CATALYTIC REFORMING OF METHANE WITH CARBON-DIOXIDE OVER NICKEL-CATALYSTS .1. CATALYST CHARACTERIZATION AND ACTIVITY

The reforming of methane with carbon dioxide was studied over nickel s upported on MgO, TiO2, SiO2, and activated carbon. The influence of th e support on catalyst activity and carbon deposition resistivity was m arkedly different in each case. Although considerable formation of fil amentous carbon was observed over Ni/SiO2 (confirmed by TEM and TPO), there was negligible initial loss of catalytic activity. The catalytic activity of Ni/C was very similar to that of Ni/SiO2, but no filament ous carbon appeared to be formed. In contrast to Ni/SiO2, substantiall y less coking was observed over either the Ni/TiO2 or the Ni/MgO catal ysts. Evidence of strong metal-support interaction (SMSI) in the Ni/Ti O2 catalyst indicated that large ensembles of nickel atoms, active for carbon deposition, are deactivated or removed by the presence of mobi le TiOx species. The identification of two TiOx phases and a Ni5TiO7 p hase was made possible by direct measurement of crystalline d spacings with TEM. The Ni/MgO catalyst was both active and very stable for up to 44 h time on stream. Chemisorption, XRD and TEM results indicate th e formation of a partially reducible NiO-MgO solid solution, which app ears to stabilize the reduced nickel surfaces and provide resistance t o carbon deposition.