Pd-activated carbon catalysts for hydrogenation and Suzuki reactions

Mesoporous activated carbons obtained by chemical activation of kraft lignin with H3PO4 were used as supports for the preparation of low loading (0.5%) Pd catalysts. Thermal treatment up to 900 degrees C, performed on activated carbon, in inert atmosphere before the Pd-deposition was analyzed. The catalyst systems obtained showed highly developed porous structures with a large contribution of mesoporosity. The activation process also yielded catalysts supports with a significant amount of surface phosphorus, in form of C-O-P, C-P-O and C3P groups, as shown by the XPS analyses. The presence of phosphorus groups on the carbons surface, especially C3P groups, avoids the need of using triphenylphosphine as ligand in the Suzuki-Miyaura reactions. TEM analyses confirmed the presence of well-dispersed Pd particles (around 5 nm in size). The high dispersion and the low particle size could be due to the high amount of surface oxygen and phosphorus groups and to the high mesopores surface of the carbon supports. The activities of the catalysts were evaluated on the Suzuki-Miyaura cross-coupling reaction and in the hydrogenation of some selected double bonds. For both reactions the catalysts show high activity and selectivity as well as a high stability and reproducibility. (C) 2009 Elsevier B.V. All rights reserved.