Elucidating the structure, redox properties and active entities of high-temperature thermally aged CuOx-CeO2 catalysts for CO-PROX

CuOx-CeO2 catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N2 adsorption-desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu-Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T50% of 62 °C and the widest operation temperature window of 85-140 °C), which provided a new strategy for the design of Cu-Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuOx species and strongly bonded Cu-[Ox]-Ce species, strengthening the Cu-Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuOx-CeO2 catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuOx species and strongly bonded Cu-[Ox]-Ce species, respectively.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation

Herein, CuO/Bi₂MoO₆ hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi₂MoO₆ nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi₂MoO₆ nanosheets by the C-H group forming CuO/Bi₂MoO₆···Ph-CH₃ surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi₂MoO₆ nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide

We reviewed recent advances in catalysts for PROX with emphasis on synergistic effects that contribute to enhanced catalytic performance.

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

Excellent catalytic performance for NO reduction by CO in the presence of 5% O₂ over Cu1:Ce3/Al₂O₃.

Experimental and computational studies on copper–cerium catalysts supported on nitrogen-doped porous carbon for preferential oxidation of CO

Geometric characteristics improve the synergy between Cu2⁺/Cu⁺ and Ce4⁺/Ce3⁺ couples.

A flower-like Zn3V2O8/Ag composite with enhanced visible light driven photocatalytic activity: the triple-functional roles of Ag nanoparticles

Coprecipitation, calcination and photoreduction, in a combined method, were successfully employed to fabricate a flower-like Zn₃V₂O₈ (ZnVO)/nano-precipitated Ag composite powder.

Hollow copper–ceria microspheres with single and multiple shells for preferential CO oxidation

The triple-shelled CuO/CeO₂ exhibits superior catalytic performance for CO-PROX due to its fine-tunable geometric and electronic interactions.

Pt-Embedded CuO x-CeO2 Multicore-Shell Composites: Interfacial Redox Reaction-Directed Synthesis and Composition-Dependent Performance for CO Oxidation

Exploring the state-of-the-art heterogeneous catalysts has been a general concern for sustainable and clean energy. Here, Pt-embedded CuO _x-CeO₂ multicore-shell (Pt/CuO _x-CeO₂ MS) composites are fabricated at room temperature via a one-pot and template-free procedure for catalyzing CO oxidation, a classical probe reaction, showing a volcano-shaped relationship between the composition and catalytic activity. We experimentally unravel that the Pt/CuO _x-CeO₂ MS composites are derived from an interfacial autoredox process, where Pt nanoparticles (NPs) are in situ encapsulated by self-assembled ceria nanospheres with CuO _x clusters adhered through deposition/precipitation-calcination process. Only Cu-O and Pt-Pt coordination structures are determined for CuO _x clusters and Pt NPs in Pt/CuO _x-CeO₂ MS, respectively. Importantly, the close vicinity between Pt and CeO₂ benefits to more oxygen vacancies in CeO₂ counterparts and results in thin oxide layers on Pt NPs. Meanwhile, the introduction of CuO _x clusters is crucial for triggering synergistic catalysis, which leads to high resistance to aggregation of Pt NPs and improvement of catalytic performance. In CO oxidation reaction, both Pt^δ+-CO and Cu⁺-CO can act as active sites during CO adsorption and activation. Nonetheless, redundant content of Pt or Cu will induce a strongly bound Pt-O-Ce or Cu-[O _x]-Ce structures in air-calcinated Pt/CuO _x-CeO₂ MS composites, respectively, which are both deleterious to catalytic reactivity. As a result, the composition-dependent catalytic activity and superior durability of Pt/CuO _x-CeO₂ MS composites toward CO oxidation reaction are achieved. This work should be instructive for fabricating desirable multicomponent catalysts composed of noble metal and bimetallic oxide composites for diverse heterogeneous catalysis.

Efficient 2-Nitrophenol Chemical Sensor Development Based on Ce2O3 Nanoparticles Decorated CNT Nanocomposites for Environmental Safety

Ce₂O₃ nanoparticle decorated CNT nanocomposites (Ce₂O₃.CNT NCs) were prepared by a wet-chemical method in basic medium. The Ce₂O₃.CNT NCs were examined using FTIR, UV/Vis, Field-Emission Scanning Electron Microscopy (FESEM), X-ray electron dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). A selective 2-nitrophenol (2-NP) sensor was developed by fabricating a thin-layer of NCs onto a flat glassy carbon electrode (GCE, surface area = 0.0316 cm²). Higher sensitivity including linear dynamic range (LDR), long-term stability, and enhanced electrochemical performances towards 2-NP were achieved by a reliable current-voltage (I-V) method. The calibration curve was found linear (R² = 0.9030) over a wide range of 2-NP concentration (100 pM ~ 100.0 mM). Limit of detection (LOD) and sensor sensitivity were calculated based on noise to signal ratio (~3N/S) as 60 ± 0.02 pM and 1.6×10⁻³ μAμM^-1cm^-2 respectively. The Ce₂O₃.CNT NCs synthesized by a wet-chemical process is an excellent way of establishing nanomaterial decorated carbon materials for chemical sensor development in favor of detecting hazardous compounds in health-care and environmental fields at broad-scales. Finally, the efficiency of the proposed chemical sensors can be applied and utilized in effectively for the selective detection of toxic 2-NP component in environmental real samples with acceptable and reasonable results.

CeO2 nanowires self-inserted into porous Co3O4 frameworks as high-performance "noble metal free" hetero-catalysts

Recently, mixed metal oxides have attracted tremendous interest because of their great importance for fundamental studies and practical applications in the catalytic field to replace expensive noble metals. Herein, we report the designed synthesis of novel CeO2-Co3O4 mixed metal oxides with complex nanostructures using uniform short CeO2 nanowires self-inserted into ZIF-67 nanocrystals as precursors followed by a thermal annealing treatment. Interestingly, such a synthetic strategy can be easily extended to fabricate other CeO2 nanowires inserted into metal oxide nanoframeworks such as NiCo2O4 and ZnCo2O4. Choosing the NO reduction reaction by CO as the catalytic model, the as-obtained CeO2-Co3O4 hybrids exhibited enhanced catalytic performance, which could be attributed to the strong two-phase interaction between each component.

The promoter effect of potassium in CuO/CeO2 systems supported on carbon nanotubes and graphene for the CO-PROX reaction

Improved performance of catalysts promoted with K was obtained in the CO-PROX reaction.