Mechanism of efficient carbon monoxide oxidation at Ru(0001)

TL;DR

This study uses density-functional theory to elucidate the catalytic mechanism of CO oxidation on Ru(0001), revealing how electron transfer and adsorption dynamics facilitate high CO_2 production rates.

Contribution

It provides a detailed electronic and bonding analysis of the reaction pathway, highlighting the role of a bent transition state and electron transfer in catalysis.

Findings

High CO_2 turnover linked to oxygen monolayer coverage.

Reaction involves a bent transition state due to electron transfer.

Efficient CO oxidation occurs via scattering and vacancy mechanisms.

Abstract

We performed density-functional theory calculations using the generalized gradient approximation for the exhange-correlation functional to investigate the unusual catalytic behavior of Ru under elevated gas pressure conditions for the carbon monoxide oxidation reaction, which includes a particularly high CO_2 turnover. Our calculations indicate that a full monolayer of adsorbed oxygen actuates the high rate, enabling CO_2 formation via both scattering of gas-phase CO molecules as well as by CO molecules adsorbed at oxygen vacancies in the adlayer, where the latter mechanism is expected to be very efficient due to the relatively weak adsorption energy of both CO and O, as well as the close proximity of these reactants. In the present paper we analyse the bonding and electronic properties associated with the reaction pathway for CO_2 production via the scattering reaction. We find that the identified ``bent'' transition state is due to electron transfer into the unoccupied 2 pi orbitals of the CO molecule which reduces the Pauli repulsion between the impinging CO and the O-covered surface. Bond formation to CO_2 then proceeds by electron transfer back from the CO 2 pi orbitals into the bonding region between CO and the adsorbed O atom.