Strong Metal-Support Interactions for Palladium Supported on TiO2 Catalysts in the Heterogeneous Hydrogenation with Parahydrogen

Parahydrogen-induced polarization (PHIP) was successfully utilized to demonstrate the strong metal-support interaction (SMSI) effect for palladium supported on titania catalysts. Heterogeneous hydrogenation of 1,3-butadiene over Pd/TiO2 catalysts led to the formation of 1- and 2-butenes and butane, and hyperpolarized products were obtained if parahydrogen was used in the reaction. However, if the catalysts were reduced in H-2 flow at 500 degrees C before the hydrogenation reaction, the observed polarization levels were significantly lower or even zero, which was indicative of the suppression of the pairwise addition of hydrogen route. This observation indicated the possibility to detect the SMSI effect by the PHIP technique. Moreover, by using X-ray photoelectron spectroscopy it was shown that Pd is partially present as Pd delta+ after reduction under a hydrogen atmosphere at 500 degrees C. These results were confirmed by transmission electron microscopy, which revealed the formation of Pd delta+ and the dissolution of Pd in the titania lattice.