A theoretical study of single-atom catalysis of CO oxidation using Au embedded 2D h-BN monolayer: a CO-promoted O₂ activation

Metal single-atom coordinated graphitic carbon nitride as an efficient catalyst for CO oxidation

Single-atom catalysts (SACs) often present outstanding activity due to their high ratio of low-coordinated metal atoms and can be applied to the activation of strong chemical bonds such as C[triple bond, length as m-dash]O. Herein, we investigate the potential usage of a single-atom catalyst, in which isolated cobalt atoms are supported on porous graphitic carbon nitride (Co/g-C₃N₄), for CO oxidation. Based on the adsorption/co-adsorption energies of O₂, CO, 2O₂, CO + O₂ and 2CO, the screening criteria and the reaction mechanisms of CO oxidation, including the Eley-Rideal, New Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal mechanisms, are established and compared. In particular, the energy barriers of the rate-limiting steps for the CO oxidation process by all possible reaction pathways are in a range from 0.21 to 0.59 eV, suggesting that the Co/g-C₃N₄ catalyst can boost CO oxidation at low temperature. Moreover, the preparation of the SAC (Co/g-C₃N₄) by using CoCl₂ as an appropriate metal precursor and the stability (up to 600 K) are evaluated by ab initio molecular dynamics simulations. The high stability and excellent activity of the Co/g-C₃N₄ SAC for CO oxidation offer a high possibility of clean energy production.

Single-atom metal-modified graphenylene as a high-activity catalyst for CO and NO oxidation

Herein, the adsorption behaviors and interactions of different gas species on single-metal atom-anchored graphenylene (M–graphenylene, M = Mn, Co, Ni, and Cu) sheets were investigated by first-principles calculations.

Catalytic oxidation mechanisms of carbon monoxide over single- and double-vacancy Mn-embedded graphene

CO oxidation on MnC₃ and MnC₄ has fast kinetics and a low energy barrier.

AlN4-Graphene as an efficient catalyst for CO oxidation: a DFT study

DFT investigations suggest that AlN₄-Gr shows high stability and superior catalytic performance towards CO oxidation without CO poisoning.

Atomic site electrocatalysts for water splitting, oxygen reduction and selective oxidation

This review summarized the fabrication routes and characterization methods of atomic site electrocatalysts (ASCs) followed by their applications for water splitting, oxygen reduction and selective oxidation.

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.

An effective approach for tuning catalytic activity of C3N nanosheets: Chemical-doping with the Si atom

It is well-known that the catalytic oxidation of CO molecule into CO₂ is one of the most important strategies for the removing of this toxic gas from the atmosphere. In the present study, we investigate the reaction pathways and energy barriers for the oxidation of CO by O₂ molecule over the Si-doped C₃N nanosheet. According to our results, doping of C₃N nanosheet with a Si atom could greatly modify its surface reactivity and electronic structure. Due to the large positive charge on the Si, this atom acts as the most active site to adsorb CO and O₂ molecules. Three possible reaction mechanisms are studied for the CO oxidation, namely the Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and new Eley-Rideal (NER). Comparing the activation energies indicates that the CO oxidation reaction proceeds via the LH mechanism over the title surface. The energy barrier needed to remove the activated oxygen atom (O*) from the Si atom is only 0.22 eV, which is most likely to overcome at room temperature. The results of this study may be useful to fabricate noble-metal free catalysts to remove toxic CO molecules from the atmosphere.

First-Principles Investigations of Single Metal Atoms (Sc, Ti, V, Cr, Mn, and Ni) Embedded in Hexagonal Boron Nitride Nanosheets for the Catalysis of CO Oxidation

We evaluated isolated transition metal atoms (Sc, Ti, V, Cr, Mn, and Ni) embedded in hexagonal-BN as novel single atom catalysts for CO oxidation. We predicted that embedded Ni atoms should have superior performance for this task. Ti, V, and Mn bind CO2 too strongly and so the reaction will not proceed smoothly. We studied the detailed reaction processes for Sc, Cr, and Ni. The Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and the new termolecular Eley–Rideal (TER) processes for CO oxidation were investigated. Sc was not effective. Cr primarily used the ER process, although the barrier was relatively large at 1.30 eV. Ni was the best of the group, with a 0.44 eV barrier for LH, and a 0.47 eV barrier for TER. Therefore, we predicted that the LH and TER processes could operate at relatively low temperatures between 300 and 500 K.

Computational Electrochemistry of Water Oxidation on Metal-Doped and Metal-Supported Defective h-BN

Metal-doped and metal-supported two-dimensional materials are attracting a lot of interest as potentially active electrocatalysts for reduction and oxidation processes. Previously, when a non-regular 2 D h-BN layer was grown on a Cu(111) surface, metal adatoms were found to spontaneously emerge from the bulk to fill the atomic holes in the structure and become available for surface catalysis. Herein, computational electrochemistry is used to investigate and compare the performance of Cu-doped and Cu-supported pristine and defective h-BN systems for the electrocatalytic water oxidation reaction. For the various model systems, the intermediate species of this multistep oxidation process are identified and the free-energy variations for each step of reaction are computed, even for those steps that do not involve an electron or a proton transfer. Both associative and O₂ direct evolution mechanisms are considered. On this thermodynamic basis, the potential-determining step, the thermodynamic-determining step, and consequently the theoretical overpotential are determined for comparison with experiments. Small Cu clusters (tetramers) trapped in the h-BN defective lattice on a Cu(111) support are found to be very active for the water oxidation reaction since such systems are characterized by a low overpotential and by a small energy cost for O₂ release from the catalyst, which is often observed to be a major limit for other potential electrocatalysts.

A DFT study on NO reduction to N2O using Al- and P-doped hexagonal boron nitride nanosheets

Using the dispersion-corrected DFT calculations, the catalytic reduction of NO molecules to N₂O is investigated over Al- and P-doped hexagonal boron nitride nanosheets (h-BNNS). It is found that NO dissociation over both these surfaces needs a very large energy barrier, which indicates it cannot proceed at normal temperature. In contrast, the results show that NO molecules can be easily reduced into N₂O via a dimer mechanism. The obtained activation energies reveal that the catalytic activity of Al-doped h-BNNS is better than that of P-doped one, mainly due to the moderate coadsorption energies of NO molecules over this surface.

Single-atom Pt on non-metal modified graphene sheets as efficient catalysts for CO oxidation

By the density functional theory (DFT) calculations, the formation geometries, electronic structures and catalytic properties of metal Pt and nonmetal (NM) atom-co-modified graphene (Pt–3NM–graphene, NM = N, Si, P) as reactive substrates were investigated.

Pd/Pt embedded CN monolayers as efficient catalysts for CO oxidation

The catalytic performance of Pd/Pt embedded planar carbon nitride for CO oxidation has been investigated via spin-polarized density functional theory calculations.

The interplay between structural perfectness and CO oxidation catalysis on aluminum, phosphorous and silicon complexes of corroles

Catalytic oxidation of carbon monoxide on perfect and defective structures of corrole complexes with aluminum, phosphorous and silicon have been investigated by performing density functional theory calculations.

Single Pt atom supported on penta-graphene as an efficient catalyst for CO oxidation

We performed a systematic study of CO oxidation on a single Pt atom supported on penta-graphene (Pt/PG) by utilizing spin-polarized first-principles calculations. The results manifested that Pt/PG, as a single-atom catalyst, exhibited excellent catalytic activity toward CO oxidation and provided a novel strategy for the design of single-atom catalysts based on penta-graphene.

A comparative DFT study on single-atom catalysis of CO oxidation over Al- and P-embedded hexagonal boron-nitride nanosheets

Density functional theory calculations are performed to compare catalytic oxidation of CO molecule over Al- and P-embedded hexagonal boron nitride nanosheet (h-BN). It is found that the Al and P adatom can be stably anchored on the boron-vacancy site of h-BN, as evidenced by a relatively large adsorption energy and charge-transfer value. According to our findings, the oxidation of CO over these surfaces proceeds via the Langmuir-Hinshelwood mechanism, followed by the elimination of the remaining atomic O by another CO molecule. Meanwhile, the stronger adsorption of O₂ than CO avoids poisoning of the active site of both surfaces. The results of the present study indicate that Al-doped h-BN exhibits higher catalytic activity for CO oxidation than P-doped one, which may provide a valuable guidance on design metal-free catalysts to remove toxic CO molecules.

Cu dimer anchored on C2N monolayer: low-cost and efficient Bi-atom catalyst for CO oxidation

By means of density functional theory (DFT) computations, we systemically investigated CO/O2 adsorption and CO oxidation pathways on a bi-atom catalyst, namely, a copper dimer anchored on a C2N monolayer (Cu2@C2N), and we compared it with its monometallic counterpart Cu1@C2N. The Cu dimer could be stably embedded into the porous C2N monolayer. The reactions between the adsorbed O2 and CO via both bi-molecular and tri-molecular Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms were comparably studied, and we found that the bi-atom catalyst Cu2@C2N possessed superior performance toward CO oxidation as compared to the single-atom catalyst Cu1@C2N. Our comparative study suggested that the newly predicted bi-atom catalyst, i.e., a copper dimer anchored on a suitable support is highly active for CO oxidation, which can provide a useful guideline for further developing highly effective and low-cost green nanocatalysts.

Cation vacancy stabilization of single-atomic-site Pt1/Ni(OH)x catalyst for diboration of alkynes and alkenes

Development of single-atomic-site catalysts with high metal loading is highly desirable but proved to be very challenging. Although utilizing defects on supports to stabilize independent metal atoms has become a powerful method to fabricate single-atomic-site catalysts, little attention has been devoted to cation vacancy defects. Here we report a nickel hydroxide nanoboard with abundant Ni²⁺ vacancy defects serving as the practical support to achieve a single-atomic-site Pt catalyst (Pt₁/Ni(OH)_x) containing Pt up to 2.3 wt% just by a simple wet impregnation method. The Ni²⁺ vacancies are found to have strong stabilizing effect of single-atomic Pt species, which is determined by X-ray absorption spectrometry analyses and density functional theory calculations. This Pt₁/Ni(OH)_x catalyst shows a high catalytic efficiency in diboration of a variety of alkynes and alkenes, yielding an overall turnover frequency value upon reaction completion for phenylacetylene of ~3000 h^-1, which is much higher than other reported heterogeneous catalysts.

Small stoichiometric (MoS2)n clusters with the 1T phase

Stoichiometric (MoS₂)_n clusters (n = 1–6) were systematically studied by density functional theory calculations with hybrid B3LYP and pure GGA PW91 functionals.

Combinatorial selection of a two-dimensional 3d-TM-tetracyanoquinodimethane (TM-TCNQ) monolayer as a high-activity nanocatalyst for CO oxidation

CO catalytic oxidation on Sc-TCNQ.

Single Pd atomic catalyst on Mo2CO2 monolayer (MXene): unusual activity for CO oxidation by trimolecular Eley–Rideal mechanism

A Pd atom Mo₂CO₂ exhibits excellent stability and high activity to CO oxidation.

Confinement boosts CO oxidation on an Ni atom embedded inside boron nitride nanotubes

Because of the confinement effect, Ni embedded on the interior surface of BNNT exhibits a much higher catalytic activity for CO oxidation by comparing with that embedded in h-BN or on the outside surface of BNNT.

Catalytic CO oxidation on B-doped and BN co-doped penta-graphene: a computational study

The catalytic reaction of carbon monoxide oxidation on boron-doped and boron–nitrogen co-doped penta-graphene materials has been systematically studied by utilizing spin-polarized density functional theory (DFT) calculations.

A computational study of CO oxidation reactions on metal impurities in graphene divacancies

Based on the density functional theory calculations, the formation geometry, electronic properties, and catalytic activity of metal impurities in divacancy graphene (M-DG, M = Mo, Fe, Co, and Ni) were systematically investigated.

Recent Advances in Atomic Metal Doping of Carbon-based Nanomaterials for Energy Conversion

Nanostructured metal-contained catalysts are one of the most widely used types of catalysts applied to facilitate some of sluggish electrochemical reactions. However, the high activity of these catalysts cannot be sustained over a variety of pH ranges. In an effort to develop highly active and stable metal-contained catalysts, various approaches have been pursued with an emphasis on metal particle size reduction and doping on carbon-based supports. These techniques enhances the metal-support interactions, originating from the chemical bonding effect between the metal dopants and carbon support and the associated interface, as well as the charge transfer between the atomic metal species and carbon framework. This provides an opportunity to tune the well-defined metal active centers and optimize their activity, selectivity and stability of this type of (electro)catalyst. Herein, recent advances in synthesis strategies, characterization and catalytic performance of single atom metal dopants on carbon-based nanomaterials are highlighted with attempts to understand the electronic structure and spatial arrangement of individual atoms as well as their interaction with the supports. Applications of these new materials in a wide range of potential electrocatalytic processes in renewable energy conversion systems are also discussed with emphasis on future directions in this active field of research.

Theoretical investigation on the photocatalytic activity of the Au/g-C3N4 monolayer

Two-dimensional optical catalysis materials have a wonderful potential application. Here, a new two-dimensional material consisting of the supported single-atom Au on a graphite carbon nitride (g-C3N[Formula: see text] single layer has been designed and its electronic and optical properties have been characterized by density functional calculations. The bandgap of 1.82[Formula: see text]eV calculated by the hybrid functional HSE06 shows that the Au/g-C3N4 is an indirect semiconductor, and the electron can easily be excited from the single-atom Au to the bottom of the conduction band. This material therefore has relatively strong optical properties in the visible region. Moreover, the process of Au insertion into the cavity of g-C3N4 single layer is energy-favorable. This work may provide insights and a new avenue for fabricating supported Au catalysts with high stability.

Theoretical study on geometric, electronic and catalytic performances of Fe dopant pairs in graphene

The formation geometries, electronic structures and catalytic properties of monovacancy and divacancy graphene sheets with two embedded Fe dopants (2Fe-MG and 2Fe-DG) have been systematically investigated using the first-principles calculations.

Identification of activity trends for CO oxidation on supported transition-metal single-atom catalysts

Identification of activity trends for CO oxidation on transition-metal single-atom catalysts by using E_ad(CO) and E_ad(O₂) as descriptors.

Mechanistic study of NO oxidation on Cr–phthalocyanine: theoretical insight

A mechanistic investigation by DFT reveals that Cr–phthalocyanine is a promising catalyst for NO oxidation at low temperatures.

The effect of defects on the catalytic activity of single Au atom supported carbon nanotubes and reaction mechanism for CO oxidation

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.

A promising single atom catalyst for CO oxidation: Ag on boron vacancies of h-BN sheets

Due to “CO-Promoted O₂ Activation”, the termolecular Eley–Rideal (TER) mechanism is the most relevant one for CO oxidation over the SAC, Ag₁/BN.

Enhanced selective oxidation of h-BN nanosheet through a substrate-mediated localized charge effect

First-principles calculations reveal a spatially confined enhancement in the chemical reactivity of h-BN sheets towards O₂, mediated via a substrate-induced charge effect.

Oxide-based nanomaterials for fuel cell catalysis: the interplay between supported single Pt atoms and particles

Nanomaterials coated with atomically dispersed platinum on ceria are structurally dynamic and show high potential for applications in fuel cells.