Hydrogenation of dodecanoic acid over niobium oxide-supported Ir–Pd bimetallic nanoparticles

Abstract

Various combinations of Nb₂O₅-supported Ir-based catalysts (Ir–X/Nb₂O₅, X = Mn, Fe, Co, Ni, Cu, Zn, Pd, Sn, and Au) were investigated for an efficient conversion of dodecanoic acid to dodecanol. The Ir and Pd combination, i.e. Ir–Pd/Nb₂O₅, showed a higher conversion of dodecanoic acid (>90%) with significant selectivity towards dodecanol (>70%) when the Ir : Pd ratio was 50 : 50 and 75 : 25 in comparison with the Nb₂O₅-supported monometal Ir or Pd catalyst. The synergistic enhancement could be explained by the suppression of Ir aggregation and changes in Ir reduction properties in the presence of adjacent Pd. Based on the survey of various supports including MoO₃, SiO₂, α-Al₂O₃, ZrO₂, Ta₂O₅, and Nb₂O₅ for the Ir–Pd catalysts, it was found that Nb₂O₅ made a unique contribution to enhancing the catalytic reactivity. It was concluded that both Ir–Pd alloying and electron-rich cation sites of Nb oxide synergistically mediated the hydrogenation of medium-chain fatty acids to the corresponding alcohols.