Gas phase hydrogenolysis mediated by activated carbon: substituted chlorobenzenes Original Research Article

The hydrogenolysis of vapors of chlorobenzene derivatives (ZPhCl, where Ph denotes a benzene ring) when passed over a bed of activated carbon (AC) in a H2/N2 atmosphere was investigated. Dehalogenation occurred readily between 200 and 550°C, depending on the derivative. The less volatile compounds were more strongly adsorbed, and their conversion occurred at lower temperatures. Common dehalogenation pathways seem to hold for most derivatives, involving both formation of the corresponding desubstituted benzene derivatives (ZPhH), and attachment to the AC surface. The other product was HCl. Chlorine atoms at ortho and/or para positions to Z=OH in mono- and dichlorophenols were removed at much lower temperatures and with a high selectivity to phenol or less chlorinated phenols. In these cases, at the lowest temperatures applied (<300°C) chlorine became partially attached to the carbon surface, and it could be removed only at much higher temperatures. However, upon hydrogenolysis at temperatures above 300°C chlorination of the carbon did not occur. Mechanisms are discussed.