Structure sensitivity and kinetics of d-glucose oxidation to d-gluconic acid over carbon-supported gold catalysts

The heterogeneously catalyzed oxidation of d-glucose to d-gluconic acid over Au/C catalysts has been studied. A series of Au/C catalysts were prepared by the gold sol method with different reducing agents and different kinds of carbon support providing Au mean particle diameters in the range 3–6 nm. The activities of these catalysts with respect to d-glucose oxidation were compared, and several aspects influencing activity, especially Au particle size, were discussed. The influence of reaction conditions (T=30–90 °C, pH 7.0–9.5) on the kinetics of the d-glucose oxidation has been examined using the most active Au/C catalyst. By a detailed analysis of all reaction products under different reaction conditions, a reaction network of the d-glucose oxidation is presented, and a reaction mechanism for d-glucose oxidation that explains the influence of pH on reaction rate is proposed. Ensuring that d-glucose oxidation takes place in the kinetic regime (sufficient stirring rate and airflow rate), a semiempirical model based on a Langmuir–Hinshelwood-type reaction pathway is assumed. At 50 °C and pH 9.5 kinetic parameters were calculated by an optimization routine. The resulting concentration courses of d-glucose and d-gluconic acid were in good agreement with the experimental data. All experiments were carried out in a semibatch reactor under pH control at atmospheric pressure.