Reaction Mechanism For CO Oxidation Research Articles

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.

Influence of Time Scale on the Reaction Mechanism of CO Oxidation over a Au/TiO2 Catalystt.

Knowledge of the reaction mechanism is key for rational catalyst improvement. Traditionally mechanistic studies focus on structure and the reaction conditions like temperature, pH, pressure, etc, whereas the time dimension is often overlooked. Here, we demonstrate the influence of time on the mechanism of a catalytic reaction. A dual catalytic mechanism was identified for the CO oxidation over Au/TiO2 by time-resolved infrared spectroscopy coupled with modulation excitation spectroscopy. During the first seconds CO on the gold particles is the only reactive species. As the reaction proceeds the redox properties of TiO2 dominate the catalytic activity through electronic metal-support interaction (EMSI). CO induces the reduction and reconstruction of TiO2 whereas oxygen leads to its oxidation. The activity of the catalyst follows the spectroscopic signature of the EMSI. These findings demonstrate the power of studying the short-time kinetics for mechanistic studies.

Theoretical investigation on CO oxidation by single nickel atom within two-dimensional porphyrin sheet

Catalysts for CO oxidation are usually precious metals, whose high cost restricts their widespread use. In order to reduce costs and improve catalytic activity, a two-dimensional porphyrin sheet with single nickel atoms (Ni−TDPS) was used as a catalyst for CO oxidation, and the detailed reaction path was studied by DFT. The stability of Ni−TDPS was determined by AIMD simulations. Three typical reaction mechanisms of CO oxidation on Ni−TDPS were discussed, including LH, ER, and TER mechanisms. The results showed that the TER mechanism is feasible due to the minimum reaction energy barrier in the rate-determining step. Therefore, Ni−TDPS is a potential candidate catalyst for CO oxidation in theory.

CO oxidation mechanism on surfaces of B-site doped SrFeO3-δ-based perovskite materials for thermochemical water splitting

Density functional theory (DFT) calculations were performed to explore the reaction mechanism of CO oxidation on both the perfect and O pre-adsorbed surfaces of B-site (B = Al, Zr, Nb and W) doped SrFeO3-δ-based perovskite materials. Our calculations showed that metal doping benefited the adsorption of molecular CO over the perfect surface, while it inhibited the adsorption of molecular CO over the O pre-adsorbed surface. The reaction of CO with lattice oxygen of SrFeO3 was inhibited with the doping of Zr, Nb and W, but promoted by the doping of Al. The reaction of CO with surface pre-adsorbed O of SrFeO3 was found to be thermodynamically inhibited by the doping of Al, Zr, Nb and W. This study provided significant insights into the interaction of CO with the surfaces of doped SrFeO3-δ perovskite materials for thermochemical water splitting applications.

Insight into the Effect of Oxygen Vacancy Prepared by Different Methods on CuO/Anatase Catalyst for CO Catalytic Oxidation

In this study, CuO loaded on anatase TiO2 catalysts (CuO/anatase) with oxygen vacancies was synthesized via reduction treatments by NaHB4 and H2 (CuO/anatase-B, CuO/anatase-H), respectively. The characterizations suggest that different reduction treatments bring different concentration of oxygen vacancies in the CuO/anatase catalysts, which finally affect the CO catalytic performance. The CuO/anatase-B and CuO/anatase-H exhibit CO conversion of 90% at 182 and 198 °C, respectively, which is lower than what occurred for CuO/anatase (300 °C). The XRD, Raman, and EPR results show that the amount of the oxygen vacancies of the CuO/anatase-H is the largest, indicating a stronger reduction effect of H2 than NaHB4 on the anatase surface. The in situ DRIFTS results exhibit that the Cu sites are the adsorption sites of CO, and the oxygen vacancies on the anatase can active the O2 molecules into reactive oxygen species. According to the in situ DRIFTS results, it can be concluded that in the CO oxidation reaction, only the CuO/anatase-H catalyst can be carried out by the Mvk mechanism, which greatly improves its catalytic efficiency. This study explained the reaction mechanisms of CO oxidation on various anatase surfaces, which offers detailed insights into how to prepare suitable catalysts for low-temperature oxidation reactions.

Surface engineered active Co3+ species in alkali doped Co3O4 spinel catalyst with superior O2 activation for efficient CO oxidation

CO oxidation is one of the most extensively investigated fields of research as it takes prime importance in environmental fortification and is highly challenging to explore efficient heterogeneous catalysts to achieve effectual conversion. In the present work, Co3O4 and alkali metal-doped Co3O4 spinel materials were obtained by the co-precipitation method and employed as suitable catalysts for CO oxidation. The catalysts were prepared by calcining the precipitated hydroxides of Co at 300°C, and 800°C (with and without the presence of water vapor) in the air atmosphere. The synthesized materials were characterized by powder X-ray diffraction, N2-sorption analysis, H2-TPR, SEM, and XPS techniques. Then the catalytic activity of catalysts is evaluated for CO oxidation using molecular O2 as an oxidizing agent. The effect of thermal treatment and also the role of alkali metal in CO oxidation are studied. The promotional effect of alkali (Li, Na, and K) in Co3O4 materials was observed with higher CO conversion, where the influence of Li ions in the Co3O4 catalyst was far greater than in other doped catalysts. Definite characteristics, nature of alkali-doped catalysts, and oxidative influence involved in CO oxidation reaction mechanism were carefully studied. In a general perspective, this work shows the influence of surface properties of alkali ion-doped Co3O4 spinel catalysts that consequently control the reactivity toward CO oxidation.

Electronic and catalytic properties of Ti single atoms@SnO2 and its implications on sensing mechanism for CO

Inspired by the unprecedented catalyzing effect of single-atom catalysts, the atomically scattered Ti single-atom significantly enhancing the CO sensing performance of the SnO2(110) are investigated by using DFT-D calculations. The Ti single-atom prefers to stay on the top layer of six-fold Sn atoms. Two reaction mechanisms for CO oxidation are found on the Ti single-atom doped SnO2(110) with the moderate reaction barriers of 0.53 eV (Path I) and 0.83 eV (Path II), respectively for the rate-determining steps. The Ti single-atom doped SnO2(110) can be active and selective sensing catalyst for CO oxidation with their activation barrier (0.53 eV) is comparable with those of Pt6c/SnO2 (0.62 eV) and In-doped SnO2(110) (1.03 eV). Furthermore, the microkinetic investigation reveals that the maximum CO oxidation ratealong the Path I is 4.29 × 104s−1. This finding suggests that Ti single-atom doping can effectively improve CO oxidation at low-temperature, hence improving the SnO2 to CO sensing performance. Our study enlightens the perspective application of single-atom catalysts on gas sensing fields and provides new routes for designing new gas sensing materials.

Elucidating Active CO–Au Species on Au/CeO2(111): A Combined Modulation Excitation DRIFTS and Density Functional Theory Study

In this work we elucidate the main steps of the CO oxidation mechanism over Au/CeO2(111), clarifying the course of CO adsorption at a broad variety of surface sites as well as of transmutations of one CO species into another. By combining transient spectroscopy with DFT calculations we provide new evidence that the active centers for CO conversion are single gold atoms. To gain insight into the reaction mechanism, we employ Modulation Excitation (ME) DRIFT spectroscopy in combination with the mathematical tool of Phase Sensitive Detection to identify the active species and perform DFT calculations to facilitate the assignments of the observed bands. The transient nature of the ME-DRIFTS method allows us to sort the observed species temporally, providing further mechanistic insight. Our study highlights the potential of combined transient spectroscopy and theoretical calculations (DFT) to clarify the role of adsorbates observed and to elucidate the reaction mechanism of CO oxidation over supported gold and other noble-metal catalysts.

Mechanism insights into CO oxidation on a low-cost N doped pyrite: A molecular simulation study

A comprehensive understanding of the effect of N doping on CO oxidation over FeS2 is prominently meaningful for fabricating a low-cost heteroatom catalyst with an optimum structure and satisfactory activity. Herein, periodic density functional theory (DFT) calculations were performed to investigate possible reaction mechanisms for CO oxidation over FeS2 and N doped FeS2 (N-FeS2). Two kinds of active oxygen species are observed on the catalyst surfaces, including the adsorbed O2 and atomic O. The results show that the CO first prefers to react with the atomic O formed by O2 dissociation (FeS2) and the adsorbed O2 (N-FeS). Comparing to FeS2, the energy barriers of CO oxidation over N-FeS2 are lower, which indicates that N doping can improve the activity for CO oxidation. The analyses of electronic structure evidence that N doping can modify the electronic density of the adjacent Fe atoms and thus form favorable electronic configurations for O2 adsorption, which facilitates O2 activation and the succeeding CO oxidation. The whole favorable CO oxidation cycle for N-FeS2 consists of three stages: O2 adsorption → first CO oxidation → second CO oxidation. Our findings can provide a fundamental understanding to develop N doped catalysts with high activity for CO abatement.

Exploring reaction mechanism of CO oxidation over SrCoO3 catalyst: A DFT study

Perovskite-type oxides are considered to be the promising catalysts for CO oxidation. However, little attention has been paid to the SrCoO3 perovskite, and the atomic-level reaction mechanism that dictates the reactivity of CO oxidation over SrCoO3 catalyst remains elusive. Herein, the oxidation mechanism of CO on the SrCoO3 surface was studied by density functional theory (DFT) calculations. The results indicate that CO and O2 adsorption on the SrCoO3(100) surface are controlled by the chemisorption. The Co-terminated surface is more active for CO oxidation than the Sr-terminated surface. The adsorption energy (−0.94 eV) of CO is higher than that (−0.69 eV) of O2. The reaction pathway of CO oxidation over SrCoO3 catalyst was investigated by analyzing three possible reaction mechanisms, including the Eley-Rideal mechanism, Langmuir-Hinshelwood mechanism, and Mars-van Krevelen mechanism. The interaction between chemisorbed CO and surface lattice oxygen plays an important role in CO oxidation on the SrCoO3(100) surface. CO oxidation occurs mainly through the Mars-van Krevelen mechanism due to the lower energy barrier. CO* + Olattice → CO2* + Ovacancy is the rate-determining step as it has the highest activation energy barrier (0.61 eV) during CO oxidation reaction. These mechanistic insights can help to better understand the microcosmic reaction process to boost the CO oxidation activity of SrCoO3 catalyst.

Mars–van Krevelen mechanism for CO oxidation on the polyoxometalates-supported Rh single-atom catalysts: An insight from density functional theory calculations

• The mechanism of CO oxidation by O 2 was studied over two POM-supported SACs (Rh 1 /PTA and Rh 1 /PMA). • The oxidation process involves consecutive oxidation of three CO molecules via a Rh-assisted MvK mechanism. • The second CO molecule was oxidized by the corner O atom of the POM support rather than adsorbed O 2 molecule. • Oxidation state of the Rh center changes among III, II, and I, which promotes electron transfer and the whole reaction. The low and insufficient anchored site on support structure is the bottleneck problem for development of single-atom catalysts (SACs). Owing to the discrete anionic structure, the surface structure of unimolecular polyoxometalates (POMs) in solid is more like the fragments of metal oxide and possesses the unique separate structure, which can be viewed as the separate small “island” and effectively prevent agglomeration of single metal atoms. In the present paper, the mechanism of CO oxidation by O 2 was systematically studied over two POM-supported SACs, Rh 1 /PTA and Rh 1 /PMA (PTA = [PW 12 O 40 ] 3− and PMA = [PMo 12 O 40 ] 3− ) by means of density functional theory (DFT) calculations. The results indicated that this process involves consecutive oxidation of three CO molecules over Rh 1 /PTA and Rh 1 /PMA SACs via a Rh-assisted Mar-van Krevelen (MvK) mechanism. The first CO molecule was oxidized by a bridged O atom of POM support to form CO 2 molecule and an oxygen vacancy. The surface oxygen vacancy was refilled by O 2 molecule, and the second CO molecule was oxidized by a corner O atom of the POM support to form CO 2 molecule and a new oxygen vacancy. Finally, the forming surface oxygen vacancy was replenished by the O 2 molecule to form the key Mo-O-O-Mo unit, which can easily oxidize the third CO to form the CO 2 molecule. Compared with the reported MvK mechanism, the significant difference arises from oxidation of the second CO molecule, in which the second CO molecule was oxidized by the corner O atom of the POM support rather than adsorbed O 2 molecule. This is mainly due to a low reactivity for the adsorbed O 2 molecule, which comes from a bonding interaction between the adsorbed O 2 molecule and the single Rh atom. The atomic charge analysis show that the single Rh atom stabilized on the POM supports promotes the whole catalytic cycle via the change of oxidation state among III, II, and I. All these results show that the presence of single Rh atom on the unimolecular PTA and PMA supports is a key factor for determination of new reaction pathway and high reactivity. We hope our computation results can provide new physical insights to design SACs for CO oxidation by using unimolecular POM cluster. The reaction mechanism of CO oxidation by O 2 was systematically studied over two polyoxometalate-supported single-atom catalysts by means of density functional theory calculations.

Theoretical study on iron and nitrogen co-doped graphene catalyzes CO oxidation

• A novel CO oxidation reaction with trimolecular co-adsorption mechanism has been first proposed on FeN-SV. • The CO reaction on FeN-SV favor 2*CO+*O 2 →*OOCO+*CO→*O+*CO+CO 2 →*CO 2 1 →*CO 2 2 , with barrier as 0.525 eV. • For FeN-SV and FeN-DV, the LH mechanism was also very favorable for CO oxidation, and the energy barriers were 0.604 eV and 0.660 eV, respectively. Carbon monoxide oxidation is a famous typical polyphase catalytic reaction, which can convert toxic gases into non-toxic substances, thus reducing environmental pollution. The traditional catalytic reaction has high energy barriers and low energy efficiency, while the single metal atom was inserted into the thin graphene with excellent electronic properties to form a special structure, which has extraordinary catalytic properties. Based on the first principle calculation method, the different reaction mechanism of CO oxidation in nitrogen co-doped single vacancy and double vacancy (FeN-SV and FeN-DV) was studied systematically, and its stable structure was analyzed to find the optimal catalytic reaction path. For FeN-SV, the energy barriers of a new trimolecular co-adsorption mechanism (2*CO+*O 2 →*OOCO+*CO→*O+*CO+CO 2 →*CO 2 1 →*CO 2 2 ), which has not been reported yet, was only 0.525 eV. The rate-determining step (RDS) for FeN-SV (FeN-DV) is *CO+*O 2 →*OOCO→*O+CO 2 →*O+CO→CO 2 , which is also very beneficial to CO oxidation, was 0.604 eV (0.660 eV). The findings revealed FeN-SV and FeN-DV can be used as a low cost, high efficiency for CO catalytic oxidation. Conversion of toxic CO to non-toxic CO 2 on FeN-SV by trimolecular co-adsorption mechanism.

Triazine COF-supported single-atom catalyst (Pd1/trzn-COF) for CO oxidation

Single-atom catalysts (SACs) with well-defined and specific single-atom dispersion on supports offer great potential for achieving both high catalytic activity and selectivity. Covalent organic frameworks (COFs) with tailor-made crystalline structures and designable atomic composition is a class of promising supports for SACs. Herein, we have studied the binding sites and stability of Pd single atoms (SAs) dispersed on triazine COF (Pd1/trzn-COF) and the reaction mechanism of CO oxidation using the density functional theory (DFT). By evaluating different adsorption sites, including the nucleophilic sp2 C atoms, heteroatoms and the conjugated π-electrons of aromatic ring and triazine, it is found that Pd SAs can stably combine with trzn-COF with a binding energy around −5.0 eV, and there are two co-existing dynamic Pd1/trzn-COFs due to the adjacent binding sites on trzn-COF. The reaction activities of CO oxidation on Pd1/trzn-COF can be regulated by the anion-π interaction between a + δ phenyl center and the related −δ moieties as well as the electron-withdrawing feature of imine in the specific complexes. The Pd1/trzn-COF catalyst is found to have a high catalytic activity for CO oxidation via a plausible tri-molecular Eley-Rideal (TER) reaction mechanism. This work provides insights into the d-π interaction between Pd SAs and trzn-COF, and helps to better understand and design new SACs supported on COF nanomaterials.

Pt-embedded bismuthene as a promising single-atom catalyst for CO oxidation: A first-principles investigation

In this paper, the potential of transition metal atom (Fe, Co, Ni, Mn, Pt, Ag and Au) embedded bismuthene as the single-atom catalyst for CO oxidation has been systematically studied using first-principles calculation. Owing to the relatively high stability and strong adsorption energy for CO and O2 molecules, Pt embedded bismuthene (Pt/bismuthene) is demonstrated as the most suitable catalyst among the above transition metal embedded bismuthene. By exploring three reaction mechanism for CO oxidation, it is found that the calculated reaction barrier via tri-molecular Eley–Rideal mechanism is as low as 0.37 eV, suggesting that Pt/bismuthene has high catalytic activity for CO oxidation. The electronic structure analysis along the rate-determining step shows that the high catalytic activity of Pt/bismuthene is ascribed to the hybridization between the CO and O2 2π* orbitals and the Pt 5d orbital. Overall, our studies propose that Pt/bismuthene appears to be an excellent candidate of single-atom catalyst for CO oxidation.

Influence of lattice oxygen on the catalytic activity of blue titania supported Pt catalyst for CO oxidation

The role of oxygen defect sites in the reaction mechanism for CO oxidation using blue TiO2with a higher concentration of oxygen vacancies deposited by Pt nanoparticles is investigated.

Theoretical study of CO oxidation on Au1/Co3O4 (110) single atom catalyst using density functional theory calculations

Single-atom catalyst (SAC) using Au1/Co3O4 has been under investigation experimentally for CO oxidation in recent years. However, the reaction mechanisms for CO oxidation on Au1/Co3O4 are still poorly understood. In this paper, theoretical investigations have been conducted to elucidate the catalytic mechanism of CO oxidation on the Au1/Co3O4 (110) and the pristine Co3O4 (110) by means of the spin-polarized density functional theory puls Hubbard U (DFT + U) calculations, respectively. The calculation results show that 1) the top site of Co3+ (site 1) is the most favorable anchored site for single Au atom on the Co3O4 (110); 2) CO molecule always anchored on the top of the Au atom by a C–Au bond; 3) O2 molecules can be only physisorbed on the single Au atom in whatever way; 4) CO2 molecule can be easily escaped from Au1/Co3O4 (110) at low temperature; 5) the catalytic mechanisms for CO oxidation by extracting the twofold-coordinate oxygen and threefold-coordinate oxygen on the pristine Co3O4 (110) are follow the Mars-van Krevelen mechanism, and the catalytic activity of CO oxidation on the pristine Co3O4 (110) O2f is better than that on O3f; 6) although the pristine Co3O4 (110) has some catalytic activities for CO oxidation, the catalytic activities are far below those of the Au1/Co3O4 (110) via the Eley-Rideal mechanism. In other words, the introducing of single atom Au into the pristine Co3O4 (110) can greatly enhance the catalytic activity of the pristine Co3O4 (110) for CO oxidation. The above results will help in understanding the theoretical mechanisms and the previous experimental results at the molecular lever, and provide a theory base for designing and fabrication of highly active and stable Co3O4 supported SACs.

CO oxidation on Ni-based single-atom alloys surfaces

CO oxidation on single-atom alloys (SAAs) surfaces is of potential importance in automobile industry. The relatively simple mechanism of CO oxidation reaction and the well-organized possible active sites in SAAs enable accurate modeling with theory, making the rational design of SAAs catalysts feasible. Van der Waals density functional theory (DFT), combined with micro-kinetic modelling, is used to study CO oxidation on 12 M-Ni(111) SAAs and pure Ni(111) surfaces. On Fe-, Co-, Ru-, Rh-, and Ir-Ni(111) SAAs surfaces, CO oxidation takes place over the region containing the alloying atom, while for the other SAAs, it occurs at the pure-Ni area. Micro-kinetic modelling reveals that Rh-Ni(111) SAA surface presents the largest reaction rate, followed by Au-Ni(111) and Ir-Ni(111) under our considered reaction conditions, consistent with the experimental observations on the corresponding nanoparticles. Among 12 SAAs, only Zn-Ni(111), Cu-Ni(111), and Cd-Ni(111) yields the poorer catalytic activity than pure Ni(111) for CO oxidation. The origin of catalytic reactivity sequence of SAAs for CO oxidation is discussed from the analyses of rate-limiting steps, electronic property and alloying effects.

Theoretical Calculation of Different Reaction Mechanisms for CO Oxidation on MnN3-Doped Graphene.

In recent decades, great expectation has always been placed on catalysts that can convert toxic CO into CO2 under mild conditions. The catalytic mechanism of CO oxidation by Mn-coordinated N-doped graphene with a single vacancy (MnN3-SV) and a double vacancy (MnN3-DV) was studied by density functional theory (DFT) calculations. Molecular dynamics simulations showed that CO2 on MnN3-SV could not be desorbed from the substrate and MnN3-SV was not suitable for use as a CO oxidation catalyst. MnN3-DV was more suitable for CO oxidation (COOR) and from the electronic structure it was found that the Mn atom was the main active site, which was the reaction site for CO oxidation. At temperatures of 0 and 298.15 K, CO oxidation on MnN3-DV via the Langmuir–Hinshelwood (LH) mechanism was the best reaction pathway. The rate-determining step using MnN3-DV as the catalyst for CO oxidation through the LH mechanism was O2 + CO → OOCO, and the energy barrier was 0.861 eV at 298.15 K. MnN3-DV was suitable as a catalyst for CO oxidation in terms of both thermodynamics and kinetics. This study provides a comprehensive understanding of the various reaction mechanisms of CO oxidation on MnN3-DV, which is conducive to guiding the development and design of efficient catalysts for CO oxidation.

Density functional study on the CO oxidation reaction mechanism on MnN2-doped graphene.

The CO oxidation mechanisms over three different MnN2-doped graphene (MnN2C2: MnN2C2-hex, MnN2C2-opp, MnN2C2-pen) structures were investigated through first-principles calculations. The vacancy in graphene can strongly stabilize Mn atoms and make them positively charged, which promotes O2 activation and weakens CO adsorption. Hence, CO oxidation activity is enhanced and the catalyst is prevented from being poisoned. CO oxidation reaction (COOR) on MnN2C2 along the Eley–Rideal (ER) mechanism and the Langmuir–Hinshelwood (LH) mechanism will leave one O atom on the Mn atom, which is difficult to react with isolated CO. COOR on MnN2C2-opp along the ER mechanism and termolecular Eley–Rideal (TER) mechanism need overcome low energy barriers in the rate limiting step (RLS), which are 0.544 and 0.342 eV, respectively. The oxidation of CO along TER mechanism on MnN2C2-opp is the best reaction pathway with smallest energy barrier. Therefore, the MnN2C2-opp is an efficient catalysis and this study has a guiding role in designing effective catalyst for CO oxidation.

Oxygen activation on the interface between Pt nanoparticles and mesoporous defective TiO2 during CO oxidation.

Platinum-based heterogeneous catalysts are mostly used in various commercial chemical processes because of their high catalytic activity, influenced by the metal/oxide interaction. To design rational catalysts with high performance, it is crucial to understand the relationship between the metal-oxide interface and the reaction pathway. Here, we investigate the role of oxygen defect sites in the reaction mechanism for CO oxidation using Pt nanoparticles supported on mesoporous TiO2 catalysts with oxygen defects. We show an intrinsic correlation between the catalytic reactivity and the local properties of titania with oxygen defects (i.e., Ti3+ sites). In situ infrared spectroscopy observations of the Pt/mesoporous TiO2-x catalyst indicate that an oxygen molecule bond can be activated at the perimeter between the Pt and an oxygen vacancy in TiO2 by neighboring CO molecules on the Pt surface before CO oxidation begins. The proposed reaction pathways for O2 activation at the Pt/TiO2-x interface based on density functional theory confirm our experimental findings. We suggest that this provides valuable insight into the intrinsic origin of the metal/support interaction influenced by the presence of oxygen vacancies, which clarifies the pivotal role played by the support.