Ruthenium and platinum catalyzed carbon oxidation: A comparative kinetic study

Carbon oxidation catalyzed by Ru/Na-Y zeolite under conditions relevant to automotive exhaust gas after treatment was experimentally investigated. In the presence of Ru/Na-Y zeolite catalyst carbon oxidation can be described by three mechanisms, viz. (i) reaction between carbon and NO2; (ii) reaction between carbon and O2 and (iii) cooperative reaction of carbon involving O2 and NO2 simultaneously. The kinetic analysis suggested that the direct C–O2 and the cooperative C–NO2–O2 reaction in the presence of Ru/Na-Y catalyst proceeded according to the adsorption of oxygen on carbon surface followed by a decomposition of these oxygenate surface complexes. The kinetic description of the Ru/Na-Y zeolite catalyst is compared with kinetic models of platinum based carbon oxidation from literature. The catalytic properties of ruthenium and platinum based catalysts were found to be fundamentally different. On the ruthenium catalyst the activation energy for the cooperative C–O2–NO2 reaction and the direct C–O2 reaction is similar, whereas on platinum, the direct C–O2 reaction is slower. In the presence of platinum catalyst NO2 molecules intervene in the decomposition of surface oxygenated carbon complexes, formed by the oxygen adsorption on carbon surface. The kinetic models based on the occurring of direct and cooperative reactions may be applied for the catalytic oxidation of soot in the regenerative particle trap conditions.