Abstract
M
n+1
AX
n
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, Ti
2
InB
2
, a stable boron-based ...ternary phase in the Ti-In-B system, using a computational structure search strategy. This predicted Ti
2
InB
2
compound is successfully synthesized using a solid-state reaction route and its space group is confirmed as
P
$$\bar 6$$
6
¯
m2
(No. 187), which is in fact a hexagonal subgroup of
P6
3
/mmc
(No. 194), the symmetry group of conventional M
n+1
AX
n
phases. Moreover, a strategy for the synthesis of MXenes from M
n+1
AX
n
phases is applied, and a layered boride, TiB, is obtained by the removal of the indium layer through dealloying of the parent Ti
2
InB
2
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 Ti
3
C
2
.
Abstract
Single-atom catalysts (SACs) have attracted significant attention because they exhibit unique catalytic performance due to their ideal structure. However, maintaining atomically dispersed ...metal under high temperature, while achieving high catalytic activity remains a formidable challenge. In this work, we stabilize single platinum atoms within sub-nanometer surface cavities in well-defined 12CaO·7Al
2
O
3
(C12A7) crystals through theoretical prediction and experimental process. This approach utilizes the interaction of isolated metal anions with the positively charged surface cavities of C12A7, which allows for severe reduction conditions up to 600 °C. The resulting catalyst is stable and highly active toward the selective hydrogenation of nitroarenes with a much higher turnover frequency (up to 25772 h
−1
) than well-studied Pt-based catalysts. The high activity and selectivity result from the formation of stable trapped single Pt atoms, which leads to heterolytic cleavage of hydrogen molecules in a reaction that involves the nitro group being selectively adsorbed on C12A7 surface.
Ammonia (NH3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals1. The direct use of atmospheric nitrogen (N2) had been challenging, owing to its large bond energy ...(945 kilojoules per mole)2,3, until the development of the Haber-Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N^N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance oftraditional iron- and ruthenium-based catalysts4-6 via electron transfer from the promoters to the antibonding bonds of N2 through transition metals78. An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals9,10. This strategy has facilitated ammonia synthesis from N2 dissociation11 and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N2 (refs. 12-15). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N2. In addition, the nickel metal loaded onto the nitride dissociates H2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturally abundant elements.
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.
The water (H2O) dissociation is critical for various H2O‐associated reactions, including water gas shift, hydrogen evolution reaction and hydrolysis corrosion. While the d‐band center concept offers ...a catalyst design guideline for H2O 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 H2O dissociation. The H2O dissociation kinetics can be enhanced using MgxMey (Me=Co, Ni, Cu, Si and Al) as catalysts, and the hydrogen generation rate of Mg2Ni‐loaded Mg reached 80 times as high as Ni‐loaded Mg. The adsorbed H2O molecules strongly couple with the Mg−Me dipole of MgxMey, lowering the H2O dissociation barrier. The dipole‐based H2O dissociation mechanism is applicable to non‐transition metal‐based systems, such as Mg2Si and Mg17Al12, offering a flexible catalyst design strategy for controllable H2O dissociation.
While the d‐band center is widely cited to predict the catalytic activity, the other factors, such as Coulomb interaction, have little been considered to design a catalyst for H2O‐associated reactions. Using hydrolysis corrosion of Mg as an example, we demonstrate the impact of dipole coupling on the H2O adsorption and dissociation processes.
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, Y
Pd
, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y
Pd
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 Y
Pd
is ten times higher than that of pure Pd and the activation energy is lower by nearly 35%. The Y
Pd
intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.
Oxygen reduction reaction (ORR) is regarded as the rate-determining step in a fuel cell or a metal-air battery because of the kinetically retarded four-electron process. Among the substantial types ...of catalysts developed for decades, Pt-based catalysts are almost still the most promising electrode materials with outstanding comprehensive performance and commercial potential. For the widely used Pt/C catalysts, the rapid degradation of performance in ORR tests exposed serious problems due to severe carbon corrosion and Pt deterioration. Non-carbon supports can avoid the direct connection between Pt and carbon materials, resulting in reduction (or elimination) of carbon oxidative dissolution and stabilization of Pt nanoparticles. More importantly, non-carbon supports for Pt-based catalysts may bring favorable anchoring and synergetic effects, which have been widely proved to enhance the durability and catalytic activity. In this review, the inorganic non-carbon support materials are classified as metal oxides, carbides, nitrides, and other metal compounds. Among them, the metal oxide supports manifest excellent stability during the ORR process but may lack electrical conductivity, while metal carbides and nitrides possess both high stability and high electrical conductivity in suitable electrolytes. We aim to summarize the applications of non-carbon supported Pt catalysts in ORR, the relevant mechanisms and the properties of the hybrid catalysts, with emphasis on the anchoring and synergetic effects.
In oxygen reduction reaction, Pt/C catalysts are prone to carbon corrosion, resulting in reduced activity. The use of non-carbon inorganic supports not only improves corrosion resistance, but also provides synergetic effects to increase activity and stability.
A new luminescent terbium–metal–organic framework Tb3(L)2(HCOO)(H2O)5·DMF·4H2O (1) (H4L = 4,4′-(pyridine-3,5-diyl)diisophthalic acid) has been successfully assembled by Tb3+ ions and an undeveloped ...pyridyl-tetracarboxylate. Compound 1 exhibits a 3D porous (3,8)-connected (4.52)2(42.512.66.75.83) topological framework with fascinating 1D open hydrophilic channels decorated by uncoordinated Lewis basic pyridyl nitrogen atoms. In particular, the Tb-MOF (1) can detect Cu2+ ions with high selectivity and sensitivity, and its luminescence is nearly entirely quenched in N,N-dimethylformamide (DMF) solution and biological system. In addition, 1 still has high detection for the trace content of nitromethane with 70 ppm, which suggests that 1 is a promising example of dual functional materials with sensing copper ions and nitromethane.
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•One-part geopolymer was synthesized by using Bayer red mud as main raw material.•Long-term strength of binder was significantly improved with addition of 20–30wt% SF.•Lower ...water/solid ratio contributed to increasing the strength.•The compressive strength of geopolymer cured for 28d reached 31.5MPa.•Geopolymerization of dissolved aluminosilicate and silica formed dense matrices.
One-part geopolymer was synthesized from alkali–thermal activated Bayer red mud (RM) with addition of silica to optimize its composition. The RM was pretreated through alkali–thermal activation and turned to geopolymer precursor, which could be used by only adding water in blending process. However the long-term strength of the binder with only RM was poor because of the unstable polymerization due to the low SiO2/Al2O3 molar ratio (1.41). Silica fume (SF) was chosen to increase the SiO2/Al2O3 molar ratio of the geopolymer formulation. By adding 25wt% of SF, the 28d compressive strength of the geopolymer with a SiO2/Al2O3 molar ratio of 3.45 could reach 31.5MPa at a water/solid ratio of 0.45. Sodium aluminosilicate in the activated RM dissolved in water and formed an alkaline environment to dissolve SF. The dissolved silica participated in geopolymerization, leading to a satisfactory geopolymer composition. Typical amorphous geopolymer matrices were formed in the binder completely cured.
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.
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