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 solids, heat-treated from 373 to 1073 K, were examined by means of differential thermal analysis, X-ray diffraction, surface area, infrared, Raman, P-31 nuclear magnetic resonance analyses, and used as catalysts in the decomposition of isopropanol. Below 673 K, TPA on ZrO2 exist as distorted intact Keggin species interacting with =Zr-OH or =Zr+ groups. However, at 773 K, bulk-like intact TPA species were detected. Above 773 K, the Keggin structure of TPA collapse and transforms into WO3 and phosphorous oxides. The characteristic diffraction peaks of TPA cannot be observed even with 20 wt.% TPA loading, indicating a high dispersion or a very small crystal size of TPA, while 20 wt.% TPA loaded on SiO2 clearly shows the presence of TPA particles,The heat-treatment temperature affects the catalytic activity of TPA on Zirconia. The reaction rate was 3.3 times higher in a TPA/ZrO2 calcined at 773 than that at 473 K. (C) 2000 Elsevier Science B.V. All rights reserved.