Partial oxidation of methane over SiO2 supported Ni and NiCe catalysts

Nickel and nickel-ceria catalysts supported on high surface area silica, with 6 wt% Ni and 20 wt% CeO2 were prepared by microwave assisted (co) precipitation method. The catalysts were investigated by XRD, TPR and XPS analyses and they were tested in partial oxidation of methane (CPO). The catalytic reaction was carried out at atmospheric pressure in a temperature range of 400-800 °C with a feed gas mixture containing methane and oxygen in a molecular ratio CH4/O2 =2. The Ni catalyst exhibited 60% methane conversion with 60% selectivity to CO already at 500 °C. On the contrary, the Ni-Ce catalyst was inert to CPO up to 700 °C. Moreover, the former catalyst reproduced its activity at the descending temperatures maintaining a good stability at 600 °C, over a reaction time of 80 h, whereas the latter one completely deactivated. Test of CH4 temperature programmed surface reaction (CH4-TPSR) revealed a higher methane activation temperature (> 100°C) for the Ni-Ce catalyst as compared to the Ni one. Noticeable improvement of the ceria containing catalyst occurred when the reaction test started at a temperature higher than the methane decomposition temperature. In this case, the sample achieved the same catalytic behavior of the Ni catalyst. As confirmed by XPS analyses, the distinct electronic state of the supported nickel was responsible for the differences in catalytic behavior.