Kinetics of the Complete Oxidation of Methane over Supported Palladium Catalysts

The complete oxidation of methane by supported Pd was studied in a reaction mixture of 2% CH4 in air at 550 K, and atmospheric pressure. The catalysts were Pd supported on Al2O3 and ZrO2 deposited from PdCl2 or Pd(NH3)2(NO2)2 precursors. For the determination of how the turnover rate varies with the structure of the catalyst, the average Pd particle size on the series of catalysts was varied in the critical size range (1-10 nm). The number of active sites were measured before and after reaction by the method of H2 titration of adsorbed oxygen at 373 K. The number of active sites remained the same, although the rate per gram of catalyst increased with time on stream for all catalysts. At steady-state, the turnover rate for the series of catalysts tested varied in the range 2 × 10−2 to 8 × 10−2 s−1 under the conditions of these experiments. It is concluded that the reaction is structure insensitive. In an investigation of the kinetics of methane oxidation on palladium, the reaction products were found to strongly inhibit the oxidation of methane.