Water-assisted ketonization of methyl palmitate to palmitone over metal incorporated TiO2 catalysts†

Abstract

Ketonization of methyl palmitate to palmitone, a bio-lube precursor, was investigated over noble metal (Pt, Ru, and Pd) incorporated TiO₂ catalysts in the presence of water under an atmospheric H₂/N₂ flow. Methyl palmitate underwent hydrolysis to palmitic acid that ketonized to palmitone over Lewis Ti³⁺ sites. The water co-feeding also suppressed hydrodeoxygenation of methyl palmitate and palmitone cracking leading to high palmitone selectivity. The incorporated metals facilitated H₂ dissociation/spillover on TiO₂ which generated more Lewis Ti³⁺ sites for higher ketonization activity. At 400 °C, 0.5Pd/TiO₂ provided ∼90% conversion with >85% palmitone selectivity and >25 h stability, due to its efficient H₂ dissociation/spillover to continually recover Lewis Ti³⁺ sites. Meanwhile 0.5Pt/TiO₂ promoted excessive hydrodeoxygenation, leading to the deactivation from CO poisoning at the metallic Pt sites. The findings of this study offer a sustainable approach for the selective production of bio-lube precursors from renewable fatty acid methyl esters.