Characterization of carbon supported palladium catalysts: inference of electronic and particle size effects using reaction probes Original Research Article

Carbon supported palladium catalysts have been used in a wide range of industrial reactions, especially hydrogenation in the fine chemical industry. However, there are a lot of difficulties to characterize this system, mainly due to intrinsic characteristics of the carbon materials. This work aimed to evaluate the effect of dispersion and electronic density of palladium on the catalytic performance of different reactions, besides characterizing Pd/C system by several techniques. Two samples of activated carbon and graphite were used in this work. Some pretreatments of activated carbon samples with HCl, HNO3 and O2 were performed before the impregnation with palladium. Supports and catalysts were characterized by atomic absorption spectroscopy, N2 adsorption isotherms at 77 K, temperature programmed desorption (TPDHe), temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS). Four reaction probes were performed with the catalysts: cyclohexane dehydrogenation, 1,3-butadiene hydrogenation, dichlorodifluoromethane (CFC-12) and trichloromethane hydrodechlorination. Depending on the electronic density, which is affected by the chemical environment of metal, carbene intermediate formation can be favored, yielding a particular selectivity pattern. The dispersion seems to influence the activity of the reactions, but not selectivity patterns.