Synthesis, Characterization, and Catalytic Properties of SiPW‐X Mesoporous Silica with Heteropolyacid Encapsulated into Their Framework

A series of SiPW‐X mesoporous silica with Keggin‐type heteropolyacids (HPAs) encapsulated into their framework have been synthesized under strong acidic conditions. During hydrolysis of tetraethyl orthosilicate (TEOS), Na2HPO4 (P source) and Na2WO4 (W Source) are added into the initial sol‐gel system to form Keggin type HPAs. The final products have been intensively characterized by various techniques, such as XRD, TEM, N2 adsorption isotherm analysis, and by IR, UV/Visible, and 31P Magic Angle Spinning (MAS) NMR spectroscopy. Characterization results suggest that samples with an HPA weight percent of 13.3–20.7 % show very ordered hexagonal mesostructures. In addition, HPAs incorporated in the mesosilica are insoluble during catalysis. Results of catalytic tests show that SiPW‐X materials have catalytic activities that are comparable to bulk HPA in catalytic tests implementing chemical reactions of both small (cumene cracking and esterification of ethanol with acetic acid) and bulky (1,3,5‐triisopropylbenzene cracking and esterification of benzoic acid with tert‐butyl alcohol) molecules. It can be readily separated from the reaction system for reuse, which suggests the potential industrial application. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)