Palladium (Pd) Loading-Controlled Catalytic Activity and Selectivity for Chlorophenol Hydrodechlorination and Hydrosaturation.

Reductive catalysis by zero-valent palladium nanoparticles (PdNPs) has emerged as an efficient strategy for promoting the detoxification of chlorophenols (CPs) hydrogenation. Most studies achieved hydrodechlorination of CP to phenol for detoxification, but it requires considerably high energy input and harsh conditions to further hydrosaturate phenol to cyclohexanone (CHN) as the most desired product for resource recovery. This study documented 4-CP hydrodechlorination and hydrosaturation catalyzed by PdNPs deposited on H-transfer membranes in the H-based membrane catalyst-film reactor, which yielded up to 99% CHN selectivity under ambient conditions. It was further discovered that the Pd morphology and size, both determined by Pd loading, were the key factors controlling the catalytic activity and selectivity: while sub-nano Pd particles catalyzed only 4-CP hydrodechlorination, PdNPs were able to catalyze the subsequent hydrosaturation that requires more Pd reactive sites than hydrodechlorination. In addition, better dispersion of Pd, caused by lower Pd loading, yielded higher activity for hydrodechlorination but lower activity for hydrosaturation. During the 15 day continuous tests, the substantial product from 4-CP hydrogenation was constantly phenol (>98%) for 0.2 g-Pd/m and CHN (>92%) for 1.0 g-Pd/m. This study opens the door for selectively manipulating desired products from Pd-catalyzed CP hydrogenation under ambient conditions.