Characterization and catalytic performance of heteropoly acid H4SiW12O40 supported on nanoporous materials.

Abstract

Heteropoly acid H4SiW12O40 (SiW) has been supported on different nanoporous materials and characterized by powder X-ray diffraction (XRD), FTIR, HRTEM, N2 physisorption, and thermal analysis. No SiW diffraction peaks are observed after loading 33-50 wt% of SiW on various mesoporous materials (pore size: -30 Å) except for siliceous MCM-48. In contrast, the SiW diffraction peaks appear at 14 wt% loading on zeolite EMT with micropore size of ca. 7.4 x 6.5 Å. Supported SiW retains the Keggin structure on mesopore surface. The cubic mesostructure of MCM-48 is stable while MCM-41 loses its regular hexagonal mesostructure upon loading SiW. Several factors account for different behaviours of various supports, including pore size, curvature of mesopore interface and interaction between SiW and aluminium sites in the framework. The resulting 33-50 wt% SiW/MCM-48 solid acid catalysts have large surface area (- 550 m2/g), regular pore arrangement with uniform pore size (- 25 Å), finely dispersed SiW and good thermal stability. They exhibit significantly improved activity in acid-catalyzed cracking of long-chain hydrocarbons in comparison with bulk SiW and SiW/MCM-41.