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[Display omitted] • Effect Mn promotion Co-catalyzed Fischer-Tropsch reaction strongly pressure dependent. • MnO dispersed on Co metal particles provides additional sites for CO dissociation. • Mn raises selectivity at low pressure and promotes CO dissociation not chain growth. • At low pressure, Mn enhances activity and C 5+ selectivity. • At high pressure, Mn enhances activity but lowers C 5+ selectivity. The mechanism of Mn promotion of a silica-supported Co catalyst in the Fischer-Tropsch reaction has been studied at varying pressures up to 20 bar. IR spectroscopy in combination with DFT calculations suggest adsorbed CO is activated by reaction with an oxygen vacancy in the MnO, which covers the Co surface. This leads to a higher activity, higher CH x coverage and thus higher C 5+ and lower CH 4 selectivity. Increasing the pressure magnifies the selectivity differences. However, above around 4 bar, the effect of Mn on the selectivities is reversed and the C 5+ selectivity is decreased by Mn addition. This is tentatively attributed to Mn promoting the C-O bond dissociation but not the chain growth. Formed monomers have to migrate to stepped sites for chain growth on the Co surface. Whilst this is migration is not impeded by co-adsorbates at low pressure, migration could be hindered by especially the high CO coverage at high pressure. [ABSTRACT FROM AUTHOR]

Strong metal–support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au‐TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au‐TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2{101} facets. The resulting capsulating TiO2−x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au‐to‐TiO2−x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2−x overlayers and TiO2−x‐Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low‐temperature CO oxidation than the starting Au‐TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis. [ABSTRACT FROM AUTHOR]

Strong metal–support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au‐TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au‐TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2{101} facets. The resulting capsulating TiO2−x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au‐to‐TiO2−x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2−x overlayers and TiO2−x‐Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low‐temperature CO oxidation than the starting Au‐TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis. [ABSTRACT FROM AUTHOR]

Strong metal–support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au‐TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au‐TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2{101} facets. The resulting capsulating TiO2−x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au‐to‐TiO2−x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2−x overlayers and TiO2−x‐Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low‐temperature CO oxidation than the starting Au‐TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis. [ABSTRACT FROM AUTHOR]

• Fe 3 Co@NG-C shows excellent ORR activity in alkaline solution. • Fe 3 Co@NG-C exhibits enhanced durability and tolerance to methanol. • The activity of Fe 3 Co@NG-C is determined by the strain in N-doped graphene. Nitrogen-doped graphene is a promising non-precious metal electrocatalyst for the oxygen reduction reaction (ORR). We report that distorted nitrogen-doped graphene layers encapsulating Fe 3 Co nanoparticles supported on carbon (Fe 3 Co@NG-C) display excellent activity toward ORR in alkaline media. Compared with a commercial Pt/C electrocatalyst at a loading of 80 μg Pt /cm2 on a rotating disk electrode, the Fe 3 Co@NG-C exhibits an onset potential positively shifted by 50 mV at 0.1 mA/cm2 and a nearly identical half-wave potential. The Fe 3 Co@NG-C has minimal activity degradation during accelerated durability testing and superior tolerance to methanol than commercial Pt/C. Density functional theory calculations combined with poisoning experiments reveal that the high activity of the Fe 3 Co@NG-C mainly arises from strain in nitrogen-doped graphene induced by encapsulation of Fe 3 Co nanoparticles with exposed (1 1 0) planes, which promotes stabilization of the key OOH* intermediate involved in ORR. Our study shows the rational design of improved carbon-based electrocatalysts for ORR can be achieved by using strain engineering. [ABSTRACT FROM AUTHOR]

Step sites over terrace sites have been suggested to be the active sites in many catalytic reactions particularly bond breaking of diatomic molecules. Aiming to provide insight into the role of step sites in multiatomic molecules bond breaking reactions and their dependence on catalysts, we present herein a systematic first-principles study of carbon-oxygen bond scission of diatomic CO and multiatomic HCO and CH3HCO on flat and stepped Co, Rh, and Ir surfaces. We find that multiatomic molecules exhibit distinct carbon-oxygen scission activity from diatomic molecules regardless of the metal catalysts (Co, Rh, and Ir) considered: compared to the huge enhancement of step sites for CO with a barrier 0.81-1.29 eV lower than that of flat surfaces, the role of step sites for CH3CHO is substantially weakened with a barrier 0.11-0.27 eV higher than that of flat surfaces. The reason for this is the change of adsorption configurations on flat surfaces and increase of Pauli repulsion on the congested stepped sites for the dissociation of multiatomic molecules. [ABSTRACT FROM AUTHOR]

Highlights: [•] Direct CO dissociation is structurally most sensitive, whereas CH x (x =0–3) hydrogenation is structurally least sensitive on Co (0001), and surfaces. [•] H-assisted CO dissociation pathway is favored over direct CO dissociation pathway on Co (0001), whereas both pathways contribute to CO methanation on more active Co and surfaces. [•] The rate determining step is CO activation regardless of the Co surfaces considered. [ABSTRACT FROM AUTHOR]

Understanding Ostwald ripening and disintegra-tion of supported metal particles under operating conditions has been of central importance in the study of sintering and dispersion of heterogeneous catalysts for long-term industrial implementation. To achieve a quantitative description of these complicated processes, an atomistic and generic theory taking into account the reaction environment, particle size and morphology, and metal-support interaction is developed. It includes (1) energetics of supported metal particles, (2) formation of monomers (both the metal adatoms and metal--reactant complexes) on supports, and (3) corresponding sintering rate equations and total activation energies, in the presence of reactants at arbitrary temperature and pressure. The thermodynamic criteria for the reactant assisted Ostwald ripening and induced disintegration are formulated, and the influence of reactants on sintering kinetics and redispersion are mapped out. Most energetics and kinetics barriers in the theory can be obtained conveniently by first-principles theory calculations. This allows for the rapid exploration of sintering and disintegration of supported metal particles in huge phase space of structures and compositions under various reaction environments. General strategies of suppressing the sintering of the supported metal particles and facilitating the redispersions of the low surface area catalysts are proposed. The theory is applied to TiO2(110) supported Rh particles in the presence of carbon monoxide, and reproduces well the broad temperature, pressure, and particle size range over which the sintering and redispersion occurred in such experiments. The result also highlights the importance of the metal--carbonyl complexes as monomers for Ostwald ripening and disintegration of supported metal catalysts in the presence of CO. [ABSTRACT FROM AUTHOR]

Precise regulation of the active site structure is an important means to enhance the activity and selectivity of catalysts in CO2 electroreduction. Here, we creatively introduce anionic groups, which can not only stabilize metal sites with strong coordination ability but also have rich interactions with protons at active sites to modify the electronic structure and proton transfer process of catalysts. This strategy helps to convert CO2 into fuel chemicals at low overpotentials. As a typical example, a composite catalyst, CuO/Cu−NSO4/CN, with highly dispersed Cu(II)−SO4 sites has been reported, in which CO2 electroreduction to formate occurs at a low overpotential with a high Faradaic efficiency (−0.5 V vs. RHE, FEformate=87.4 %). Pure HCOOH is produced with an energy conversion efficiency of 44.3 % at a cell voltage of 2.8 V. Theoretical modeling demonstrates that sulfate promotes CO2 transformation into a carboxyl intermediate followed by HCOOH generation, whose mechanism is significantly different from that of the traditional process via a formate intermediate for HCOOH production. [ABSTRACT FROM AUTHOR]

The performance of a chemical reaction is critically dependent on the electronic and/or geometric structures of a material in heterogeneous catalysis. Over the past century, the Sabatier principle has already provided a conceptual framework for optimal catalyst design by adjusting the electronic structure of the catalytic material via a change in composition. Beyond composition, it is essential to recognize that the geometric atomic structures of a catalyst, encompassing terraces, edges, steps, kinks, and corners, have a substantial impact on the activity and selectivity of a chemical reaction. Crystal-phase engineering has the capacity to bring about substantial alterations in the electronic and geometric configurations of a catalyst, enabling control over coordination numbers, morphological features, and the arrangement of surface atoms. Modulating the crystallographic phase is therefore an important strategy for improving the stability, activity, and selectivity of catalytic materials. Nonetheless, a complete understanding of how the performance depends on the crystal phase of a catalyst remains elusive, primarily due to the absence of a molecular-level view of active sites across various crystal phases. In this review, we primarily focus on assessing the dependence of catalytic performance on crystal phases to elucidate the challenges and complexities inherent in heterogeneous catalysis, ultimately aiming for improved catalyst design. [ABSTRACT FROM AUTHOR]

Site activity and density are two key factors in determining the overall activity of catalysts in heterogeneous catalysis. Combined DFT calculation, Wulff construction and micro‐kinetic analysis, we reveal here a significant interplay between site activity and density of bcc iron catalyzed ammonia synthesis at low coverage regime. It is found that for large size particles, Fe (111) and (311) surfaces that consist of active C7 sites are limited by their low site density, whereas those with the most abundant sites are limited by their low activity. In contrast, Fe (221), (211) and (310) surfaces which consist of active C7 and/or B5 sites and remain abundant, dominate the overall reaction rate, turn‐over‐frequency and mass specific activity. Turn‐over‐frequency of the smaller Fe particles (2–6 nm) decreases by a factor of two or three due to the absence of (221) surface. For the particle size less than 2 nm, the corresponding activity decreases dramatically owing to the absence of all active C7 and/or B5 sites. Interplay of site abundance and intrinsic activity of catalysts is highlighted, and the insights revealed could be used to design and develop better catalysts for ammonia synthesis and other important reactions of technological interest. Give me the 221! Fe (221), (211) and (310) surfaces which consist of C7 and/or B5 sites and remain abundant, dominate the overall reactivity of the particles larger than 6 nm. The absence of (221) surface at the particle size of 2–6 nm lowers the corresponding TOF. With particle size below 2 nm, the TOF dramatically decreases because of no C7 and B5 sites exposed. [ABSTRACT FROM AUTHOR]

Synthesis of atomically dispersed catalysts with high metal loading and thermal stability is challenging but particularly valuable for industrial application in heterogeneous catalysis. Here, we report a facile synthesis of a thermally stable atomically dispersed Ir/α-MoC catalyst with metal loading as high as 4 wt%, an unusually high value for carbide supported metal catalysts. The strong interaction between Ir and the α-MoC substrate enables high dispersion of Ir on the α-MoC surface, and modulates the electronic structure of the supported Ir species. Using quinoline hydrogenation as a model reaction, we demonstrate that this atomically dispersed Ir/α-MoC catalyst exhibits remarkable reactivity, selectivity and stability, for which the presence of high-density isolated Ir atoms is the key to achieving high metal-normalized activity and mass-specific activity. We also show that the water-promoted quinoline hydrogenation mechanism is preferred over the Ir/α-MoC, and contributes to high selectivity towards 1,2,3,4-tetrahydroquinoline. The present work demonstrates a new strategy in constructing a high-loading atomically dispersed catalyst for the hydrogenation reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Regardless of morphology, 3-fold S vacancy on MoS 2 is poisoned by O, retarding CO 2 + H 2. • Bridge S vacancy on MoS 2 destabilizes O, increasing the rate by 7 orders of magnitude. • Distinct mechanism is found on 3-fold (direct) and bridge S vacancy (associative) • Optimal S vacancy type is identified on MoS 2 , providing an alternative to noble metal. • Coordination of vacancy tuned activity illustrates a promising way to design catalyst. Vacancies, typically exist in various types and morphologies on the surfaces of transition metal compound catalysts, have been shown to play an important role in many catalytic reactions. However, identifying the optimal type and morphology of vacancy and the key factors that control its performance remains a significant challenge. By density functional theory calculations and microkinetic modeling, we show that compared to various threefold S vacancy morphologies on the basal plane, the lower coordination number at the bridge S vacancy of Mo edge on MoS 2 tunes the relative adsorption strength of key intermediates (such as O relative to OH). This not only increases CO 2 hydrogenation rate by 7–11 orders of magnitude, but also leads to clearly distinct mechanism (associative & redox). The large destabilization of O and low H coverage on the Mo edge also hinder C-O scission and hydrogenation (give CH 4 and CH 3 OH) relative to CO desorption, leading to almost 100% CO selectivity. The inexpensive MoS 2 catalyst provides an alternative to the traditional noble metal catalysts for reverse water gas shift, and the coordination number of vacancy modulated catalytic performance illustrates a promising way to design transition metal compound catalysts for other important reactions of technological interest. [ABSTRACT FROM AUTHOR]

Rather than multivalence molybdenum (Mo), the low valence Mo has rarely been reported as active site for nitrogen reduction. Herein, molybdenum borides with various Mo-B stoichiometry ratios (Mo 2 B, α-MoB, and Mo 2 B 4) in which Mo shows low valence (<1) are synthesized as electrochemical nitrogen reduction reaction (eNRR) catalysts. Mo 2 B 4 demonstrates the highest NH 3 yield of 7.65 µg h− 1/mg at − 0.15 V with Faradaic efficiency (FE) of 12.47 %, while α-MoB exhibits the fastest intrinsic eNRR reaction rate with a higher FE of 17.17 % after considering electrochemically active surface area. DFT calculations reveal that both enzymatic and consecutive mechanisms via side-on configuration can proceed on α-MoB. Additionally, α-MoB exhibits suppressed HER activity due to an optimal surface B occupancy. The eNRR of molybdenum borides were verified qualitatively and quantitatively by 15N 2 isotope experiments. This study demonstrated a synergistic design of eNRR and HER activity to achieve efficient electrocatalytic ammonia production with high eNRR selectivity. [Display omitted] • Phase-pure molybdenum borides with tunable composition are synthesized without high pressure. • eNRR performance depends strongly on the crystallographic structure of molybdenum borides. • A synergistic design of eNRR and HER to achieve efficient electrocatalytic ammonia production with high eNRR selectivity was demonstrated. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of CO 2 can contribute to the storage of excess renewable electricity in chemical bonds. Here we incorporate reaction energetics for CO 2 reduction on Cu(111) and Cu(211) determined by DFT calculations in microkinetics simulations to predict the influence of surface topology, the presence of water and possible diffusion limitations on current density-potential curves and Faradaic efficiencies. A reaction-diffusion model was used that takes into account the effect of electrochemical potential on the stability of intermediates and associated activation barriers in proton-coupled electron transfer steps as well as diffusion of protons and CO 2 from the bulk electrolyte to the electrode surface. The basic model can well reproduce hydrogen evolution including the effect of proton diffusion limitations and a shift of proton reduction (low potential) to water reduction (high potential). Considering CO 2 electro-reduction, the stepped Cu(211) surface is more active than the Cu(111) terrace towards HCOO(H), CO and CH 4. The presence of a catalytic H 2 O molecule increases the overall rate and selectivity to products (CO and CH 4) derived from dissociated CO 2. A catalytic H 2 O molecule facilitates the difficult electrochemical CO 2 activation step to COOH and suppresses the competing activation step towards HCOO, which mainly yields HCOO(H). In general, the current densities increase at higher negative potential and the products follow the sequence CO 2 → CO → CH 4. That is to say, CO 2 is converted to CO via COOH dissociation, followed by CO hydrogenation. Trendwise, the simulated product distribution follows the potential-dependent distribution observed in experiment. The low selectivity to CH 3 OH can be understood from the fast electrochemical steps that lead to CH x -OH dissociation. At high overpotentials the hydrogenation step from CO 2 to COOH controls both activity and selectivity towards CH 4. At high potential CO 2 reduction becomes increasingly diffusion-limited, thus limiting the selectivity of CO 2 reduction vs. hydrogen evolution. This aspect supports the need for better design of mass transfer in electrochemical reactors, which operate at high current density. Image 1 • We simulated electrochemical CO 2 reduction on Cu(111) and Cu(211) surfaces. • The model includes water reduction, a diffusion layer for CO 2 , and pH gradients. • The simulations predict realistic current densities and Faradaic efficiencies. • Water molecules stabilize essential transition states for CO 2 activation. • Step-edge sites show high methane production via the CO 2 → COOH → CO → CH 4 pathway. [ABSTRACT FROM AUTHOR]

The replacement of platinum group metals by non-noble metals has attracted significant attention in the field of three-way catalysis. Here, we use DFT calculations to comprehensively study NO reduction by CO and CO oxidation on Pd(1 1 1) and transition metal doped Pd(1 1 1). Whilst direct NO dissociation is very difficult on metallic Pd(1 1 1), doping with transition metals can substantially lower the reaction barrier for NO dissociation. The lowest barrier is predicted for Ti-doped Pd(1 1 1). An electronic structure analysis shows that the low barrier is due to the strong adsorption of N and O on surface sites involving Ti atoms. It relates to strong hybridization of the N and O orbitals with the half-filled d -band of the metallic surface. At the same time, the anti-bonding states are shifted above the Fermi level, which further strengthens the adsorption of N and O. A Brønsted-Evans-Polanyi relation for NO dissociation on TM-doped Pd(1 1 1) surfaces is identified. The complete reaction pathway for N 2 , N 2 O and CO 2 formation on Pd(1 1 1) and Ti-doped Pd(1 1 1) was considered. Besides more facile NO dissociation, the energy barrier for CO oxidation is decreased for the Ti-doped surface. Microkinetics simulations confirm that the activity and selectivity for NO reduction and CO oxidation are drastically improved after Ti doping. Our findings indicate that doping of Pd with non-noble metal can further improve the performance of three-way catalysts. [ABSTRACT FROM AUTHOR]

Developing advanced Fischer-Tropsch synthesis (FTS) technology to acquire fuel and valuable chemicals from non-petroleum sources more efficiently is one of the important tasks in heterogeneous catalysis and chemical engineering research. With the purpose of improving iron-based FTS catalyst, we explored the modification effect of boron on the χ-Fe 5 C 2 catalyst by density functional theory (DFT) calculations. Boron atom adsorption on χ-Fe 5 C 2 surfaces is considered to modulate the stability as well as the activity of CO activation on FTS process. Anti-coking can be observed when boron atom adsorbs on χ-Fe 5 C 2 catalyst due to the competitive adsorption and repulsive interactions between carbon and boron atoms. More open and active planes, such as (311), (021), and (31 2 ̅) facets, can expose in the morphology of χ-Fe 5 C 2 when boron atom adsorbs on χ-Fe 5 C 2. It is found that co-adsorbed boron atoms have little effect on the barrier of CO direct dissociation in most cases, while there is also particular situation that CO is adsorbed and activated on boron with carbon termination. Our work shed light on the promoting effects of boron adsorption on CO activation, which can provide useful guide for the design of novel iron-based FTS catalysts. [Display omitted] Boron atoms adsorption increases the ratio of (311), (021) and (31 2 ̅) surfaces which are of lower CO activation barrier exposed. • Adsorbed boron atoms on χ-Fe 5 C 2 surfaces occupy the site for carbon deposition and repel carbon atom at near site. • The area of more active and open surfaces increases in the presence of boron atom. • Boron atoms adsorption increase the activity of CO direct activation on χ-Fe 5 C 2 surfaces. [ABSTRACT FROM AUTHOR]