Selective catalytic conversion of glycerol to lactic acid over CuO-NiO complex oxides

Abstract

One of the most essential techniques to achieve effective usage of the principal by-product (glycerol) in the manufacturing of biodiesel is catalytic conversion of glycerol to lactic acid. In this paper, CuO-NiO composite metal oxides with different Cu/Ni molar ratios were prepared by co-precipitation method to catalyze the conversion of glycerol to lactic acid in alkaline medium. By using XRD, SEM, TEM, BET, XPS, and H2-TPR characterisation, the catalysts' crystalline phase, shape, and performance were assessed. The results show that the electronic synergy of CuO-NiO composite metal oxides plays a positive role in catalyzing the conversion of glycerol to lactic acid. The production of lactic acid might reach 90.08 % when Cu/Ni molar ratio (CuO1NiO2) and reaction conditions are optimum. In conjunction with the analysis using Density Functional Theory: due to the formation of heterojunctions in CuO1NiO2 the formation of good contacts between the atoms at the CuO and NiO interfaces is conducive to promoting charge transfer and electron mobility, thus enhancing the synergistic effect of electron transfer. Meanwhile, DFT calculations revealed that the Cu-Ni composite metal oxides had stronger adsorption energy for glycerol, which favored the bonding of glycerol on their surfaces.