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.

Strong metal–support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au‐TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au‐TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2{101} facets. The resulting capsulating TiO2−x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au‐to‐TiO2−x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2−x overlayers and TiO2−x‐Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low‐temperature CO oxidation than the starting Au‐TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis.

A series of CuO/CeO 2 and inverse CeO 2 /CuO catalysts were prepared by an incipient wetness impregnation method and tested for CO oxidation. Crystallite sizes of CeO 2 and CuO were evaluated by X-ray diffraction and N 2 O chemisorption, as well as transmission electron microscopy. It was found that a CuO(5)/CeO 2 -500 catalyst with a CuO crystallite size of 4.1 nm and a CeO 2 (5)/CuO-500 catalyst with a CeO 2 crystallite size of 4.0 nm had identical activities, indicating that the reaction may occur at the interface of CuO-CeO 2 . According to the turnover frequency based on CuO sites located on the CuO-CeO 2 interface, the activity on the larger CuO crystallite was much higher than that on the smaller one, indicating that CuO-CeO 2 catalyst for CO oxidation is structure-sensitive. The enhanced activity was ascribed to a higher density of chemisorbed CO on the active sites for the larger CuO crystallite.

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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.

Ce 0.9 Pr 0.1 O 2-δ , Ce 0.95 Cu 0.05 O 2-δ , and Ce 0.9 Pr 0.05 Cu 0.05 O 2-δ mixed oxides and pure CeO 2 were prepared with a sol-gel method and were characterized by XRD, in situ Raman, and in situ DRIFTS techniques. The XRD results confirmed the formation of Ce-Pr-O solid solution. The Raman results indicated that a higher concentration of oxygen vacancies was obtained on the Pr-doped samples compared to the Ce 0.95 Cu 0.05 O 2-δ and pure CeO 2 samples. Surface chemical states of the Ce 0.9 Pr 0.1 O 2-δ and Ce 0.9 Pr 0.05 Cu 0.05 O 2-δ mixed oxides were determined by in situ Raman spectroscopy, which indicated that the surfaces of the two mixed oxides were both close to oxidation state during the reaction, despite of the presence of reducing reactant CO in the gas mixture. The in situ DRIFTS results evidenced the chemisorption of CO in the Cu-containing samples. The catalysts were tested for CO oxidation, and it was found that the enhanced reactivity was closely related to the higher concentrations of the oxygen vacancies and the chemisorbed CO in the catalysts, due to the fact that the oxygen vacancies provide activation centers for O 2 and the Cu + ions provide chemisorption sites for CO.

The PdO/Ce1–x Pd x O2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–x Pd x O2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–x Pd x O2−δ catalyst had the highest activity (969.3 μmolCO gPd –1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd –1 s–1), and the PdO species in the Ce1–x Pd x O2−δ solid solution had the lowest activity (13.2 μmolCO gPd –1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–x Pd x O2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–x Pd x O2−δ solid solution generated more oxygen vacancies for oxygen activation.

Cu–ZnO–Al2O3 catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the ZnO–Cu catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of CuCu(100)-hydroxylated ZnO ensemble and CuCu(611)Zn alloy, respectively. These results provide insights into the active sites of Cu–ZnO catalysts for the WGS and CO hydrogenation reactions and reveal the Cu structural effects, and offer the feasible guideline for optimizing the structures of Cu–ZnO–Al2O3 catalysts.