Selectivity tailoring of Pd/CNTs in phenol hydrogenation by surface modification: Role of C-O oxygen species

The effect of different types of oxygen containing groups (OCGs) on the catalytic performance was investigated in this paper by performing the selective hydrogenation of phenol in aqueous phase over the carbon supported Pd catalysts. The type of OCGs on carbon nanotubes (CNTs) was regulated by pretreating it with HNO3, or HNO3 followed by hydrothermal or thermal oxidation treatment. A distinct difference in the amount of phenolic/ether groups (C-O) was observed for CNTs treated by different methods, while the difference in the amount of carbonyl groups (C==O) and carboxylic groups was much smaller. The results showed that the selectivity to cyclohexanone decreased with the increase of C-O amount on carbon surface. C-O groups played an important role in adsorption/desorption behavior of phenol/cyclohexanone and was considered to be responsible for the dramatic selectivity difference.