阴离子改性MCM-22分子筛的制备及其在催化合成聚甲氧基二甲醚中的应用

以硅溶胶为硅源,偏铝酸钠为铝源、环己亚胺为模板剂,采用水热合成法和离子交换法合成了HMCM-22分子筛,通过在合成凝胶时引入不同的阴离子制备了改性分子筛HMCM-22(X),利用XRD、FTIR、SEM、N2吸附-脱附、27Al NMR和NH3-TPD等方法分析了阴离子对Al在MCM-22结构中落位的影响,同时考察了HMCM-22(X)骨架中酸中心位置和酸性质对合成聚甲氧基二甲醚(PODEn)的影响。实验结果表明,HMCM-22(X)的拓扑结构未发生改变。阴离子并未掺杂到MCM-22的晶体结构中,但对试样的比表面积影响较大。阴离子的存在使催化剂的酸性位点更多地分布在催化剂的外表面和超笼处。阴离子不同,外表面形成的酸量和酸强度不同。PODEn的形成受酸性位点和酸性质的共同影响,外表面的中强酸更有利于增链反应进行,HMCM-22(NO3-)和HMCM-22(ClO4-)的催化效果好于HMCM-22(SO42-)。

Preparation of anionically modified MCM-22 zeolites and application in catalytic synthesis of polyoxymethylene dimethyl ether

HMCM-22 zeolites were prepared by a hydrothermal synthesis method and an ion exchange method using silica sol as silicon source,sodium aluminate as aluminum source and hexamethyleneimine as template.HMCM-22(X)zeolites were prepared by introducing different anions to the synthesis gel.XRD,FTIR,SEM,N2 adsorption-desorption,27Al NMR and NH3-TPD were carried out to characterize the influence of anions on the location of Al in MCM-22.The effects of acid center positions and acidity on the synthesis of PODEn were also investigated.The results showed that the topology structure of HMCM-22(X)was not changed.The anions were not doped in the crystal structure,but it had a large influence on the specific surface area,and allowed the acid sites of the catalyst to be distributed more at the outer surface of the catalyst and at the supercage.The influence on the amount of acid and acid strength was different by introducing different anions The synthesis of PODEn was affected by the acid center positions and acid properties,and the mediate strong acid on the outer surface was more favorable for the chain extension.The catalytic performances of HMCM-22(NO3-)and HMCM-22(ClO4-)were better than that of HMCM-22(SO42-).