Activation of methane to syngas over a Ni/TiO2 catalyst

Partial oxidation of methane (POM) to syngas and CH4/CO2 reforming have been investigated over a Ni/TiO2 catalyst in a fixed-bed reactor. The Ni/TiO2 catalyst has high initial activity but undergoes significant deactivation during the partial oxidation of methane reaction. Deactivation is due largely to the oxidation of Ni(0) to NiTiO3. After the partial oxidation of methane at 700degreesC the catalyst was pale yellow. XRD confirmed that Ni(0) had been converted to NiTiO3 and oxygen pulse reactions found only traces of carbon were present after the POM reaction. The Ni/TiO2 catalyst has a high activity and a long term stability in the CO2 reforming reaction. XRD found Ni(0) was present after the reforming reaction but NiO and NiTiO3 were absent. Activation of methane over Ni/TiO2 was also investigated using pulse reaction techniques in the absence of gas phase oxygen. Methane pulse reactions demonstrated that the mechanism of methane oxidation changes as the oxidation state of nickel changes. CH4 may have been oxidized by oxygen from solid NiO or by active oxygen within the TiO2 Support via the non-selective Rideal-Eley mechanism over the oxidized Ni/TiO2 catalyst surface. In contrast, CH4 is efficiently converted to CO and H-2 via a direct oxidation mechanism when Ni/TiO2 is reduced. Pulse reaction studies provide evidence that the oxidation state of nickel controls the methane activation mechanism and the product distribution. (C) 2002 Elsevier Science B.V. All rights reserved.