Aqueous-phase hydrodeoxygenation of carboxylic acids to alcohols or alkanes over supported Ru catalysts

For the aqueous-phase hydrodeoxygenation (APHDO) of carboxylic acids over the Ru/C, Ru/ZrO2 and Ru/Al2O3 catalysts, the CO hydrogenation and C–C bond cleavage reactions were studied by collecting reaction kinetics data and the measures of DRIFTS. The C–C bond cleavage was improved at high temperature and with high metal loadings. The acidic supports in combination with Ru metal can favor the CO hydrogenation of carboxyl. The C–C bond cleavage derived from the decarbonylation of acyl on the catalyst was studied by the measures of DRIFTS. The APHDO and DRIFTS results demonstrated that the C–C bond cleavage was favored in the order of Ru/C > Ru/ZrO2 > Ru/Al2O3. The catalysts were characterized by multiple methods (H2-TPR, NH3-TPD, CO-FTIR and DRIFTS of propanoic acid). It is concluded that the effect of support on the reaction routes may be attributed to these factors of catalysts, i.e., surface acidity, metal–support interaction and electronic state of Ru species.

The hydrodeoxygenation routes of carboxylic acids over the supported Ru catalysts was elucidated: the CO hydrogenation of acyl intermediate gives the production of alcohol, the C–C bond cleavage gives the adsorbed CO and hydrocarbon moieties by the decarbonylation of acyl intermediate, and then the adsorbed CO and hydrocarbon moieties hydrogenate to methane and Cn−1-alkane.Figure optionsDownload high-quality image (130 K)Download as PowerPoint slideHighlights
► The APHDO of carboxylic acids was studied over the supported Ru catalysts.
► The C–C bond cleavage reaction is derived from the decarbonylation of acyl.
► The C–C bond cleavage reaction is dominant over the Ru/ZrO2 at high temperature.
► The C–C bond cleavage reaction is greatly inhibited over the Ru/Al2O3.
► The C–C bond cleavage or CO hydrogenation strongly depends on the nature of support.