NO reduction by CH4 over a 40% La2O3/gamma-Al2O3 catalyst in the absence and presence of O-2 in the feed was studied. The addition of either Co-2 or H2O to the feed produced a reversible inhibitory effect on the rate similar to that observed with unsupported La2O3; however, the extent of rate inhibition was considerably smaller than on unsupported La2O3. At 973 K, either CO2 (9%) or H2O (2%) in the feed decreased activity by about 35% in the absence of O-2 and by only 20% with excess O-2 in the feed. In the absence of O-2, a reaction mechanism previously proposed for La2O3 was altered to include competitive CO2 and H2O adsorption and to give the following rate expression for N-2 formation:r(N2) = k'PNOPCH4/(1 + KNOPNO + K-CH4 P-CH4 + K-CO2 P-CO2 + K-H2O P-H2O)(2).This equation fit the data well, had apparent activation energies of 14-25 kcal/mol, and gave thermodynamically consistent enthalpies and entropies of adsorption. Stable rates at 973 K with O-2 and either CO2 or H2O in the feed were between 0.94 and 0.99 mumol N-2/s/g catalyst. In the presence of excess O-2, after CO2 and H2O adsorption were again included, a rate equation proposed earlier for La2O3 again provided a good fit to the data with H2O in the feed as well as thermodynamically consistent parameters determined under integral reaction operation. However, with both CO2 and excess O-2 in the feed, this rate expression could not provide thermodynamically meaningful parameters from the fitting constants even though it fit the data well. This was attributed to a major contribution from the alumina to the overall rate, because CO2 had no significant effect on NO reduction on alumina, but it inhibited this reaction on La2O3. A reaction model was proposed for gamma-Al2O3 that gave the rate expression for total CH4 disappearance due to both combustion and NO reduction over gamma-Al2O3(r(CH4))(T) = kcom' P-CH4 P-O2(0.5) + k(NO)' P-NO P-CH4 P-O2(0.5)/(1 + K-NO2' P-NO P-O2(0.5) + K-CH4 P-CH4 + K-O2(0.5) P-O2(0.5) + K-CO2 P-CO2 + K-H2O P-H2O)(2),which gave a satisfactory fit to the data along with thermodynamically consistent parameters. The second term in this equation, which represents the rate of N-2 formation, was then combined with the rate equation for N-2 formation on pure La2O3 in the presence of O-2 to describe overall catalyst performance, and the data were fit well, assuming that La2O3 composed 6.8% of the total surface area, a value close to that of 6.1% obtained from XRD line-broadening calculations. (C) 2003 Elsevier Science (USA). All rights reserved.