Catalytic reforming of methane with carbon dioxide over nickel catalysts I. Catalyst characterization and activity

The reforming of methane with carbon dioxide was studied over nickel supported on MgO, TiO2, SiO2, and activated carbon. The influence of the support on catalyst activity and carbon deposition resistivity was markedly different ineach case. Although considerable formation of filamentous 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 filamentous carbon appeared to be formed. In contrast to Ni/SiO2, substantially less coking was observed over either the Ni/TiO2 or the Ni/MgO catalysts. Evidence of strong metal-support interaction (SMSI) in the Ni/TiO2 catalyst indicated that large ensembles of nickel atoms, active for carbon deposition, are deactivated or removed by the presence of mobile TiOx species. The identification of two TiOx phases and a Ni5TiO7 phase 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 the formation of a partially reducible NiO—MgO solid solution, which appears to stabilize the reduced nickel surfaces and provide resistance to carbon deposition.