Influence of Template Extraction on Structure, Activity, and Stability of MCM-41 Catalysts

Abstract

Up to 73% of the template in MCM-41 can be removed by extraction with solutions of an acid or salt in ethanol. When extracting with acidic ethanol, ion exchange of the sodium ions for protons is achieved simultaneously. After calcination to remove the residual template, the resulting catalysts show high activity for the acetylation of 2-methoxynaphthalene. The activity depends on the sodium content and on the Si/Al ratio of the catalyst. MCM-41 materials which had not been extracted, but directly calcined to remove all template ions and subsequently ion exchanged, had a mesoporous structure that deteriorated with repeated calcinations. The acid extracted catalysts, on the other hand, retained their highly ordered pore structure throughout several thermal treatments. This stabilization results from the precondensation of silanol groups previously associated with template ions during the extraction. The extraction in acidic medium produced a MCM-41 catalyst with more Brønsted acid sites than the not extracted material.27Al-NMR measurements showed that the observed increase in octahedral aluminium upon calcination usually ascribed to dealumination can also be explained by a change of coordination number depending on chemical environment as previously reported for zeolite β.