Pieter van Helden

Hydrogen-assisted CO dissociation on the Co(211) stepped surface

In the Fischer–Tropsch synthesis (FT) process the mechanism of CO dissociation is of fundamental importance. In this study we compare hydrogen-assisted CO dissociation mechanisms to direct CO dissociation on the B5 site as exposed on the fcc-Co(211) surface. Whereas direct CO dissociation is calculated to have an overall barrier of 142 kJ mol−1, the alternative mechanism involving a HCO intermediate proceeds with a lower overall barrier of 123 kJ mol−1. Using these calculated values we show that hydrogen-assisted CO dissociation will result in an overall rate corresponding to the same order as the considered FT experiments.

On the Kinetic Interpretation of DFT-Derived Energy Profiles: Cu-Catalyzed Methanol Synthesis

A mean field microkinetic evaluation of previously reported DFT-derived Gibbs free energy profiles for CO and CO2 hydrogenation to methanol on Cu(111), Cu(211) and Zn-modified Cu(211) is presented. It is demonstrated that explicit consideration of the effect of surface coverages of reaction intermediates on rates is needed in order to arrive at a realistic evaluation of the activity and selectivity. In particular, both the methanol formation rate and the CO/CO2 selectivity for methanol production are demonstrated to be highly sensitive to the saturation coverage of formate at steady state. In general, the study emphasises the importance of including explicit kinetic analyses when mechanistic DFT-derived energy profiles are interpreted for catalytic processes.Graphical Abstract