Pd⁰–O_v–Ce³⁺ Interfacial Sites with Charge Redistribution for Enhanced Hydrogenation of Methyl Oleate to Methyl Stearate

Abstract

Improving the efficiency of metal/reducible metal oxide interfacial sites for hydrogenation reactions of unsaturated groups (e.g., C=C and C=O) is a promising yet challenging endeavor. In our study, we developed a Pd/CeO₂ catalyst by enhancing the oxygen vacancy (O_V) concentration in CeO₂ through high-temperature treatment. This process led to the formation of an interface structure ideal for supporting the hydrogenation of methyl oleate to methyl stearate. Specifically, metal Pd⁰ atoms bonded to the O_V in defective CeO₂ formed Pd⁰–O_V–Ce³⁺ interfacial sites, enabling strong electron transfer from CeO₂ to Pd. The interfacial sites exhibit a synergistic adsorption effect on the reaction substrate. Pd⁰ sites promote the adsorption and activation of C=C bonds, while O_V preferably adsorbs C=O bonds, mitigating competition with C=C bonds for Pd⁰ adsorption sites. This synergy ensures rapid C=C bond activation and accelerates the attack of active H* species on the semi-hydrogenated intermediate. As a result, our Pd/CeO₂-500 catalyst, enriched with Pd⁰–O_V–Ce³⁺ interfacial sites, demonstrated excellent hydrogenation activity at just 30 °C. The catalyst achieved a Cis–C18:1 conversion rate of 99.8% and a methyl stearate formation rate of 5.7 mol/(h·g_metal). This work revealed the interfacial sites for enhanced hydrogenation reactions and provided ideas for designing highly active hydrogenation catalysts.

Keywords

Hydrogenation / Interfacial sites / Oxygen vacancy / C=C bond

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