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In heterogeneous catalysis, supported single-atom, single-cluster, and nanocatalysts have attracted wide attention. The interaction of single atoms and single clusters with support determines the stability and activity of the catalysts. To understand the type and strength of metal–support interaction, the adsorption structures and energies of transition metals (Mn= Fe, Ru, Os, Co, Ni, and Cu, n= 1–6) on the fully dehydrated silica (001) surface have been systematically computed based on spin-polarized density functional theory (GGA-rPBE-D3). It is found that aggregated structures are more stable than singly dispersed structures, indicating stronger metal–metal interaction. The adsorption energy increases from Fe, Ru to Os, while decreases from Fe, Co, Ni to Cu. Electron transfer from the metal to support has been found for Fe, Co, Ni, and Cu, while that from the metal to support and within the metal cluster has been found for Ru and Os, indicating the additional polarization and electrostatic interaction.

Ternary intermetallic electrides (LaTMSi) are a class of electride materials that show excellent catalytic performance in hydrogenation reactions due to their unique geometric and electronic structures. Compared with conventional electrides, such as C12A7: e–, LaTMSi show higher structural stability of bulk phase in air and water. However, their catalytic activities decrease gradually in reaction systems with H2O as the product. In the previous literatures, the deactivation behavior was attributed to the fact that H atoms enter into the LaTMSi lattice, occupy the electron sites, and lower the electron-donating ability. As a solution, the catalytic activities were supposed to be recovered by calcinating LaTMSi at high temperatures. Herein, under a H2O-containing atmosphere, TEM observations reveal that an amorphous shell with a thickness of ∼3 nm can form on the surface of the LaCu0.67Si1.33phase even at room temperature. This amorphous layer is relatively stable at room temperature and can prevent the bulk phase from further structural evolution. However, the amorphous layer will undergo peeling off at a high temperature, thus resulting in a new catalytic active surface. Therefore, high-temperature calcination is an effective method to strip away the deactivated surface on LaTMSi which was caused by occasional exposures to H2O. However, for H2O-containing catalytic systems, frequently alternating reactions with H2O and calcination will lead to complete phase transition from LaTMSi to the corresponding oxides. Taking the LaCu0.67Si1.33sample as an example, X-ray powder diffraction proves the formation of the CuO2phase at 500 °C under a H2O atmosphere. Therefore, LaTMSi materials should not be applied as catalysts in H2O-containing systems. In addition, the facile H2O dissociation over the LaCu0.67Si1.33phase is verified by using various experimental approaches (e.g., cyclic H218O pulse-TPD, high-temperature H218O pulse-TPSR, and IR) and theoretical calculations. Moreover, similar surface dissociation of H2O and phase transition are also observed over LaCoSi and LaNiSi ternary intermetallic electrides.

The chain growth mechanisms of Fischer–Tropsch synthesis (FTS) remain a controversial topic, especially considering the much stronger adsorption ability of CO over H2, resulting in CO pre-adsorption or saturation. Systematic periodic density functional theory computations (GGA-rPBE), and the analysis of ab initioatomistic thermodynamics and micro-kinetics on the Ru(111) surface revealed that the dense CO layer at a very early stage of FTS suppresses CO activation, promotes the coupling of CHx(x= 0–3) and C1 as an insertion monomer (C1 = C, CH, CH2, CH3, CO, HCO and COH) under favorable conditions, especially for CH2(or CH3) + CO coupling mechanisms. An HCO-insertion mechanism into RCH (R = H, CH3, …) [HCO + CH2→ CH2CHO → CH2CO → CH3CO → CH3C + O → CH3CH (+ HCO) → …] was proposed at the lowest coverage, while a CO insertion mechanism into RCH (R = H, CH3, …) [CO + CH2→ CH2CO (CH3+ CO) → CH2C + O (CH3CO) → CH3C + O → CH3CH (+ CO) → …] was proposed at CO pre-saturation coverage (423 K, 10 atm) on the Ru(111) surface.

Solid surfaces usually reach thermodynamic equilibrium through particle exchange with their environment under reactive conditions. A prerequisite for understanding their functionalities is detailed knowledge of the surface composition and atomistic geometry under working conditions. Owing to the large number of possible Miller indices and terminations involved in multielement solids, extensive sampling of the compositional and conformational space needed for reliable surface energy estimation is beyond the scope of ab initiocalculations. Here, we demonstrate, using the case of iron carbides in environments with varied carbon chemical potentials, that the stable surface composition and geometry of multielement solids under reactive conditions, which involve large compositional and conformational spaces, can be predicted at ab initioaccuracy using an approach that combines the bond valence model, Gaussian process regression, and ab initiothermodynamics. Determining the atomistic structure of surfaces under working conditions paves the way toward identifying the true active sites of multielement catalysts in heterogeneous catalysis.

To understand the reaction mechanisms of the dehydrogenation and retrosynthesis of alkanes, the consecutive dissociation of methane, ethane, ethene and ethyne, as well as propane, propene and propyne, on the fcc Ru(111) surface has been investigated using periodic density functional theory computations (rPBE). Methane dissociation has the energy minimum path of → → → CH* → C*. Although ethane dissociation does not have ethene and ethyne as intermediates, they have the same final surface species with the minimum energy paths for ethane [→ → CH3CH* → CH3C* → → HC*C* → HC* + C*], ethene [→ → → HC*C* → HC* + C*] and ethyne [CH*CH* → HC*C* → HC* + C*]. Propane dissociation has the competitive routes of n-propyl [→ CH3CH2CH* → CH3CH2C* → CH3CH*C* → CH3C*C* → CH3C* + C* →→ HC* + C*] and isopropyl with propyne as an intermediate [CH3CH*CH3→ CH3C*CH3→ → CH3C*CH* → CH3C*C* →→ HC* + C*], and the n-propyl route has propene as an intermediate for dissociation [→ CH3C*CH2*/CH3CH*CH* → CH3CH*C*/CH3C*CH* → CH3C*C* →→ HC* + C*]. In these reactions, the most stable surface intermediates are HC*, CH3C* and CH3CH2C* as homologs, as found experimentally on other metal surfaces. Our results rationalized the experimentally observed interconversion between + H* and CH3C* as well as surface HC*C* and CH3C*C* as key intermediates for the first C–C bond dissociation [HC*C* → HC* + C*; CH3C*C* → CH3C* + C*]. On the basis of surface C* and H2gas, the retrosynthesis of methane, ethane and propane has increasing apparent barriers of 1.08, 1.51 and 1.66 eV, respectively, at 490 K and 1 atm H2and 0.83, 1.14 and 1.15 eV, respectively, at 19.7 atm H2. Surface carbon coverage changes the formation of alkanes from endergonic to exergonic. This pressure- and coverage-dependency is very important for understanding the reaction mechanism and selectivity. Surface alkynyl groups should be the intermediates for C–C coupling. The computed vibrational frequencies of CH*, CH3C*, CH2C*, HC*C* and agree with the experiments. The comparison in adsorption energies and reaction barriers and energies shows that the fcc Ru(111) surface is more active than the hcp Ru(0001) surface despite their very similar surface structures.

Deep insights into the chemical nature of surface free energy are important to achieve a rational design of solid materials with desired morphologies and functionalities such as electronic properties and catalytic performances. Practically, the determination of surface free energy and crystal morphology relies on density functional theory (DFT) calculations in a brute force way. In this work, we propose a new concept named generalized atomic valence to describe the atomic coordination environment of surface atoms. Guided by chemical intuition, we further develop a simple geometric descriptor with no adjustable parameters, the degree of surface undercoordination, to quantify the disruption of intermolecular bonds of arbitrary surface structures, which allows accurate prediction of surface free energies. Comparative calculations with DFT show that it can predict the relative surface free energy, even for the high-index and imperfect ones, and roughly estimate the crystal morphology for all group VIII transition metals other than Fe. This descriptor provides new insights into the concept of surface free energy and will potentially accelerate the discovery of solid materials with desired morphology by computational high-throughput screening.

In this study, a series of Co nanoparticles (NPs) with different sizes and Co single-atom catalysts (SACs) with different cobalt–nitrogen coordination numbers (Co–N2, Co–N3, and Co–N4) were synthesized and applied to the synthesis of ammonia catalyzed by plasma at low temperatures and atmospheric pressures. Under the same reaction conditions, the yield of nitrogen obtained from the reduction to ammonia over a series of Co NP catalysts varies with the Co particle size. The smaller the size of the Co NPs, the greater the number of exposed active centers, and the catalytic activity is higher. Among the Co SACs, the best catalyst was Co–N2with two coordinated nitrogen atoms, and the ammonia yield was 181 mg·h–1·gcat–1. The experimental and theoretical calculations were consistent in that a low Co–N coordination number was beneficial to the adsorption and dissociation of N2, thereby enhancing the reduction activity of N2and promoting the increase of ammonia production.