Mechanism Of CO Oxidation Research Articles

Operando XANES Reveals the Chemical State of Iron-Oxide Monolayers During Low-Temperature CO Oxidation.

We have used grazing incidence X-ray absorption near edge spectroscopy (XANES) to investigate the behavior of monolayer FeOxfilms on Pt(111) under near ambient pressure CO oxidation conditions with a total gas pressure of 1 bar. Spectra indicate reversible changes during oxidation and reduction by O2 and CO at 150ºC, attributed to a transformation between FeO bilayer and FeO2 trilayer phases. The trilayer phase is also reduced upon heating in CO+O2, consistent with a Mars-van-Krevelen type mechanism for CO oxidation. At higher temperatures, the monolayer film dewets the surface, resulting in a loss of the observed reducibility. A similar iron oxide film prepared on Au(111) shows little sign of reduction or oxidation under the same conditions. The results highlight the unique properties of monolayer FeO and the importance of the Pt support in this reaction. The study furthermore demonstrates the power of grazing-incidence XAFS for in situ studies of these model catalysts under realistic conditions.

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.

Boosting CO oxidation performance via reaction-induced single-atom active site: DFT and microkinetic investigation of a unified CO oxidation mechanism on Gd-doped ceria supported copper catalysts

Single-atom (SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities. However, SA catalysts are often plagued by the aggregation and deactivation of SA sites under reaction conditions. This study focuses on CO oxidation over Gd-doped ceria supported Cu catalysts and aims to provide a new strategy to stabilize the SA site, in which a Cu SA site is “prestored” in a relatively stable Cu cluster and can be dynamically activated under reaction conditions. Three typical Cu10/CeO2 catalyst models were built with different Gd-doping contents, which are pristine Cu10/CeO2, Cu10/Gd0.125Ce0.875O2, and Cu10/Gd0.25Ce0.75O2, respectively. We performed density functional theory (DFT) calculations on the Cu10/Gd-CeO2 system to investigate the adsorption of CO and O2 molecules, the formation of surface oxygen vacancy (OV) and dynamic Cu SA site, and potential energy surfaces of CO oxidation process. Ab initio thermodynamic analysis suggests that the saturation adsorption of CO on Cu10 and high Gd-doping in CeO2 lead to a spontaneously formed single Cu−CO site and an OV defect on ceria surface. The CO oxidation process is identified as a two-paths-coupled catalytic cycle, in which Path I is activated by the terminal O atom of adsorbed O2 at surface OV site while Path II initiates with the lattice O atom of CeO2 surface. The microkinetic modeling demonstrates that the dominant pathway is Path I for the undoped and low-doping cases, and Path II for the high-doping case which exhibits a novel mechanism for CO oxidation and the highest reaction activity due to the participation of the dynamic SA site.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Cover Feature: CO Oxidation Mechanism of Silver‐Substituted Mo/Cu CO‐Dehydrogenase – Analogies and Differences to the Native Enzyme (ChemPhysChem 13/2024)

Cover Feature: CO Oxidation Mechanism of Silver‐Substituted Mo/Cu CO‐Dehydrogenase – Analogies and Differences to the Native Enzyme (ChemPhysChem 13/2024)

Single‐Atom Catalysts Based on the Mo2CO2 MXene for CO Oxidation

AbstractThrough density functional theory calculations, the mechanism of CO oxidation to CO2 on single‐atom catalysts consisting of an atom of Ti, Fe, or Zn deposited on the surface of the Mo2CO2 MXene is investigated. In the case of Fe@Mo2CO2, a mechanism resembling that of Termolecular Langmuir–Hinshelwood (TLH) is thermodynamically and kinetically favored, displaying very exothermic CO2 formation, low activation energies, and easy CO2 desorption. On Ti@Mo2CO2, the dissociation of CO2 is almost barrierless and much more likely to occur than CO2 desorption, barring the usage of this surface as a catalyst for CO oxidation. Finally, on Zn@Mo2CO2, a hybrid Langmuir–Hinshelwood/Eley–Rideal (LH/ER) mechanism is thermodynamically and kinetically feasible. Here, after the first CO2 forms, with an energy barrier of only 0.62 eV, the second CO2 is formed spontaneously, and the Zn–CO2 interactions are weak enough to allow desorption. The calculated thermodynamic quantities and reaction rates at T = 300 K indicate that Fe@Mo2CO2 should be quite active toward CO oxidation, followed by Zn@Mo2CO2, while the Ti‐based model is inactive. The results add to the evidence that establishes single transition metal atoms adsorbed on MXene surfaces as cheap and easily obtainable catalysts that offer the best of both bare and functionalized MXenes.

Unveiling the mechanism of CO oxidation catalyzed by sulfur-doped fullerenes with the DFT calculations

As an important intermediate for dual carbon targets, catalytic CO oxidation under mild conditions has received sufficient attention, as the reaction mechanism is directly related to the type of employed catalyst. High performance computing is performed with density functional theory to elucidate the mechanism of CO oxidation catalyzed by sulfur doped fullerene (C60-xSx (x = 1 ∼ 3)). The total activation energy for the first CO oxidation on C59S, C58S2, and C57S3 increases gradually, as implies that the CO oxidation on C59S should be easier than those on the other two dopants. Distinct electrons (0.852 e and 1.479 e) are transferred to oxygen atoms (O2) from C59S with the adsorption of O2 and CO. There is no synergistic effect for the doping S atoms. All elementary reactions on C59S are exothermic processes. This means that C59S is a potential material for addressing environmental protection issues and H2 purification for fuel cell applications.

CO Oxidation Mechanism of Silver-Substituted Mo/Cu CO-Dehydrogenase - Analogies and Differences to the Native Enzyme.

The aerobic oxidation of carbon monoxide to carbon dioxide is catalysed by the Mo/Cu-containing CO-dehydrogenase enzyme in the soil bacterium Oligotropha carboxidovorans, enabling the organism to grow on the small gas molecule as carbon and energy source. It was shown experimentally that silver can be substituted for copper in the active site of Mo/Cu CODH to yield a functional enzyme. In this study, we employed QM/MM calculations to investigate whether the reaction mechanism of the silver-substituted enzyme is similar to that of the native enzyme. Our results suggest that the Ag-substituted enzyme can oxidize CO and release CO2 following the same reaction steps as the native enzyme, with a computed rate-limiting step of 10.4 kcal/mol, consistent with experimental findings. Surprisingly, lower activation energies for C-O bond formation have been found in the presence of silver. Furthermore, comparison of rate constants for reduction of copper- and silver-containing enzymes suggests a discrepancy in the transition state stabilization upon silver substitution. We also evaluated the effects that differences in the water-active site interaction may exert on the overall energy profile of catalysis. Finally, the formation of a thiocarbonate intermediate along the catalytic pathway was found to be energetically unfavorable for the Ag-substituted enzyme. This finding aligns with the hypothesis proposed for the wild-type form, suggesting that the creation of such species may not be necessary for the enzymatic catalysis of CO oxidation.

Study on the mechanism of CO oxidation and NO removal by CO-SCR over MFe2O4 (M=Co, Cu, Zn)

Study on the mechanism of CO oxidation and NO removal by CO-SCR over MFe2O4 (M=Co, Cu, Zn)

Progress of photocatalytic oxidation-adsorption synergistic removal of organic arsenic in water.

Photocatalytic oxidation-adsorption synergistic treatment of organic arsenic pollutants is a promising wastewater treatment technology, which not only degrades organic arsenic pollutants by photocatalytic degradation but also removes the generated inorganic arsenic by adsorption. This paper compares the results of photocatalytic oxidation-adsorption co-treatment of organic arsenic pollutants such as monomethylarsonic acid, dimethylarsinic acid, phenylarsonic acid, p-arsanilic acid, and 3-nitro-4-hydroxyphenylarsonic acid on titanium dioxide, goethite, zinc oxide, and copper oxide. It examines the influence of the morphology of organic arsenic molecules, pH, coexisting ions, and the role of natural organic matter. The photocatalytic oxidation-adsorption co-treatment mechanism is investigated, comparing the hydroxyl radical oxidation mechanism, the hydroxyl radical and superoxide anion radical cooxidation mechanism, and the hydroxyl radical and hole cooxidation mechanism. Finally, the future prospects of metal oxide photocatalytic materials and the development of robust and efficient technologies for removing organic arsenic are envisioned.

New perspectives of Pt–CeO2 system: stabilization on MWCNTs for boosting activity and water‐resistance in CO oxidation at ambient temperatures

The present study elucidates new perspectives regarding the Pt–CeO2 system for CO oxidation. The successful deposition of highly dispersed Pt–CeO2 species onto the surface of multiwalled carbon nanotubes (MWCNTs) led to the formation of abnormally active and water‐resistant catalysts. The catalysts were investigated by structural (XRD, TEM), spectral (XPS), and kinetic (TPR–CO+O2, TPR–CO, TPR–H2) methods. The application of TPR–CO+O2 revealed the remarkably high activity of all Pt–CeO2/MWCNTs catalysts at temperatures below 0 °C. The study of the catalysts at ambient temperature demonstrated high CO conversion in the presence of water vapor at a concentration of 100 ppm CO. The experimental findings suggest that active sites, comprising platinum structures stabilized directly on the surface of MWCNTs, play a pivotal role in the oxidation of CO under humid conditions. A dual–site approach was employed to develop a kinetic model that effectively describes the experimental data. This model provides valuable insights into the mechanism of wet CO oxidation.

SnO2-modified CuMnOx catalysts for humid CO oxidation at low temperature

Low-temperature CO oxidation has been widely applied in environmental pollution control, but challenges remain in CO purification in high-humidity environments. In this study, the CuMnSn8 catalyst exhibited excellent low-temperature CO oxidation performance, achieving complete CO oxidation at temperatures below 55 °C in 85 % relative humidity. A series of characterizations indicated that an appropriate amount of SnO2 doping could promote the formation of more amorphous oxides, increase the oxygen species content, and facilitate the dispersion of Cu and Mn elements. The catalytic active sites for CO oxidation and the influence of SnO2 doping on the CO oxidation mechanism were investigated through in-situ DRIFTS experiments. The results indicated that Sn enhanced the synergistic effect between Cu and Mn, altered the pathway of CO oxidation reaction, generated more easily decomposable bidentate carbonate intermediates. This work provides insight into the design of CO oxidation catalysts with high activity in high humidity.

Mechanistic insight into the catalytic CO oxidation and SO2 resistance over Mo-decorated Pt/TiO2 catalyst: The essential role of Mo

The problem of CO oxidation in incomplete combustion from steel industry is that the deactivation of Pt-based catalysts by SO2. Here, we have elaborately designed a series of Mo-decorated 0.1 wt.% Pt/TiO2 catalyst (Pt/Mo/Ti) catalyst. The catalytic test showed that the Pt/3Mo/Ti catalyst achieved 100 % CO conversion above 200 °C and maintained excellent long-term catalytic stability in the presence of SO2. The enhancement in SO2-tolerance ability was due to the suitable Brønsted acidity to weaken the SO2 adsorption and strong charge transfer ability to reduce the oxidation of SO2 to SO3. Aberration-corrected scanning transmission electron microscopy (STEM) suggests that the Pt-O-Mo species are present in atomically dispersed form in the Pt/3Mo/Ti catalyst. The surface O = MoO4 sites with terminal Mo = O bond prevented SO2 from reacting with platinum, thus inhibiting its migration to TiO2 and TiOSO4 formation. We also revealed the strong interaction between platinum and molybdenum and characterized the CO oxidation pathway in the presence of SO2. This research offers new insights into the mechanism of the catalytic CO oxidation and SO2 resistance over Mo-decorated Pt/TiO2 catalyst.

Removal of CO in flue gas by catalytic oxidation: a review

Abstract Most coal-fired industrial flue gases contained low concentration CO. How to deal with it effectively was a research hotspot in recent years. Catalytic oxidation was considered as the most promising method in the 21st century for the removement of CO with the high efficiency, environmentally friendly, easy to operate and low cost. In this review, the reaction mechanisms of CO oxidation were described, which could provide ideas for the development of new catalysts. The effects of supports and preparation methods on catalysts activity was also reviewed systematically. In addition, some suggestions and outlooks were provided for future development of CO catalytic oxidation.

Investigating NH3-SCR coupled with CO oxidation reaction mechanisms on titanium nanotube-loaded CuMnFe composite metal catalysts

NOx and CO are the primary air pollutants emitted from sintering flue gas, and their effective treatment is crucial. However, achieving good N2 selectivity with the CuMnFe composite metal oxide catalyst alone is challenging due to its oxidizing nature. Hence, in this study, titanium dioxide nanotubes were employed as carriers for the catalyst. CuMnFe composite metal oxide catalysts supported on titanium dioxide nanotubes were prepared using the co-precipitation method. The optimized catalysts demonstrated excellent performance, maintaining over 90% conversion of NOx and CO at low temperatures ranging from 120 to 200 ℃. Furthermore, significant improvement in N2 selectivity was achieved using these catalysts. Characterization results revealed several positive effects of incorporating titanium dioxide nanotube carriers into the catalyst. Firstly, it efficiently reduced the mobility of adsorbed oxygen on the catalyst surface, thus decreasing its oxidation capacity. Secondly, the addition of carriers helped balance the acidity on the catalyst surface, leading to an increase in Lewis acid sites. These modifications in the catalyst's surface properties proved advantageous for the selective catalytic reduction reaction. Moreover, the mechanisms of NH3-SCR and CO oxidation over the catalysts were extensively studied using DRIFTS. The results demonstrated that the CO oxidation reaction followed the Mars-van Krevelen mechanism, with a competitive adsorption relationship observed between O2 and CO at the active sites. On the other hand, the NH3-SCR reaction primarily followed the Eley-Rideal mechanism, with minimal occurrence of the Langmuir-Hinshelwood mechanism in the SCR reaction. The presence of NH3 inhibits CO adsorption at the active site, resulting in decreased CO oxidation performance in the NH3-SCR-coupled CO oxidation reaction at low temperatures. Nevertheless, NH3-SCR can enhance NO conversion by utilizing some of the latent heat generated from the exothermic CO oxidation.

Towards bridging thermo/electrocatalytic CO oxidation: from nanoparticles to single atoms.

Proton exchange membrane fuel cells (PEMFCs), as a feasible alternative to replace the traditional fossil fuel-based energy converter, contribute significantly to the global sustainability agenda. At the PEMFC anode, given the high exchange current density, Pt/C is deemed the catalyst-of-choice to ensure that the hydrogen oxidation reaction (HOR) occurs at a sufficiently fast pace. The high performance of Pt/C, however, can only be achieved under the premise that high purity hydrogen is used. For instance, in the presence of trace level carbon monoxide, a typical contaminant during H2 production, Pt is severely deactivated by CO surface blockage. Addressing the poisoning issue necessitates for either developing anti-poisoning electrocatalysts or using pre-purified H2 obtained via a thermo-catalysis route. In other words, the CO poisoning issue can be addressed by either thermal-catalysis from the H2 supply side or electrocatalysis at the user side, respectively. In spite of the distinction between thermo-catalysis and electro-catalysis, there are high similarities between the two routes. Essentially, a reduction in the kinetic barrier for the combination of CO to oxygen containing intermediates is required in both techniques. Therefore, bridging electrocatalysis and thermocatalysis might offer new insight into the development of cutting edge catalysts to solve the poisoning issue, which, however, stands as an underexplored frontier in catalysis science. This review provides a critical appraisal of the recent advancements in preferential CO oxidation (CO-PROX) thermocatalysts and anti-poisoning HOR electrocatalysts, aiming to bridge the gap in cognition between the two routes. First, we discuss the differences in thermal/electrocatalysis, CO oxidation mechanisms, and anti-CO poisoning strategies. Second, we comprehensively summarize the progress of supported and unsupported CO-tolerant catalysts based on the timeline of development (nanoparticles to clusters to single atoms), focusing on metal-support interactions and interface reactivity. Third, we elucidate the stability issue and theoretical understanding of CO-tolerant electrocatalysts, which are critical factors for the rational design of high-performance catalysts. Finally, we underscore the imminent challenges in bridging thermal/electrocatalytic CO oxidation, with theory, materials, and the mechanism as the three main weapons to gain a more in-depth understanding. We anticipate that this review will contribute to the cognition of both thermocatalysis and electrocatalysis.

Impact of catalyst support on water-assisted CO oxidation over PdO/MO2 (M = Sn, Ti, and Si) catalysts: experimental and theoretical investigation.

This study examines the impact of different supports, SnO2, TiO2, and SiO2, on the catalytic performance and water resistance of PdO-based catalysts for CO oxidation. By merging experimental data with DFT calculations, we reveal the distinct characteristics exhibited by each catalyst. Specifically, PdO/TiO2 stands out with exceptional CO oxidation activity, attributed to its minute Pd grain size, robust CO adsorption capacity, and optimal Pd dispersion on the TiO2 surface. In stark contrast, PdO/SnO2 demonstrates heightened activity in the presence of water vapor, whereas PdO/SiO2 experiences minimal effects, as evidenced by quantitative H2O-TPD analysis and DFT simulations of surface interactions. Water vapor exerts differential impacts on the catalytic performance of these catalysts by modulating the energy barriers associated with the CO oxidation mechanisms. On PdO/TiO2, the presence of H2O or H-OH elevates the energy barrier for CO to abstract surface oxygen, thereby diminishing catalyst activity under humid conditions and gradually leading to deactivation due to accumulated surface H2O and OH species. Conversely, on PdO/SnO2, when H2O is present in the form of OH, the energy barrier diminishes, augmenting CO oxidation activity owing to the beneficial effects of surface OH groups.

Theoretical investigation of the CO oxidation mechanism over Mn-corrole as a Single Atom Catalyst

Theoretical investigation of the CO oxidation mechanism over Mn-corrole as a Single Atom Catalyst

Diving into the interface-mediated Mars-van Krevelen (M−vK) characteristic of CuOx-supported CeO2 catalysts

The unique interface synergistic catalytic properties for metal oxide-supported catalysts have long been explored in several critical heterogeneous catalytic processes (e.g., CO oxidation reactions). However, interfacial synergistic catalysis is still a hitherto undescribed mechanism due to the lack of direct evidence at the atomic level. Thereinto, the CuOx-supported CeO2 (CuOx/CeO2) catalyst is a typical case. Herein, a combination study including representative theoretical calculations, in situ DRIFTS spectra and tailored molecular probe experiments supports a new carbonate-interface mediated Mars-van Krevelen (M−vK) mechanism for CO oxidation, i.e., CO molecules form carbonate intermediate species directly between spatial proximity (2.99 Å) double lattice oxygen sites with low oxygen vacancies formation energy (EformOv = 0.82 eV/0.83 eV) at the copper−ceria interface. The reaction energy barrier of this process is 0.32 eV, much lower than the 1.23 eV of the conventional M−vK mechanism. Besides, the spatial effect of double oxygen vacancies (Ov) generated by the depletion of intermediate carbonate species promotes the sustained and dynamic activation of O2, hence facilitating the efficient operation of the M−vK mechanism at low temperatures.

A New Mars‐van Krevelen Mechanism for CO Oxidation on a Ti‐Decorated MXene

AbstractFirst‐principles computations are performed to investigate the catalytic oxidation of CO on a Ti‐decorated Cr2TiC2O2 MXene monolayer, through comprehensive analysis of charge transfer, electronic density of states, and charge density difference of the interacting systems. By comparing the reaction energy barriers, it is found that, rather than the traditional Langmuir–Hinshelwood, Eley–Rideal, and Mars‐van Krevelen (MvK) mechanisms, the CO oxidation favours a new variant of the MvK mechanism, in which the anchored Ti atom activates the surface oxygen to spill over from the substrate and take part in the CO oxidation. This work highlights the importance of activating the surface oxygen atoms of MXene by foreign metal atoms to improve the catalytic activity, and suggests that further studies into the new MvK mechanism for CO oxidation may prove worthwhile.