Single Atom Alloys Segregation in the Presence of Ligands

Single atom alloys (SAAs) have gained remarkable attention due to their tunable properties leading to enhanced catalytic performance, such as high activity and selectivity. The stability of SAAs is dictated by surface segregation, which can be affected by the presence of surface adsorbates. Research efforts have primarily focused on the effect of commonly found catalytic reaction intermediates, such as CO and H, on the stability of SAAs. However, there is a knowledge gap in understanding the effect of ligands from colloidal nanoparticle (NP) synthesis on surface segregation. Herein, we combine density functional theory (DFT) and machine learning to investigate the effect of thiol and amine ligands on the stability of colloidal SAAs. DFT calculations revealed rich segregation energy (Eseg) data of SAAs with d8 (Pt, Pd, Ni) and d9 (Ag, Au, Cu) metals exposing (111) and (100) surfaces, in the presence and absence of ligands. Using these data, we developed an accurate four-feature neural network using a multilayer perceptron regression (NN MLP) model. The model captures the underlying physics behind surface segregation in the presence of adsorbed ligands by incorporating features representing the thermodynamic stability of metals through the bulk cohesive energy, structural effects using the coordination number of the dopant and the ligands, the binding strength of the adsorbate to the metals, strain effects using the Wigner-Seitz radius, and electronic effects through electron affinities. We found that the presence of ligands makes the thermodynamics of segregation milder compared to the bare (nonligated) SAA surfaces. Importantly, the adsorption configuration (e.g., top vs bridge) and the binding strength of the ligand to the SAA surface (e.g., amines vs thiols) play an important role in altering the Eseg trends compared to the bare surface. We also developed an accurate NN MLP model that predicts Eseg in the presence of ligands to find thermodynamically stable SAAs, leading to the rapid and efficient screening of colloidal SAAs. Our model captures several experimental observations and elucidates complex physics governing segregation at nanoscale interfaces.

Design of Single-Atom Catalysts and Tracking Their Fate Using Operando and Advanced X-ray Spectroscopic Tools

The potential of operando X-ray techniques for following the structure, fate, and active site of single-atom catalysts (SACs) is highlighted with emphasis on a synergetic approach of both topics. X-ray absorption spectroscopy (XAS) and related X-ray techniques have become fascinating tools to characterize solids and they can be applied to almost all the transition metals deriving information about the symmetry, oxidation state, local coordination, and many more structural and electronic properties. SACs, a newly coined concept, recently gained much attention in the field of heterogeneous catalysis. In this way, one can achieve a minimum use of the metal, theoretically highest efficiency, and the design of only one active site-so-called single site catalysts. While single sites are not easy to characterize especially under operating conditions, XAS as local probe together with complementary methods (infrared spectroscopy, electron microscopy) is ideal in this research area to prove the structure of these sites and the dynamic changes during reaction. In this review, starting from their fundamentals, various techniques related to conventional XAS and X-ray photon in/out techniques applied to single sites are discussed with detailed mechanistic and in situ/operando studies. We systematically summarize the design strategies of SACs and outline their exploration with XAS supported by density functional theory (DFT) calculations and recent machine learning tools.

Single Metal Atoms Embedded in the Surface of Pt Nanocatalysts: The Effect of Temperature and Hydrogen Pressure

Embedding energetically stable single metal atoms in the surface of Pt nanocatalysts exposed to varied temperature (T) and hydrogen pressure (P) could open up new possibilities in selective and dynamical engineering of alloyed Pt catalysts, particularly interesting for hydrogenation reactions. In this work, an environmental segregation energy model is developed to predict the stability and the surface composition evolution of 24 Metal M-promoted Pt surfaces (with M: Cu, Ag, Au, Ni, Pd, Co, Rh and Ir) under varied T and P. Counterintuitive to expectations, the results show that the more reactive alloy component (i.e., the one forming the strongest chemical bond with the hydrogen) is not the one that segregates to the surface. Moreover, using DFT-based Multi-Scaled Reconstruction (MSR) method and by extrapolation of M-promoted Pt nanoparticles (NPs), the shape dynamics of M-Pt are investigated under the same ranges of T and P. The results show that under low hydrogen pressure and high temperature ranges, Ag and Au—single atoms (and Cu to a less extent) are energetically stable on the surface of truncated octahedral and/or cuboctahedral shaped NPs. This indicated that coinage single-atoms might be used to tune the catalytic properties of Pt surface under hydrogen media. In contrast, bulk stability within wide range of temperature and pressure is predicted for all other M-single atoms, which might act as bulk promoters. This work provides insightful guides and understandings of M-promoted Pt NPs by predicting both the evolution of the shape and the surface compositions under reaction gas condition.

Electrocatalytic Reduction of CO2 to C1 Compounds by Zn-Based Monatomic Alloys: A DFT Calculation

Electrocatalytic reduction of carbon dioxide to produce usable products and fuels such as alkanes, alkenes, and alcohols, is a very promising strategy. Recent experiments have witnessed great advances in precisely controlling the synthesis of single atom alloys (SAAs), which exhibit unique catalytic properties different from alloys and nanoparticles. However, only certain precious metals, such as Pd or Au, can achieve this transformation. Here, the density functional theory (DFT) calculations were performed to show that Zn-based SAAs are promising electrocatalysts for the reduction of CO2 to C1 hydrocarbons. We assume that CO2 reduction in Zn-based SAAs follows a two-step continuous reaction: first Zn reduces CO2 to CO, and then newly generated CO is captured by M and further reduced to C1 products such as methane or methanol. This work screens seven stable alloys from 16 SAAs (M = Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, V, Mo, Ti, Cr). Among them, Pd@Zn (101) and Cu@Zn (101) are promising catalysts for CO2 reduction. The reaction mechanisms of these two SAAs are discussed in detail. Both of them convert CO2 into methane via the same pathway. They are reduced by the pathway: *CO2 → *COOH → *CO + H2O; *CO → *CHO → *CH2O → *CH3O → *O + CH4 → *OH + CH4 → H2O + CH4. However, their potential determination steps are different, i.e., *CO2 → *COOH (ΔG = 0.70 eV) for Cu@Zn (101) and *CO → *CHO (ΔG = 0.72 eV) for Pd@Zn, respectively. This suggests that Zn-based SAAs can reduce CO2 to methane with a small overpotential. The solvation effect is simulated by the implicit solvation model, and it is found that H2O is beneficial to CO2 reduction. These computational results show an effective monatomic material to form hydrocarbons, which can stimulate experimental efforts to explore the use of SAAs to catalyze CO2 electrochemical reduction to hydrocarbons.

Tuning crystal-phase of bimetallic single-nanoparticle for catalytic hydrogenation

Bimetallic nanoparticles afford geometric variation and electron redistribution via strong metal-metal interactions that substantially promote the activity and selectivity in catalysis. Quantitatively describing the atomic configuration of the catalytically active sites, however, is experimentally challenged by the averaging ensemble effect that is caused by the interplay between particle size and crystal-phase at elevated temperatures and under reactive gases. Here, we report that the intrinsic activity of the body-centered cubic PdCu nanoparticle, for acetylene hydrogenation, is one order of magnitude greater than that of the face-centered cubic one. This finding is based on precisely identifying the atomic structures of the active sites over the same-sized but crystal-phase-varied single-particles. The densely-populated Pd-Cu bond on the chemically ordered nanoparticle possesses isolated Pd site with a lower coordination number and a high-lying valence d-band center, and thus greatly expedites the dissociation of H2 over Pd atom and efficiently accommodates the activated H atoms on the particle top/subsurfaces.

Machine-Learning-Assisted Catalytic Performance Predictions of Single-Atom Alloys for Acetylene Semihydrogenation

Selective semihydrogenation of acetylene for the production of polymer-grade ethylene is a significant chemical industrial process. Facile activization of acetylene and weak adsorption of ethylene are critical requirements for high-performance catalysis. Single-atom alloys (SAAs) have strong binding effect on acetylene and weak effect on ethylene, which have been regarded as the superior catalysts for acetylene semihydrogenation. Herein, we established a pioneering machine learning (ML) assisted approach to investigate the reaction activity and selectivity of 70 SAA catalysts for acetylene semihydrogenation. As the most desirable ML model, the gradient boosting regression (GBR) algorithm has been extended to predict the energy barrier of *C₂H_n (n = 2-4) hydrogenation with a root-mean-square error (RMSE) of only 0.02 eV. Notably, five candidate SAAs with excellent activity and selectivity for acetylene semihydrogenation are screened out via accessible descriptors. These data of ML prediction have been verified by DFT calculation with a high-accuracy (error less than 0.07 eV). This work demonstrates the potential of ML-assisted approach for predicting the energy barrier of transition state and simultaneously provides a convenient approach for the rational design of efficient catalysts.

Single-Atom Catalysts: A Review of Synthesis Strategies and Their Potential for Biofuel Production

Biofuels have been derived from various feedstocks by using thermochemical or biochemical procedures. In order to synthesise liquid and gas biofuel efficiently, single-atom catalysts (SACs) and single-atom alloys (SAAs) have been used in the reaction to promote it. SACs are made up of single metal atoms that are anchored or confined to a suitable support to keep them stable, while SAAs are materials generated by bi- and multi-metallic complexes, where one of these metals is atomically distributed in such a material. The structure of SACs and SAAs influences their catalytic performance. The challenge to practically using SACs in biofuel production is to design SACs and SAAs that are stable and able to operate efficiently during reaction. Hence, the present study reviews the system and configuration of SACs and SAAs, stabilisation strategies such as mutual metal support interaction and geometric coordination, and the synthesis strategies. This paper aims to provide useful and informative knowledge about the current synthesis strategies of SACs and SAAs for future development in the field of biofuel production.

Selective hydrogenation of acetylene on Cu-Pd intermetallic compounds and Pd atoms substituted Cu(111) surfaces

The selective hydrogenation of acetylene was studied on the ordered Cu-Pd intermetallic compounds (L1₀-type CuPd, L1₂-type Cu₃Pd, and L1₂-type CuPd₃) and Pd-modified Cu(111) surfaces through first-principles calculations. The catalytic selectivity and activity of Cu-Pd alloy catalysts are closely related to the crystal structure and composition of Cu-Pd intermetallic compounds and the size of Pd ensembles of Cu-based dilute alloy surface for the selective hydrogenation of acetylene to ethylene. Significantly, we found that the ordered Cu-Pd alloy surface containing isolated Pd atoms (i.e., L1₂-type Cu₃Pd(111) surface) is highly efficient for the selective hydrogenation reaction of C₂H₂ + H₂→ C₂H₄. The contiguous Pd atom ensembles (Pd dimer and trimer) are catalytically active towards C₂H₂ + H → C₂H₃ and C₂H₃ + H → C₂H₄ reactions than the single Pd atom on a Pd-decorated Cu(111) surface. However, the small Pd ensembles on Cu(111) present a low chemical activity for H₂ dissociation compared with the ordered Cu-Pd intermetallic compounds. Our theoretical results provide a strategy of crystal phase and composition control for enhancing the selectivity and activity of Cu-Pd catalysts towards acetylene selective hydrogenation.

Addressing the uncertainty of DFT-determined hydrogenation mechanisms over coinage metal surfaces

Density functional theory (DFT) has been considered as a powerful tool for the identification of reaction mechanisms. However, it is still unclear whether the error of DFT calculations would lead to mis-identification of mechanisms. Here, taking the hydrogenation of acetylene and 1,3-butadiene as model reactions and employing a well-trained Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), we try to estimate the error of DFT calculation results statistically, and therefore predict the reliability of the hydrogenation mechanisms identified. With an ensemble of 2000 functionals obtained around the BEEF-vdW functional as well as a descriptor developed to represent the possibility of different mechanisms, we found that the non-Horiuti-Polanyi mechanism is preferred on Ag(211) and Au(211), while the Horiuti-Polanyi mechanism is dominant on Cu(211). We further discovered that the descriptor is linearly correlated with the adsorption energies of reaction intermediates during acetylene and butadiene hydrogenation, and the hydrogenation of strongly adsorbed species are more likely to follow the Horiuti-Polanyi mechanism. We found the probability of following the non-HP mechanism obeys the order Cu(211) < Au(211) < Ag(211). Our work gives a more comprehensive explanation for the mechanisms of coinage metal catalyzed hydrogenation reactions, and also provides more theoretical insights into the development of new high-performance catalysts for selective hydrogenation reactions.

Mo single atoms in the Cu(111) surface as improved catalytic active centers for deoxygenation reactions

The surface Mo-doped Cu(111) catalyst feature improved performance towards deoxygenation reactions, acting as a single-atom alloy capable of breaking Brønsted–Evans–Polanyi relations for carbonyl bond scissions.

Single-atom alloy catalysts: structural analysis, electronic properties and catalytic activities

Monometallic catalysts, in particular those containing noble metals, are frequently used in heterogeneous catalysis, but they are expensive, rare and the ability to tailor their structures and properties remains limited. Traditionally, alloy catalysts have been used instead that feature enhanced electronic and chemical properties at a reduced cost. Furthermore, the introduction of single metal atoms anchored onto supports provided another effective strategy to increase both the atomic efficiency and the chance of tailoring the properties. Most recently, single-atom alloy catalysts have been developed in which one metal is atomically dispersed throughout the catalyst via alloy bonding; such catalysts combine the traditional advantages of alloy catalysts with the new feature of tailoring properties achievable with single atom catalysts. This review will first outline the atomic scale structural analysis on single-atom alloys using microscopy and spectroscopy tools, such as high-angle annular dark field imaging-scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy. Next, progress in research to understand the electronic properties of single-atom alloys using X-ray spectroscopy techniques and quantum calculations will be presented. The catalytic activities of single-atom alloys in a few representative reactions will be further discussed to demonstrate their structure-property relationships. Finally, future perspectives for single-atom alloy catalysts from the structural, electronic and reactivity aspects will be proposed.

Controlling Hydrocarbon (De)Hydrogenation Pathways with Bifunctional PtCu Single-Atom Alloys

The conversions of surface-bound alkyl groups to alkanes and alkenes are important steps in many heterogeneously catalyzed reactions. On the one hand, while Pt is ubiquitous in industry because of its high activity toward C-H activation, many Pt-based catalysts tend to overbind reactive intermediates, which leads to deactivation by carbon deposition and coke formation. On the other hand, Cu binds intermediates more weakly than Pt, but activation barriers tend to be higher on Cu. We examine the reactivity of ethyl, the simplest alkyl group that can undergo hydrogenation and dehydrogenation via β-elimination, and show that isolated Pt atoms in Cu enable low-temperature hydrogenation of ethyl, unseen on Cu, while avoiding the decomposition pathways on pure Pt that lead to coking. Furthermore, we confirm the predictions of our theoretical model and experimentally demonstrate that the selectivity of ethyl (de)hydrogenation can be controlled by changing the surface coverage of hydrogen.

Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor

By using the pyramidalization angle as a localized geometric descriptor for oxygen reduction reaction (ORR) activity of carbon nanotubes (CNTs), we show the ORR activity of these systems can be readily predicted with mere structural optimization of CNTs.

Adsorption energy scaling relation on bimetallic magnetic surfaces: role of surface magnetic moments

The scaling relationships between the adsorption energies of different reaction intermediates have a tremendous effect in the field of surface science, particularly in predicting new catalytic materials. In the last few decades, these scaling laws have been extensively studied and interpreted by a number of research groups which makes them almost universally accepted. In this work, we report the breakdown of the standard scaling law in magnetic bimetallic transition metal (TM) surfaces for hydrogenated species of oxygen (O), carbon (C), and nitrogen (N), where the adsorption energies are estimated using density functional theory (DFT). We propose that the scaling relationships do not necessarily rely solely on the adsorbates, they can also be strongly dependent on the surface properties. For magnetic bimetallic TM surfaces, the magnetic moment plays a vital role in the estimation of adsorption energy, and therefore towards the linear scaling relation.

Mechanistic insights into higher alcohol synthesis from syngas on Rh/Cu single-atom alloy catalysts

DFT calculations show that C–C coupling is more favored on Rh/Cu single-atom alloy catalysts than on pure metal catalysts.

Predicting aggregation energy for single atom bimetallic catalysts on clean and O* adsorbed surfaces through machine learning models

Machine learning models are successfully developed for simultaneous prediction of stability and adsorption energy at single-atom bimetallic sites.

A DFT Study of Acetylene Hydrogenation Catalyzed by S-Doped Pd1/g-C3N4

To exploit the excellent properties of g-C3N4, more and more studies have been carried out in various fields in recent years to improve the selectivity of catalysts, especially for selective acetylene hydrogenation. To our best knowledge, Pd catalyst is of great importance to hydrogenate acetylene in ethylene feed. Though we have explored the hydrogenation of acetylene catalyzed by Pd1/g-C3N4 before, doping with non-metals has never been studied. In this work, the mechanisms of selective hydrogenation of acetylene to ethylene on S-doped Pd1/g-C3N4 were investigated and we also compared this result with undoped Pd1/g-C3N4. By comparing the activation energy and selectivity of undoped Pd1/g-C3N4 with those of S-doped C and N sites of Pd1/g-C3N4, we found that S-doped C sites can improve the reactivity, but with a poor selectivity, while the activity of S atom doped N sites was not improved, but the selectivity has improved. Our work provides significant insights to explore the development of high efficiency non-metallic doping single metal atoms supported on 2D layered materials.

Theoretical study on the reaction mechanism and selectivity of acetylene semi-hydrogenation on Ni-Sn intermetallic catalysts

Recently, Ni-Sn intermetallic compounds (IMCs) with unique geometric structures have been proved to be selective catalysts for acetylene hydrogenation to ethylene, but the origin of the selectivity remains unclear. In this work, a density functional theory (DFT) study has been carried out to investigate the mechanism of acetylene hydrogenation on six surfaces of Ni-Sn IMCs, and the geometric effects towards ethylene selectivity were revealed. Two key parameters (adsorption energy and the hydrogenation barrier of ethylene), which determine the ethylene selectivity, were studied quantitatively. The adsorption sites for C2Hy (y = 2, 3, 4) can be classified into three types: Type 1 (Ni3Sn(111) and Ni3Sn2(101)-2) with Ni trimers, Type 2 (Ni3Sn(001) and Ni3Sn2(001)) with Ni monomers, and Type 3 (Ni3Sn2(101) and Ni3Sn2(001)-2) with reconstructed metal trimers. The adsorption energy (Ead) decreases following the order: Type 1 > Type 3 > Type 2, which indicates that the adsorption strength depends significantly on site ensemble: a more isolated Ni site would facilitate the desorption of ethylene. However, the surface roughness mainly dominates the hydrogenation barrier of ethylene. Either low or high roughness decreases the interactions between H and C2H4 (Eint), resulting in an enhanced energy barrier for over-hydrogenation of C2H4 (Ea,hydr); while moderate roughness benefits Eint and lowers Ea,hydr. The selectivity to ethylene is denoted as ΔEa = Ea,hydr - |Ead|, thus depending on the interplay of site ensemble effects and surface roughness. From this point of view, Ni3Sn(001) and Ni3Sn2(101) surfaces with well-isolated Ni ensembles and low (or high) surface roughness exhibit decreased |Ead| and increased Ea,hydr, giving rise to excellent selectivity to ethylene. This work provides significant understanding of the origin of ethylene selectivity in terms of geometric effects, which gives helpful instruction for the design and preparation of intermetallic catalysts for acetylene semi-hydrogenation.

Single-Atom Alloys as a Reductionist Approach to the Rational Design of Heterogeneous Catalysts

Heterogeneous catalysts are workhorses in the industrial production of most commodity and specialty chemicals, and have widespread energy and environmental applications, with the annual market value of the catalysts themselves reaching almost $20 billion in 2018. These catalysts are complex, comprising multicomponent materials and multiple structures, making their rational design challenging, if not impossible. Furthermore, typical active metals like Pt, Pd, and Rh are expensive and can be susceptible to poisoning by CO, coking, and they are not always 100% selective. Efforts to use these elements sparingly and improve their selectivity has led to recent identification of single-atom heterogeneous catalysts in which individual transition metal atoms anchored on oxide or carbon-based supports are excellent catalysts for reactions like the CO oxidation, water-gas shift, alcohol dehydrogenation, and steam reforming. In this Account, we describe a new class of single-atom heterogeneous catalysts, namely, Single-Atom Alloys (SAAs) that comprise catalytically active elements like Pt, Pd, and Ni alloyed in more inert host metals at the single-atom limit. These materials evolved by complementary surface science and scanning probe studies using single crystals, and catalytic evaluation of the corresponding alloy nanoparticles with compositions informed by the surface science findings. The well-defined nature of the active sites in SAAs makes accurate modeling with theory relatively easy, enabling the rational design of SAA catalysts via a complementary three-prong approach, encompassing surface science model catalysts, theory, and real catalyst synthesis and testing under industrially relevant conditions. SAAs constitute one of just a few examples of when heterogeneous catalyst design has been guided by an understanding of fundamental surface processes. The Account starts by describing scanning tunneling microscopy studies of highly dilute alloys formed by doping small amounts of a catalytically active element into a more inert host metal. We first discuss hydrogenation reactions in which dissociation of H₂ is often rate limiting. Results indicate how the SAA geometry allows the transition state and the binding site of the reaction intermediates to be decoupled, which enables both facile dissociation of reactants and weak binding of intermediates, two key factors for efficient and selective catalysis. These results were exploited to design the first PtCu SAA hydrogenation catalysts which showed high selectivity, stability and resistance to poisoning in industrially relevant hydrogenation reactions, such as the selective conversion of butadiene to butenes. Model studies also revealed spillover of hydrogen atoms from the Pt site where dissociation of H₂ occurs to Cu sites where selective hydrogenation is facilitated in a bifunctional manner. We then discuss selective dehydrogenations on SAAs demonstrating that they enable efficient C-H activation, while being resistant to coking that plagues typical Pt catalysts. SAA PtCu nanoparticle catalysts showed excellent stability in butane dehydrogenation for days-on-stream at 400 °C. Another advantage of SAA catalysts is that on many alloy combinations CO, a common catalyst poison, binds more weakly to the alloy than the pure metal. We conclude by discussing recent theory results that predict the energetics of many key reaction steps on a wide range of SAAs and the exciting possibilities this reductionist approach to heterogeneous catalysis offers for the rational design of new catalysts.

Lonely Atoms with Special Gifts: Breaking Linear Scaling Relationships in Heterogeneous Catalysis with Single-Atom Alloys

We discuss a simple yet effective strategy for escaping traditional linear scaling relations in heterogeneous catalysis with highly dilute bimetallic alloys known as single-atom alloys (SAAs). These systems, in which a reactive metal is atomically dispersed in a less reactive host, were first demonstrated with the techniques of surface science to be active and selective for hydrogenation reactions. Informed by these early results, PdCu and PtCu SAA nanoparticle hydrogenation catalysts were shown to work under industrially relevant conditions. To efficiently survey the many potential metal combinations and reactions, simulation is crucial for making predictions about reactivity and guiding experimental focus on the most promising candidate materials. This recent work reveals that the high surface chemical heterogeneity of SAAs can result in significant deviations from Brønsted-Evans-Polanyi scaling relationships for many key reaction steps. These recent insights into SAAs and their ability to break linear scaling relations motivate discovery of novel alloy catalysts.

The DFT study of Si-doped Pd6Si clusters for selective acetylene hydrogenation reaction

Recently, it has been demonstrated that Si-modified Pd catalyst shows excellent selectivity and produces less amount of green oil than the unmodified Pd catalyst in acetylene hydrogenation. Motivated by experiment works, we systematically investigate the mechanism of the selective acetylene hydrogenation reactions over pristine Pd₇ and Si-doped Pd₆Si clusters by using the B3LYP method of density functional theory. Our result confirms that both the Pd₇ and Pd₆Si clusters catalytic hydrogenation of acetylene are mainly through two different pathways and a series of intermediates can be transformed into each other by proton transfer, which link the two independent reaction paths into a network path. Among these reaction paths, activation energies for all steps of the reaction have been calculated and it is illustrated that the lowest activation energy in the process of ethylene generation are 22.59 kcal/mol for Pd₇ cluster and 11.25 kcal/mol for Pd₆Si cluster, which indicate that the Pd₆Si cluster perform better than Pd₇ cluster in the aspect of catalytic activity. Besides, it has also been demonstrated that the selectivity for the reaction is enhanced after doping a Si atom.

Carbon Monoxide Poisoning Resistance and Structural Stability of Single Atom Alloys

Platinum group metals (PGMs) serve as highly active catalysts in a variety of heterogeneous chemical processes. Unfortunately, their high activity is accompanied by a high affinity for CO and thus, PGMs are susceptible to poisoning. Alloying PGMs with metals exhibiting lower affinity to CO could be an effective strategy toward preventing such poisoning. In this work, we use density functional theory to demonstrate this strategy, focusing on highly dilute alloys of PGMs (Pd, Pt, Rh, Ir and Ni) with poison resistant coinage metal hosts (Cu, Ag, Au), such that individual PGM atoms are dispersed at the atomic limit forming single atom alloys (SAAs). We show that compared to the pure metals, CO exhibits lower binding strength on the majority of SAAs studied, and we use kinetic Monte Carlo simulation to obtain relevant temperature programed desorption spectra, which are found to be in good agreement with experiments. Additionally, we consider the effects of CO adsorption on the structure of SAAs. We calculate segregation energies which are indicative of the stability of dopant atoms in the bulk compared to the surface layer, as well as aggregation energies to determine the stability of isolated surface dopant atoms compared to dimer and trimer configurations. Our calculations reveal that CO adsorption induces dopant atom segregation into the surface layer for all SAAs considered here, whereas aggregation and island formation may be promoted or inhibited depending on alloy constitution and CO coverage. This observation suggests the possibility of controlling ensemble effects in novel catalyst architectures through CO-induced aggregation and kinetic trapping.

CO2 adsorption on gas-phase Cu4−xPtx (x = 0–4) clusters: a DFT study

Transition and noble metal clusters have proven to be critical novel materials, potentially offering major advantages over conventional catalysts in a range of value-added catalytic processess such as carbon dioxide transformation to methanol.

Theoretical understanding on the selectivity of acrolein hydrogenation over silver surfaces: the non-Horiuti–Polanyi mechanism is the key

The significance of the non-Horiuti–Polanyi mechanism in understanding heterogeneous catalytic hydrogenation reactions is highlighted.