Acetalization of glycerol using mesoporous MoO 3/SiO 2 solid acid catalyst

Abstract

Acetalization of glycerol with various aldehydes has been carried out using mesoporous MoO 3/SiO 2 as a solid acid catalyst. A series of MoO 3/SiO 2 catalysts with varying MoO 3 loadings (1–20 mol%) were prepared by sol–gel technique using ethyl silicate-40 and ammonium heptamolybdate as silica and molybdenum source respectively. The sol–gel derived samples were calcined at 500 °C and characterized using various physicochemical characterization techniques. The XRD of the calcined samples showed the formation of amorphous phase up to 10 mol% MoO 3 loading and at higher loading of crystalline α-MoO 3 on amorphous silica support. TEM analyses of the materials showed the uniform distribution of MoO 3 nanoparticles on amorphous silica support. Raman spectroscopy showed the formation of silicomolybdic acid at low Mo loading and a mixture of α-MoO 3 and polymolybdate species at high Mo loadings. Moreover the Raman spectra of intermediate loading samples also suggest the presence of β-MoO 3. Acetalization of glycerol with benzaldehyde was carried out using series of MoO 3/SiO 2 catalysts with varying MoO 3 loadings (1–20 mol%). Among the series, MoO 3/SiO 2 with 20 mol% MoO 3 loadings was found to be the most active catalyst in acetalization under mild conditions. Maximum conversion of benzaldehyde (72%) was obtained in 8 h at 100 °C with 60% selectivity for the six-membered acetal using 20% MoO 3/SiO 2. Interestingly with substituted benzaldehydes under same reaction conditions the conversion of aldehydes decreased with increase in selectivity for six-membered acetals. These results indicate the potential of this catalyst for the acetalization of glycerol for an environmentally benign process.