Supported Pt-Re catalysts for the selective hydrogenation of methyl and ethyl esters to alcohols

- Pt-Re synergy in the hydrogenation of methyl and ethyl hexanoate.
- Optimal activity of TiO2-supported Pt:Re = 1:2 catalysts.
- Methanol by-product of methyl ester hydrogenation deactivates catalyst.
- Origin of deactivation is decarbonylation of methanol.

The effect of Re-addition to Pt/TiO2 catalysts for the hydrogenation of carboxylic acids and esters to their corresponding alcohols was investigated. The highest catalytic activity was observed for the materials with Pt:Re molar ratio of 1:2, which allowed for a complete conversion of hexanoic acid under mild conditions. The hydrogenation of esters over the same catalysts was much more difficult. The reactions showed only moderate alcohol yields which also depended strongly on the alkoxy moiety of the ester substrate. The highest yield of ca. 25% was achieved by the hydrogenation of ethyl hexanoate. Conversion of methyl hexanoate was much less efficient. This was attributed to the inhibiting effect of methanol by-product. In situ FTIR spectroscopy suggests that the decarbonylation of methanol and the resulting CO poisoning of the catalyst surface in the course of the reaction is the most likely cause of the low activity of Pt and Pt-Re/TiO2 towards methyl ester hydrogenation.

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