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    Chinese Journal of Catalysis
    2020, Vol. 41, No. 6
    Online: 18 June 2020

    Cover: The articles in this issue on pages 901–914 illustrate the wide range of applications for ceria in heterogeneous catalysis. Ceria has demonstrated remarkable ability to catalyze hydrogenation, oxidation, various acid-base and redox reactions. In this issue, recent developments in catalysis using ceria and ceria-supported metals are discussed, and directions for future study of ceria are proposed.
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    Contents
    Table of Contents for VOL.41 No.6
    2020, 41 (6):  0-0. 
    Abstract ( 12 )   PDF (2372KB) ( 24 )  
    Editorial
    Preface to Special Issue on Advances in Ceria Catalysis
    Feng Wang, Zili Wu
    2020, 41 (6):  899-900.  DOI: 10.1016/S1872-2067(20)63579-3
    Abstract ( 76 )   [Full Text(HTML)] () PDF (185KB) ( 232 )  
    Reviews
    A review of the interactions between ceria and H2 and the applications to selective hydrogenation of alkynes
    James Kammert, Jisue Moon, Zili Wu
    2020, 41 (6):  901-914.  DOI: 10.1016/S1872-2067(19)63509-6
    Abstract ( 219 )   [Full Text(HTML)] () PDF (1038KB) ( 418 )  
    Cerium oxide (ceria) has found a wide variety of applications in catalysis including as a catalyst, a modifier, or a support, largely thanks to its robust redox properties and versatile acid-base function. While it is often utilized for oxidation reactions, ceria has recently attracted intense research interest for its unusual ability to selectively hydrogenate alkynes to alkenes. The intriguing hydrogenation ability of ceria has sparked renewed research efforts to understand how pure ceria works as a hydrogenation catalyst. In this review, recent advances in both experimental and computational studies of ceria are summarized, focusing on the interaction of ceria with H2 and in hydrogenation reactions. Significant insights from various studies including in situ spectroscopy/microscopy and theoretic modeling of ceria in hydrogen-involved reactions are discussed, which shed light on the origin of the hydrogenation ability of ceria and the reaction mechanisms involved in ceria-catalyzed alkyne hydrogenation. Ways to further improve both the mechanistic understanding and catalytic performance of ceria-based materials for hydrogenation reactions are proposed at the end in the summary and outlook section.
    Ceria in halogen chemistry
    Matthias Scharfe, Guido Zichittella, Vladimir Paunovic, Javier Pérez-Ramírez
    2020, 41 (6):  915-927.  DOI: 10.1016/S1872-2067(19)63528-X
    Abstract ( 97 )   [Full Text(HTML)] () PDF (1209KB) ( 229 )  
    Halogen chemistry constitutes an essential part in the industrial production of polymers and gains increasing attention as an attractive strategy to activate light alkanes that constitute natural gas. CeO2-based catalysts offer an exciting potential for advances in hydrogen halide recovery that enables a high efficiency of halogen-based processes for activation of small molecules. This review provides an overview of recently developed ceria-based catalysts in the context of polymer industry (polyvinyl chloride, polyurethanes, and polycarbonates) and activation of light hydrocarbons for natural gas upgrading. In addition, mechanistic insight and the challenges of ceria catalysts are provided, aiding the design of future catalytic materials and applications
    Electronic and geometric structure of the copper-ceria interface on Cu/CeO2 catalysts
    Yan Zhou, Aling Chen, Jing Ning, Wenjie Shen
    2020, 41 (6):  928-937.  DOI: 10.1016/S1872-2067(20)63540-9
    Abstract ( 391 )   [Full Text(HTML)] () PDF (1189KB) ( 484 )  
    The atomic structure of the active sites in Cu/CeO2 catalystsis intimately associated with the copper-ceria interaction. Both the shape of ceria and the loading of copper affect the chemical bonding of copper species on ceria surfaces and the electronic and geometric character of the relevant interfaces. Nanostructured ceria, including particles (polyhedra), rods, and cubes, provides anchoring sites for the copper species. The atomic arrangements and chemical properties of the (111), (110) and (100) facets, preferentially exposed depending on the shape of ceria, govern the copper-ceria interactions and in turn determine their catalytic properties. Also, the metal loading significantly influences the dispersion of copper species on ceria with a specific shape, forming copper layers, clusters, and nanoparticles. Lower copper contents result in copper monolayers and/or bilayers while higher copper loadings lead to multi-layered clusters and faceted particles. The active sites are usually generated via interactions between the copper atoms in the metal species and the oxygen vacancies on ceria, which is closely linked to the number and density of surface oxygen vacancies dominated by the shape of ceria.
    Structure-activity relationship in Pd/CeO2 methane oxidation catalysts
    Sara Colussi, Paolo Fornasiero, Alessandro Trovarelli
    2020, 41 (6):  938-950.  DOI: 10.1016/S1872-2067(19)63510-2
    Abstract ( 217 )   [Full Text(HTML)] () PDF (1145KB) ( 529 )  
    Palladium based catalysts are the most active for methane oxidation. The tuning of their composition, structure and morphology at macro and nanoscale can alter significantly their catalytic behavior and robustness with a strong impact on their overall performances. Among the several combinations of supports and promoters that have been utilized, Pd/CeO2 has attracted a great attention due to its activity and durability coupled with the unusually high degree of interaction between Pd/PdO and the support. This allows the creation of specific structural arrangements which profoundly impact on methane activation characteristics. Here we want to review the latest findings in this area, and particularly to envisage how the control (when possible) of Pd-CeO2 interaction at nanoscale can help in designing more robust methane oxidation catalysts.
    Influence of metal nuclearity and physicochemical properties of ceria on the oxidation of carbon monoxide
    Linxi Wang, Shyam Deo, Kerry Dooley, Michael J. Janik, Robert M. Rioux
    2020, 41 (6):  951-962.  DOI: 10.1016/S1872-2067(20)63557-4
    Abstract ( 83 )   [Full Text(HTML)] () PDF (1364KB) ( 275 )  
    The redox properties of ceria make it suitable as a catalyst or support in oxidation reactions. Ceria-supported transition metal nanoparticles or isolated single atoms provide a metal-support interface that reduces the energy cost to remove interfacial oxygen atoms, providing active oxygen species that can participate in Mars van Krevelen oxidation processes. CO oxidation is a key probe reaction to test the reducibility of ceria-supported catalysts and is also practically important in the elimination of CO at relatively low temperatures in various applications. Preferential oxidation of CO (PROX) in excess H2 controls the CO concentration to ultra-low levels to prevent poisoning of hydrogen oxidation electrocatalysts. The reactivity of catalysts in CO oxidation and selectivity towards CO over H2 in PROX is dependent on the type and dispersion of metal species, the structural and chemical properties of CeO2, and the synthetic preparation methods of the catalysts. In this review, we summarize recently published works on catalytic CO oxidation and PROX reactions on ceria-supported metal nanoparticles and single atoms. We summarize the reactivity on different supported metals, and on different CeO2 surfaces with the same metal. We summarize the most likely reaction mechanisms as suggested by density functional theory calculations. The factors contributing to selectivity towards CO oxidation in PROX reactions on various supported metals are also discussed.
    Communication
    Linear-regioselective hydromethoxycarbonylation of styrene using Ru-clusters/CeO2 catalyst
    Jinghua An, Yehong Wang, Zhixin Zhang, Jian Zhang, Martin Gocyla, Rafal E. Dunin-Borkowski, Feng Wang
    2020, 41 (6):  963-969.  DOI: 10.1016/S1872-2067(19)63527-8
    Abstract ( 95 )   [Full Text(HTML)] () PDF (547KB) ( 253 )  
    Hydroalkoxycarbonylation of olefins has been considered to be one of the most attractive methods to synthesize esters. Controlling the regioselectivities of linear esters (L) and branched esters (B) is a challenging project for researchers working in this reaction. Although most of the attention has been paid to control the regioselectivity through ligand design in homogeneous catalytic systems, study in the area is still limited. Herein, Ru-clusters/CeO2 is employed as a heterogeneous catalyst for the hydromethoxycarbonylation of styrene without any additives. After optimization of the reaction conditions, the conversion of styrene is> 99% with 83% and 12% regioselectivity of linear and branched ester, respectively. By using different supports (CeO2 (nanoparticle), CeO2-rod, and CeO2-cube), three catalysts including Ru-clusters/CeO2, Ru/CeO2-rod, and Ru/CeO2-cube are prepared and applied in the reaction. Structural characterizations demonstrate that the L/B ratio is related to the Ru size of supported Ru catalysts. Further Raman characterization and NH3-TPD demonstrate that the metal-support interaction and the concentration of oxygen vacancy of the catalyst have a great influence on the Ru size. The mechanism and kinetic analysis for this reaction are also investigated in this work.
    Articles
    Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO2 catalyst
    Md. Nurnobi Rashed, Abeda Sultana Touchy, Chandan Chaudhari, Jaewan Jeon, S. M. A. Hakim Siddiki, Takashi Toyao, Ken-ichi Shimizu
    2020, 41 (6):  970-976.  DOI: 10.1016/S1872-2067(19)63515-1
    Abstract ( 58 )   [Full Text(HTML)] () PDF (587KB) ( 175 )  
    We report herein that a commercially available CeO2 is an active and reusable catalyst for the C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This catalytic method is generally applicable to different aromatic and aliphatic aldehydes, giving 3-alkyledene-oxindoles in high yields (87%-99%) and high stereoselectivities (79%-93% to E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO2 and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO2 catalysts with different sizes suggests that defect-free CeO2 surface is the active site for this reaction.
    Lattice oxygen activation in transition metal doped ceria
    Ya-Qiong Su, Long Zhang, Valery Muravev, Emiel J. M. Hensen
    2020, 41 (6):  977-984.  DOI: 10.1016/S1872-2067(19)63468-6
    Abstract ( 150 )   [Full Text(HTML)] () PDF (618KB) ( 307 )  
    Density functional theory calculations were carried out to investigate the influence of doping transition metal (TM) ions into the ceria surface on the activation of surface lattice oxygen atoms. For this purpose, the structure and stability of the most stable (111) surface termination of CeO2 modified by TM ions was determined. Except for Zr and Pt dopants that preserve octahedral oxygen coordination, the TM dopants prefer a square-planar coordination when substituting the surface Ce ions. The surface construction from octahedral to square-planar is facile for all TM dopants, except for Pt (1.14 eV) and Zr (square-planar coordination unstable). Typically, the ionic radius of tetravalent TM cations is much smaller than that of Ce4+, resulting a significant tensile-strained lattice and explaining the lowered oxygen vacancy formation energy. Except for Zr, the square-planar structure is the preferred one when one oxygen vacancy is created. Thermodynamic analysis shows that TM-doped CeO2 surfaces contain oxygen defects under typical conditions of environmental catalysis. A case of practical importance is the facile lattice oxygen activation in Zr-doped CeO2(111), which benefits CO oxidation. The findings emphasize the origin of lattice oxygen activation and the preferred location of TM dopants in TM-ceria solid solution catalysts.
    Nanoscale architecture of ceria-based model catalysts: Pt-Co nanostructures on well-ordered CeO2(111) thin films
    Yaroslava Lykhach, Tomá? Skála, Armin Neitzel, Nataliya Tsud, Klára Beranová, Kevin C. Prince, Vladimír Matolín, J?rg Libuda
    2020, 41 (6):  985-997.  DOI: 10.1016/S1872-2067(19)63462-5
    Abstract ( 79 )   [Full Text(HTML)] () PDF (1616KB) ( 312 )  
    We have prepared and characterized atomically well-defined model systems for ceria-supported Pt-Co core-shell catalysts. Pt@Co and Co@Pt core-shell nanostructures were grown on well-ordered CeO2(111) films on Cu(111) by physical vapour deposition of Pt and Co metals in ultrahigh vacuum and investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy. The deposition of Co onto CeO2(111) yields Co-CeO2(111) solid solution at low Co coverage (0.5 ML), followed by the growth of metallic Co nanoparticles at higher Co coverages. Both Pt@Co and Co@Pt model structures are stable against sintering in the temperature range between 300 and 500 K. After annealing at 500 K, the Pt@Co nanostructure contains nearly pure Co-shell while the Pt-shell in the Co@Pt is partially covered by metallic Co. Above 550 K, the re-ordering in the near surface regions yields a subsurface Pt-Co alloy and Pt-rich shells in both Pt@Co and Co@Pt nanostructures. In the case of Co@Pt nanoparticles, the chemical ordering in the near surface region depends on the initial thickness of the deposited Pt-shell. Annealing of the Co@Pt nanostructures in the presence of O2 triggers the decomposition of Pt-Co alloy along with the oxidation of Co, regardless of the thickness of the initial Pt-shell. Progressive oxidation of Co coupled with adsorbate-induced Co segregation leads to the formation of thick CoO layers on the surfaces of the supported Co@Pt nanostructures. This process is accompanied by the disintegration of the CeO2(111) film and encapsulation of oxidized Co@Pt nanostructures by CeO2 upon annealing in O2 above 550 K. Notably, during oxidation and reduction cycles with O2 and H2 at different temperatures, the changes in the structure and chemical composition of supported Co@Pt nanostructures were driven mainly by oxidation while reduction treatments had little effect regardless of the initial thickness of the Pt-shell.
    Determining number of sites on ceria stabilizing single atoms via metal nanoparticle redispersion
    Aisulu Aitbekova, Cody J. Wrasman, Andrew R. Riscoe, Larissa Y. Kunz, Matteo Cargnello
    2020, 41 (6):  998-1005.  DOI: 10.1016/S1872-2067(19)63504-7
    Abstract ( 94 )   [Full Text(HTML)] () PDF (607KB) ( 309 )  
    Single atom catalysts have recently attracted interest due to their maximization of the utilization of expensive noble metals as well as their unique catalytic properties. Based on its surface atomic properties, CeO2 is one of the most common supports for stabilizing single metal atoms. Many single atom catalysts are limited in their metal contents by the formation of metal nanoparticles once the catalyst support capacity for single atoms has been exceeded. Currently, there are no direct measurements to determine the capacity of a support to stabilize single atoms. In this work we develop a nanoparticle-based technique that allows for quantification of that capacity by redispersing Ru nanoparticles into single atoms and taking advantage of the different catalytic properties of Ru single atoms and nanoparticles in the CO2 hydrogenation reaction. This method avoids complications in metal loading caused by counterions in incipient wetness impregnation and can eventually be applied to a variety of different metals. Results using this technique follow trends in oxygen vacancy concentration and surface oxygen content and show promise as a new method for quantifying support single atom stabilization capacity.
    Understanding morphology-dependent CuOx-CeO2 interactions from the very beginning
    Yuxian Gao, Zhenhua Zhang, Zhaorui Li, Weixin Huang
    2020, 41 (6):  1006-1016.  DOI: 10.1016/S1872-2067(19)63503-5
    Abstract ( 173 )   [Full Text(HTML)] () PDF (1518KB) ( 313 )  
    Elucidation of the CuOx-CeO2 interactions is of great interest and importance in understanding complex CuOx-CeO2 interfacial catalysis in various reactions. In the present work, we have investigated structures and catalytic activity in CO oxidation of CuOx species on CeO2 rods, cubes and polyhedra predominantly exposing {110}+{100}, {100} and {111} facets by the incipient wetness impregnation method with the lowest Cu loading of 0.025%. The structural evolution of CuOx species was found to depend on both the Cu loading and the CeO2 morphology. As the Cu loading increases, CuOx species are deposited preferentially on the surface defect of CeO2 and then aggregate and grow, accompanied by the formation of isolated Cu ions, CuOx clusters strongly/weakly interacting with the CeO2, highly dispersed CuO nanoparticles, and large CuO nanoparticles. The isolated Cu+ species and CuOx clusters weakly interacting with the CeO2 were observed mainly on the O-terminated CeO2{100} facets. Meanwhile, more Cu(I) species are stabilized during CO reduction processes in CuOx/c-CeO2 catalysts than in CuOx/r-CeO2 and CuOx/p-CeO2 catalysts. The catalytic activities of various CuOx/CeO2 catalysts in CO oxidation vary with both the CuOx species and the CeO2 morphology. These results comprehensively elucidate the CuOx-CeO2 interactions and exemplify their morphology-dependence.
    Insights into facet-dependent reactivity of CuO-CeO2 nanocubes and nanorods as catalysts for CO oxidation reaction
    Yu Aung May, Wei-Wei Wang, Han Yan, Shuai Wei, Chun-Jiang Jia
    2020, 41 (6):  1017-1027.  DOI: 10.1016/S1872-2067(20)63533-1
    Abstract ( 297 )   [Full Text(HTML)] () PDF (745KB) ( 445 )  
    Copper-ceria (CuO-CeO2) catalysts have been known to be very effective for the oxidation of CO, and their chemical behavior has been extensively studied during the last decades. However, the effect of different CeO2 crystal surfaces on the catalytic activity of CuO-CeO2 for the oxidation of CO is still unclear and should be further elucidated. In this study, we deposited 1 wt% Cu on mostly {100}-exposed CeO2 nanocubes (1CuCe NC) and mostly {110}-exposed CeO2 nanorods (1CuCe NR), respectively. Both 1CuCe NC and 1CuCe NR have been used as catalysts for the oxidation of CO and achieved 100% and 50% CO conversion at 130℃, respectively. The differences in the catalytic activity of 1CuCe NC and 1CuCe NR were analyzed using temperature-programmed reduction of H2 and temperature-programmed desorption of CO techniques. The results confirmed the excellent reducibility of the 1CuCe NC catalyst, which was attributed to the weak interactions between Cu and the CeO2 support. Moreover, in situ diffuse reflectance infrared Fourier-transform spectroscopy studies indicated that the {100} planes of 1CuCe NC facilitated the generation of active Cu(I)sites, which resulted in the formation of highly reactive Cu(I)-CO species during the oxidation of CO. Both the excellent redox properties and effective CO adsorption capacity of the 1CuCe NC catalyst increased its catalytic reactivity.