Insights into facet-dependent reactivity of CuO–CeO2 nanocubes and nanorods as catalysts for CO oxidation reaction

Unraveling distinct effects between CuOx and PtCu alloy sites in Pt-Cu bimetallic catalysts for CO oxidation at different temperatures

In situ exploration of the dynamic structure evolution of catalysts plays a key role in revealing reaction mechanisms and designing efficient catalysts. In this work, PtCu/MgO catalysts, synthesized via the co-impregnation method, outperforms monometallic Pt/MgO and Cu/MgO. Utilizing quasi/in-situ characterization techniques, it is discovered that there is an obvious structural evolution over PtCu/MgO from PtxCuyOz oxide cluster to PtCu alloy with surface CuOx species under different redox and CO oxidation reaction conditions. The synergistic effect between PtCu alloy and CuOx species enables good CO oxidation activity through the regulation of CO adsorption and O2 dissociation. At low temperatures, CO oxidation is predominantly catalyzed by surface CuOx species via the Mars-van Krevelen mechanism, in which CuOx can provide abundant active oxygen species. As the reaction temperature increases, both surface CuOx species and PtCu alloy collaborate to activate gaseous oxygen, facilitating CO oxidation mainly through the Langmuir-Hinshelwood mechanism.

Enhancing low-temperature CO removal in complex flue gases: A study on La and Cu doped Co3O4 catalysts under real-world combustion environment

Designing CO oxidation catalysts for complex flue gases conditions is particularly challenging in fire scenarios. Traditional flue gas simulations use a few representative gases but often fail to adequately evaluate catalyst performance in real-world combustion conditions. In this study, we developed doping strategies using La and Cu to enhance the water resistance of Co3O4 catalysts. Catalyst 0.1La-Co3O4-CuO/CeO2 exhibits exceptional low-temperature catalytic activity, achieving 100% conversion at 130 °C. This enhancement is largely due to the introduction of La, which increases the active Co3+/Co2+ ratio and suppresses hydroxyl group formation on the Co3O4 surface. Cu doping also changes the Co3O4 lattice structure, forming Cu+ as active sites and enhancing the activity at low temperatures. For the first time, steady-state tube furnace and fixed bed were employed to evaluate the catalytic performance of CO in actual combustion atmosphere. Catalyst 0.1La-Co3O4-CuO/CeO2 maintains excellent catalytic efficiency (T100 = 120 °C) under well-ventilated conditions. However, its activity significantly decreases in poorly ventilated environments, due to the competitive adsorption of small molecules at active sites, such as acetone, commonly found in smoke. This study provides valuable insights for designing water-resistant, low-temperature, non-noble metal catalysts and offers a methodology for evaluating CO catalytic activity in real-world environments.

Hydroxyls on CeO2 Support Promoting CuO/CeO2 Catalyst for Efficient CO Oxidation and NO Reduction by CO

Transition metal catalysts, such as copper oxide, are more attractive alternatives to noble metal catalysts for emission control due to their higher abundance, lower cost, and excellent catalytic activity. In this study, we report the preparation and application of a novel CuO/CeO2 catalyst using a hydroxyl-rich Ce(OH)x support for CO oxidation and NO reduction by CO. Compared to the catalyst prepared from a regular CeO2 support, the new CuO/CeO2 catalyst prepared from the OH-rich Ce(OH)x (CuO/CeO2-OH) showed significantly higher catalytic activity under different testing conditions. The effect of OH species in the CeO2 support on the catalytic performance and physicochemical properties of the CuO/CeO2 catalyst was characterized in detail. It is demonstrated that the abundant OH species enhanced the CuOx dispersion on CeO2, increased the CuOx-CeO2 interfaces and surface defects, promoted the oxygen activation and mobility, and boosted the NO adsorption and dissociation on CuO/CeO2-OH, thus contributing to its superior catalytic activity for both CO oxidation and NO reduction by CO. These results suggest that the OH-rich Ce(OH)x is a superior support for the preparation of highly efficient metal catalysts for different applications.

Structure engineering of CeO2 for boosting the Au/CeO2 nanocatalyst in the green and selective hydrogenation of nitrobenzene

Exploring eco-friendly and cost-effective strategies for structure engineering at the nanoscale is important for boosting heterogeneous catalysis but still under a long-standing challenge. Herein, multifunctional polyphenol tannic acid, a low-cost natural biomass containing catechol and galloyl species, was employed as a green reducing agent, chelating agent, and stabilizer to prepare Au nanoparticles, which were dispersed on different-shaped CeO₂ supports (e.g., rod, flower, cube, and octahedral). Systematic characterizations revealed that Au/CeO₂-rod had the highest oxygen vacancy density and Ce(III) proportion, favoring the dispersion and stabilization of the metal active sites. Using isopropanol as a hydrogen-transfer reagent, deep insights into the structure-activity relationship of the Au/CeO₂ catalysts with various morphologies of CeO₂ in the catalytic nitrobenzene transfer hydrogenation reaction were gained. Notably, the catalytic performance followed the order: Au/CeO₂-rod (110), (100), (111) > Au/CeO₂-flower (100), (111) > Au/CeO₂-cube (100) > Au/CeO₂-octa (111). Au/CeO₂-rod displayed the highest conversion of 100% nitrobenzene and excellent stability under optimal conditions. Moreover, DFT calculations indicated that nitrobenzene molecules had a suitable adsorption energy and better isopropanol dehydrogenation capacity on the Au/CeO₂ (110) surface. A reaction pathway and the synergistic catalytic mechanism for catalytic nitrobenzene transfer hydrogenation are proposed based on the results. This work demonstrates that CeO₂ structure engineering is an efficient strategy for fabricating advanced and environmentally benign materials for nitrobenzene hydrogenation.

Crystal Faces-Tailored Oxygen Vacancy in Au/CeO2 Catalysts for Efficient Oxidation of HMF to FDCA

Developing an efficient catalyst to upgrade 5-hydroxymethylfurfural (HMF) to high-value-added downstream chemicals is of great significance in biomass conversion. Nanorod (110)-, nanocube (100)-, and nanooctaheron (111)-CeO₂ -supported Au nanoparticles were prepared to investigate the intrinsic effect of CeO₂ crystal faces on the oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The experimental results and density functional theory calculation revealed that the concentration of oxygen vacancy (V_O ) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod-CeO₂ with the highest V_O concentration promoted the formation of more oxygen active species (superoxide radical) on CeO₂ (110) crystal face than (100) and (111) crystal faces. Besides, the higher V_O concentration could provide a strong adsorption ability of HMF, greatly boosting the activation of HMF. Thus, these results led to a superior catalytic activity for HMF oxidation over Au/nanorod-CeO₂ (FDCA yield of 96.5 %). In-situ Fourier-transform (FT)IR spectroscopy uncovered the HMF oxidation pathway, and the possible catalytic mechanism was proposed. The deep insight into the role of regulation for crystal faces provides a basis for the rational design of highly active facets for the oxidation of HMF and related reactions.

Effects of the Crystalline Properties of Hollow Ceria Nanostructures on a CuO-CeO2 catalyst in CO Oxidation

The development of an efficient and economic catalyst with high catalytic performance is always challenging. In this study, we report the synthesis of hollow CeO2 nanostructures and the crystallinity control of a CeO2 layer used as a support material for a CuO-CeO2 catalyst in CO oxidation. The hollow CeO2 nanostructures were synthesized using a simple hydrothermal method. The crystallinity of the hollow CeO2 shell layer was controlled through thermal treatment at various temperatures. The crystallinity of hollow CeO2 was enhanced by increasing the calcination temperature, but both porosity and surface area decreased, showing an opposite trend to that of crystallinity. The crystallinity of hollow CeO2 significantly influenced both the characteristics and the catalytic performance of the corresponding hollow CuO-CeO2 (H-Cu-CeO2) catalysts. The degree of oxygen vacancy significantly decreased with the calcination temperature. H-Cu-CeO2 (HT), which presented the lowest CeO2 crystallinity, not only had a high degree of oxygen vacancy but also showed well-dispersed CuO species, while H-Cu-CeO2 (800), with well-developed crystallinity, showed low CuO dispersion. The H-Cu-CeO2 (HT) catalyst exhibited significantly enhanced catalytic activity and stability. In this study, we systemically analyzed the characteristics and catalyst performance of hollow CeO2 samples and the corresponding hollow CuO-CeO2 catalysts.

Heterostructured Ceria-Titania-Supported Platinum Catalysts for the Water Gas Shift Reaction

The water gas shift (WGS) reaction is a key process in the industrial hydrogen production and the development and application of the proton exchange membrane fuel cell. Metal oxide-supported highly dispersed Pt has been proved as an efficient catalyst for the WGS reaction. In this work, a series of supported 0.5Pt/xCe-10Ti (x = 1, 3, or 5) catalysts with different Ce/Ti molar ratios were prepared by a simple deposition-precipitation method. Compared with single TiO₂- or CeO₂-supported Pt catalysts, it was found that the 0.5Pt/3Ce-10Ti catalyst showed an obvious advantage in activity for the WGS reaction. In this catalyst, dispersed CeO₂ nanoparticles were supported on the TiO₂ sheets, and Pt single atoms and nanoparticles were located on CeO₂ and at the boundary of TiO₂ and CeO₂, respectively. It found that the reduction ability of the supported Pt catalyst was remarkably improved; meanwhile, the adsorption strength of CO on the surface of 0.5Pt/3Ce-10Ti was moderate. The heterostructured CeO₂-TiO₂ support gave an effective regulation on the Pt status and further influenced the CO adsorption ability, inducing excellent WGS reaction activity. This work provides a reference for the development and application of heterostructured materials in heterogeneous catalysis.

Highly Active CuO/KCC−1 Catalysts for Low-Temperature CO Oxidation

Copper catalysts have been extensively studied for CO oxidation at low temperatures. Previous findings on the stability of such catalysts, on the other hand, revealed that they deactivated badly under extreme circumstances. Therefore, in this work, a series of KCC−1-supported copper oxide catalysts were successfully prepared by impregnation method, of which 5% CuO/KCC−1 exhibited the best activity: CO could be completely converted at 120 °C. The 5% CuO/KCC−1 catalyst exhibited better thermal stability, which is mainly attributed to the large specific surface area of KCC−1 that facilitates the high dispersion of CuO species, and because the dendritic layered walls can lengthen the movement distances from particle-to-particle, thus helping to slow down the tendency of active components to sinter. In addition, the 5% CuO/KCC−1 has abundant mesoporous and surface active oxygen species, which are beneficial to the mass transfer and promote the adsorption of CO and the decomposition of Cu+–CO species, thus improving the CO oxidation performance of the catalyst.

Effect of CeO2 morphology on the catalytic properties of Au/CeO2 for base-free glucose oxidation

The Au/R-CeO2 catalyst with strong metal–support interaction and abundant oxygen vacancies displays superior glucose oxidation performance, as compared with Au/C-CeO2 and Au/O-CeO2.

Facile Fabrication of CeO2-Al2O3 Hollow Sphere with Atomically Dispersed Fe via Spray Pyrolysis

A facile spray pyrolysis method is introduced to construct the hollow CeO₂-Al₂O₃ spheres with atomically dispersed Fe. Only nitrates and ethanol were involved during the one-step preparation process using the ultrasound spray pyrolysis approach. Detailed explorations demonstrated that differences in the pyrolysis temperature of the precursors and heat transfer are crucial to the formation of the hollow nanostructure. In addition, iron species were in situ atomically dispersed on the as-formed CeO₂-Al₂O₃ hollow spheres via this strategy, which demonstrated promising potential in transferring syn-gas to valuable gasoline products.

Facet-selective charge separation in two-dimensional bismuth-based photocatalysts

In this review, we summarize recent advances in the facet design of bismuth-based single-crystal plates based on facet-dependent charge separation for photocatalytic reactions, and the manipulation of the spatial charge separation is highlighted.

High-heat treatment enhanced catalytic activity of CuO/CeO2 catalysts with low CuO content for CO oxidation

CuO/CeO₂ catalysts with low CuO content and calcined at 800 °C exhibited better catalytic performance than those calcined at 500 °C. The coordinatively unsaturated copper atoms were proved to be the main active sites in the CuO/CeO₂ catalysts.

The solid-state in situ construction of Cu2O/CuO heterostructures with adjustable phase compositions to promote CO oxidation activity

Cu₂O/CuO heterojunctions were fabricated via in situ solid-state technology. Tuning the ratio of reactants enables optimization of the components of the Cu₂O/CuO heterostructures and their catalytic activities for CO oxidation.