyst. Therefore,it could be concluded that the increase in the relative acid amount on the catalyst surface is unfavourable for the formation of effective products（HCFC-123＋HCFC-124＋ HFC-125）.