Breaking the scaling relations for efficient N_(2)-to-NH_(3) conversion by a bowl active site design:Insight from LaRuSi and isostructural electrides

The design of optimal heterogeneous catalysts for N_(2)-to-NH_(3) conversion is often dictated by the scaling relations,which result in a volcano curve that poses a limit on the catalytic performance.Herein,we reveal a bowl active site that can break the scaling relations,through investigating the catalytic mechanisms of N_(2)-to-NH_(3) conversion on the lanthanide intermetallic electride catalyst LaRuSi by first-principles modeling.This bowl active site,composed of four surface La cations and one subsurface Si atom rich in electrons,plays the key role in enabling efficient catalysis.With adaptive electrostatic and orbital interactions,the bowl active site promotes the adsorption and activation of N_(2) that delivers facile cleavage of N-N bond,while destabilizes the adsorptions of ^(*)NH_(x)(x=1,2,3)species,which facilitates the release of the final NH_(3) product.By comparison with other electride catalysts isostructural to LaRuSi,we confirm the breaking of scaling relations between the adsorptions of ^(*)NH_(x) species and that of^(*)N on the bowl active site.Thus,this bowl active site presents a design concept that breaks the scaling relations for highly efficient heterogeneous catalysis of N_(2)-to-NH_(3) conversion.

Assessing Dual Rh/Ru Cascade Catalysts in One-Pot Homogeneous Synthesis of Ethanol from Syngas and Methanol

The direct conversion of cheap syngas into value-added ethanol at an industrial scale is in high demand.Herein we disclose a one-pot homogeneous homologation of methanol to ethanol with syngas via a rhodium/ruthenium bimetallic catalytic approach.By introducing a catalytic amount of methyl iodide,methanol can be converted to ethanol with high selectivity(>91%ethanol).A syngas ratio of H_(2)/CO=4:1 was found to be optimal.Among various phosphine ligands tested,Rh-dppp catalyst gave the highest aldehyde pathway selectivity,thus providing an effective route for the synthesis of ethanol upon coupling with a Ru hydrogenation catalyst.The bite angle of the bisphosphine ligands dramatically influences the selectivity of the dual Rh/Ru metallic cascade catalysts.In line with the experimental findings,theoretical calculations predicted a rational trend of the selectivity of different bisphosphine ligands via varying bite angle properties.

Ultrastable single-atom gold catalysts with strong covalent metal-support interaction （CMSI）

Supported noble metal nanoparticles （including nanoclusters） are widely used in many industrial catalytic processes. While the finely dispersed nanostructures are highly active, they are usually thermodynamically unstable and tend to aggregate or sinter at elevated temperatures. This scenario is particularly true for supported nanogold catalysts because the gold nanostructures are easily sintered at high temperatures, under reaction conditions, or even during storage at ambient temperature. Here, we demonstrate that isolated Au single atoms dispersed on iron oxide nanocrystallites （Aul/FeOx） are much more sintering- resistant than Au nanostructures, and exhibit extremely high reaction stability for CO oxidation in a wide temperature range. Theoretical studies revealed that the positively charged and surface-anchored Aul atoms with high valent states formed significant covalent metal-support interactions （CMSIs）, thus providing the ultra-stability and remarkable catalytic performance. This work may provide insights and a new avenue for fabricating supported Au catalysts with ultra-high stability.

Catalytic mechanism and bonding analyses of Au–Pd single atom alloy(SAA):CO oxidation reaction

Single-atom catalysts(SACs),including metalmetal-bonded bimetallic ones named single-atom alloys(SAAs),have aroused significant interest in catalysis.In this article,the catalytic mechanism and bonding analysis of CO oxidation reaction on bimetallic gold–palladium(Au–Pd)model of single atom alloy Au37Pd1 are investigated by using quantum chemical calculations.The molecular geometries and adsorbate/substrate binding energies of CO@Au–Pd,O2@Au–Pd and CO/O2@Au–Pd configurations are identified.The core-shell structure is confirmed to be the most stable structure for Au–Pd SAA,where the Pd atom prefers to situate at the core site.Charge transfer from the Pd atom to the Au atoms has been confirmed to stabilize the structure.According to the binding energy and chemical bonding analysis,both CO and O2 prefer to bind to the Pd atom at the hex site with low coordination number.The formation of new co-adsorption species is identified,in which vertical and parallel bridging adsorptions of CO and O2 on the Au–Pd bonds are observed.CO oxidation on Au–Pd SAA is found to be feasible with low energy barriers and follows the Langmuir-Hinshewood(L-H)mechanism.Our work offers insights into the significant role of single atom of the SAAs in catalytic reactions and can provide evidence for designing new SAAs with high-performance catalytic activities.

Theoretical studies of MXene-supported single-atom catalysts:Os_(1)/Ti_(2)CS_(2) for low-temperature CO oxidation

We report herein a new sulfur-functionalized MXene Ti_(2)C(Ti_(2)CS_(2))-supported osmium-metal single-atom catalyst(SAC) Os_(1)/Ti_(2)CS_(2)with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os_(1)/Ti_(2)CS_(2), has been screened from a series of group 8–11 transition metal SACs M_(1)/Ti_(2)CS_(2)(M = Fe, Co, Ni, Cu;Ru, Rh, Pd, Ag;Os, Ir,Pt, Au). The calculations show that it is favorable for O;and CO to be coadsorbed on the Os;single atom(SA) of Os_(1)/Ti_(2)CS_(2)and the adsorption energy of the first O_(2) molecule is slightly higher than that of CO. Moreover, the termolecular co-adsorption of O_(2)+ 2CO on Os_(1) SA is also possible, which is favorable for CO oxidation on Os_(1) SA through a novel threemolecule reaction mechanism. Accordingly, four different catalytic mechanisms, the Langmuir–Hinshelwood(L–H),Eley–Rideal(E–R), termolecular Langmuir–Hinshelwood-A(TLH-A) and termolecular Langmuir–Hinshelwood-B(TLHB), are systematically studied for CO oxidation by O_(2) on Os_(1)/Ti_(2)CS_(2). The theoretical studies indicate that the TLH-B mechanism is the most feasible for CO oxidation with the reaction barrier energy of only 0.74 e V, which is far lower than for L–H, E–R and TLH-A with barrier energies of 1.06, 1.09 and1.47 e V, respectively. The results provide fundamental understanding to the surface chemistry of MXene and designing new sulfur-functionalized two-dimensional MXene catalytic nanomaterials.

Recent Developments of Dinitrogen Activation on Metal Complexes and Clusters

Dinitrogen(N_(2)) is the major component of the atmosphere and many factors bring about dinitrogen inertness with low reactivity. Dinitrogen activation on metal complexes and clusters under ambient condition is the long-standing goal in the modern chemistry. In this review,an attempt has been made to survey the mechanistic aspects of dinitrogen activation and functionalization based on different coordination binding modes of dinitrogen. Our goal is to provide a comprehensive survey of dinitrogen activation in order to guide the relevant research in the future.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Fundamental knowledge of structure-activity correlations for heterogeneous single-atom catalysts(SACs)is essential in guiding catalytic design.While linear scaling relations are powerful for predicting the performance of traditionalmetal catalysts,they appear to fail with the involvement of SACs.Comparing the catalytic CO oxidation activity of different atomically dispersed metals(3d,4d,and 5d)in conjunction with computational modeling enabled us to establish multiple scaling relations between the activity and simply calculated descriptors.

Understanding the Electronic Structure and Stability of B_(n)X_(n)^(0/2-)(n=4,6;X=H,F,Cl,Br,I,At,Ts)Clusters

Main observation and conclusion Borane clusters and their derivatives have attracted extensive attention in inorganic chemistry due to their fascinating multi-center bonding patterns and physicochemical properties.Here we report a systematic theoretical investigation on the geometry.

A binding-block ion selective mechanism revealed by a Na/K selective channel

Mechanosensitive （MS） channels are extensively stud- ied membrane protein for maintaining intracellular homeostasis through translocating solutes and ions across the membrane, but its mechanisms of channel gating and ion selectivity are largely unknown. Here, we identified the Ynal channel as the Na^＋/K^＋ cation-selec- tive MS channel and solved its structure at 3.8 A by cryo- EM single-particle method. Ynal exhibits low conduc- tance among the family of MS channels in E. coil, and shares a similar overall heptamer structure fold with previously studied MscS channels. By combining structural based mutagenesis, quantum mechanical and electrophysiological characterizations, we revealed that ion selective filter formed by seven hydrophobic methionine （Ynal^Met158） in the transmembrane pore determined ion selectivity, and both ion selectivity and gating of Ynal channel were affected by accompanying anions in solution. Further quantum simulation and functional validation support that the distinct binding energies with various anions to Ynal^Met158 facilitate Na^＋/K^＋ pass through, which was defined as binding-block mechanism. Our structural and functional studies provided a new perspective for understanding the mechanism of how MS channels select ions driven by mechanical force.