SILICA-SUPPORTED ZIRCONIA .2. EFFECT OF SULFATION ON THE SURFACE-ACIDITY AND ITS POTENTIAL AS A CATALYST FOR METHANE-OLEFIN COUPLING

A 10 wt % silica-supported zirconia catalyst has been sulfated by oxidation of SO2 or by impregnation with H2SO4, and its surface properties and acidity have been characterized by infrared spectroscopy. The supported catalyst shows IR bands due to the sulfate species which are present when either oxide alone has been sulfated (1390 cm(-1) for ZrO2 and 1440 cm(-1) for SiO2); these sulfates are at least as thermally stable as that on ZrO2 and more stable than that on pure SiO2. Uniquely, SiO2 in the mixed oxide catalyst can be sulfated by oxidation of SO2 whereas this could only be effected via impregnation with H2SO4 for the pure oxide. The acidity, which has been characterized by IR spectroscopy of adsorbed ammonia or pyridine and temperature-programmed desorption (TPD) of adsorbed NH3, is much greater than that of the unsulfated mixed oxide or of pure ZrO2, particularly with respect to the presence of strong Bronsted acid sites, The latter are absent on pure ZrO2 or are very weak and not numerous on the unsulfated SiO2/ZrO2 catalyst, Finally, the potential for sulfated SiO2/ZrO2 to catalyze the coupling reaction between methane and ethylene or propylene to give propane or butane, respectively, has been assessed at temperatures between 225 and 275 degrees C where either reaction is thermodynamically favorable. In common with many other strongly acidic catalysts, rapid deactivation of the catalyst occurred, presumably due to the deposition of carbonaceous products on the discolored catalyst, and no significant coupling products were detected.