Origin of the strong metal-support interaction in Pd/TiO2

Strong metal-support interaction (SMSI) is a crucial factor in stabilizing metal nanoparticles (NPs) on reducible metal-oxides, affecting their dispersion, morphology, and catalytic properties. In this study, we show that tuning the synthesis protocol allows for the preparation of Pd/TiO2 catalysts with distinctly different metal-support interactions, and we investigate the underlying mechanisms behind these variations. Catalysts prepared via deposition–precipitation exhibit weak Pd-TiO2 interactions, whereas an evident SMSI effect is observed in the ones prepared by photodeposition. The latter samples demonstrate remarkable stability of the metallic phase even under high-temperature oxidizing conditions, unusual for Pd NPs. A comprehensive multi-technique study allowed attributing the SMSI effect to the presence of Ti3+ sites at the Pd/TiO2 interface, detected by electron paramagnetic resonance (EPR) and electron energy loss (EELS) spectroscopies, and direct Pd‒Ti interactions, observed in X-ray absorption spectroscopy (XAS) data, in the photodeposited Pd/TiO2 catalyst. These features were not observed in the case of the deposition–precipitation method, due to the distinct formation mechanisms of the Pd NPs.