The influence of point defects on the resistance of ceria to carbon deposition in hydrocarbon catalysis

The reactivity of methane with ceria, doped with either 10 cation% Gd, 1.4 cation% Nb, 5 cation% Nh, or undoped has been investigated using micro-reactor techniques. Temperature programmed reduction (TPR) was carried out in a mixture of 5% hydrogen in argon and both temperature programmed reaction (TPRx) and isothermal reaction at 900 degreesC were carried out in 5% methane in argon. Oxidation of deposited carbon was investigated by temperature programmed oxidation (TPO) in 10% oxygen in helium. All cerias had good catalytic activity for conversion of methane to hydrogen and carbon monoxide until oxygen exhaustion. Exposure to methane resulted in only small amounts of carbon deposition. Doping was found to have a relatively minor effect on reaction with methane, but Nb-doped ceria was capable of oxidizing carbon deposits at lower temperatures than undoped or Gd-doped ceria. (C) 2000 Elsevier Science B.V. All rights reserved.