Immobilization of the heteropoly acid (HPA) H₄SiW₁₂O₄₀ (SiW₁₂) on mesoporous molecular sieves (HMS and MCM-41) and their catalytic behavior

Abstract

Supported catalysts, consisting of SiW₁₂ immobilized on hexagonal mesoporous silica (HMS) and its aluminum-substituted derivative (MCM-41) with different loadings and calcination temperatures, have been prepared and characterized by X-ray diffraction, FT-IR and NH₃-temperature programmed desorption. It is shown that SiW₁₂ retains the Keggin structure on the mesoporous molecular sieves and no HPA crystal phase is developed, even at SiW₁₂ loadings as high as 50 wt%. In the esterification of acetic acid byn-butanol, supported catalysts exhibit a higher catalytic activity and stability and held some promise of practical application. In addition, experimental results indicate that the loaded amount of SiW₁₂ and the calcination temperatures have a significant influence on the catalytic activity, and the existence of aluminum has also an effect on the properties of supported catalysts.