Synergetic effect of ruthenium and basicity sites in the Ru–MgAl catalyst for hydrogen-free production of conjugated linoleic acids

Abstract

A series of Ru–MgAl composite oxide catalysts prepared by calcining the ruthenium grafted hydrotalcite-like precursor at various temperatures were used in the hydrogen-free production of conjugated linoleic acid. The effect of calcination temperature on the textural, base and catalytic properties of the materials was investigated. Results indicated that the Ru–MgAl composite oxides calcined at 450 °C showed high activity, namely, CLA productivity, CLA production rate and TOF up to 1.52 g CLA g (CLA) L⁻¹ (solvent) min⁻¹, 284 g (CLA) g⁻¹ (Ru) h⁻¹ and 102.6 mol (LA converted) mol⁻¹ (Ru) h⁻¹. Moreover, the biologically active CLA isomers, cis-9, trans-11, trans-10, cis-12 and trans-9, trans-11-CLA, were the main products, while almost no hydrogenated products were formed. Meanwhile, the role of ruthenium and basicity sites in the catalytic reaction has been studied. It was found that the basicity sites of the Ru–MgAl catalyst and the ruthenium activity sites seem to have a synergic effect on the catalytic reaction. The possible reaction mechanism for the isomerization was also proposed.