Carboxylate-type palladium(II) complexes as soluble precursors for the preparation of carbon-supported Pd/C catalysts

Palladium-based carboxylate-type compounds were synthesized and used as precursors for the preparation of heterogeneous carbon-supported Pd/C catalysts. The selected compounds corresponded to the general formula Pd(O2CR)(2), Pd(O2CR)(2)L-2 or Pd(O2CR)(2)L', with R = CH3, C2H5, or C6H5, L = pyridine or diethylamine, and L' = 2,2'-bipyridine or 1,10-phenanthroline. The precursors were characterized by means of FTIR and XPS. Thermogravimetric analyses allowed us to study the way they decompose under nitrogen: X-ray diffraction investigations indicated they were converted mainly into Pd metal and PdO. Pd/C catalysts were prepared by impregnation from solutions of these complexes in water, benzene or acetone, followed by thermal activation under nitrogen. Catalysts were engaged in the partial oxidation of glucose to gluconic acid and have been characterized by XRD and XPS before and after their use in the catalytic reaction. Catalysts prepared in benzene showed better performances and higher Pd dispersion on the surface than the catalysts prepared in water or acetone. Activity was also found to be enhanced by monomeric, instead of trimeric, structure of the precursor. (C) 1998 Elsevier Science B.V. All rights reserved.