Oxidation Of D-glucose Over Plasma Reduced Pd/AC Catalysts

Glucose oxidation to gluconic acid is an important reaction for carbohydrate oxidation, which is an important method utilizing the renewable resource. Gluconic acid is conventionally produced via biological fermentation or electrolytic oxidation. The heterogeneous catalytic oxidation has attracted increasing interests because it is a simple, quick and environmentally friendly process.Palladium catalyst on activated carbon (AC) has shown very good activity and selectivity for glucose oxidation, while AC has large surface area, well developed pore structure and abundant surface functional groups. Palladium catalysts are normally reduced by hazardous chemicals. Therefore it's necessary to develop a green reduction method which is environmentally benign with low cost. In this work, a glow discharge plasma technology is utilized to reduce Pd/AC catalyst for glucose oxidation. Some unique effects of plasma reduction are carefully investigated.Results of physical adsorption, XRD, XPS, FTIR, TEM and TPR suggest that plasma reduction does not change the pore structure of AC while dramatically increase surface oxygen-containing functional groups. Plasma can decompose the precursor and reduce it into metallic palladium. Compared to Pd/AC catalysts with chemical reduction, metal particles reduced by plasma are smaller and better dispersed. What's more, large quantities of defect are generated on the surface during plasma reduction. In conlusion, as an effective low-temperature reduction method for metal-loaded catalysts, plasma technology can successfully achieve structural adjustment and chemical modification. The process is simple, safe and environmental- ly friendly. It has a potential to be widely applied in catalyst preparation.In the reaction of glucose oxidation, the catalysts reduced by plasma shows much higher activity than those reduced by hydrogen, even for the repeated reaction. However, the selectivity of plasma-reduced catalyst is inferior by comparison due to more side reactions. Based on the discussion of reaction mechanism, surface dehydrogenation becomes the rate-determining step, which can be accelerated by amounts of defects on the catalyst surface and then promotes the overall reaction.