STUDY ON D STATE OF PLATINUM IN PT/SIO2 AND NA/PT/SIO2 CATALYSTS UNDER C=C HYDROGENATION CONDITIONS BY X-RAY ABSORPTION NEAR-EDGE STRUCTURE SPECTROSCOPY

The change in the d-electron density of platinum during D2 + CH2 = CHX reactions on Pt/SiO2 and Na/Pt/SiO2 catalysts and its influence on the catalysis were studied by X-ray absorption near-edge structure (XANES) spectroscopy, kinetics and FT-IR. It was demonstrated from the change of the white lines in XANES spectra at Pt L2 and L3 edges that CH2 = CHX (X = H, CH3, COCH3, CF3, and CN) is adsorbed on the Pt surface and extracts the electrons of the d state. Hence, the deuterogenation rate is reduced as the value of Hammett's sigma-P increases. The linear free energy relationship between the reaction rate and sigma-P was observed for the deuterogenation of CH2 = CHX. The rate of ethene deuterogenation was promoted by Na2O addition. The electron density of unoccupied d states of Pt under vacuum decreased by Na2O addition, indicating the electron donation from Na2O to Pt particles. However, most of these additional electrons were observed to move to ethene under reaction conditions. The acceptor of the electrons was suggested to be di-sigma-ethene by the shift of nu-(C-H). The kinetic parameters are discussed in relation to the change in the d state of Pt as a function of sigma-P and Na quantity.