Kinetics of reverse water gas shift (RWGS) reaction on metal disulfide catalysts

Abstract

The hydrogenation of CO 2 was studied on disulfides of molybdenum and tungsten by comparison with that on the group VIII metals of Fe, Co, and Ni supported on Al 2O 3. The hydrogenation activity was lower on the disulfides on a per active site of catalyst basis than on the transition metals, however, the selective reverse water gas shift (RWGS) reaction (CO 2 + H 2 → CO + H 2O) was observed on the disulfides. The selectivity was close to ca. 100% in the reaction conditions examined. The rate was expressed by the equation: r = kP 0.61–0.73 CO 2 P 0.36 H 2 on the disulfides, and the activation energy was ca. 18.0–19.1 kcal mol −1. The disulfides exhibited little activities for the hydrogenation of CO (viz. CO + 3H 2 → CH4 + H 2O) and also for the disproportionation of CO (viz. 2CO → C + CO 2). These results were in contrast to those for the transition metals where high activities were observed for both reactions, suggesting that the retardation of CO bond cleavage in the CO molecule produced by the CO 2 hydrogenation must be the cause for the selective hydrogenation of CO 2 to CO on the disulfides. The effect of supports on the hydrogenation of CO 2 was also investigated for MoS 2. The reaction rate on a per active site of catalyst basis was not influenced by the supports, suggesting that the CO 2H 2 reaction is insensitive to the morphology of MoS 2 supported on metal oxides.