Dipole Coupling Accelerated H2 O Dissociation by Magnesium-Based Intermetallic Catalysts

The water (H2 O) dissociation is critical for various H2 O-associated reactions, including water gas shift, hydrogen evolution reaction and hydrolysis corrosion. While the d-band center concept offers a catalyst design guideline for H2 O activation, it cannot be applied to intermetallic or main group elements-based systems because Coulomb interaction was not considered. Herein, using hydrolysis corrosion of Mg as an example, we illustrate the critical role of the dipole of the intermetallic catalysts for H2 O dissociation. The H2 O dissociation kinetics can be enhanced using Mgx Mey (Me=Co, Ni, Cu, Si and Al) as catalysts, and the hydrogen generation rate of Mg2 Ni-loaded Mg reached 80 times as high as Ni-loaded Mg. The adsorbed H2 O molecules strongly couple with the Mg-Me dipole of Mgx Mey , lowering the H2 O dissociation barrier. The dipole-based H2 O dissociation mechanism is applicable to non-transition metal-based systems, such as Mg2 Si and Mg17 Al12 , offering a flexible catalyst design strategy for controllable H2 O dissociation.

A simplified and facile preparation method for the [Ca24Al28O64]4+(e-)4 electride

Wide application of novel materials often requires low-cost preparation methods. In this study, we present a simplified and facile preparation method for the [Ca24Al28O64]4+(e-)4 electride material (C12A7:e-). Successful preparation of the C12A7:e- electride was confirmed by XRD patterns and magnetic behavior analysis. The concentration of electrons in the prepared C12A7:e- powder was calculated to be approximately 2.23 × 1021 cm-3, as evaluated by iodometry and TPD. DFT calculations provided insight into the unique electronic structure of C12A7:e-. Additionally, the substitution of the Ca reductant with CaH2 led to a reduction in the solid-state reaction temperature from 1100 to 950 °C, which can be attributed to thermodynamic effects such as a reduction in ΔG°.

Multiple reaction pathway on alkaline earth imide supported catalysts for efficient ammonia synthesis

The tunability of reaction pathways is required for exploring efficient and low cost catalysts for ammonia synthesis. There is an obstacle by the limitations arising from scaling relation for this purpose. Here, we demonstrate that the alkali earth imides (AeNH) combined with transition metal (TM = Fe, Co and Ni) catalysts can overcome this difficulty by utilizing functionalities arising from concerted role of active defects on the support surface and loaded transition metals. These catalysts enable ammonia production through multiple reaction pathways. The reaction rate of Co/SrNH is as high as 1686.7 mmol·gCo-1·h-1 and the TOFs reaches above 500 h-1 at 400 °C and 0.9 MPa, outperforming other reported Co-based catalysts as well as the benchmark Cs-Ru/MgO catalyst and industrial wüstite-based Fe catalyst under the same reaction conditions. Experimental and theoretical results show that the synergistic effect of nitrogen affinity of 3d TMs and in-situ formed NH2- vacancy of alkali earth imides regulate the reaction pathways of the ammonia production, resulting in distinct catalytic performance different from 3d TMs. It was thus demonstrated that the appropriate combination of metal and support is essential for controlling the reaction pathway and realizing highly active and low cost catalysts for ammonia synthesis.

Topological insulator as an efficient catalyst for oxidative carbonylation of amines

Topological materials have received much attention because of their robust topological surface states, which can be potentially applied in electronics and catalysis. Here, we show that the topological insulator bismuth selenide functions as an efficient catalyst for the oxidative carbonylation of amines with carbon monoxide and dioxygen to synthesize urea derivatives. For example, the carbonylation of butylamine can be completed over bismuth selenide nanoparticle catalyst in 4 hours at 20°C with a yield of 99%, whereas most noble metal-based catalysts do not function at such a low temperature. Density functional theory calculations further reveal that the topological surface states facilitate the activation of dioxygen through a triplet-to-singlet spin-conversion reaction, in which active oxygen species are formed with a barrier of 0.4 electron volts for the subsequent reactions with amine and carbon monoxide.

Intermetallic Copper-Based Electride Catalyst with High Activity for C-H Oxidation and Cycloaddition of CO2 into Epoxides

Inorganic electrides have been proved to be efficient hosts for incorporating transition metals, which can effectively act as active sites giving an outstanding catalytic performance. Here, it is demonstrated that a reusable and recyclable (for more than 7 times) copper-based intermetallic electride catalyst (LaCu0.67 Si1.33 ), in which the Cu sites activated by anionic electrons with low-work function are uniformly dispersed in the lattice framework, shows vast potential for the selective C-H oxidation of industrially important hydrocarbons and cycloaddition of CO2 with epoxide. This leads to the production of value-added cyclic carbonates under mild reaction conditions. Importantly, the LaCu0.67 Si1.33 catalyst enables much higher turnover frequencies for the C-H oxidation (up to 25 276 h-1 ) and cycloaddition of CO2 into epoxide (up to 800 000 h-1 ), thus exceeding most nonnoble as well as noble metal catalysts. Density functional theory investigations have revealed that the LaCu0.67 Si1.33 catalyst is involved in the conversion of N-hydroxyphthalimide (NHPI) into the phthalimido-N-oxyl (PINO), which then triggers selective abstraction of an H atom from ethylbenzene for the generation of a radical susceptible to further oxygenation in the presence of O2 .

First-Principles Study of Three-Dimensional Electrides Containing One-Dimensional [Ba3N]3+ Chains

Electrides, a unique type of compound where electrons act as anions, have a high electron mobility and a low work function, which makes them promising for applications in electronic devices and high-performance catalysts. The discovery of novel electrides and the expansion of the electride family have great significance for their promising applications. Herein, we reported four three-dimensional (3D) electrides by coupling crystal structure database searches and first-principles electronic structure analysis. Subnitrides (Ba₃N, LiBa₃N, NaBa₃N, and Na₅Ba₃N) containing one-dimensional (1D) [Ba₃N]³⁺ chains are identified as 3D electrides for the first time. The anionic electrons are confined in the 3D interstitial space of Ba₃N, LiBa₃N, NaBa₃N, and Na₅Ba₃N. Interestingly, with the increase of Na content, the excess electrons of Na₅Ba₃N play two roles of metallic bonding and anionic electrons. Therefore, the subnitrides containing 1D [Ba₃N]³⁺ chains can be regarded as a new family of 3D electrides, where anionic electrons reside in the 3D interstitial spaces and provide a conduction path. These materials not only are experimentally synthesizable 3D electrides but also are promising to be exfoliated into advanced 1D nanowire materials. Furthermore, our work suggests a discovery strategy of novel electrides based on one parent framework like [Ba₃N]³⁺ chains, which would accelerate the mining of electrides from the crystal structure database.

Dissociative and Associative Concerted Mechanism for Ammonia Synthesis over Co-Based Catalyst

The current catalytic reaction mechanism for ammonia synthesis relies on either dissociative or associative routes, in which adsorbed N₂ dissociates directly or is hydrogenated step-by-step until it is broken upon the release of NH₃ through associative adsorption. Here, we propose a concerted mechanism of associative and dissociative routes for ammonia synthesis over a cobalt-loaded nitride catalyst. Isotope exchange experiments reveal that the adsorbed N₂ can be activated on both Co metal and the nitride support, which leads to superior low-temperature catalytic performance. The cooperation of the surface low work function (2.6 eV) feature and the formation of surface nitrogen vacancies on the CeN support gives rise to a dual pathway for N₂ activation with much reduced activation energy (45 kJ·mol^-1) over that of Co-based catalysts reported so far, which results in efficient ammonia synthesis under mild conditions.

Contribution of Nitrogen Vacancies to Ammonia Synthesis over Metal Nitride Catalysts

Ammonia is one of the most important feedstocks for the production of fertilizer and as a potential energy carrier. Nitride compounds such as LaN have recently attracted considerable attention due to their nitrogen vacancy sites that can activate N₂ for ammonia synthesis. Here, we propose a general rule for the design of nitride-based catalysts for ammonia synthesis, in which the nitrogen vacancy formation energy (E_NV) dominates the catalytic performance. The relatively low E_NV (ca. 1.3 eV) of CeN means it can serve as an efficient and stable catalyst upon Ni loading. The catalytic activity of Ni/CeN reached 6.5 mmol·g^-1·h^-1 with an effluent NH₃ concentration (E_NH3) of 0.45 vol %, reaching the thermodynamic equilibrium (E_NH3 = 0.45 vol %) at 400 °C and 0.1 MPa, thereby circumventing the bottleneck for N₂ activation on Ni metal with an extremely weak nitrogen binding energy. The activity far exceeds those for other Co- and Ni-based catalysts, and is even comparable to those for Ru-based catalysts. It was determined that CeN itself can produce ammonia without Ni-loading at almost the same activation energy. Kinetic analysis and isotope experiments combined with density functional theory (DFT) calculations indicate that the nitrogen vacancies in CeN can activate both N₂ and H₂ during the reaction, which accounts for the much higher catalytic performance than other reported nonloaded catalysts for ammonia synthesis.

Palladium-bearing intermetallic electride as an efficient and stable catalyst for Suzuki cross-coupling reactions

Suzuki cross-coupling reactions catalyzed by palladium are powerful tools for the synthesis of functional organic compounds. Excellent catalytic activity and stability require negatively charged Pd species and the avoidance of metal leaching or clustering in a heterogeneous system. Here we report a Pd-based electride material, Y3Pd2, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y3Pd2 realizes negatively charged Pd species, a low work function and a high carrier density, which are expected to be beneficial for the efficient Suzuki coupling reaction of activated aryl halides with various coupling partners under mild conditions. The catalytic activity of Y3Pd2 is ten times higher than that of pure Pd and the activation energy is lower by nearly 35%. The Y3Pd2 intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.

Discovery of hexagonal ternary phase Ti2InB2 and its evolution to layered boride TiB

Mn+1AXn phases are a large family of compounds that have been limited, so far, to carbides and nitrides. Here we report the prediction of a compound, Ti2InB2, a stable boron-based ternary phase in the Ti-In-B system, using a computational structure search strategy. This predicted Ti2InB2 compound is successfully synthesized using a solid-state reaction route and its space group is confirmed as P[Formula: see text]m2 (No. 187), which is in fact a hexagonal subgroup of P63/mmc (No. 194), the symmetry group of conventional Mn+1AXn phases. Moreover, a strategy for the synthesis of MXenes from Mn+1AXn phases is applied, and a layered boride, TiB, is obtained by the removal of the indium layer through dealloying of the parent Ti2InB2 at high temperature under a high vacuum. We theoretically demonstrate that the TiB single layer exhibits superior potential as an anode material for Li/Na ion batteries than conventional carbide MXenes such as Ti3C2.

Copper-Based Intermetallic Electride Catalyst for Chemoselective Hydrogenation Reactions

The development of transition metal intermetallic compounds, in which active sites are incorporated in lattice frameworks, has great potential for modulating the local structure and the electronic properties of active sites, and enhancing the catalytic activity and stability. Here we report that a new copper-based intermetallic electride catalyst, LaCu_0.67Si_1.33, in which Cu sites activated by anionic electrons with low work function are atomically dispersed in the lattice framework and affords selective hydrogenation of nitroarenes with above 40-times higher turnover frequencies (TOFs up to 5084 h^-1) than well-studied metal-loaded catalysts. Kinetic analysis utilizing isotope effect reveals that the cleavage of the H-H bond is the rate-determining step. Surprisingly, the high carrier density and low work function (LWF) properties of LaCu_0.67Si_1.33 enable the activation of hydrogen molecules with extreme low activation energy (E_a = 14.8 kJ·mol^-1). Furthermore, preferential adsorption of nitroarenes via a nitro group is achieved by high oxygen affinity of LaCu_0.67Si_1.33 surface, resulting in high chemoselectivity. The present efficient catalyst can further trigger the hydrogenation of other oxygen-containing functional groups such as aldehydes and ketones with high activities. These findings demonstrate that the transition metals incorporated in the specific lattice site function as catalytically active centers and surpass the conventional metal-loaded catalysts in activity and stability.

Electronic interactions between a stable electride and a nano-alloy control the chemoselective reduction reaction

The electronic effects induced by the synergy of stable C12A7:e^– electride and bimetallic Ru–Fe nanoparticles efficiently control the chemoselective reduction reaction.

Controlling the electronic structure of heterogeneous metal catalysts is considered an efficient method to optimize catalytic activity. Here, we introduce a new electronic effect induced by the synergy of a stable electride and bimetallic nanoparticles for a chemoselective reduction reaction. The electride [Ca₂₄Al₂₈O₆₄]⁴⁺·(e^–)₄, with extremely low work function, promotes the superior activity and selectivity of a Ru–Fe nano-alloy for the conversion of α,β-unsaturated aldehydes to unsaturated alcohols in a solvent-free system. The catalyst is easily separable from the product solution and reusable without notable deactivation. Mechanistic studies demonstrate that electron injection from the electride to the Ru–Fe bimetallic nanoparticles promotes H₂ dissociation on the highly charged active metal and preferential adsorption of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O bonds over C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Cs bond of the unsaturated aldehydes, to obtain the thermodynamically unfavorable but industrially important product.

In situ catalytic growth of large-area multilayered graphene/MoS2 heterostructures

Stacking various two-dimensional atomic crystals on top of each other is a feasible approach to create unique multilayered heterostructures with desired properties. Herein for the first time, we present a controlled preparation of large-area graphene/MoS₂ heterostructures via a simple heating procedure on Mo-oleate complex coated sodium sulfate under N₂ atmosphere. Through a direct in situ catalytic reaction, graphene layer has been uniformly grown on the MoS₂ film formed by the reaction of Mo species with S pecies, which is from the carbothermal reduction of sodium sulfate. Due to the excellent graphene “painting” on MoS₂ atomic layers, the significantly shortened lithium ion diffusion distance and the markedly enhanced electronic conductivity, these multilayered graphene/MoS₂ heterostructures exhibit high specific capacity, unprecedented rate performance and outstanding cycling stability, especially at a high current density, when used as an anode material for lithium batteries. This work provides a simple but efficient route for the controlled fabrication of large-area multilayered graphene/metal sulfide heterostructures with promising applications in battery manufacture, electronics or catalysis.

The crystallinity effect of mesocrystalline BaZrO3 hollow nanospheres on charge separation for photocatalysis

Mesocrystalline BaZrO₃ hollow nanospheres were used as an ideal model to study the crystallinity effect of mesocrystals on charge separation for photocatalysis.