Sulfated CexZr1−xO2 oxides. Surface properties and performance for methane oxidation under fuel-rich conditions

Two series of sulfated zirconia-ceria based catalysts have been prepared by coprecipitation of the Zr4+ and Ce3+ salts, which were then sulfated by impregnation using H2SO4 and [(NH4)2S2O8] and calcined at 650 °C for 4 h. The sulfated and persulfated Zr-Ce-O samples were synthesized with Zr/Ce ratios ranging from 1 to 15. The textural, structural and surface characteristics of the resulting modified catalysts were determined by N2 adsorption-desorption, XRD, XPS spectroscopy and TPD of NH3, and results were related to their catalytic behaviour. The catalysts were tested in the direct conversion of methane at high temperature (650 °C) under fuel-rich conditions to obtain C1 oxygenates (CH3OH and HCHO). Experiments were conducted using low O2/CH4 ratio mixtures and high space velocity. It was shown that O2/CH4 feeds resulted in practically total combustion of CH4 when sulfated/persulfated ceria-zirconia catalysts are used, while the nature of the different phases modifies the surface acidity, which plays a crucial role on the extent of deep oxidation reactions.