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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]

Increasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd‐based catalysts from first‐principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts. [ABSTRACT FROM AUTHOR]

The active site of the industrial Cu/ZnO/Al2O3 catalyst used in CO2 hydrogenation to methanol has been debated for decades. Grand challenges remain in the characterization of structure, composition, and chemical state, both microscopically and spectroscopically, and complete theoretical calculations are limited when it comes to describing the intrinsic activity of the catalyst over the diverse range of structures that emerge under realistic conditions. Here a series of inverse model catalysts of ZnO on copper hydroxide were prepared where the size of ZnO was precisely tuned from atomically dispersed species to nanoparticles using atomic layer deposition. ZnO decoration boosted methanol formation to a rate of 877 gMeOH kgcat−1 h−1 with ≈80 % selectivity at 493 K. High pressure in situ X‐ray absorption spectroscopy demonstrated that the atomically dispersed ZnO species are prone to aggregate at oxygen‐deficient ZnO ensembles instead of forming CuZn metal alloys. By modeling various potential active structures, density functional theory calculations and microkinetic simulations revealed that ZnO/Cu interfaces with oxygen vacancies, rather than stoichiometric interfaces, Cu and CuZn alloys were essential to catalytic activation. [ABSTRACT FROM AUTHOR]

The active site of the industrial Cu/ZnO/Al2O3 catalyst used in CO2 hydrogenation to methanol has been debated for decades. Grand challenges remain in the characterization of structure, composition, and chemical state, both microscopically and spectroscopically, and complete theoretical calculations are limited when it comes to describing the intrinsic activity of the catalyst over the diverse range of structures that emerge under realistic conditions. Here a series of inverse model catalysts of ZnO on copper hydroxide were prepared where the size of ZnO was precisely tuned from atomically dispersed species to nanoparticles using atomic layer deposition. ZnO decoration boosted methanol formation to a rate of 877 gMeOH kgcat−1 h−1 with ≈80 % selectivity at 493 K. High pressure in situ X‐ray absorption spectroscopy demonstrated that the atomically dispersed ZnO species are prone to aggregate at oxygen‐deficient ZnO ensembles instead of forming CuZn metal alloys. By modeling various potential active structures, density functional theory calculations and microkinetic simulations revealed that ZnO/Cu interfaces with oxygen vacancies, rather than stoichiometric interfaces, Cu and CuZn alloys were essential to catalytic activation. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) are among the most active and studied catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. However, previous studies have generally either focused on a small number of LDHs, applied synthetic routes with limited structural control, or used non‐intrinsic activity metrics, thus hampering the construction of consistent structure–activity‐relations. Herein, by employing new individually developed synthesis strategies with atomic structural control, we obtained a broad series of crystalline α‐MA(II)MB(III) LDH and β‐MA(OH)2 electrocatalysts (MA=Ni, Co, and MB=Co, Fe, Mn). We further derived their intrinsic activity through electrochemical active surface area normalization, yielding the trend NiFe LDH > CoFe LDH > Fe‐free Co‐containing catalysts > Fe‐Co‐free Ni‐based catalysts. Our theoretical reactivity analysis revealed that these intrinsic activity trends originate from the dual‐metal‐site nature of the reaction centers, which lead to composition‐dependent synergies and diverse scaling relationships that may be used to design catalysts with improved performance. [ABSTRACT FROM AUTHOR]

It is of pivotal importance to develop efficient catalysts and investigate the intrinsic mechanism for CO2 methanation. Now, it is reported that PdFe intermetallic nanocrystals afforded high activity and stability for CO2 methanation. The mass activity of fct‐PdFe nanocrystals reached 5.3 mmol g−1 h−1, under 1 bar (CO2:H2=1:4) at 180 °C, being 6.6, 1.6, 3.3, and 5.3 times as high as that of fcc‐PdFe nanocrystals, Ru/C, Ni/C, and Pd/C, respectively. After 20 rounds of successive reaction, 98 % of the original activity was retained for PdFe intermetallic nanocrystals. Further mechanistic studies revealed that PdFe intermetallic nanocrystals enabled the maintenance of metallic Fe species via a reversible oxidation–reduction process in CO2 methanation. The metallic Fe in PdFe intermetallic nanocrystals induced the direct conversion of CO2 into CO* as the intermediate, contributing to the enhanced activity. [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]

Abstract: Stability of dispersed particles on their supports is one of the central topics in heterogeneous catalysis and quantifying the influence of the particle size distribution on lifetime and thermal stability is highly valuable for rational design of efficient nanocatalysts. We report here a theoretical study of Ostwald ripening of supported particles, in particular, the kinetic evolution of particle number, average size, and dispersion with respect to time and thermal temperature in a wide range of size and monodispersity. Phase diagrams of half‐lifetime and onset temperature of ripening as functions of size and monodispersity were constructed. If decreasing the average particle size, though there is a modest gain in the dispersion, the stability declines dramatically; specifically, the half‐lifetime of ripening decreases exponentially and the corresponding onset temperature decreases by hundreds of Kelvin. Decline in stability owing to the decrease in size could, however, be systematically compensated by increasing the monodispersity of the size distribution. We find that the supported particles with the same half‐life time and onset temperature could originate from different particle size distributions, whereas the particle size distribution with the same apparent dispersion could have very different onset temperature and half‐lifetime. The result highlights the importance of both size and monodispersity in particle size distribution to the ripening resistance of supported particles, and the methodology developed for simulating ripening kinetics could be used to accelerate the aging protocols. [ABSTRACT FROM AUTHOR]

Abstract: The stability of supported metal particles is one of the key issues for successful industrialization of catalysts. A theoretical study of Ostwald ripening of supported particles and its dependence on metal‐support interactions, sublimation energy, and surface energy is reported. Two distinct metal‐support interactions are differentiated: metal particle‐support and metal atom‐support. Although strong metal particle‐support interaction (small contact angle) stabilizes the supported particles and improve the ripening resistance, strong metal atom‐support interactions decrease the total activation energy and dramatically lower the onset temperature and half‐life time of ripening, a fact that should be prevented. Moreover, supported particles with low surface energy and/or high sublimation energy of supported particles would have a high onset temperature and a long half‐life time. Compared to the metal particle‐support interaction and surface energy, the metal atom‐support interaction and sublimation energy are most influential to the overall ripening resistance. The present work highlights the importance of interplay between two types of metal‐support interactions on the overall stability of supported particles. [ABSTRACT FROM AUTHOR]

Cobalt-based nanomaterials have been intensively explored as promising noble-metal-free oxygen evolution reaction (OER) electrocatalysts. Herein, we report phase-selective syntheses of novel hierarchical CoTe2 and CoTe nanofleeces for efficient OER catalysts. The CoTe2 nanofleeces exhibited excellent electrocatalytic activity and stablity for OER in alkaline media. The CoTe2 catalyst exhibited superior OER activity compared to the CoTe catalyst, which is comparable to the state-of-the-art RuO2 catalyst. Density functional theory calculations showed that the binding strength and lateral interaction of the reaction intermediates on CoTe2 and CoTe are essential for determining the overpotential required under different conditions. This study provides valuable insights for the rational design of noble-metal-free OER catalysts with high performance and low cost by use of Co-based chalcogenides. [ABSTRACT FROM AUTHOR]

Density functional theory ( DFT) is a powerful tool to study heterogeneous catalysis nowadays. In past decades, numerous DFT calculations have been conducted to investigate the mechanism of catalytic reaction from which the rationale of catalyst design can be revealed. Because the catalyst electronic and geometric structures determine the intrinsic activity, corresponding composition, size, and morphology have been explored extensively to tune the structure-activity relationship for higher activity and selectivity. In this review, we focus on the recent theoretical progress of the crystal phase effect on catalysis. Catalysts with different crystal phases have different symmetries, and could expose very different facets with distinct electronic and geometrical properties, which would have significant influential on the activity and selectivity of the active sites as well as the site density. Exploration of the dependence of catalysis on the crystal phases provides a new rationale of catalysts design toward a high-specific activity. WIREs Comput Mol Sci 2016, 6:571-583. doi: 10.1002/wcms.1267 For further resources related to this article, please visit the . [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]

The selective oxidation of propylene with O2 to propylene oxide and acrolein is of great interest and importance. We report the crystal-plane-controlled selectivity of uniform capping-ligand-free Cu2O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O2: Cu2O octahedra exposing {111} crystal planes are most selective for acrolein; Cu2O cubes exposing {100} crystal planes are most selective for CO2; Cu2O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One-coordinated Cu on Cu2O(111), three-coordinated O on Cu2O(110), and two-coordinated O on Cu2O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO2, respectively. These results reveal that crystal-plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level. [ABSTRACT FROM AUTHOR]

The active site of the industrial Cu/ZnO/Al2O3 catalyst used in CO2 hydrogenation to methanol has been debated for decades. Grand challenges remain in the characterization of structure, composition, and chemical state, both microscopically and spectroscopically, and complete theoretical calculations are limited when it comes to describing the intrinsic activity of the catalyst over the diverse range of structures that emerge under realistic conditions. Here a series of inverse model catalysts of ZnO on copper hydroxide were prepared where the size of ZnO was precisely tuned from atomically dispersed species to nanoparticles using atomic layer deposition. ZnO decoration boosted methanol formation to a rate of 877 gMeOH kgcat−1 h−1 with ≈80 % selectivity at 493 K. High pressure in situ X‐ray absorption spectroscopy demonstrated that the atomically dispersed ZnO species are prone to aggregate at oxygen‐deficient ZnO ensembles instead of forming CuZn metal alloys. By modeling various potential active structures, density functional theory calculations and microkinetic simulations revealed that ZnO/Cu interfaces with oxygen vacancies, rather than stoichiometric interfaces, Cu and CuZn alloys were essential to catalytic activation. [ABSTRACT FROM AUTHOR]

The active site of the industrial Cu/ZnO/Al2O3 catalyst used in CO2 hydrogenation to methanol has been debated for decades. Grand challenges remain in the characterization of structure, composition, and chemical state, both microscopically and spectroscopically, and complete theoretical calculations are limited when it comes to describing the intrinsic activity of the catalyst over the diverse range of structures that emerge under realistic conditions. Here a series of inverse model catalysts of ZnO on copper hydroxide were prepared where the size of ZnO was precisely tuned from atomically dispersed species to nanoparticles using atomic layer deposition. ZnO decoration boosted methanol formation to a rate of 877 gMeOH kgcat−1 h−1 with ≈80 % selectivity at 493 K. High pressure in situ X‐ray absorption spectroscopy demonstrated that the atomically dispersed ZnO species are prone to aggregate at oxygen‐deficient ZnO ensembles instead of forming CuZn metal alloys. By modeling various potential active structures, density functional theory calculations and microkinetic simulations revealed that ZnO/Cu interfaces with oxygen vacancies, rather than stoichiometric interfaces, Cu and CuZn alloys were essential to catalytic activation. [ABSTRACT FROM AUTHOR]