Esterification of biomass-derived levulinic acid using molybdate-intercalated hydrotalcite materials

Abstract

In this paper, we report the synthesis methodology of a series of molybdate-intercalated hydrotalcite-like materials and their catalytic applications for the esterification of biomass-derived levulinic acid. A simple hydrothermal method was used to synthesize molybdate-intercalated MgFe, MgAl, and MgCr hydrotalcites in the presence of an ammonia solution as a hydrolyzing agent. The intercalation of molybdate was confirmed via X-ray diffraction (XRD) studies based on line broadening in the XRD pattern and peaks characteristic of a layered hydrotalcite structure with short-range ordering were observed. The introduction of the molybdate species resulted in strong Lewis-acidic sites, as evident from FT-IR pyridine desorption and temperature-programmed desorption studies. The resulting material exhibited a significant activity for the esterification of the biomass-derived levulinic acid. The reaction conditions were systematically optimized. The molybdate-intercalated magnesium iron hydrotalcite exhibited 93% conversion of levulinic acid to butyl levulinate (120 °C, 4 h) with 95% selectivity. Good recyclability of the catalysts was demonstrated using recyclability studies, in which the catalysts showed excellent stability and high conversion even after five cycles.