Single-atom Catalyst For CO Oxidation Research Articles

Superior single-atom Pt/TiO2 mesoporous microspheres via microdrops-confined pyrolysis/deposition for low-temperature CO oxidation

This work demonstrate a polymer micelle-induced mesoporous single-atom Pt1/TiO2 microspheres with a mixed mother solution of triblock copolymer (Pluronic F127), H2PtCl6 and tetrabutyl titanate (TBT). The specific surface area and pore volume of mesoporous single-atom Pt1/TiO2 microspheres reach 179 m2/g and 0.39 cm3/g, respectively. The synthesis reaction is spatially confined in microdrops via aerosol spray. The obtained catalysts present superior activity for CO oxidation at low temperature. Typically, T100 (Temperature required to reach 100% conversion) of CO conversion (1.0% CO + 1.0% O2) is achieved at 120 °C with 0.5 at% Pt1/TiO2 catalysts, 50–60 °C lower than that with the same Pt loaded non-mesoporous catalysts from conventional photo-deposition and immersion-deposition of Pt on commercial TiO2 nanoparticles. Thus, this work paves a way to access efficient single-atom catalysts for CO oxidation.

The CO oxidation on Mn atom embedded in N vacancy of C3N monolayer: A DFT-D study

In this study, the use of a single Mn atom anchored to a nitrogen vacancy in a C3N monolayer ([email protected]3N) for CO oxidation is investigated using first-principles calculations. The stability of [email protected]3N is confirmed through the analysis of binding energy, the movement of the Mn atom within the N vacancy, and ab initio molecular dynamics simulations at 400K for a period of 6 ps. O2 is found to have more favorable adsorption on [email protected]3N compared to CO, and the direct dissociation barrier for O2 is only 0.69 eV. The Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms are also examined on the [email protected]3N, and it is found that the ER mechanism was preferred due to its lower rate limiting barrier (0.57 eV compared to 0.91 eV for the LH mechanism). In addition, the oxidation of CO by the leftover O atom on the [email protected]3N is found to be facile, with a small barrier of 0.05 eV via the ER mechanism. These findings provide insight into the potential of the [email protected]3N as a single-atom catalyst for CO oxidation at low temperatures.

Cu-doped fullerene: An efficient single-atom catalyst for CO oxidation under mild conditions

The catalytic CO oxidation under mild conditions attracts extensive interests. The exploration about the catalytic CO oxidation mechanism illustrates that the conversion from the triplet state to the singlet state takes place during the adsorption of O2, which is followed by CO adsorption. The barrier of the first CO oxidation, which corresponds to the rate-determining step, can be lowered distinctly by Cu-doping. A quartet-to-doublet spin crossing facilitates the CO oxidation by C59Cu. Significant electron transfer from the C59Cu dopant activates the O2 and CO molecules, then decreases the barrier and accelerates the reaction rate. The C59Cu dopant is an efficient catalyst for CO oxidation owing to the low-barrier (2.1 kcal/mol) CO oxidation reaction. It would be a potential material in solving the environmental protection problems and the purification of H2 for fuel cell applications

Effects of Subsurface Oxide on Cu1/CeO2 Single-Atom Catalysts for CO Oxidation: A Theoretical Investigation.

Supported atomic dispersion metals are of great interest, and the interfacial effect between isolated metal atoms and supports is crucial in heterogeneous catalysis. Herein, the behavior of single-atom Cu catalysts dispersed on CeO2 (100), (110), and (111) surfaces has been studied by DFT + U calculations. The interactions between ceria crystal planes and isolated Cu atoms together with their corresponding catalytic activities for CO oxidation are investigated. The CeO2 (100) and (111) surfaces can stabilize active Cu+ species, while Cu exists as Cu2+ on the (110) surface. Cu+ is certified as the most active site for CO adsorption, which can promote the formation of the reaction intermediates and reduce reaction energy barriers. For the CeO2 (100) surface, the interaction between CO and Cu is weak and the CO adsorbate is more likely to activate the subsurface oxygen. The catalytic performance is closely related to the binding strength of CO to the active Cu single atoms on the different subsurfaces. These results bring a significant insight into the rational design of single metal atoms on ceria and other reducible oxides.

Titanium-doped Boron Nitride Fullerenes as Novel Single-atom Catalysts for CO Oxidation

Titanium-doped Boron Nitride Fullerenes as Novel Single-atom Catalysts for CO Oxidation

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.

High-Performance Single-Atom Catalysts for CO Oxidation: the Importance of Hydrogen Bonds and Adsorption Strength of the Reactant

High-Performance Single-Atom Catalysts for CO Oxidation: the Importance of Hydrogen Bonds and Adsorption Strength of the Reactant

A comparative study of CO catalytic oxidation on the single vacancy and di-vacancy graphene supported single-atom iridium catalysts: A DFT analysis

Engineering of high-performance catalysts is of great importance for reducing the greenhouse gas emission by the electrocatalytic oxidation of CO. Single-atom-catalysts (SACs) have gained substantial attention thanks to their superior catalytic activity for CO oxidation, and graphene has been considered as one most promising supporting material owing to its peculiar physicochemical properties. In this work, the mechanism of CO oxidation over iridium (Ir) embedded on both single vacancy graphene (Ir-GNSV) and di-vacancy graphene (Ir-GNDV) has been investigated with the aid of density functional theory (DFT). The structural properties of Ir-GNSV and Ir-GNDV were analyzed by Bader charge analysis and electron density difference map. The calculated adsorption energy values of CO and O2 molecules on both the Ir-GNSV and Ir-GNDV have validated that both molecules can be molecularly adsorbed on the surface of each catalyst at room temperature. The results put forth that the reaction mechanism of CO + O2 → OOCO → CO2 + O* prefers to Langmuir − Hinshelwood (LH) mechanism. The activation energy for the transition-state for Ir-GNSV has been calculated to be 0.31 eV, whereas the first transition state (TS1) and the second transition state (TS2) of Ir-GNDV have been determined as 0.30 eV and 0.26 eV, respectively. Moreover, the results have confirmed that Ir-GNSV and Ir-GNDV surfaces have high catalytic activity and selectivity towards CO oxidation. On the basis of these findings, the proposed Ir-GNSV and Ir-GNDV catalysts are considered to be promising SAC for CO oxidation at low-temperature. It can be speculated that this work paves the way for the engineering of boosted-performance Ir-based heterogeneous catalysts by providing deeper mechanistic insights.

CO oxidation on atomic nickel/phosphorene nanosheet: An efficient single-atom catalyst

• Single Ni atom doped into phosphorene has better stability than other metals supported or doped conditions. • Ni-phosphorene single-atom catalyst can improve the adsorption capacity of O 2 and CO, better catalyzing CO oxidation. • The LH mechanism is more reasonable with low energy barrier of 0.59 eV. • Results demonstrate that Ni-phosphorene can serve as a potential single-atom catalyst for CO oxidation. Various metals decorated phosphorene nanosheet as single-atom catalyst (SAC) for CO oxidation have been investigated systematically by employing spin-polarized density functional theory. Ni-phosphorene is found to be the promising SAC for CO oxidation after comparing with other noble and non-noble metal candidates, such as Fe, Co, Cu, Al, Ag, Au, and Pt. Moreover, the structure of Ni-phosphorene remains stable at the end of 5 ps under 300 K using first-principles molecular dynamics simulations. Additionally, O 2 and CO are difficult to dissociate on Ni-phosphorene at room temperature because their dissociation energies are greater than 1 eV in possible paths. Three feasible reaction mechanisms (Langmuir-Hinshelwool (LH), Eley-Rideal, and Termolecular Eley-Rideal) are taken into account to seek the path with the lowest energy barrier. The LH mechanism is the most favorable one with the lowest energy barrier (0.59 eV) in the rate-determining step, which is facile to occur under ambient temperature. Our results provide theoretical guidance to design highly active heterogeneous catalysts based on phosphorene substrate for CO oxidation at low temperature. A single atom catalyst Ni-phosphorene can catalyze CO oxidation with low activation energy of 0.59 eV for rate-determining step.

Phosphorene Supported Single-Atom Catalysts for CO Oxidation: A Computational Study.

Single-atom catalysts (SACs) have attracted extensive attention owing to their high catalytic activity. The development of efficient SACs is crucial for applications in heterogeneous catalysis. In this article, the geometric configuration, electronic structure, stabilitiy and catalytic performance of phosphorene (Pn) supported single metal atoms (M=Ru, Rh, Pd, Ir, Pt, and Au) have been systematically investigated using density functional theory calculations and ab initio molecular dynamics simulations. The single atoms are found to occupy the hollow site of phosphorene. Among the catalysts studied, Ru-decorated phosphorene is determined to be a potential catalyst by evaluating adsorption energies of gaseous molecules. Various mechanisms including the Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and trimolecular Eley-Rideal (TER) mechanisms are considered to validate the most favourable reaction pathway. Our results reveal that Ru-Pn exhibits outstanding catalytic activity toward CO oxidation reaction via TER mechanism with the corresponding rate-determining energy barrier of 0.44 eV, making it a very promising SAC for CO oxidation under mild conditions. Overall, this work may provide a new avenue for the design and fabrication of two-dimensional materials supported SACs for low-temperature CO oxidation.

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.

Fe-doped C3N monolayer as a promising SAC for CO oxidation with low temperature and high reactivity

In this work, we investigate the CO oxidation on the Fe-doped N-vacancy C3N (Fe-C3N) monolayer by first-principle theory. Single Fe atom is doped on the N-vacancy site of C3N surface with a binding energy of −6.65 eV. The better performance of Fe-C3N upon O2 adsorption determines the preferred CO oxidation pathway by Eley-Rideal (ER) mechanism. Results indicate that the energy barriers in the two steps of ER mechanism are obtained as 0.45 and 0.47 eV, which could be feebly overcome at room temperature. Moreover, the physicochemical properties of the recovered Fe-C3N monolayer are unchanged compared with the original counterpart, manifesting that the CO oxidation on the Fe-C3N monolayer is energy-favorable at room temperature and the strong potential of Fe-C3N monolayer as a promising single-atom catalyst (SAC) for CO oxidation with high reactivity and low temperature. This work would be meaningful for the exploration of novel SAC in the field of heterogeneous catalysis.

Recent advances in single-atom catalysts for CO oxidation

ABSTRACT Single-atom catalysts (SACs) have received boosting attention due to their high atom utilization and incredible activities in a wide range of catalytic processes. Numerous SACs have been investigated for CO oxidation both experimentally and theoretically, including noble-metal catalysts (Pt, Au, Pd, etc.) and non-noble-metal catalysts (Fe, Co, Ni, etc.), in which the atomically dispersed metal atoms are anchored on supports via strong metal-support interactions. This unique structure of SACs contributes to activating the adsorbed CO and O2 and stabilizing the intermediates. Electron transfer between the metal atom and the support plays an important role in tuning the electronic structure, which can greatly influence the activity, selectivity, and stability of SACs. In this review, the design principles and synthesis methods of SACs for CO oxidation are discussed with emphasis on single-atom active sites and metal-support interactions. Four CO oxidation mechanisms over SACs are evaluated. Moreover, the challenges and future research directions for SAC-catalyzed CO oxidation are outlined.

Pd-doped C3N monolayer: A promising low-temperature and high-activity single-atom catalyst for CO oxidation

Using the first-principles theory, we theoretically investigated the CO/O2 adsorption and CO oxidation on the Pd-doped C3N (Pd-C3N) monolayer which we proposed as a low-temperature and high-activity catalyst for CO oxidation. Pd dopant is stably anchored on the N vacancy of C3N monolayer, forming the large binding energy of −4.00 eV without the cluster possibility. Given the larger adsorption energy of Pd-C3N monolayer upon O2 compared to CO molecule, we assume that Eley-Rideal (ER) mechanism is the preferred pathway for CO oxidation. For comparison, we also implemented the Langmuir-Hinshelwood (LH) mechanism to comprehensive understand the CO oxidation processes. Our calculations indicated that the energy barriers for ER and LH in the first step are 0.64 and 0.72 eV, with quite large energy drop of 2.99 and 2.0 eV to release a CO2 molecule, respectively. That means, the CO oxidation using Pd-C3N monolayer is fully-energetically favorable even at room temperature, which could give a novel insight into developing novel single-atom catalyst (SAC) based on C3N monolayer with high-efficiency and low-temperature.

Fe doped BN monolayer: A promising low-cost single atom catalyst for promoted CO oxidation activity

A Single Atom Catalyst (SAC) for CO oxidation based on Boron-Nitrogen (BN) has been systematically investigated using spin-polarized density functional theory. Nine noble and non-noble metals including Fe, Co, Ni, Cu, Al, Zn, Ag, Au, and Pt are chosen as candidates for the sake of appropriate catalytic metal. Fe doped BN at B site (Fe-BNB) is the most promising SAC for CO oxidation after careful screening. Then, the structures of Fe-BNB and gases adsorbed systems can keep stably after 2.5 ps of first-principles molecular dynamics simulations at 300 K. Three possible reaction mechanisms are discussed (Langmuir-Hinshelwool, Eley-Rideal, and Termolecular Eley-Rideal), and the LH mechanism shows the lowest potential energy pathway (0.52 eV) with the highest exothermic energy (4.37 eV), which is comparable to the Graphene and other BN based catalysts with regard to energy barrier of the rate determination step (0.52 eV vs 0.08–0.68 eV). On the basis of rational first-principles calculations, the proposed Fe-BNB is a convincing SAC for CO oxidation. Our results provide reliable insights to design promising heterogeneous catalysts based on BN monolayer.

A novel single-atom catalyst for CO oxidation in humid environmental conditions: Ni-embedded divacancy graphene

A termolecular Eley–Rideal (TER) mechanism is preferred for CO oxidation on Ni-DG in humid environments, and the energy barrier for the rate limiting step (2CO + O2 → OCOOCO) is only 0.34 eV.

Superior activity of Rh1/ZnO single-atom catalyst for CO oxidation

AbstractCO oxidation is of great importance in both fundamental study and industrial application. Supported noble metal catalysts are highly active for CO oxidation but suffer from the scarcity and high cost. Single-atom catalysts (SACs) can maximize the metal atom efficiency. Herein, ZnO nanowire (ZnO-nw) supported Rh, Au, and Pt SACs were successfully developed to investigate their CO oxidation performance. Interestingly, it was found that Rh1/ZnO-nw showed much higher activity than the other noble metals which are usually regarded as good candidates for CO oxidation. In addition, the Rh SAC possessed high stability in high-temperature CO oxidation under simulated conditions in the presence of water and hydrocarbons. The high activity and stability make Rh1/ZnO-nw promising for practical applications, especially in the automotive exhaust emission control. Theoretical calculations indicate that the CO oxidation proceeds via the Mars-van Krevelen mechanism and the lowest barrier for the rate-limiting O2 dissociation at a surface oxygen vacancy site is a key factor in determining the observed highest activity of Rh1/ZnO-nw amongst the studied SACs.

Strain Engineering of a Defect-Free, Single-Layer MoS2 Substrate for Highly Efficient Single-Atom Catalysis of CO Oxidation.

Single-atom catalysts (SACs) are of great scientific and technical importance due to their low cost, high site density, and high specificity to enhance chemical reactions. Nevertheless, a major issue that severely limits the practical exploration of SACs is their instability, i.e., the preference of sintering and clustering over a defect-free substrate during operation. Here, we employ first-principles calculations to investigate how substrate engineering can stabilize SACs by strain-tuning the electronic interactions between the metal and the substrate using two Pd adatoms on a defect-free, single-layer MoS2 as a typical example. It is identified that the Pd2 dimer is prone to dissociate and form highly efficient SACs for CO oxidation due to the enhanced charge transfer and orbital hybridization with the MoS2 substrate under a suitable tensile strain. The straining induces a semiconductive-to-metallic phase transition of the substrate. Moreover, low-cost elements, such as Ag, Ni, Cu, and Cr, can also be stabilized into high-performance SACs for CO oxidation with tunable reaction barriers by straining. The present findings offer a new avenue to inhibit the transition metal atoms from clustering into nanoclusters/particles and provide a clear guidance for the development of highly cost-efficient and stable SACs on defect-free substrates.

A promising and new single-atom catalyst for CO oxidation: Si-embedded MoS2 monolayer

Using dispersion-corrected density functional theory calculations, we introduce a silicon atom embedded MoS2 (Si–MoS2) as new and robust catalyst for oxidation of CO to CO2. According to our results, CO and O2 molecules are largely activated over Si–MoS2 due to considerable hybridization between the Si-3d and O2-2π* or CO-2π* states. The first step of CO oxidation (i.e., CO + O2 → CO2 + O*) preferably proceeds via the Langmuir-Hinshelwood (LH) mechanism. This includes the formation of a peroxo-type OOCO intermediate by overcoming an activation energy of 0.38 eV. The results show that the energy barrier for the removing the O* moiety left on the Si atom is only 0.32 eV. The calculated energy barriers are comparable with other theoretical reports of some noble metals. The results of the present study suggest that Si–MoS2 could be considered as a promising and low-cost catalyst for high performance oxidation of CO.

In situ spectroscopy-guided engineering of rhodium single-atom catalysts for CO oxidation

Single-atom catalysts have recently been applied in many applications such as CO oxidation. Experimental in situ investigations into this reaction, however, are limited. Hereby, we present a suite of operando/in situ spectroscopic experiments for structurally well-defined atomically dispersed Rh on phosphotungstic acid during CO oxidation. The identification of several key intermediates and the steady-state catalyst structure indicate that the reactions follow an unconventional Mars-van Krevelen mechanism and that the activation of O2 is rate-limiting. In situ XPS confirms the contribution of the heteropoly acid support while in situ DRIFT spectroscopy consolidates the oxidation state and CO adsorption of Rh. As such, direct observation of three key components, i.e., metal center, support and substrate, is achieved, providing a clearer picture on CO oxidation on atomically dispersed Rh sites. The obtained information are used to engineer structurally similar catalysts that exhibit T20 values up to 130 °C below the previously reported Rh1/NPTA.