Catalytic efficiency of cesium and potassium salts of dodecatungstophosphoric acid supported on silica and comparison with H <inf>3</inf>PW<inf>12</inf>O<inf>40</inf>/SiO<inf>2</inf>

Abstract

Pure tungstophosphoric acid, potassium tungstophosphate, and cesium tungstophosphate with varying extent of substitution of protons by Cs or K ions x (x = 1, 2, 2.5, and 3) have been prepared and are supported on silica by the wet impregnation method. The extent of loading was fixed at 20 wt %. For the sake of comparison, unloaded Cs x and K x (x = 1) salts of tungstophosphoric acid were prepared by the precipitation method. The supported catalysts were characterized by FT-IR, XRD, specific surface area measurements, and catalytic conversion of tert-butanol. The results revealed that the catalytic conversion of tert-butanol proceeds mainly via dehydration yielding isobutene. The Cs1PW/SiO2, HPW/SiO2, and K 1PW/SiO2 catalysts were more active than their unsupported samples. The previous solids showed greater catalytic activity and stability. Unexpectedly, substitution of one proton of tungstophosphoric acid by a cesium or potassium ion exerted no measurable effect on the catalytic activity of the treated solids, in spite of decreasing the Brønsted acidity of Cs 1PW/SiO2 and K1PW/SiO2 indicating that the acidity of HPW/SiO2 decrease may be due to the interaction between HPW and the SiO2 surface. On the other hand, significant decrease in the catalytic activity took place upon increasing the cation content (x) to x = 2, 2.5, and 3. © 2008 MAIK Nauka.