Thermal stability of 12-tungstophosphoric acid supported on zirconia

A freshly precipitated zirconia was impregnated with an ethanol solution of H-3[W12PO40].6H(2)O (TPA) in order to obtain 0-25 wt.% TPA/ZrO2, The solid s, heat-treated from 373 to 1073 K, were examined by means of differential thermal analysis, X-ray diffraction, surface area, infrared, Raman, P-31 nu clear magnetic resonance analyses, and used as catalysts in the decompositi on of isopropanol. Below 673 K, TPA on ZrO2 exist as distorted intact Keggi n species interacting with =Zr-OH or =Zr+ groups. However, at 773 K, bulk-l ike intact TPA species were detected. Above 773 K, the Keggin structure of TPA collapse and transforms into WO3 and phosphorous oxides. The characteri stic diffraction peaks of TPA cannot be observed even with 20 wt.% TPA load ing, indicating a high dispersion or a very small crystal size of TPA, whil e 20 wt.% TPA loaded on SiO2 clearly shows the presence of TPA particles,Th e heat-treatment temperature affects the catalytic activity of TPA on Zirco nia. The reaction rate was 3.3 times higher in a TPA/ZrO2 calcined at 773 t han that at 473 K. (C) 2000 Elsevier Science B.V. All rights reserved.