改性H-ZSM-34上氯甲烷催化转化制低碳烯烃

比较了几种典型的沸石分子筛在氯甲烷转化制乙烯、丙烯和丁烯等低碳烯烃反应中的催化性能, 发现H-ZSM-34具有较佳的催化活性和选择性. 经乙二胺四乙酸二钠(Na₂H₂EDTA)水溶液处理, 并经离子交换及焙烧后, H-ZSM-34上氯甲烷转化制低碳烯烃的催化性能显著改善. 当Na₂H₂EDTA浓度为0.1 mol/L, 反应温度为673 K, CH₃Cl分压9.2 kPa时, C₂-C₄烯烃选择性和收率分别达82%和61%. 研究还发现, Ce修饰H-ZSM-34催化剂同样可改善氯甲烷制低碳烯烃的选择性和收率. 表征结果表明, Na₂H₂EDTA处理和Ce修饰均降低了H-ZSM-34的酸性. 酸性的降低可抑制低碳烯烃的氢转移反应, 继而避免了其进一步转化为低碳烷烃.

Catalytic conversion of methyl chloride to lower olefins over modified H-ZSM-34

Among several typical zeolites, H-ZSM-34 was found to be an efficient catalyst for the conversion of methyl chloride to lower olefins, i.e., ethylene, propylene, and butenes. Treatment of H-ZSM-34 with a Na₂H₂EDTA (EDTA = ethylenediaminetetraacetate) aqueous solution followed by ion exchange and calcination enhanced the catalytic performance significantly. The selectivity to lower olefins increased significantly for certain Na₂H₂EDTA aqueous solution concentrations; when the H-ZSM-34 catalyst was treated with a 0.1 mol/L Na₂H₂EDTA solution, the selectivity and yield of C₂-C₄ olefins reached 82% and 61%, respectively, at 673 K and a CH₃Cl partial pressure of 9.2 kPa. The modification of H-ZSM-34 with Ce ions improved C₂-C₄ olefin selectivity and yield. Catalyst characterization suggests that treatment with Na₂H₂EDTA or modification by Ce decreases the acidity of H-ZSM-34. The weakened acidity of the treated or modified H-ZSM-34 may suppress the hydrogen transfer reaction and prevent lower olefins from further transformation to paraffins.