A series of Fe 2 O 3 -CeO 2 composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe 2 O 3 -CeO 2 composites with an Fe molar percentage below 0.3 form solid solutions with the CeO 2 cubic fluorite structure, in which the doped Fe 3+ initially substitutes Ce 4+ in fluorite cubic CeO 2 , but then mostly locate in the interstitial sites after a critical concentration of doped Fe 3+ . With an Fe molar percentage between 0.3 and 0.95, the Fe 2 O 3 -CeO 2 composites are mixed oxides of the cubic fluorite CeO 2 solid solution and the hematite Fe 2 O 3 . XPS results indicate that CeO 2 is enriched in the surface region of Fe 2 O 3 -CeO 2 composites. The Fe 2 O 3 -CeO 2 composites have much higher catalytic activities in CO oxidation than the individual pure CeO 2 and Fe 2 O 3 , and the Fe 0.1 Ce 0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe 2 O 3 -CeO 2 composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO 2 -like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.

Industrial catalysts usually consist of nanoparticles exposing different crystal planes and atomic terminations that play an important role in their catalytic performance. [1,2] Catalysts for heterogeneous catalytic reactions operate under pressures up to several hundred atmospheres and at temperatures up to several hundred degrees Celsius, so that the catalyst nanoparticles can easily undergo surface restructuring to adopt the thermodynamically most stable structure. Thus, it is crucial to explore the restructuring process of catalyst surfaces under the reaction conditions to understand catalytic processes at the microscopic level; moreover, it is desirable to tune the catalytic performance of the catalyst nanoparticles by controlling the surface restructuring process in reactive atmospheres.The direct study of catalyst nanoparticles is challenging because of the complexity of their structures. Model catalysts such as single crystals and vicinal surfaces have been extensively investigated to understand the surface restructuring phenomenon, and these studies have provided deep insights. Strongly chemisorbed adsorbates are well known to induce structural changes to metal surfaces. [3][4][5] More profound restructuring of metal surfaces has been demonstrated to be driven by the formation of dense adsorbate layers, [6][7][8] moreover, it has been argued that the catalytic activities of Ru, Rh, Pd, and Ag in oxidation reactions are related to ultrathin oxide films on their surfaces. [6,7,[9][10][11][12][13] Recently, microscopic and spectroscopic experimental results [14][15][16][17][18][19][20] have directly revealed changes in the surface structure of metal nanoparticles and changes in both the surface structure and surface composition of bimetallic nanoparticles in reactive atmospheres. Reactive gases can also change the structure and composition of oxide nanoparticles to form a catalytically active surface phase in situ. [21,22] Thus, the concept of surface restructuring of catalyst nanoparticles during heterogeneous catalysis reactions has been well accepted, and therefore a challenging and inspiring task is to further explore whether such surface restructuring processes can be controlled and utilized as a novel strategy to improve and design efficient nanocatalysts.In the present study, in which CO oxidation catalyzed by uniform Cu 2 O nanocrystals with different well-defined structures is employed as a model system, we not only clearly demonstrate that the in situ formed CuO thin film on the Cu 2 O nanocrystals is responsible for their catalytic activity but also unambiguously identify the key role of the crystal plane exposed on the Cu 2 O nanocrystals in the surface restructuring process. Our findings revealed the novel concept that the surface restructuring process of catalyst nanoparticles and the structure and catalytic performance of the restructured surface can be controlled by engineering the shape of the nanoparticles and the exposed crystal plane.Uniform octahedral (o-Cu 2 O) and cubic (c-Cu 2 O) Cu ...

We have successfully prepared visible-light-active mesoporous N-doped TiO 2 (N-TiO 2 ) photocatalysts by the precipitation of titanyl oxalate complex ([TiO(C 2 O 4 ) 2 ] 2-) by ammonium hydroxide at a low temperature followed by calcination at different temperatures. The structures of N-TiO 2 photocatalysts have been characterized in detail by means of powder X-ray diffraction, N 2 adsorption-desorption isotherms, infrared spectroscopy, diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscope. The calcination process of the catalyst precursor was also studied by means of temperatureprogrammed reaction spectroscopy. N-TiO 2 photocatalysts exhibit comparable UV-light activity and visiblelight activity in the photodegradation of methyl orange. The doped N species locates at the interstitial sites in TiO 2 , which leads to the band gap narrowing of TiO 2 . A novel and interesting result is that N-doped TiO 2 calcined at 400 °C (N-TiO 2 -400) has Bro ¨nsted acid sites arising from covalently bonded dicarboxyl groups, which greatly enhances the adsorption capacity for methyl orange. The N-TiO 2 -400 catalyst is a promising adsorption-photodegradation integration catalyst; meanwhile, it is also a promising acid catalysis-photocatalysis bifunctional catalyst.