Comparative chemistries of CO and NO oxidation over RuO₂(110): insights from first-principles thermodynamics and kinetics

Abstract

In this contribution, we review our plane wave, supercell density functional theory-based comparisons of CO and NO oxidation chemistry at a RuO₂(110) surface. Base metal oxides have long been of interest as catalysts for the oxidation of small molecules such as CO and NO, and understanding of their comparative chemistries on this scientifically important model metal oxide is important for understanding the factors of the control activity. The structures and energies of CO _x and NO _x adsorbates on the RuO₂(110) surface are contrasted, and their thermodynamic stability is quantified using a first-principles phase diagram approach. Distinctly different surface species dominate the two diagrams, reflecting the very different adsorptions and oxidation chemistries of CO and NO. Furthermore, H₂O has a dramatic effect on the CO oxidation phase diagram that suggests a bicarbonate () as an important and unrecognised surface poison. These thermodynamic phase diagrams are complemented with mean-field microkinetic models that quantify absolute activity, provide a different window onto surface coverage and highlight the role of various surface species in poisoning activity. Consistent with experiment and previous simulations, CO oxidation is facile under conditions at which both CO and oxygen compete effectively for surface sites. Carbonates are unstable and unimportant to catalysis; facile bicarbonate formation poisons activity in the presence of even small amounts of H₂O. An intermediate CO adsorption energy and weak CO₂ binding make RuO₂ much more effective in oxidising CO than NO, which adsorbs strongly and self-poisons even at high temperatures. RuO₂ is predicted to be effective as a reversible NO adsorber. Finally, we reviewed the kinetics of several NO surface reactions and the pathway that may contribute to the decomposition of NO to N₂ and N₂O over partially reduced surfaces.

Keywords:

• CO oxidation
• NO oxidation
• RuO₂
• adsorption
• microkinetic

Acknowledgements

Financial support for this work was provided by the University of Notre Dame and the US Department of Energy under grant DE-FG02-06ER15830.

Notes

1. Email: [email protected]

Additional information

Notes on contributors

Hangyao Wang

1