Palladium catalysts on activated carbon supports - Influence of reduction temperature, origin of the support and pretreatments of the carbon surface

A number of activated carbons produced from peat, coconut shell, and by pyrolysis of hydrocarbons have been subjected to treatment with oxygen, chlorine, hydrogen or ammonia at elevated temperatures to get a representative series of catalyst supports differing in porous structure and surface chemistry (characterized by nitrogen adsorption and selective titrations). Palladium was deposited from anionic (H2PdCl4), neutral (Pd(OAc)(2), in acetone), and cationic ([Pd(NH3)(4)](NO3)(2)) complexes. Temperature-programmed reduction, CO chemisorption, and testing in olefin hydrogenation were used to study the possible effects of preparation variables. The origin of the carbon support and the temperature of the catalyst reduction with hydrogen proved to have a profound influence on the properties of the catalysts. in contrast, no unambiguous correlation has been found between catalyst properties and the pretreatments of the carbons. It is concluded that the effect of the support comes mainly from the differences in the porous structure of the carbons, and occurrence of steric hindrance for organic substrates in contacting the metal particles on the microporous supports is suggested. (C) 2000 Elsevier Science Ltd. All rights reserved.