Enhancing gluconic acid selectivity in catalytic oxidation: the synergetic effect of glucose-fructose mixtures and kinetic insights

Gluconic acid is a chemical raw material widely used in the food and chemical industries that can be produced by oxidizing glucose and available sugar-rich substrates such as biomass. The abundance of glucose and fructose in industrial waste from lignocellulose and inverted sugar makes them a promising sustainable feedstock. In this work, the catalytic conversion of a glucose and fructose mixture into gluconic acid in an alkaline medium using Pd (4%)—Pt (1%)—Bi (5%)/C catalysts under flowing air was studied. Previously, the traditional chemical conversion of glucose into gluconic acid produced large amounts of by-products. In this work, we combined glucose and fructose to investigate the latter's influence on conversion. The selectivity to gluconic acid was significantly improved by fructose, indicating a new approach for using biomass and by-products such as glucose and fructose syrup. The first step was to conduct a series of experiments at different temperatures and pH levels. The second step was to experiment with adding fructose under optimal conditions. The gluconic acid was about 90%. The yield was approximately 79% at 55 °C and pH 9.5 using the same method with only glucose. Combining experimental data, we propose a kinetic model with a TOF (turnover frequency) between 1.0 and 5.5.