First Principles Study on the CO Oxidation on Mn-Embedded Divacancy Graphene.

The mechanism of CO oxidation by O2 on a single Au atom supported on pristine, mono atom vacancy (m), di atom vacancy (di) and the Stone Wales defect (SW) on single walled carbon nanotube (SWCNT) surface is systematically investigated theoretically using density functional theory. We determine that single Au atoms can be trapped effectively by the defects on SWCNTs. The defects on SWCNTs can enhance both the binding strength and catalytic activity of the supported single Au atom. Fundamental aspects such as adsorption energy and charge transfer are elucidated to analyze the adsorption properties of CO and O2 and co-adsorption of CO and O2 molecules. It is found that CO binds stronger than O2 on Au supported SWCNT. We clearly demonstrate that the defected SWCNT surface promotes electron transfer from the supported single Au atom to O2 molecules. On the other hand, this effect is weaker for pristine SWCNTs. It is observed that the high density of spin-polarized states are localized in the region of the Fermi level due to the strong interactions between Au (5d orbital) and the adjacent carbon (2p orbital) atoms, which influence the catalytic performance. In addition, we elucidate both the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms of CO oxidation by O2. For the LH pathway, the barriers of the rate-limiting step are calculated to be 0.02 eV and 0.05 eV for Au/m-SWCNT and Au/di-SWCNT, respectively. To regenerate the active sites, an ER-like reaction occurs to form a second CO2 molecule. The ER pathway is observed on Au/m-SWCNT, Au/SW-SWCNT and Au/SWCNT in which the Au/m-SWCNT has a smaller barrier. The comparison with a previous study (Lu et al., J. Phys. Chem. C, 2009, 113, 20156-20160.) indicates that the curvature effect of SWCNTs is important for the catalytic property of the supported single Au. Overall, Au/m-SWCNT is identified as the most active catalyst for CO oxidation compared to pristine SWCNT, SW-SWCNT and di-SWCNT. Our findings give a clear description on the relationship between the defects in the support and the catalytic properties of Au and open a new avenue to develop carbon nanomaterial-based single atom catalysts for application in environmental and energy related fields.

The direct methanol fuel cell (DMFC) is considered as a promising power source, because of its abundant fuel source, high energy density and environmental friendliness. Among DMFC anode materials, Pt and Pt group metals are considered to be the best electrocatalysts. The combination of Pt with some specific transition metal can reduce the cost and improve the tolerance toward CO poisoning of pure Pt catalysts. In this paper, the geometric stabilities of PtFe/PdFe atoms anchored in graphene sheet and catalytic CO oxidation properties were investigated using the density functional theory method. The results show that the Pt (Pd) and Fe atoms can replace C atoms in graphene sheet. The CO oxidation reaction by molecular O2 on PtFe–graphene and PdFe–graphene was studied. The results show that the Eley–Rideal (ER) mechanism is expected over the Langmuir–Hinshelwood mechanism for CO oxidation on both PtFe–graphene and PdFe–graphene. Further, complete CO oxidation on PtFe–graphene and PdFe–graphene proceeds via a two‐step ER reaction: CO(gas) + O2(ads) → CO2(ads) + O(ads) and CO(gas) + O(ads) → CO2(ads). Our results reveal that PtFe/PdFe commonly embedded in graphene can be used as a catalyst for CO oxidation. The microscopic mechanism of the CO oxidation reaction on the atomic catalysts was explored.

Using density functional theory, we investigated the electronic properties of SiC monolayer and tested its catalytic activity toward CO oxidation. The planar nature of a SiC monolayer is found to stable and is a high band gap semiconductor. CO interacts physically with SiC surface, whereas O2 is adsorbed with moderate binding. CO oxidation on SiC monolayer prefers the Eley Rideal mechanism over the Langmuir Hinshelwood mechanism, with an easily surmountable activation barrier during CO2 formation. Overall metal free SiC monolayer can be used as efficient catalyst for CO oxidation.

We report a detailed theoretical investigation on the possible reaction mechanisms of CO oxidation catalyzed by a single Ti atom supported on divacancy defective graphene (Ti DVG ). The reaction between the adsorbed O 2 with CO molecules on Ti DVG is compared via three different mechanisms, i. e. Eley‐Rideal (ER), Langmuir‐Hinshelwood (LH) and termolecular Eley‐Rideal (TER). According to our results, the energy barrier for the rate determining step of CO + O 2 reaction in the TER mechanism is smaller than those of ER and LH ones. This can be attributed to the significant mixing of electronic states of adsorbed CO and O 2 at the reaction site, as well as due to a sizable charge‐transfer from the surface to these molecules. On the other hand, the calculated adsorption energies indicate that the coadsorption of O 2 and CO molecules is slightly more energetically favored with respect to the coadsorption of two CO molecules. This result together with the relatively small reaction barriers reveal that the LH mechanism is also possible to occur at low temperature. Our results reported here suggest that Ti DVG can be regarded as a green, low‐cost and highly active catalyst for CO oxidation at room temperature.

In recent decades,great expectation has always been placed oncatalysts that can convert toxic CO into CO2 under mildconditions. The catalytic mechanism of CO oxidation by Mn-coordinatedN-doped graphene with a single vacancy (MnN3-SV) and adouble vacancy (MnN3-DV) was studied by density functionaltheory (DFT) calculations. Molecular dynamics simulations showed thatCO2 on MnN3-SV could not be desorbed from thesubstrate and MnN3-SV was not suitable for use as a COoxidation catalyst. MnN3-DV was more suitable for CO oxidation(COOR) and from the electronic structure it was found that the Mnatom was the main active site, which was the reaction site for COoxidation. At temperatures of 0 and 298.15 K, CO oxidation on MnN3-DV via the Langmuir–Hinshelwood (LH) mechanism wasthe best reaction pathway. The rate-determining step using MnN3-DV as the catalyst for CO oxidation through the LH mechanismwas O2 + CO → OOCO, and the energybarrier was 0.861 eV at 298.15 K. MnN3-DV was suitableas a catalyst for CO oxidation in terms of both thermodynamics andkinetics. This study provides a comprehensive understanding of thevarious reaction mechanisms of CO oxidation on MnN3-DV,which is conducive to guiding the development and design of efficientcatalysts for CO oxidation.

Promoting reactivity of graphene based catalysts to achieve LH mechanism for CO oxidation

We have elucidated the mechanism of CO oxidation catalyzed by gold nanoparticles through first-principle density-functional theory (DFT) calculations. Calculations on selected model show that the low-coordinated Au atoms of the Au(29) nanoparticle carry slightly negative charges, which enhance the O(2) binding energy compared with the corresponding bulk surfaces. Two reaction pathways of the CO oxidation were considered: the Eley-Rideal (ER) and Langmuir-Hinshelwood (LH). The overall LH reaction O(2(ads)) + CO((gas)) --> O(2(ads)) + CO((ads)) --> OOCO((ads)) --> O((ads)) + CO(2(gas)) is calculated to be exothermic by 3.72 eV; the potential energies of the two transition states (TS(LH1) and TS(LH2)) are smaller than the reactants, indicating that no net activation energy is required for this process. The CO oxidation via ER reaction Au(29) + O(2(gas)) + CO((gas)) --> Au(29)-O(2(ads)) + CO((gas)) --> Au(29)-CO(3(ads)) --> Au(29)-O((ads)) + CO(2(gas)) requires an overall activation barrier of 0.19 eV, and the formation of Au(29)-CO(3(ads)) intermediate possesses high exothermicity of 4.33 eV, indicating that this process may compete with the LH mechanism. Thereafter, a second CO molecule can react with the remaining O atom via the ER mechanism with a very small barrier (0.03 eV). Our calculations suggest that the CO oxidation catalyzed by the Au(29) nanoparticle is likely to occur at or even below room temperature. To gain insights into high-catalytic activity of the gold nanoparticles, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis.

Mechanistic insight into the selective catalytic oxidation for NO and CO on co-doping graphene sheet: A theoretical study

Single–atom manganese and nitrogen co-doped graphene as low-cost catalysts for the efficient CO oxidation at room temperature

Cobalt oxide confined in mesoporous SiO2 as effective catalyst for CO oxidation

Boosting graphene reactivity with co-doping of boron and nitrogen atoms: CO oxidation by O2 molecule

Comparative Study on Redox Properties and Catalytic Behavior for CO Oxidation of CuO/CeO2 and CuO/ZrCeO4 Catalysts

Metal-supported cerium dioxide catalysts are widely used in industrial processes. This study investigates copper-cerium dioxide (Cu-CeO2) as a promising catalyst for CO oxidation, noted for its cost-effectiveness and low activation temperature. However, the reaction mechanism remains unclear. We examine the effects of copper ion doping into CeO2 nanoparticles at 0, 5, 15 at%, synthesized via precipitation. X-ray diffraction (XRD) analysis confirmed sample purity, revealing partial amorphization at a higher doping level. Lower Cu concentration in CeO2 facilitated CO oxidation at a lower temperature. X-ray absorption spectroscopy (XAS) investigated the electronic and atomic structures, showing that CeO2 with a lower Cu doping resulted in a higher lattice oxygen content and moderate Cu ion reduction. Increased Cu doping decreased Ce-O coordination numbers, while Cu-O radial distance was larger at lower doping. In situ XAS identified moderate reduction of Ce and Cu, elucidating CO oxidation via the Langmuir-Hinshelwood (LH) mechanism at lower Cu concentration. The superior low-temperature CO oxidation performance is attributed to moderate Ce and Cu ion reduction coupled with increased oxygen adsorption on the catalyst surface. These findings provide insights into the relationship between the dopant concentration, electronic structure, and catalytic activity for optimizing ceria-based catalysts for efficient CO oxidation.

The mechanism of CO oxidation on the WO3(001) surface for gas sensing performance has been systematically investigated by means of first principles density functional theory (DFT) calculations. Our results show that the oxidation of CO molecule on the perfect WO3(001) surface induces the formation of surface oxygen vacancies, which results in an increase of the surface conductance. This defective WO3(001) surface can be re-oxidized by the O2 molecules in the atmosphere. During this step, the active O2− species is generated, accompanied with the obvious charge transfer from the surface to O2 molecule, and correspondingly, the surface conductivity is reduced. The O2− species tends to take part in the subsequent reaction with the CO molecule, and after releasing CO2 molecule, the perfect WO3(001) surface is finally reproduced. The activation energy barriers and the reaction energies associated with above surface reactions are determined, and from the kinetics viewpoint, the oxidation of CO molecule on the perfect WO3(001) surface is the rate-limiting step with an activation barrier of about 0.91 eV.

The geometry, electronic structure, and catalytic properties of nitrogen- and phosphorus-doped graphene (N-/P-graphene) are investigated by density functional theory calculations. The reaction between adsorbed O2 and CO molecules on N- and P-graphene is comparably studied via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. The results indicate that a two-step process can occur, namely, CO+O2 →CO2 +Oads and CO+Oads →CO2 . The calculated energy barriers of the first step are 15.8 and 12.4 kcal mol(-1) for N- and P-graphene, respectively. The second step of the oxidation reaction on N-graphene proceeds with an energy barrier of about 4 kcal mol(-1) . It is noteworthy that this reaction step was not observed on P-graphene because of the strong binding of Oads species on the P atoms. Thus, it can be concluded that low-cost N-graphene can be used as a promising green catalyst for low-temperature CO oxidation.