(647a) Modeling of Single Atom Catalysis for CO Oxidation

It is well known that a catalytic converter is used in a gasoline engine to control its emissions. CO oxidation is one of the three types of reactions occurring over the catalytic converter. This three way catalyst is very effective at high temperatures, but loses its performance at cold start conditions due to CO poisoning. In order to fulfill more stringent environmental regulations, there is a need to improve this performance and reach lower light-off temperatures. To this end, the application of well dispersed metal catalysts is expected to improve the performance and cut down the cost of emission control technologies. In addition, this cost can be further reduced by replacing the platinum group metals typically used in three-way catalysts by less precious transition state metals. Fundamental studies on atomically dispersed supported metal catalysts can provide a measure of the strength of the metal-support interaction at the single-atom limit and assess their activity for low temperature CO oxidation. In the present study, density functional theory calculations are performed for CO oxidation over Pd supported on alumina. Multiple catalytic cycles are considered including carbonate-mediated and self-promoted CO oxidation. Microkinetic modeling is used to quantify the effect of reaction conditions and the rate-determining steps along with the most important reaction intermediates. A reduced reaction model is also developed. It is shown that the carbonate-mediated catalytic cycle without Eley-Rideal steps is most dominant for CO oxidation over a single Pd atom supported on alumina. Low temperatures favor the co-adsorption of O₂ with two CO molecules on the supported Pd atom, in contrast to larger Pd ensembles that are mainly covered by CO. Finally, the stability of the catalyst is also discussed.

Acknowledgements: This work is performed in the framework of a European Union’s Horizon 2020 research and innovation programme (Partial-PGMs).