Carbon-supported Pd complex as catalyst for cyclohexene hydrogenation

Phenolformaldehyde polymer resins chars with different surface areas and oxygen surface groups have been used as supports for the [PdCl2(NH2(CH2)(12)CH3)(2)] complex, with the aim of preparing hydrogenation catalysts with high activity and sulfur resistance. Unsupported and gamma-Al2O3-supported complexes have been studied for comparative purposes. The incipient wetness impregnation technique has been used to prepare catalysts with 0.3% Pd content. Catalytic activity and sulfur resistance were determined in the hydrogenation of cyclohexene to cyclohexane at 353 K in toluene. Poisoning experiments were performed with 300 ppm tetrahydrothiophene. Carbon-supported catalysts are more active and sulfur resistant than gamma-Al2O3-supported catalyst. XPS has been used for catalysts characterization, atomic ratios x/Pd (x = N, Cl and S) for fresh and used samples allow to observe no changes in Pd coordination after reaction in a poison-free medium. However, in the presence of tetrahydrotiophene, the Pd coordination number for the carbon-supported catalysts is lower than 4 (value obtained for the unsupported and gamma-Al2O3-supported complex). The higher sulfur resistance of carbon-supported catalysts can be attributed to an electronic effect and to the retention of the poison molecule on the carbon surface. The effect of surface chemistry on catalyst activity seems to be more important than the porosity. (C) 1998 Elsevier Science B.V. All rights reserved.