Inverse CeO2/CuO Catalyst As an Alternative to Classical Direct Configurations for Preferential Oxidation of CO in Hydrogen-Rich Stream

Construction of Cu–Ce/graphene catalysts via a one-step hydrothermal method and their excellent CO catalytic oxidation performance

Cu–Ce/graphene catalysts show high dispersion of metal particles and excellent activity and stability for catalytic oxidation. In this study, a hydrothermal method was used to synthesize a series of bimetallic Cu–Ce/graphene catalysts, and the effects of the proportions of Cu and Ce on CO oxidation were investigated in detail. Indispensable characterizations such as XPS, XRD, TEM, BET, and H₂-TPR were conducted to explore the effect of the Cu/Ce molar ratio and the metal valence on the activity and determine the structure–performance relationship. The results showed that bimetallic supported catalysts, such as 3Cu5Ce/graphene, 1Cu1Ce/graphene, and 5Cu3Ce/graphene, possessed significant catalytic activity. Especially, the 5Cu3Ce/graphene catalyst showed highest catalytic activity for CO oxidation, the T₁₀₀ value was 132 °C, and the apparent activation energy was 68.03 kJ mol⁻¹. Furthermore, the stability of the 5Cu3Ce/graphene catalyst was outstanding, which could be maintained for at least 12 h. Moreover, the CeO₂ particles were well crystalline with the size 5–9 nm in these catalysts, and the CuO nanoparticles were well dispersed on CeO₂ and graphene. Notably, the ratio of Cu/Ce in the catalyst was higher, the interaction between the Ce species and the graphene was stronger, and the Cu species were more easily reduced; this was beneficial for the oxidation of CO.

Cu–Ce/graphene catalysts show high dispersion of metal particles and excellent activity and stability for catalytic oxidation.

Combinatorial selection of a two-dimensional 3d-TM-tetracyanoquinodimethane (TM-TCNQ) monolayer as a high-activity nanocatalyst for CO oxidation

CO catalytic oxidation on Sc-TCNQ.

Controlled Construction of Supported Cu+ Sites and Their Stabilization in MIL-100(Fe): Efficient Adsorbents for Benzothiophene Capture

Cu⁺-containing materials have drawn much attention in various applications because they are versatile, nontoxic, and low-cost. However, the difficulty of selective reduction and the poor stability of Cu⁺ species are now pretty much the agendas. Here, controlled construction of supported Cu⁺ sites in MIL-100(Fe) was realized under mild conditions (200 °C, 5 h) via a vapor-reduction strategy (VRS). Remarkably, the yield of Cu⁺ reaches 100%, which is quite higher than the traditional high-temperature autoreduction method with a yield less than 50% even at 700 °C for 12 h. More importantly, during the treatment via VRS some Fe³⁺ in MIL-100(Fe) are reduced to Fe²⁺, which prevent the frequently happened oxidation of Cu⁺ due to the higher oxidation potential of Fe²⁺. These properties make Cu⁺/MIL-100(Fe) efficient in the capture of typical aromatic sulfur, benzothiophene, with regard to both adsorption capacity and stability. To our knowledge, the stabilization of Cu⁺ using the oxidation tendency of supports is achieved for the first time, which may offer a new idea to utilize active sites with weak stability.

Ceria-based model catalysts: fundamental studies on the importance of the metal–ceria interface in CO oxidation, the water–gas shift, CO2 hydrogenation, and methane and alcohol reforming

Model metal/ceria and ceria/metal catalysts have shown to be excellent systems for studying fundamental phenomena linked to the operation of technical catalysts.

Theoretical investigation of CO catalytic oxidation by a Fe–PtSe2 monolayer

Theoretical prediction of efficient catalytic CO oxidation over a Fe–PtSe₂ monolayer.

Effect of crystallite size on the performance and phase transformation of Co3O4/Al2O3 catalysts during CO-PrOx – an in situ study

The preferential oxidation of carbon monoxide has been identified as an effective route to remove trace amounts of CO (approx. 0.5–1.0 vol%) in the H₂-rich reformate gas stream after the low-temperature water–gas shift. Instead of noble metal-based catalysts, Co₃O₄-based catalysts were investigated in this study as cheaper and more readily available alternatives. This study aimed at investigating the effect of crystallite size on the mass- and surface area-specific CO oxidation activity as well as on the reduction behaviour of Co₃O₄. Model Co₃O₄ catalysts with average crystallite sizes between 3 and 15 nm were synthesised using the reverse micelle technique. Results from the catalytic tests revealed that decreasing the size of the Co₃O₄ crystallites increased the mass-specific CO oxidation activity in the 50–200 °C temperature range. On the other hand, the surface area-specific CO oxidation activity displayed a volcano-type behaviour where crystallites with an average size of 8.5 nm were the most active within the same temperature range. In situ characterisation in the magnetometer revealed that the Co₃O₄ crystallites are partially reduced to metallic Co above 225 °C with crystallites larger than 7.5 nm showing higher degrees of reduction under the H₂-rich environment of CO-PrOx. In situ PXRD experiments further showed the presence of CoO concurrently with metallic fcc Co in all the catalysts during the CO-PrOx runs. In all experiments, the formation of fcc Co coincided with the formation of CH₄. Upon decreasing the reaction temperature below 250 °C under the reaction gas, both in situ techniques revealed that the fcc Co previously formed is partially re-oxidised to CoO.

Oxygen Gateway Effect of CeO2/La2O2SO4 Composite Oxygen Storage Materials

A synergistic enhancement in oxygen release/storage performance was achieved with composites formed between CeO₂ as an oxygen gateway and La₂O₂SO₄ as an oxygen reservoir. CeO₂ smoothly transfers oxygen atoms between La₂O₂SO₄ and the gas phase, whereas La₂O₂SO₄ stores a large amount of oxygen. The composite materials exhibited enhanced anaerobic CO oxidation and reversible oxygen storage in the presence of impregnated Pt catalysts as compared to their individual constituents (Pt/CeO₂ and Pt/La₂O₂SO₄). In situ X-ray diffraction and Raman experiments demonstrated that CeO₂ significantly accelerated the redox reaction between La₂O₂SO₄ (S⁶⁺) and La₂O₂S (S^2-), while preserving its structure. The reaction between CO and CeO₂/¹⁸O-labeled La₂O₂SO₄ composites suggested that CO mainly reacted with the lattice oxygen atoms of CeO₂, and the resulting oxygen vacancies were subsequently filled with oxygen atoms supplied by La₂O₂SO₄. This oxygen gateway effect of CeO₂ greatly enhanced the oxygen release/storage rates of La₂O₂SO₄, while maintaining the high oxygen storage capacity, which is an advanced feature of oxysulfate materials. The synergistic effect is mostly pronounced when the two different oxygen storage materials are in intimate contact to form a three-phase boundary.

Inverse Oxide/Metal Catalysts in Fundamental Studies and Practical Applications: A Perspective of Recent Developments

Inverse oxide/metal catalysts have shown to be excellent systems for studying the role of the oxide and oxide-metal interface in catalytic reactions. These systems can have special structural and catalytic properties due to strong oxide-metal interactions difficult to attain when depositing a metal on a regular oxide support. Oxide phases that are not seen or are metastable in a bulk oxide can become stable in an oxide/metal system opening the possibility for new chemical properties. Using these systems, it has been possible to explore fundamental properties of the metal-oxide interface (composition, structure, electronic state), which determine catalytic performance in the oxidation of CO, the water-gas shift and the hydrogenation of CO2 to methanol. Recently, there has been a significant advance in the preparation of oxide/metal catalysts for technical or industrial applications. One goal is to identify methods able to control in a precise way the size of the deposited oxide particles and their structure on the metal substrate.

Nitrogen-doped carbon nanotube as a potential metal-free catalyst for CO oxidation

We elucidate the possibility of nitrogen-doped carbon nanotube as a robust catalyst for CO oxidation.

CuO/cryptomelane catalyst for preferential oxidation of CO in the presence of H2: deactivation and regeneration

Cryptomelane and CuO/cryptomelane catalysts have been tested in the preferential oxidation of CO in the presence of H₂ (CO-PROX reaction), paying special attention to deactivation and regeneration issues.

Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection

Surface defects of Fe-doped CeO₂ nanorods were found to be active sites for increasing peroxidase mimetic activity.

Highly efficient CuxO/TiO2 catalysts: controllable dispersion and isolation of metal active species

Cu_xO/TiO₂ architectures with enhanced dispersion of the active phase are synthesized by a MOF-templated method. Such composites show excellent catalytic activity for CO oxidation.

Catalytic activity of silicon carbide nanotubes and nanosheets for oxidation of CO: a DFT study

The use of SiC nanosheets and nanotubes as active metal-free catalysts is recommended for the oxidation of CO.

CeO2 decorated CuO hierarchical composites as inverse catalyst for enhanced CO oxidation

CeO₂ decorated CuO hierarchical composites were prepared and was used as inverse catalyst for enhanced CO oxidation.

Anchoring High-Concentration Oxygen Vacancies at Interfaces of CeO(2-x)/Cu toward Enhanced Activity for Preferential CO Oxidation

Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2-x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.

Methanol Adsorption and Reaction on Samaria Thin Films on Pt(111)

We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmO_x) grown on Pt(111) in ultrahigh vacuum. The methanol decomposition was studied by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), while structural changes of the oxide surface were monitored by low-energy electron diffraction (LEED). Methanol dehydrogenates to adsorbed methoxy species on both the continuous and discontinuous SmO_x films, eventually leading to the desorption of CO and H₂ which desorbs at temperatures in the range 400–600 K. Small quantities of CO₂ are also detected mainly on as-prepared Sm₂O₃ thin films, but the production of CO₂ is limited during repeated TPD runs. The discontinuous film exhibits the highest reactivity compared to the continuous film and the Pt(111) substrate. The reactivity of methanol on reduced and reoxidized films was also investigated, revealing how SmO_x structures influence the chemical behavior. Over repeated TPD experiments, a SmO_x structural/chemical equilibrium condition is found which can be approached either from oxidized or reduced films. We also observed hydrogen absence in TPD which indicates that hydrogen is stored either in SmO_x films or as OH groups on the SmO_x surfaces.

A density functional theory study of CO oxidation on CuO1-x(111)

The surface structures, CO adsorption, and oxidation-reaction properties of CuO1-x(111) with different reduction degree have been investigated by using density functional theory including on-site Coulomb corrections (DFT + U). Results indicate that the reduction of Cu has a great influence on the adsorption of CO. Electron localization caused by the reduction turns Cu(2+) to Cu(+), which interacts much stronger with CO, and the adsorption strength of CO is related to the electronic interaction with the substrate as well as the structural relaxation. In particular, the electronic interaction is proved to be the decisive factor. The surfaces of CuO1-x(111) with different reduction degree all have good adsorption to CO. With the expansion of the surface reduction degree, the amount of CO that is stably adsorbed on the surface increases, while the number of surface active lattice O decreases. In general, the activity of CO oxidation first rises and then declines.

Glutamine-assisted synthesis of Cu-doped CeO2 nanowires with an improved low-temperature CO oxidation activity

Glutamine (GLN)-assisted Cu-doped CeO₂ nanowires exhibit an outstanding performance for CO oxidation and can completely convert CO at 90 °C.

CO oxidation over Cu2O deposited on 2D continuous lamellar g-C3N4

The changing trend of adsorption ability and the catalytic activity of Cu₂O/g-C₃N₄ moved in the same direction.

Structural features and catalytic performance in CO preferential oxidation of CuO–CeO2 supported on multi-walled carbon nanotubes

MWCNT supported CuO–CeO₂ catalysts show enhanced performance in CO-PROX due to unusual structure features induced by interactions between metal oxides and MWCNT.

High-performance ZnCo₂O₄@CeO2₂₄ core@shell microspheres for catalytic CO oxidation

In this paper, we report a self-assembly method to synthesize high-quality ZnCo2O4@CeO2 core@shell microspheres with tunable CeO2 thickness. ZnCo2O4 spheres were first synthesized as the core, followed by a controlled CeO2 shell coating process. The thickness of CeO2 shell could be easily tuned by varying the feeding molar ratio of Ce/Co. Transmission electron microscope (TEM) images and scanning transmission electron microscope (STEM) image have identified the core@shell structure of these samples. In CO oxidation tests these ZnCo2O4@CeO2 core@shell microspheres exhibited promising catalytic performance, and the catalytic activity of the best sample is even close to the traditional noble metal-CeO2 system, attaining 100% CO conversion at a relatively low temperature of 200 °C. Cycling tests confirm their good stability of these core@shell microspheres besides activity. Their high catalytic performance should be attributed to the core@shell structure formation, and moreover further H2-temperature-programmed reduction (TPR) results revealed the possible synergistic effects between the two components of ZnCo2O4 and CeO2.