Abstract: The adsorption and activation of CH4 and CO2 on Ni/SiO2 catalyst with different Ni particle sizes were investigated by diffuse reflectance infrared Fourier transform spectroscopy. CHx species (x=1-3) were observed on the catalyst with different Ni particle sizes when CH4 was adsorbed on its surface. The CH3-O species was also detected as the result of an interaction of CHx species with surface hydroxyl groups. The dissociation of CH4 depended intensively on the Ni particle size. CH4 dissociated more easily on the Ni/SiO2 catalyst with a Ni particle size of approximate 8 nm. CO2 was very difficult to dissociate on the Ni/SiO2 catalyst, while the adsorbed H from CH4 dissociation promoted the dissociation of CO2. Small Ni particles might be helpful to hydrogen overflow to the support for CO2 activation. In co-adsorption of CH4 and CO2, the monodentate carbonate species was observed on the Ni/SiO2 catalyst with smaller Ni particle size, which indicated that smaller Ni particles could promote the reaction of CO2 with surface oxygen species.

Key words: methane, carbon dioxide, nickel, silica, supported catalyst, adsorption, activation, infrared spectroscopy