| AVS 56th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS3-TuA |
| Session: | Catalysis: Mechanisms & Morphology |
| Presenter: | C.T. Campbell, University of Washington |
| Authors: | L.G. Cameron, University of Washington C.T. Campbell, University of Washington L. Grabow, University of Wisconsin M. Mavrikakis, University of Wisconsin |
| Correspondent: | Click to Email |
The kinetics of the reverse water gas shift (RWGS) reaction (CO2 + H2 → CO + H2O) have been measured over clean and annealed Pt powder at a variety of conditions, and the surface coverage of adsorbed intermediates was verified by transient techniques. Under conditions were the surface coverage is very low and the reaction is occurring on essentially adsorbate-free Pt, the RWGS rate is 1000-fold faster than the rate of dissociative CO2 adsorption (CO2 → CO + Oad), estimated from measurements of the reverse rate and equilibrium constant for this elementary step. This proves that the dominant mechanism for the RWGS reaction is not via dissociative CO2 adsorption. The energetics estimated from DFT calculations of potential alternate pathways on Pt(111) suggests that CO2 is instead activated by reaction with Had to make a COOHad intermediate, which dissociates to make COad and OHad. A microkinetic model based on these DFT energetics reproduces well the measured absolute rate per Pt atom, its activation energy, and its dependences on CO2 and H2 partial pressures. This offers strong support for this alternate “carboxylate” pathway as dominating the mechanism. Estimates of the degrees of rate control of this reaction’s elementary steps and intermediates will also be discussed.