Abstract
A series of Ru/FeOx catalysts were synthesized for the selective hydrogenation of CO2 to CO. Detailed characterizations of the catalysts through X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and temperature-programmed techniques were performed to directly monitor the surface chemical properties and the catalytic performance to elucidate the reaction mechanism. Highly dispersed Ru species were observed on the surface of FeOx regardless of the initial Ru loading. Varying the Ru loading resulted in changes to the Ru coverage over the FeOx surface, which had a significant impact on the interaction between Ru and adsorbed H, and concomitantly, the H2 activation capacity via the ability for H2 dissociation. FeOx having 0.01% of Ru loading exhibited 100% selectivity toward CO resulting from the very strong interaction between Ru and adsorbed H, which limits the desorption of the activated H species and hinders over-reduction of CO to CH4. Further increasing the Ru loading of the catalysts to above 0.01% resulted in the adsorbed H to be easily dissociated, as a result of a weaker interaction with Ru, which allowed excessive CO reduction to produce CH4. Understanding how to selectively design the catalyst by tuning the initial loading of the active phase has broader implications on the design of supported metal catalysts toward preparing liquid fuels from CO2.
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