The present invention relates to a novel process for the preparation of a reusable heterogeneous nanopalladium (0) catalysts, which is a eco-friendly and economical process employing re-usable heterogeneous catalyst in place of soluble palladium catalysts for preparing coupling products by C—C bond formation reaction of haloarenes that include unreactive chloroarenes in the presence of base. The use of heterogeneous nanopalladium catalyst precludes the presence of palladium in traces with the product.

Layered double hydroxides supported nanopalladium catalysts for Heck-, Suzuki, Sonogashira-, and Stille type coupling reactions of haloarenes

Characterization of Pd/γ-alumina catalysts containing ceria

An XPS study of metal-support interactions on Pd/SiO2 and Pd/La2O3

Alumina-supported palladium-copper catalysts, which promote liquid-phase nitrate reduction, have been prepared according to different impregnation sequences of γ-Al 2 O 3 support and characterized by X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and temperature-programmed reduction (TPR). Analysis of Pd XPS/XAES spectra reveals that palladium is present on the γ-alumina support in the metallic form. Copper is reduced at lower temperatures in the presence of palladium particles compared to the CuO/γ-Al 2 O 3 sample. Due to the low copper content in catalysts ( σ Cu ≈10 14 atoms cm −2 ), the XPS/XEAS spectral features of reduced copper species are quite different from those of bulk copper. As shown by TPR and XPS/XAES data, formation of highly dispersed Pd-Cu bimetallic clusters is suggested. It was discovered by means of TPR analysis that the catalyst preparation in which the γ-alumina support is impregnated first by copper salt, results in higher formation of the Pd-Cu alloy.

XPS and TPR examinations of γ-alumina-supported Pd-Cu catalysts

Palladium–alumina catalysts prepared from various precursors and by different preparation methods have been studied after calcination by O2 and reduction by H2, using IR spectroscopy of adsorbed CO, EPR and diffuse reflectance measurements. In addition to Pd2+ ions, the unreduced samples contain Pd3+ and Pd+ species. Pd2+ and Pd– entities are still present on catalysts reduced at 573 K. The influence of the precursor on the metal fraction exposed (MFE) and on the nature of adsorbed CO species is clearly shown. Bridged entities are more sensitive to the MFE value than the linear ones. At 100 Torr [1 Torr ≈(101 325/760) Pa], the bridged entities are compressed, which leads to a CO-(surface Pd) ratio of near unity. The MFE increases when the precursors are taken in the following order nitrate < chloride (impregnated)≈ acetylacetonate < chloride (exchanged). The sintering brought about by increasing the reduction temperature seems to affect the largest metal particles rather than the small ones which strongly interact with the carrier.

J. Escard

Papers

Chemical state and reactivity of supported palladium: I. Characterization by XPS and uv-visible spectroscopy