Gas phase hydrogenation of levulinic acid to γ-valerolactone over supported Ni catalysts with formic acid as hydrogen source
The catalytic continuous vapor phase hydrogenation of levulinic acid (P = 1 atm; T = 250 °C) in the absence of external hydrogen was investigated over inorganic oxide (Al2O3, MgO and hydrotalcite) supported Ni (30 wt%) catalysts. The present protocol enables the utilization of the unavoidable co-product (i.e. formic acid) formed during the production of levulinic acid as a hydrogen source. Among the tested catalysts, the Ni/Al2O3 catalyst was an efficient catalyst for the production of γ-valerolactone through hydrogen-independent hydrogenation. A significant decrease in catalytic performance of Ni/MgO and Ni/hydrotalcite catalysts was observed during the time-on-stream; while a gradual decrease was noted in the catalytic performance of the Ni/Al2O3 catalyst. The considerable decline in catalytic performance of Ni/MgO and Ni/hydrotalcite catalysts was attributed to water generation during the course of the reaction, rather than the coking of reaction intermediates (angelica lactone). Furthermore, the co-feeding of water and formic acid with levulinic acid was performed and a significant decrease was noted in the catalytic performance of Ni/MgO and Ni/hydrotalcite catalysts compared to the Ni/Al2O3 catalyst. The results evidently signify the role of water in the activity of Ni/MgO and Ni/hydrotalcite catalysts, which could be ascribed to brucite–periclase transition of MgO with the water, which was formed during the hydrogenation of levulinic acid.