Study into the influence of support pore size on the structure and activity of Pd/C catalysts

Abstract

Palladium on carbon catalysts (Pd/C) are of great importance as a hydrogenation catalyst in chemical industry. In 2013, a quarter of drugs involved at least one hydrogenation step during their synthesis. Nevertheless, hydrogenation over Pd/C catalysts is not fully understood. Cinnamaldehyde hydrogenation is used as a model hydrogenation reaction, as cinnamaldehyde has two different sites that can be hydrogenated. Earlier research shows that the selectivity towards hydrogenation of the C C or C O bond is controlled by the palladium particle size. In this research, the influence of the pores in the carbon support on the palladium particles and the catalytic performance in the hydrogenation of cinnamaldehyde was explored. To this end, a method was developed using thermoporometry experiments to selectively impregnate pores of different sizes with a palladium tetraamine solution, which functions as a precursor to the palladium particles. These impregnations were performed by dry impregnation as overall impregnation method, partial impregnation to impregnate the smaller pores and micropore and small mesopore blocking with subsequent partial impregnation to selectively impregnate larger mesopores. The final catalysts showed different selectivity according to intended impregnation location: palladium particles intended in small pores showed a higher selectivity towards hydrocinnamaldehyde formation and palladium particles in intended larger pores showed a slightly higher selectivity towards cinnamyl alcohol formation.