Selective Oxidation of Glucose Over Carbon-supported Pd and Pt Catalysts

Abstract

Selective oxidation of glucose into gluconic acid by molecular oxygen over carbon-supported Pt and Pd catalysts was studied. Under examination were kinetic regularities of the process in respect of the electronic state of the noble metal surface, dispersion of the active component particles as well as substrate:Pt(Pd) ratio. Catalytic activity of the Pt/C catalysts being normalized to the dispersion of the platinum particles appeared independent of the particles mean diameter in the 1–5 nm range. A negative particle size effect for the Pd/C catalysts, caused by feasibility of oxidation of the surface of noble metal particles with the size less than 3 nm, was observed. Pt/C catalysts exhibited lower specific activity and provided poor selectivity of the glucose oxidation in comparison with Pd/C. Deactivation of Pd/C catalysts arising from the formation of surface Pd(II) oxides was retarded when the reaction was carried out under an oxygen-diffusion control. Selective oxidation of glucose to gluconic acid over carbon supported palladium and platinum catalysts proceeds with the selectivity up to 97 and 77%, respectively. Catalytic activity of the carbon-supported Pt nanoparticles with diameters ranging from 1 to 5 nm towards the selective oxidation of glucose is directly proportional to platinum surface area. Finely dispersed Pd/C catalysts (〈d Pd〉 =3 nm) are prone to deactivation due to oxidation of their surface, while larger metal particles (〈d Pd〉 =6 nm) are more tolerant and stable. The activity of Pd nanoparticles can be maintained when the process is controlled by diffusion of oxygen towards the active component of the catalyst.