Oxidative esterification of furfural by Au nanoparticles supported CMK-3 mesoporous catalysts

Furfural which is derived from the hemicellulose fraction of abundant lignocellulose has received significant attention to many researchers as its valorization yields useful products such as fine chemicals and transportation fuels. Methyl 2-furoate is one of the important valorized products of furfural as it finds applications in flavor and fragrance industries. Methyl 2-furoate is generally obtained by oxidation followed by esterification of furfural but under acidic and corrosive conditions. Uniform rods of CMK-3 mesoporous materials were successfully synthesized by using nanocasting method. Au nano particles were impregnated into the pores of CMK-3 by wet impregnation method followed by hydrogen reduction at high temperature (673 K). All the catalysts were thoroughly characterized by various analytical techniques. Homogeneous dispersion of Au nano particles ≈3 nm size was found over CMK-3 materials. Qualitative and quantitative analyses of Au were made by XPS and ICP techniques. The effect of impregnating metal ions (Ni, Pt and Pd) and supports (SBA-15, graphite, graphene, MWCNT, activated carbon and TiO2) was studied on the catalytic conversion of furfural. Among them, Au/CMK-3 catalyst was found to be the best. Among the Au/CMK-3 catalysts, 5% Au/CMK-3 catalyst showed remarkable conversion of furfural (99.7%) with very high selectivity towards methyl 2-furoate (99.6%). The stability and reusability of the 5% Au/CMK-3 catalyst was found to be very good even after five catalytic cycles.