Preparation, Quantification, and Reaction of Pd Hydrides on Pd/ Al2O3 in Liquid Environment

The ability to study in situ the formation and consumption of Pd hydrides (PdH) in liquid environments is a significant challenge hampering a deeper understanding of catalyzed liquid-phase hydrogenation reactions. Here, using quick scanning X-ray absorption spectroscopy (QEXAFS), we present a detailed kinetic study of Pd hydride formation and reactivity on Pd/Al2O3 in 2propanol solvent. By calibrating the changes in the QEXAFS spectra with temperature-programmed reduction (TPR), we show that the extent of Pd hydride formed or consumed can be assessed quantitatively. This methodology was subsequently used to follow the fate of hydrides during furfural hydrogenation in 2-propanol where their displacement was observed to take place upon coordination of the CO derived from furfural decarbonylation on palladium. The time-resolved quantitative methodology can be used to determine the fraction of Pd hydrides, to assess the kinetics of their displacement and consumption in both the gas and liquid phases.