Kinetics of the reverse water-gas shift reaction over Cu(110)

The reverse water-gas shift reaction (CO2 + H2 → H2O + CO) has been studied over a clean Cu(110) single-crystal model catalyst at temperatures between 573 and 723 K. The steady-state kinetic measurements were carried out at medium pressures (10-2000 Torr) in a microreactor after cleaning and characterization of the sample under UHV conditions. The H2/CO2-pressure ratios varied from 1000: 1 to 1 : 10. The product buildup was monitored with a gas chromatograph (GC). The apparent activation energy is about 18 kcal/mol, and the reaction orders in H2 and CO2 depend strongly on the H2/CO2 ratio and temperature. The steady-state kinetics are compared favorably with the rates of elementary steps potentially involved in a "surface redox" reaction mechanism of the reverse and forward water-gas shift reaction involving the formation and removal of oxygen adatoms. Kinetic evidence that is tentatively attributed to a hydrogen-induced surface phase transition that affects the reaction rate, is also presented.