X-ray Photoelectron Spectroscopy and the Auger Parameter As Tools for Characterization of Silica-Supported Pd Catalysts for the Suzuki−Miyaura Reaction

Abstract

Palladium has been immobilized on thiol-modified mesoporous and amorphous silicates and used as a catalyst for the Suzuki−Miyaura reaction. Heterogeneous catalysts are difficult to characterize due to the difficulty of applying traditional solution state characterization methods like NMR to solid samples. As such, the catalysts are often poorly understood. In an effort to better understand the oxidation state and electronic environment of both the reactive palladium center and the thiol ligands through which it is bound in the catalyst, we characterized a wide range of both Suzuki−Miyaura catalysts and Pd compounds by both X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger spectroscopy (XAES) focusing on Pd, S, and Si. The use of XAES data allows determination of the Auger parameter for Pd and S, which provides information not only on oxidation state but also on the polarizability of the surrounding ligands in the catalyst. Changes in XPS binding energy and XAES kinetic energy are discussed pa...