Catalytic Hydrodechlorination of 4-Chlorophenol in an Aqueous Solution with Pd/Ni Catalyst and Formic Acid

Palladized foam nickel (Pd/Ni) catalyst was prepared by replacement deposition and employed to hydrodechlorinate 4-chlorophenol (4-CP) with formic acid (FA). 4-CP was rapidly transformed to phenol by means of hydrogenolysis. Major factors that may influence the 4-CP conversion rate, including the Pd loading amount, FA dosage, and solution pH value, were investigated. A moderate Pd loading amount (1.0 wt %), an excess of FA dosage (FA/4-CP ratio of 51.4:1), and a relatively low pH (4.0) were found to be the optimal operational conditions under which 4-CP was degraded up to 96.2% within 2 h and the catalytic activity of Pd/Ni reduced negligibly after three recycles. The dechlorination pathway is postulated as follows: (1) HCOOH (or HCOO-) decomposed on Pd particles with atomic hydrogen ([H]) generated; (2) [H] served as the direct reducing agent in the hydrodechlorination of 4-CP adsorbed on both Pd particles and Ni substrate, through the radical mechanism. Pd/Ni is found to be a promising catalyst in the elimination of organochlorines.