Catalytic selective hydrogenation of acetic acid to acetaldehyde over the surface of the iron shell on Pd–Fe alloy nanoparticles

Abstract

Since hydrogenation of acetic acid readily leads to ethanol formation, it is challenging to selectively obtain acetaldehyde in a high yield. The present study demonstrates the highly-selective synthesis of acetaldehyde by the hydrogenation of acetic acid catalyzed by the iron surface on Pd–Fe alloy nanoparticles derived from Pd/Fe₂O₃. The catalyst from Pd/Fe₂O₃ with low Pd loading amount provoked the deposition of carbonaceous species, including iron carbides, in the prolonged reaction, resulting in a low acetaldehyde yield. On the contrary, Pd/Fe₂O₃ with high Pd loading amount (28–44 wt%) prevented the formation of iron carbides. It led to the formation of aldehyde in an excellent yield, that was maintained even after 200 h. Further Pd loading increased the ethanol formation. In situ XAFS measurements showed that the reductive pretreatment under hydrogen flow of Pd/Fe₂O₃ formed the core–shell type Pd–Fe alloy nanoparticles. Acetic acid would convert to acetaldehyde with concomitant oxidation of the surface of the metallic iron shell, and H₂ would reduce the thus-partially oxidized shell to regenerate the initial metallic surface.