The interaction of hydrogen with reduced ceria (CeO2−x) powders and CeO2−x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce3+ species to hydrogen, which results in the formation of Ce4+, and thus in oxidation of ceria.

The study reports the first attempt to address the interplay between surface and bulk in hydride formation in ceria (CeO2) by combining experiment, using surface sensitive and bulk sensitive spectroscopic techniques on the two sample systems, i.e., CeO2(111) thin films and CeO2 powders, and theoretical calculations of CeO2(111) surfaces with oxygen vacancies (Ov) at the surface and in the bulk. We show that, on a stoichiometric CeO2(111) surface, H2 dissociates and forms surface hydroxyls (OH). On the pre‐reduced CeO2−x samples, both films and powders, hydroxyls and hydrides (Ce−H) are formed on the surface as well as in the bulk, accompanied by the Ce3+ ↔ Ce4+ redox reaction. As the Ov concentration increases, hydroxyl is destabilized and hydride becomes more stable. Surface hydroxyl is more stable than bulk hydroxyl, whereas bulk hydride is more stable than surface hydride. The surface hydride formation is the kinetically favorable process at relatively low temperatures, and the resulting surface hydride may diffuse into the bulk region and be stabilized therein. At higher temperatures, surface hydroxyls can react to produce water and create additional oxygen vacancies, increasing its concentration, which controls the H2/CeO2 interaction. The results demonstrate a large diversity of reaction pathways, which have to be taken into account for better understanding of reactivity of ceria‐based catalysts in a hydrogen‐rich atmosphere.

Selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols is important for the synthesis of fine chemicals, yet very challenging. Herein, we reported a metal-free CeO2 nanorods (r-CeO2) catalyst for gas-phase transformation of crotonaldehyde to crotyl alcohol with the highest selectivity of 93.2% at 323 K. Compared to CeO2 nanocubes and nanopolydra, r-CeO2 shows a much higher crotyl alcohol production rate, comparable turnover frequency to those of noble-metal-based catalysts, and very high crotyl alcohol selectivity. This can be associated with a relatively high density of surface oxygen vacancies on r-CeO2, which constructs the solid frustrated Lewis pair sites with enhanced heterolytic H2 dissociation and preferred crotonaldehyde adsorption via the CO bond. However, a further reduction of r-CeO2 by H2 was observed to be unfavorable with regard to both catalytic activity and selectivity, because of the emergence of crotonaldehyde adsorption via the CC bond. These findings provide a potential approach to fabricate high-performance and low-cost catalysts for selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols using bare CeO2 with a rigid surface structure design.

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO2 catalysts with porous Al2O3 overlayers coated by atomic layer deposition (ALD). 27Al magic angle spinning NMR analysis showed that Al2O3 overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al3+ sites capable of strongly interacting with adjacent surface PdOx phases on supported Pd particles. Consequently, Al2O3‐decorated Pd/SiO2 catalysts exhibit active and stable PdOx and Pd–PdOx structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al2O3 overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.

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