Ceria (CeO2)‐supported metals are widely used as catalysts because of their exceptional redox properties. Here, we use surface contrast NMR methods to investigate the hydrogenation of phenol by Pd supported on ceria nanoparticles. We show that the rigid and planar binding of phenol to Pd is mediated by a weak and highly mobile association of the small molecule to ceria. Interestingly, while addition of phosphate to the mixture does not perturb the adsorption of phenol on Pd, it destabilizes its interaction with ceria and proportionally decreases the rate of catalytic conversion. Our data provide strong experimental evidence that weak interactions between adsorbate and ceria are catalytically competent and explain the exceptional performance of Pd/CeO2 for reductive conversions under mild reaction conditions.

Ceria-supported palladium (Pd/CeO2) has spawned significant attention in recent years due to its ability to catalyze selective hydrogenation of phenolic compounds to cyclohexanones and cyclohexanols at a mild temperature and pressure. However, the mechanistic basis by which ceria enhances catalytic conversion is still unclear. Here, we use the increase in the 13C transverse relaxation rate upon the addition of nanoparticles (NPs) (13C ΔR2) to investigate the adsorption of phenolic compounds on the surface of the Pd/CeO2 catalyst by solution NMR. We show that hydroxyphenols adsorb on the support more efficiently than underivatized phenol and methoxyphenols and that phenol derivatives with an oxygen atom at position 2 (i.e., 2-hydroxyphenol and 2-methoxyphenol) form very stable interactions with the Pd site of Pd/CeO2. An analysis of the kinetics of hydrogenation revealed that catalytic conversion is linearly correlated with the ability of the substrate to form interactions with the CeO2 support and is inhibited by the formation of stable substrate-Pd adducts. Our data suggest that CeO2-substrate interactions mediate phenol hydrogenation more efficiently than Pd-substrate interactions and explain the exceptional catalytic performance reported for Pd/CeO2.

Characterization of dynamic processes occurring at the nanoparticle (NP) surface is crucial for developing new and more efficient NP catalysts and materials. Thus, a vast amount of research has been...

The hydrodehalogenation (HDH) of halophenols is efficiently catalyzed by palladium supported on high surface ceria (Pd/CeO2) under mild conditions (35 °C, 1 atm H2). A combination of NMR, DRIFTS, Raman spectroscopy and XPS studies as well as HDH kinetics of substituted halobenzenes suggest the reaction proceeds mainly via a sequence of dissociative adsorption of phenolic hydroxyl onto the support, oxidative addition of Pd into the C-halogen bond and reductive elimination to give phenol and hydrogen halide. The dissociative adsorption of -OH group onto oxygen vacancies of the ceria support results in an electron-rich intermediate that facilitates the turnover-limiting reductive elimination step. In contrast, the direct pathway catalyzed by Pd without dissociative adsorption of the reactants on the support takes place at a slower rate. The mechanistic insights gained in this study were used to modify reaction conditions for enabling HDH of recalcitrant halides such as fluorides and iodides.

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