Impact of palladium distribution in alumina on low-temperature oxidation of carbon monoxide

When emission standards for vehicles are becoming more stringent, catalysts that efficiently oxidize CO and HC (hydrocarbons) are a necessity. One of the important aspects here is to improve efficiency at low temperatures. This is emphasized by the change in technology towards more fuel-efficient engines which results in colder emissions and the need for reducing cold-start emissions [1]. Low-temperature oxidation can be enhanced using different strategies [2]. New materials and combinations of materials could be one solution and in that context the distribution of the active phase in the support material is crucial [3]. The distribution of the active phase will influence mass and heat transfer and thereby control the conversion of the reactants. Previously, it has been shown that heterogeneous distribution of the active phase (Pt) in the support material can improve the oxidation of CO at low temperatures [3]. The idea was that concentrate the active phase locally in the support material would result in a better utilization of generated reaction heat leading to higher temperatures of the active sites and, therefore, promote higher activity. The study showed an increase in activity for the samples with heterogeneous distribution of the active phase but it was also concluded that the enhancement in activity most likely arises from mass transfer effects