The influence of hydrogen over platinum and combined platinum–palladium diesel oxidation catalysts were investigated on the oxidation kinetics of CO, HC and NO. Although H2 has been reported to have a positive effect on CO and HC oxidation as well as NO2 formation over platinum catalysts, there is still uncertainty whether this is due to the temperature rise caused by H2 oxidation or the result of a change in the reaction kinetics of CO, HC and NO oxidation by the production of intermediate species. The results have showed smaller H2 concentrations are more effective in improving the catalyst light-off temperature as well as promoting NO oxidation over both platinum and platinum–palladium catalysts. It is suggested that these benefits are a result of not only the exothermic reactions which in turn increase the local catalyst temperature but also H2 increasing the rate of reactions and the species accessibility to the catalyst active sites thus further CO, HC and NO oxidation can occur at lower catalyst temperatures.
- Diesel oxidation catalyst
- Exhaust emissions