Platinum-nickel catalysts: Characterisation, methanation and carbon deposition.

Abstract

In this work we investigated the effect of platinum on nickel-on-silica catalysts. We prepared the catalysts utilizing deposition precipitation of nickel hydrosilicate with urea and simultaneous chemisorption of a platinum complex. Alloy formation was established by magnetic and X-ray diffraction measurements. Thermogravimetric and temperature programmed reduction results showed that reduction was being accelerated by the addition of platinum. The particle size was found to be not significantly different from a pure nickel catalyst. Activity in methanation decreases upon alloying, mainly due to a decrease in frequency factor, whereas the reaction orders are not significantly different from a pure nickel catalyst. A raise in the rate of hydrogenation of surface carbon is not apparent. The tendency to grow carbon is due to the crystallite size rather than the platinum content up to 10 wt% Pt in the particles. A nickel catalyst with larger particles does grow carbon at 773 K and a CO/H 2 ratio of unity whereas the platinum nickel catalysts and a nickel catalyst with smaller particles do not. At 801 K and a CO/H 2 ratio of 1.9 the platinum-nickel catalysts as well as the nickel catalyst with smaller particles also grow carbon. At a platinum content of 27 wt% we could not detect carbon. Up to a percentage of 10 wt% the decrease in activity is larger than the decrease in the growth of carbon.