Dissociative adsorption of CH4 on NiAu/YSZ:The nature of adsorbed carbonaceous species and the inhibition of graphitic C formation

Methane dissociative adsorption and partial oxidation reaction were studied by means of adsorption equilibrium and transient experiments on Au-modified Ni/YSZ powders. It was found that the addition of 1% atomic ratio of Au with respect to Ni on Ni/YSZ cermet catalyst (total metal loading 50 wt%) significantly affects both the kinetics of CH 4 dissociative adsorption and the binding strength of the adsorbed CH x species on the Ni surface. The formation of graphitic carbon is significantly inhibited, whereas the hydrogenation of CH x species into CH4 , studied by means of temperature-programmed reaction spectroscopy (TPRS), occurs at temperatures 100 K higher than on the unmodified Ni/YSZ surface. This implies higher stability and elongation of the CH x species lifetime on the NiAu/YSZ surface before their decomposition into surface carbidic species. The oxidation reactions involve both the oxidation of CH x species into CH x O and its subsequent decomposition at elevated temperatures (700 K) into CO and H2 , whereas carbidic species are selectively oxidized into CO2 at temperatures as low as 500 K. In this respect, the higher CH x surface concentration on the Au-modified Ni/YSZ species will result in higher selectivity toward the production of synthesis gas, with greatly suppressed graphitic carbon formation.