Heterogeneous catalytic oxidation of furfural with hydrogen peroxide over sulfated zirconia

Furfural oxidation with hydrogen peroxide was performed using sulfated zirconia as an acid catalyst within the temperature range of 40–90 °C. The catalytic behavior of sulfated zirconia due to its acidic character was different from a previously studied fibrous polymer-supported sulfonic acid catalyst Smopex-101. While maleic and succinic acids along with 2(5-H)-furanone and formic acid were formed, selectivity to succinic acid was lower. Moreover, significant amounts of 5-hydroxy-2(5-H)-furanone were generated as confirmed by nuclear magnetic resonance (NMR). In parallel to furfural oxidation giving products with four carbon atoms and formic acid, also furoic acid was formed and oxidized further. The reaction network proposed previously was modified and extended to account for these observations. In particular, the oxidation of 2(5-H)-furanone to maleic acid, considered to be a plausible step over Smopex-101, turned out to be very slow in the presence of sulfated zirconia. The kinetic model developed on the basis of the reaction network was able to describe the concentration profiles of the reactants, intermediates, and products as a function of reaction time at different temperatures including decomposition of hydrogen peroxide.