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 oxid ation of SO2 or by impregnation with H2SO4, and its surface properties and acidity have been characterized by infrared spectroscopy. The sup ported catalyst shows IR bands due to the sulfate species which are pr esent 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 st able 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 th e pure oxide. The acidity, which has been characterized by IR spectros copy of adsorbed ammonia or pyridine and temperature-programmed desorp tion (TPD) of adsorbed NH3, is much greater than that of the unsulfate d mixed oxide or of pure ZrO2, particularly with respect to the presen ce of strong Bronsted acid sites, The latter are absent on pure ZrO2 o r are very weak and not numerous on the unsulfated SiO2/ZrO2 catalyst, Finally, the potential for sulfated SiO2/ZrO2 to catalyze the couplin g reaction between methane and ethylene or propylene to give propane o r 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 deactivat ion of the catalyst occurred, presumably due to the deposition of carb onaceous products on the discolored catalyst, and no significant coupl ing products were detected.