Sustainable production of propionic acid: catalytic deoxygenation of lactic acid over MoOx/Fe

Abstract

The synergistic effect between Mo and Fe on deoxygenation of lactic acid to propionic acid was studied in this work. The catalyst structure and its chemical composites were characterized by XRD, FT-IR and EDS, respectively. The morphology of the catalyst was observed by SEM, and the reducibility was evaluated by H₂-TPR. According to its structure characterization, Mo species were coated on the surface of iron powders as MoO₃, and the interactions between Mo and Fe species were investigated by H₂-TPR under calcination at high temperatures. A reduction peak at 650 °C moved toward low temperatures with the addition of an iron component, suggesting that iron promoted the reduction of Mo species. Due to this reason, catalytic performances are rapidly enhanced, being far more superior to any one of the Mo–Fe components. However, an excess of Fe content, ca. Fe/Mo molar ratios >0.908, decreases the activity on lactic acid deoxygenation, suggesting that the redox property of the catalyst is a major factor. Catalysts with Co and Ni substituting for Fe displayed lower selectivity to propionic acid, demonstrating that regulating appropriately the redox properties is a key to improve lactic acid deoxygenation again. The hydrothermal temperature and calcination temperature have an important influence on the formation of MoO₃ and its decomposition, which then affects its activity. Inspiringly, the catalyst with a Fe/Mo molar ratio of 0.908 offered an excellent stability, which proceeded efficiently for 120 h on stream under a high LHSV of 37 h⁻¹ at 390 °C.