PEG2000对MCM-22分子筛结构特性和催化性能的影响

以六亚甲基亚胺为模板剂,在动态水热合成MCM-22分子筛的过程中,加入有机辅助剂聚乙二醇2000(PEG2000),考察有机辅助剂PEG2000对MCM-22分子筛结构、酸性以及催化性能的影响。由X射线衍射谱图可以看出,合成时加入适量的PEG2000,可以得到结晶较好的MCM-22晶体,但结晶度稍微有些降低。由氮吸附脱附测试结果可以看出,适量助剂PEG2000的加入,改变了分子筛的最可几孔径分布,最可几孔径由0.556 nm提高至0.587 nm,孔容由0.35 m3/g增加到0.59 m3/g,BET比表面积由410 m2/g增加到456 m2/g。NH3-TPD方法测试样品的酸性结果显示,加入适量的PEG2000后,分子筛的强酸位得到加强。另外用合成的分子筛作为催化剂,以苯与丙烯烷基化为模型反应,考察了MCM-22分子筛的活性以及选择性,结果显示催化剂的活性有较大提高,然而对异丙苯的初始选择性降低,随着反应的进行,异丙苯的选择性却很快地增长。

Effect of PEG2000 on structural characteristics and catalytic performances of MCM -22 molecular sieve

MCM-22 zeolite(molecular sieve) was synthesized by dynamic hydrothermal crystallization method with polyethylene glycol 2000(PEG2000) as organic accessory ingredient and with hexamethyleneimine as template.Effect of PEG2000 on the structure,acidity and catalytic performances of MCM-22 molecular sieve has been investigated.From XRD spectrum,adding proper amount of PEG2000 while synthesizing MCM-22,better MCM-22 crystal could be obtained,but the degree of crystallinity decreased slightly.From the results of nitrogen adsorption-desorption analysis,proper amount of PEG2000 changed the distribution of the most probable pore size,which was increased to 0.587 nm from 0.556 nm;additionally,the specific pore volume was increased to 0.59 cm3/g from 0.35 cm3/g and BET specific surface area was increased to 456 m2/g from 410 m2/g.Acidity results tested by NH3-TPD showed that by adding appropriate amount of PEG2000 the strong acid intensity was strengthened.Moreover,the synthesized molecular sieve was used as catalyst in alkylation reaction of benzene and propylene.The activity and selectivity of MCM-22 were investigated and results showed that activity of catalyst has been improved greatly,but its initial selectivity to isopropyl benzene was reduced,however,with the reaction proceeds the selectivity to isopropyl benzene increased soon.