Methane dry reforming reaction on Ru(001) surfaces

Methane dry reforming on a Ru(0 0 1) single-crystal surface was investigated using a high-pressure reactor directly combined with an ultra-high-vacuum system for temperatures between 700 and 800 K and under initial CH4 and CO2 pressures in a range of 50-240 Pa. In the CH4-CO2 reaction, dry reforming (DRM) proceeds accompanied by a quasi-equilibrated reverse water gas shift reaction. The rate of the DRM reaction exhibits first-order dependence on CH4 pressure and is almost independent of CO2 pressure, giving an apparent activation energy of 110 kflmol. These kinetic parameters are in good agreement with those reported on Ru-supported oxide catalysts. From the exchange reaction between (CO2)-C-13 and CO, a very low activation energy of 7.2 kJ/mol and a TOF around 18 are obtained for CO2 dissociation on the bare Ru(0 0 1) surface. In the CH4-(CO2)-C-13 reaction, the exchange reaction between (CO2)-C-13 and CO is also quasi-equilibrated. These results are consistent with ultraviolet photoelectron spectroscopy and low energy electron diffraction measurements for postreaction Ru surfaces, which show that carbon species derived from the decomposition of CH4 are substantially removed as CO by oxygen atoms supplied from the dissociation of CO2. Taking the respective reaction orders of CH4 and CO2 into consideration, it is concluded that the rate-limiting step for the DRM reaction is the breaking of the C-H bond in CH4. (C) 2017 Elsevier Inc. All rights reserved.