Catalytic Oxidation Of CO Research Articles

Decoration of CeO2 nanoparticles on Cu/Co bimetallic oxide and their catalytic performance

We have developed a series of Co-Cu bimetallic oxide nanocatalysts using an environmentally friendly water phase synthesis method, demonstrating significant potential in catalyzing the CO oxidation reaction. The 0.3Co3O4/0.7CuO nano-hybrid, with a feed ratio of 3:7 for Cobalt(II) chloride hexahydrate to Copper(II) chloride dihydrate, exhibited a CO catalytic oxidation T90 approximately 70 °C lower than that of a single transition metal oxide material. Building on this, we enhanced the catalysts by incorporating CeO2 nanoparticles to produce Co3O4/CuO/CeO2 oxide nanocatalysts. By varying the amount of CeO2 nanoparticles added to the 0.3Co3O4/0.7CuO catalyst, we achieved further improvement in the CO oxidation performance. Specifically, the T90 of the CO catalytic oxidation reaction for the 0.3Co3O4/0.7CuO/0.7CeO2 material was approximately 30 °C lower than that of 0.3Co3O40.7CuO. Various characterization methods, such as XRD, EDX, and in situ FT-IR, were employed to investigate the impact of different components on the CO oxidation process and the potential reaction mechanism. The results indicated that the introduction of CeO2 successfully enhanced the activity and stability of the catalysts.

Geometrical features and chemical adsorptions of (Ag3Sn)n clusters

The Ag-Sn alloys are famous ancient intermetallics, with the Ag3Sn being a crucial component of the phase diagram. Recently, Ag3Sn nanoparticles showcase efficient catalytic CO oxidation capabilities. Here, structural features and stability of (Ag3Sn)n (n = 1–6) clusters are first analyzed in detail. The results reveal that structures of them evolve from cages to close-packed icosahedra, where Ag are distributed on cores and gradually aggregated, whereas Sn occupy edge positions and become dispersed. Moreover, the icosahedral (Ag3Sn)3 has a higher stability than that of its neighbors and can maintain the structural integrity at 700 K. The molecular orbitals reveal that the (Ag3Sn)3 has an electronic open-shell configuration of 1S21P61D102S21F1, which is confirmed by the density of states. Electrostatic potential surfaces show that (Ag3Sn)n have significant electron-deficient σ-hole regions at Ag sites, which can make CO stretching frequencies and bond lengths have red-shifts. Adsorption energies between (Ag3Sn)n and CO display odd–even oscillations, ranging from (0.43–0.68) eV, and the direction of charge flows is from CO → clusters. Our work provides inferences to structure evolutions and adsorptions of the Ag3Sn alloy at the atomic level.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation.

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity-stability trade-off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas-catalyst-support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25 - 500 °C under dry conditions and 200 - 800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation

AbstractSupported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity‐stability trade‐off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas‐catalyst‐support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25‐500 °C under dry conditions and 200‐800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Catalytic oxidation of CO over CuO@TiO2 catalyst: The relationship between activity and adsorption performance

AbstractThe emission of CO toxic gases seriously endangers environmental safety and human health. At present, the use of catalysts for catalytic oxidation of CO has become the mainstream research direction. In this study, CuO@TiO2 catalysts with different ratios were prepared by solvent hydrothermal method, and the effects of reaction pretreatment temperature and other factors on the catalytic oxidation performance of CO were investigated. The experimental results show that the catalyst can achieve 100% conversion of CO at 115°C under the condition of pretreament at 350°C for 2 h. This excellent performance is due to the uniform distribution of the active component on the surface of the TiO2 support, and the large pore structure constructed by the solvent hydrothermal method enhances the adsorption and activation of CO. This work provides an idea for the preparation of CO oxidation catalysts.

Staggered distribution structure Cu-Mn catalysts for mitigating smoke and gas toxicity in combustion: Unravelling mechanistic insight through operando studies

The integration of flame retardancy and environmental friendliness can be achieved by designing cost-effective, stable, and efficient catalysts to reduce smoke and toxicity during the combustion of polymeric materials. This work reports the development of non-precious metal catalysts for thermoplastic polyurethanes (TPU), which exhibit a significant reduction in smoke and gases toxicity while providing flame retardancy. The use of MgB2 as a support enables the in-situ growth of highly efficient Cu-Mn based catalysts, resulting in a remarkable 51.5 % decrease in total smoke release and a 49.1 % reduction in peak rate of CO generation of TPU according to cone calorimeter test results. Furthermore, Cu-Mn/MgB2 demonstrates an impressive 83.1 % reduction in total CO production rate during the steady-state tube furnace test. Additionally, density functional theory is employed to analyze the binding energy between catalysts and TPU as well as the adsorption energy of gases. This elucidates the rational reaction mechanism behind the catalyst and smoke inhibiting process. By combining transition metal oxide catalyzed CO oxidation reaction with polymeric material combustion, this study presents a promising approach for efficient smoke suppression with potential applications.

Catalytic Co-oxidation of Dichloromethane and non-chlorinated VOC over HxPO4-RuOx/CeO2, Pt/HZSM-5 and dry-mixed Ru-Pt Catalysts

Industrial flue gases contain chlorinated VOCs (CVOCs) and hydrocarbons, along with various contaminants. Although previous studies have primarily focused on the catalytic oxidation of individual VOCs, the activity of VOCs in mixtures often differs from that of individual compounds. The catalytic oxidation of dichloromethane in the presence of a second VOC (ethyl acetate, n-hexane, and toluene) was investigated using HxPO4-RuOx/CeO2, Pt/HZSM-5, and dry-mixed Pt-Ru catalysts. The dry-mixed catalyst combines the excellent dechlorination ability of HxPO4-RuOx/CeO2 with the oxidation capability of Pt/HZSM-5. A mixture of 1000 ppm toluene and 100 ppm dichloromethane is fully oxidized over the Ru-Pt catalyst at 300 °C, 30 °C lower than the T100 observed on the other two catalysts. DFT calculation reveals that the activation of toluene and dichloromethane occurs on Pt and Ru sites, respectively, dechlorinated by proton of phosphate. Furthermore, by-product dioxin content on Pt-Ru is significantly below 0.1 ng TEQ Nm−3 limit.

Two Different Atomically Dispersed Pt Atoms Supported on Ceria.

Atomically dispersed metals on oxide supports with different distribution positions or coordination environments can dictate the reactivity; they have therefore attracted tremendous attention recently. Nonetheless, the acknowledging and understanding of different single atoms remain challenging due to the reactivity controversy of the supported single atoms and clusters or nanoparticles, particularly on the widely used ceria supports. Herein, by modulating the loading amount of Pt single atoms carefully with strong electrostatic adsorption on conventionally synthesized ceria supports, we obtained two different atomically dispersed Pt atoms with similar Pt-O coordination environments and CO adsorption characteristics. One is anchored on the surface of ceria, and it can migrate and aggregate once activated with reduction-reoxidation treatments. The other may be trapped by the surface defects or vacancies in ceria and would be fixed on the ceria support firmly in isolated states during activation. Despite the similar CO adsorption during the reaction, the former can catalyze CO oxidation in both the status of single atoms and aggregated PtOx clusters. However, the latter is inactive for the reaction and would not be affected by the activation treatment. It cannot involve the CO oxidation, resulting in the waste of supported Pt atoms.

Mesostructured manganese oxides for efficient catalytic oxidation of CO, ethylene, and propylene at mild temperatures: Insight into the role of crystalline phases and physico-chemical properties

Removing pollutants for indoor air purification is a key point to ensure the health and well-being of people in confined environments. This work aims to provide new insight into the development of promising manganese oxide catalysts. The effects of different crystalline phases (MnO2 and Mn2O3) and the role of redox properties and structural defects were investigated to abate indoor pollutants at mild temperatures. These materials were extensively characterized through complementary techniques and catalytic tests were performed to oxidize 100 ppm of CO, ethylene, or propylene. The most promising catalyst was obtained through solution combustion synthesis, achieving total removal at 118, 222, and 172 °C, respectively, with the highest oxidation rate (2.41, 0.88, and 2.47 μmolg−1s−1) and lowest activation energy (50, 32, and 45 kJmol−1) for the three molecules. The synergy between crystalline phases enhanced the catalytic performance and their distribution in the structure was a crucial parameter affecting the number of structural defects.

Catalytic oxidation of Mn(II) in the co-presence of Fe(II) by free chlorine: significance of in situ formed Mn(II)-doped Fe(III) oxides

Fe(II) and Mn(II) are abundant in groundwater and require operationally simple and efficient method to remove in drinking water treatment. The rapid oxidation of Mn(II) is essential in water treatment. This study investigates the efficiency of Mn(II) oxidation by free chlorine in the presence of Fe(II). The results demonstrate that the presence of Fe(II) significantly accelerates the oxidation rate of Mn(II) by free chlorine under neutral and alkaline conditions. The rapid oxidation of Fe(II) by free chlorine and the presence of Mn(II) promote the formation of in situ Mn(II)-doped ferrihydrite. Kinetic modeling and characterization of Fe(III) oxides confirm that the heterogeneous catalytic effect of the Mn(II)-doped ferrihydrite, rather than manganese oxides or their coupled catalytic effect, is responsible for the enhanced oxidation rates. The doped Mn(II) substitutes the tetrahedral Fe(III) ions in the ferrihydrite, introducing additional negative charges at the doped sites. The increased charge enhances Mn(II) adsorption and lowers its redox potential, thereby accelerating Mn(II) oxidation rate through direct electron transfer with adjacent free chlorine. Additionally, the lepidocrocite formed by the reaction between Fe(II) and dissolved oxygen significantly impedes the catalytic performance. These findings provide new insights into the catalytic co-oxidation mechanism of Fe(II) and Mn(II), and help the optimization of water treatment engineering practices.

Efficient low-temperature CO removal from high-humidity sintering flue gas by combination Cu and OMS-2

The non-precious metal manganese-based catalysts currently show insufficient CO catalytic oxidation performance in actual sintering flue gas conditions, with increased water vapor levels causing catalyst deactivation. This study utilized a high-performance manganese dioxide octahedral molecular sieve (OMS-2). The effect of metal doping on the catalytic CO oxidation performance was investigated in preparing OMS-2 using the co-precipitation method. The experiments showed that Cu doping increased CO conversion efficiency more than other metals (Co, Ag, Zn, and Fe), with optimal performance achieved at a 1.91 wt% doping level. Besides, Cu doping significantly enhanced water resistance of the catalyst, enabling effective CO removal in high-humidity conditions. The study observed that Cu ions infiltrated the catalyst framework by substituting some of the Mn ions, creating additional active sites in the form of oxygen vacancies and improving surface oxygen mobility, thereby enhancing the performance of CO catalytic oxidation. Furthermore, Cu doping demonstrated selective absorption of water vapor, with CuxO in the catalyst, effectively adsorbing water vapor and protecting the initial active sites, thereby mitigating water vapor-induced poisoning. Even in 15 vol% H2O at 150 °C, 1.91%Cu-OMS-2 maintained total catalytic activity. Therefore, the co-precipitation method-prepared 1.91%Cu-OMS-2 catalyst holds excellent potential for CO removal in sintering flue gas and shows promise for practical applications.

CoFe Oxides-Coated 2D Black Phosphorus for Flame-Retardant Nanocoatings with Tunable Mechanical Strength and Efficient Elimination of Toxic Gases.

2D black phosphorus (BP) degrades irreversibly into phosphate compounds under ambient conditions, which limits its application in a variety of fields. In this study, by coating amorphous ferric-cobalt oxides (CoFeO)on BP nanosheets, a multifunctional CoFeO@2D BP is successfully developed that effectively inhibited combustion and catalyzed CO oxidation to eliminate toxic gases. Strong affinity between transition-metal cations and BP allowed the uniform growth of amorphous ferric‒cobalt oxides on the BP surface, which effectively prevented the spontaneous degradation of 2D BP. By combining CoFeO@2D BP with gelatin and kosmotropic salts, the as-obtained nanocoatings are used for surface treatment of flammable polyurethane foam (PU). Kosmotropic ions induced strong hydrophobic interactions and bundling within the gelatin chains which significantly enhanced the mechanical performance of the PU. BP accelerates the carbonization of gelatin to inhibit the combustion of PU, and CoFe oxides, which act as true active centers to accelerate the oxidation of CO, effectively inhibiting the production of harmful gas. The release rate of CO decreases by 73% and the limiting oxygen index (LOI) increases from 17% to ≈32% during PU combustion. The developed novel 2D material opens the way for multifunctional coatings with integrated durability, flame retardancy, and high smoke suppression efficiency.

X-ray and photoelectron spectroscopy of surface chemistry; from bonding via femtosecond to operando

For the 60th anniversary of Surface Science, I present here a personal account of some of the most significant contributions I have made to the field over the past three decades. The utilisation of X-rays serves as the foundation for these studies, encompassing X-ray spectroscopy for the mapping of surface chemical bonds, probing of surface reactions on ultrafast timescales, and X-ray photoelectron spectroscopy under operando conditions. The direct projection of electronic states onto the adsorbed atom allowed the detection of bonding and anti-bonding states within the d-band model. The selective probing of orbitals of different symmetries on the two atoms in adsorbed N2 provided a fundamental understanding of the nature of diatomic bonding to surfaces. Ultrafast optical pumping and X-ray laser techniques allowed the study of CO undergoing desorption leading to the observation of the precursor state. Pump-probed studies of co-adsorbed CO and O on Ru enabled the means to detect transition state species during catalytic CO oxidation. The use of operando X-ray photoelectron spectroscopy at near-atmospheric pressures opened the door to probe the surface chemistry and gain insight into the reaction mechanism during hydrogenation reactions to produce ammonia, hydrocarbons, methanol and ethanol. By inserting an electrochemical cell into the spectroscopic chamber, both fuel cell and water splitting electrocatalysis could be studied giving insight about the reaction mechanism.

Enhanced Low‐Temperature Oxidation Activity of Cu‐Doped Highly Active Pd‐Based Catalysts

AbstractPd‐based catalysts supported on cerium–zirconium (CZ) oxygen storage materials (OSM) have emerged as promising candidates for the catalytic oxidation of CH4 and CO. However, achieving efficient and stable treatment of CH4 and CO in exhaust gases with Pd‐based catalysts remains a long‐term challenge. To address this, we propose a straightforward strategy of doping the supports with Cu to enhance the catalytic performance of Pd/Ce0.4Zr0.5La0.1O1.95 catalysts. Performance tests revealed that the catalytic activity of the Cu‐doped catalysts significantly improved, with T90 (CH4) decreasing from 418–301 °C and T90 (CO) decreasing from 141–113 °C. Notably, the copper‐doped catalysts exhibited enhanced water and sulfur resistance while maintaining excellent thermal stability. The CO conversion decreased by less than 2 % after a thermal deactivation experiment lasting over 100 hours. The reduction in particle size and the increase in specific surface area due to copper doping are key factors contributing to the improved total oxygen storage capacity (OSC). The main reasons for the increase in total OSC are likely the reduced particle size and increased specific surface area.

Geometrical features, stability and electronic properties of (Cu3Sn)n clusters

Recently, significant advancements have been made in low-entropy Cu3Sn catalysts, showcasing their efficient catalytic CO oxidation capabilities. Hence, the atomic models of the Cu3Sn are worth established to further investigate their catalytic mechanisms. Here, the structural features and stability of (Cu3Sn)n clusters (n = 1–6) are investigated using the genetic algorithm combined with the density functional theory (DFT). The results reveal the structural evolution of these clusters from hollow cages to compact icosahedrons, where Cu atoms predominantly tend to grow together, while Sn atoms are dispersed at the edge positions. The Eb, Ef and Δ2E analyses show that the icosahedral (Cu3Sn)3 has a higher stability than that of its neighbors. The molecular dynamics simulations demonstrates its stability even at 1000 K. The molecular orbitals and density of states reveal that the (Cu3Sn)3 has an 1S21P61D102S21F1 superatomic electronic configuration. Electrostatic potential surfaces show that (Cu3Sn)n clusters have significant σ-hole regions at the Cu atomic sites, which can make the CO stretching frequency and bond length have a large red-shift. Moreover, the adsorption energy between the (Cu3Sn)3 and CO is the largest, reaching 1.17 eV. Our work provides inferences to the structural characteristics and adsorptions of the CuSn alloys at the atomic level.

One-step synthesis of Pt@(CrMnFeCoNi)3O4 high entropy oxide catalysts through flame spray pyrolysis

High entropy oxides (HEOs) show great prospects in catalysis owing to their widely tunable component structures and ease of combination with active metals. However, the development of HEO catalysts is limited by the lack of efficient synthesis methods due to the difficulty of homogeneously mixing at least five elements. In this work, flame spray pyrolysis (FSP) is successfully employed to synthesize (CrMnFeCoNi)3O4 HEO with a single phase spinel structure in one step, which is verified by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy-dispersive X-ray spectroscopy (EDS). Taking CO catalytic oxidation as a probe reaction, the Pt@(CrMnFeCoNi)3O4 HEO catalyst synthesized by FSP in one step is compared with the catalyst whose Pt is impregnated on (CrMnFeCoNi)3O4 HEO support. The FSP-made catalysts have a higher catalytic reaction rate and better redox ability, which lowers the temperature of complete CO conversion by nearly 100 °C. Furthermore, it can be observed that the flame parameters can be optimized to modify the particle size and oxygen vacancies of the HEO nanoparticles, thus enhancing the catalytic performances. This work demonstrates that FSP is an effective method for the one-step synthesis of HEO catalysts with excellent catalytic performance, providing a new perspective for the synthesis of HEO-based materials.

Synthetic opal decorated by Co and Ce oxides as a nanoreactor for the catalytic CO oxidation

Macroporous synthetic opal grown from non-porous silica nanoparticles and decorated by Co and Ce oxides was applied for the catalytic CO oxidation in the inert (TOX) and H2-rich (PROX) gas mixtures. Prepared materials were studied by methods of SEM, TEM, EDX, XRD, XPS and FTIR spectroscopy. The relationship between synthesis conditions, structure, and catalytic behavior of composites is discussed. The best Co-O-Ce interaction and the highest activity in the CO-TOX and PROX are achieved when cerium oxide was added prior to the addition of cobalt oxide. In this case highly dispersed particles of Co3O4 and CeO2 are located in close proximity on the silica surface and anchored between the opal spheres. The use of Co/Ce decorated synthetic opal as a nanoreactor for the catalytic oxidation of CO in the H2 excess makes it possible to achieve 99.5 % conversion of CO at 150°C, the high efficiency and selectivity of the process are maintained in multiple cyclic tests in heating and cooling modes. The synergistic activity of Co and Ce oxides was observed when they both were located together on the outer surface of non-porous SiO2 nanospheres. These results are superior to known data for other catalysts based on Co and Ce oxides.

The effect of SO2 on NH3-SCR reaction synergistic CO oxidation over a Mn-Co-Ti catalyst

Mn–Co–TiO2 prepared using an impregnation method was applied to synergistic NH3-based selective catalytic reduction (NH3-SCR) and CO oxidation in a simulated flue gas. The NO conversion, NO oxidation, and CO oxidation were substantially enhanced after adding 15% Co3O4 to the 20MnTi catalyst. In an NO or NO + NH3 atmosphere, CO oxidation over the Mn–Co–TiO2 catalyst was mainly restrained by the competitive adsorption and formation of sulfate species. In contrast, the NH3-SCR reaction progressed almost unimpeded in a CO atmosphere. A SO2 atmosphere drastically reduced the NO conversion of the catalyst at lower temperatures and almost completely suppressed the oxidation activities toward NO and CO. The amount of remaining NO oxidation (approximately 10%) was primarily contributed by gas-phase oxidation of NO by O2. Next, fresh and SO2-poisoned Mn–Co–TiO2 were characterized using various methods. Results indicated that no conspicuous change occurred in the crystal structure of the samples after SO2 poisoning, but numerous sulfate products were deposited on the catalyst surface. The deposition of sulfate-species byproducts decreased the specific surface area and pore volume of the catalyst and shifted the surface acid sites to a higher temperature range, further reducing the CO oxidation performance. Moreover, the catalytic reaction of CO and NO followed the Eley–Rideal mechanism. Furthermore, the mechanisms through which multicomponent flue gases influence the synergistic NH3-SCR and CO oxidation performance were proposed.

Highly efficient Rh-doped MnO2 nanocatalysts for complete elimination of CO at room temperature.

Obliteration of carbon monoxide is significant due to its hazardous effect on human health and potential application in different fields. Catalytic CO oxidation at lower temperature is the most convenient method to diminish the toxicity of CO. The low-cost catalysts which are exhibiting higher activity at lower temperature with good stability are in demand. The nanosized Rh-doped MnO2 catalysts have been prepared by dextrose-assisted co-precipitation method. Catalytic CO oxidation reaction was carried out over these prepared nanocatalysts under environmentally suitable conditions. XRD confirms the phase formation of prepared catalysts. These samples exhibit rod-like morphology with thickness of rods of less than 10nm which is substantiated from electron microscopy images. XPS data reveals the oxidation state of Mn (+ 4) and Rh (+ 3). These catalysts are highly active for CO oxidation reaction at lower temperature, and one showed complete CO conversion at room temperature. The time-on-stream studies revealed that these catalysts are highly stable for CO oxidation for several hours. These catalysts are decidedly stable in moist condition and also showed higher activity in the presence of moisture, indicating participation of moisture in the oxidation reaction at above room temperatures.

Enhanced low-temperature CO oxidation activity through crystal facet engineering of Pd/CeO2 catalysts

Cerium dioxide (CeO2) supported palladium (Pd) catalysts have found widespread application in CO oxidation reaction owing to their exceptional catalytic performance. The morphology of the CeO2 support dictates the exposed crystal plane, exerting a profound influence on surface structure and redox properties. This is crucial as the atomic arrangement at the surface directly impacts catalytic activity. In this study, a range of CeO2 supports with diverse morphologies (e.g. nano-octahedra, nano-cubes, nano-particles, nano-spheres, and nano-rods) were successfully synthesized through hydrothermal methods and subsequently supported with Pd for CO oxidation. The spherical 1Pd/CeO2–S catalyst, revealing exposed (111) + (100) crystal planes, exhibited significantly higher CO catalytic oxidation activity compared to the catalysts with other morphological CeO2 supports. The results indicated a positive correlation between the content of PdxCe1-xO2-y species and catalytic activity. Notably, this species was most abundantly formed in the spherical 1Pd/CeO2–S catalyst with exposed (111) + (100) crystal planes. The presence of this active species facilitated the formation of surface defects, increased oxygen vacancy concentration, and enhanced metal-support interaction, consequently greatly improving the CO low-temperature catalytic oxidation activity. Consequently, the oxidation state of Pd in the Pd/CeO2 catalyst could be effectively regulated by controlling the exposure of (111) + (100) crystalline surfaces of the CeO2 support, further optimizing the catalytic performance of the Pd/CeO2 catalytic system.