Characterization and Stability of Heteropolyacid Catalysts Supported on MCM-41 Materials Synthesized by Ultrasonic Irradiation

Abstract

A series of solid acid catalyst of the Keggin-type 12-phosphotungstic acid, H3PW12O40, supported on ordered mesoporous silica MCM-41 were prepared by a simple and effective impregnation method. MCM-41 supports were synthesized in a relatively short time via a recently reported ultrasonic irradiation method. The synthesis sonication time has been systematically varied in order to investigate its influence on the structural order of the resulting materials. The prepared catalysts were characterized by nitrogen adsorption, X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. The resulting materials exhibited hexagonally ordered meso structure, with high surface area of the order of several hundreds of m2g-1,relatively large pore volumes, with the pore diameter in the range of 2.19 to 2.41 nm and a corresponding pore wall thickness of over 1.67nm. The results have demonstrated that high quality MCM-41 materials can be synthesized via the ultrasonic irradiation in few tens of minutes, much shorter than the conventional synthesis methods. Despite their relatively high loading, all synthesized materials retained the characteristic MCM-41mesoporous structure after impregnation of the heteropolyacid active phase onto the inner pore surface, without crystallization, but preserving the Keggin structure as confirmed by Raman spectroscopy.

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

“…Furthermore, the regular pore structure and tuneable pore size enables rapid diffusion of reactants and products through the pores to minimize consecutive reactions. Usually, tungsten HPAs, in particular 12-tungstophosphoric acid (H 3 PW 12 O 40 , HPW, TPA), are the catalysts of choice considering their stronger Brønsted acidity, lower oxidation potential and higher thermal stability [66][67][68][69][70][71].…”

Assessing the Catalytic Potential of 12-tungstophosphoric Acid Supported on MCM-41 for the Gas Phase Etherification of Alcohols

“…MCM-41support were prepared by ultrasonic irradiation under basic environment and the HPW/MCM-41 catalysts were obtained by impregnating the heteropolyacid on the synthesized supports as described in detail elsewhere [47]. BET areas between 1435 and 460 m 2 g -1 , and pore volumes between 0.914 and 0.208 cm 3 g -1 were obtained for the samples when the HPW loading increased from 0 to 30 wt%.…”

“…We have recently prepared and characterized MCM-41 supports by ultrasonic irradiation under basic pH, used them to obtain HPW/MCM-41 catalysts, and demonstrated that the synthesized materials retained the characteristic MCM-41 mesoporous structure after impregnation of the active phase onto the mesoporous surface. Details on the synthesis route and characterization results of the HPW/ MCM-41 catalysts are given elsewhere [47].…”