Heterogeneous catalysts are generally robust and operate at low costs and thus widely used in numerous industrial applications. Unlike homogenous catalysts, their catalysis phases differ from reactants of product phases and are used without being consumed. As such, heterogenous catalysts can be recycled. Oxidation of carbon monoxide to carbon dioxide in an automotive catalytic converter is a good example of heterogenous catalysts application. This reaction, however, depends on the surface of metal particles including platinum, palladium, and rhodium. To this end, understanding of catalytic reaction mechanism depends on reaction analysis on the solid surfaces.
Oxidation of carbon monoxide on Pt (100) surface is rather simple and does not involve reconstructions of the platinum surface. Nevertheless, the reaction mechanisms on the surface are complicated owing to the inclusion of various processes: adsorption, desorption, bond rearrangement between the carbon monoxide and oxygen and surface diffusion. This requires the development of effective methods for performing systematic and automatic path searches.
Recently, Hokkaido University scientists: Kanami Sugiyama (graduate student), Dr. Yosuke Sumiya, Dr. Makito Takagi, Dr. Kenichiro Saita, and led by professor Satoshi Maeda developed an artificial force induced reaction method for studying the carbon monoxide oxidation on Pt (100) surface. Also, they investigated contribution of the two different carbon dioxide generation paths: based on oxygen dissociation and OC-OO complex formation. The work is published in the research journal, Physical Chemistry Chemical Physics.
In brief, the research team performed a systematic reaction path search for the creation of the reaction route network. The network took into consideration both the bond rearrangement paths and the migration paths of the adsorbed species. Finally, the obtained global reaction route network was systematically analyzed using the rate constant matrix contraction method.
The authors observed that the bottleneck of the overall reaction is the carbon dioxide generation step involving the recombination of the adsorbed carbon dioxide molecules and oxygen atoms. The results were in consistence to that of the Langmuir-Hinshelwood mechanism recently published in the literature. The present procedure involving the construction of a reaction route network by the artificial force induced reaction method followed by kinetics analysis proved systematic and viable for carbon monoxide oxidation on the Pt (100) surface. For instance, it revealed two aspects: entropic contributions from the migration of the adsorbed species and the impact of the existence of multiple paths in each bond rearrangement step, taking into consideration the temperature dependency.
On the other hand, the reaction route network included minor species as short-lived intermediaries. According to the authors, however, it is not advisable to make prior assumptions about the reaction mechanisms for obtaining the final results. The overall impact of the short-range migration paths was discussed. The entropy contributions of the local minima and transition state emanated from variety configurations at stable and transition states. They decreased and increased the overall rate constants respectively. Therefore, the approach proposed by professor Satoshi Maeda and his research team is ideal for obtaining accurate rate constants which would further advance the use of reaction route networks in understanding carbon monoxide oxidation on various metal surfaces.
Sugiyama, K., Sumiya, Y., Takagi, M., Saita, K., & Maeda, S. (2019). Understanding CO oxidation on the Pt (111) surface based on a reaction route network. Physical Chemistry Chemical Physics, 21(26), 14366-14375.