Aqueous-phase hydrodeoxygenation of propanoic acid over the Ru/ZrO2 and Ru–Mo/ZrO2 catalysts

The conversion of propanoic acid under high hydrogen pressure has been studied over zirconia-supported monometallic Ru and bimetallic Ru–Mo catalysts. The cleavage of C–C bond of propanoic acid to methane and ethane is improved and the formation of CO hydrogenation products (propanol and propane) is decreased with increasing the temperature. Upon addition of Mo, both the overall activity and the C–C bond cleavage selectivity decrease while the selectivity of CO hydrogenation increases. With increase of Mo contents, the C–C bond cleavage reaction is significantly inhibited, especially at high temperature. This is also confirmed by the DRIFTS of propanoic acid, showing that the propanoyl intermediate species on Ru–Mo bimetal catalysts is more difficult to dissociate to CO compared with Ru monometal catalyst. Based on H2-TPR, CO-FTIR and DRIFTS of propanoic acid characterizations, the reaction mechanisms and the resulting selectivity towards the possible reaction paths (C–C bond cleavage/CO hydrogenation) are discussed in terms of the formation of Ru–MoOx and the stability and variety of propanoyl intermediate species occurring on the Ru–Mo bimetal catalysts. It is suggested that the interaction of Ru and MoOx species and the formation of Ru–MoOx interface are the important factors for the decrease in the TOF of propanoic acid and the C–C bond cleavage selectivity.

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► The APHDO of propanoic acid over the Ru/ZrO2 and Ru–Mo/ZrO2 catalysts was studied.
► The incorporation of Mo improves the selectivity of CO hydrogenation products.
► The incorporation of Mo suppresses the C–C bond cleavage reaction greatly.
► The inhibition of CC bond cleavage is ascribed to formation of Ru–MoOx interface.