Solid acid catalysts comprising up to 70wt% tungstophosphoric acid (PW) dispersed on three mesoporous silicas with uniform pore size distributions of 18 Angstrom, 30 Angstrom, and 100 Angstrom, as well as on amorphous silica were synthesized. The effects of support pore size and catalyst preparation procedures on the chemical and physical properties of the synthesized catalysts were characterized using 31P magic angle spinning NMR, in-situ X-ray diffraction, and N2 physisorption. It was observed that right pore size of catalyst supports is important for PW dispersion via solution impregnation method and PW is highly dispersed even at a 70wt% loading when the support pore size is greater or equal to 30 Angstrom. Acid neutralization of silica supports and utilization of non-hydrolyzing organic polar solvents such as methanol are required to retain the Keggin structure of PW during sample preparation. The thermal stability of PW is enhanced when it is supported on silica supports. In addition, mesoprous silica with 30 Angstrom uniform pores eexhibits improved PW stability to polar solvent leaching, probably as a result of steric hindrance of the silica support due to the compatible size between the pores of the silica support (30 Angstrom) and the cluster of PW (12 Angstrom).
Revised: June 13, 2003 |
Published: February 1, 2000
Citation
Wang Y., A.Y. Kim, X.S. Li, L.Q. Wang, C.H. Peden, and B.C. Bunker. 2000.Shape Selective Solid Acid Catalysts Based on Tungstophosphoric Acid Supported on Mesoporous Silica. In Shape-Selective Catalysis, edited by Chunshan Song, Juan M. Garces and Yoshihiro Sugi, 738, 353-368. Washington, District Of Columbia:American Chemical Society.PNNL-SA-31580.