Catalytic reforming of methane with carbon dioxide over nickel catalysts II. Reaction kinetics

Abstract

The reforming of methane with carbon dioxide was studied over nickel supported on SiO 2, TiO 2, MgO and activated carbon. Specific activities on a turnover frequency basis were in the order: Ni/TiO 2 > Ni/C > Ni/SiO 2 > Ni/MgO. Interestingly, a 2-fold increase in activation energy for this reaction was observed over Ni/TiO 2 after several hours time on stream. The reverse water-gas shift reaction was found to be close to thermodynamic equilibrium over all catalysts. Partial pressure dependencies were obtained with the Ni/C and Ni/SiO 2 catalysts at 723 K for comparative purposes only, but a more thorough kinetic analysis was made with the Ni/MgO and Ni/TiO 2 catalysts, which were shown previously to strongly inhibit carbon deposition. Partial pressure dependencies were obtained at 673, 698, and 723 K for Ni/TiO 2 and at 773, 798, and 823 K for Ni/MgO. In situ DRIFTS studies clearly showed the presence of both linear and bridged carbon monoxide adsorption on Ni/SiO 2 under reaction conditions; however, adsorbed carbon monoxide could not be identified on Ni/TiO 2. A reaction model for CH 4—CO 2 reforming, based on CH 4 activation to form CH x and CH x O decomposition as the slow kinetic steps, successfully correlated the rate data.