钙负载量对Ca/HZSM-5甲醇制烯烃催化性能的影响

以浸渍法制备不同负载量的Ca/HZSM-5催化剂,并采用NH_3-TPD和Py-IR对改性前后样品进行表征。在连续流动固定床反应装置上,详细考察了其甲醇制烯烃(MTO)的催化性能。催化评价结果表明,Ca改性提高了催化稳定性与低碳烯烃(C_2~=～C_4~=)选择性,但负载过多的Ca不利于甲醇制烯烃反应,Ca负载量存在最佳值,约为6%。关联评价结果与酸表征数据,发现HZSM-5上几乎所有的B酸与Ca物种作用后,催化性能达到最佳。通过与Na/HZSM-5和2Ca/1Na/HZSM-5催化性能的比较,探讨了Ca在催化反应中的作用,提出Ca物种与B酸结合形成了催化活性中心,参与甲醇的催化转化。

Effects of Ca loadings on catalytic behaviors of Ca/HZSM-5 for methanol-to-olefin process

HZSM-5 zeolite was modified with different loadings of Ca by incipient impregnation and the samples were characterized by FTIR spectra of adsorbed pyridine and NH3-TPD. Methanol to olefin （MTO） over Ca modified HZSM-5 catalysts was carried in a continuous flow fixed bed reactor. The results showed that Ca modification enhanced both catalytic stability and selectivity to light olefins （C2^=- C4^= ）, whereas excessive Ca loadings resulted in declining catalytic behaviors. The optimum Ca loading was 6%. Correlating the reaction results with the acidity characterization ones, it was found that the catalyst whose Brcnsted acid sites combined almost completely with Ca species exhibited the best catalytic behaviors. Furthermore, by comparing catalytic behaviors of Ca/HZSM-5 with those of Na/HZSM-5 and 2Ca/1Na/HZSM-5, function of Ca in the catalytic reaction was discussed. It was proposed that Ca combined with Brcnsted acid sites to form catalytic centers and thus participated in conversion of methanol.