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 pyr olysis of hydrocarbons have been subjected to treatment with oxygen, chlori ne, hydrogen or ammonia at elevated temperatures to get a representative se ries of catalyst supports differing in porous structure and surface chemist ry (characterized by nitrogen adsorption and selective titrations). Palladi um was deposited from anionic (H2PdCl4), neutral (Pd(OAc)(2), in acetone), and cationic ([Pd(NH3)(4)](NO3)(2)) complexes. Temperature-programmed reduc tion, CO chemisorption, and testing in olefin hydrogenation were used to st udy 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 contra st, no unambiguous correlation has been found between catalyst properties a nd 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 c arbons, and occurrence of steric hindrance for organic substrates in contac ting the metal particles on the microporous supports is suggested. (C) 2000 Elsevier Science Ltd. All rights reserved.