High-entropy alloy catalysts:From bulk to nano toward highly efficient carbon and nitrogen catalysis

High-entropy alloys(HEAs)have attracted widespread attention as both structural and functional materials owing to their huge multielement composition space and unique high-entropy mixing structure.Recently,emerging HEAs,either in nano or highly porous bulk forms,are developed and utilized for various catalytic and clean energy applications with superior activity and remarkable durability.Being catalysts,HEAs possess some unique advantages,including(1)a multielement composition space for the discovery of new catalysts and fine-tuning of surface adsorption(i.e.,activity and selectivity),(2)diverse active sites derived from the random multielement mixing that are especially suitable for multistep catalysis,and(3)a high-entropy stabilized structure that improves the structural durability in harsh catalytic environments.Benefited from these inherent advantages,HEA catalysts have demonstrated superior catalytic performances and are promising for complex carbon(C)and nitrogen(N)cycle reactions featuring multistep reaction pathways and many different intermediates.However,the design,synthesis,characterization,and understanding of HEA catalysts for C-and N-involved reactions are extremely challenging because of both complex high-entropy materials and complex reactions.In this review,we present the recent development of HEA catalysts,particularly on their innovative and extensive syntheses,advanced(in situ)characterizations,and applications in complex C and N looping reactions,aiming to provide a focused view on how to utilize intrinsically complex catalysts for these important and complex reactions.In the end,remaining challenges and future directions are proposed to guide the development and application of HEA catalysts for highly efficient energy storage and chemical conversion toward carbon neutrality.

Electrochemical Oxygen Evolution Performance of Nitrogen-Doped Ultra-Thin Carbon Nanosheets Composite Ru1Co Single Atom Alloy Catalysts

Energy transformation is imminent,and hydrogen energy is one of the important new energy sources.One of the keys to increasing the rate of hydrogen evolution during electrolysis is the use of high-performance catalysts for oxygen evolution reactions(OER).Single-atom alloys(SAAs)have garnered significant attention because they partially reduce costs and combine the advantages of both single-atom catalysts(SACs)and alloy catalysts.Herein,an efficient pyrolysis strategy based on a mixing and drying process is designed to anchor ultra-small Co cluster particles,combined with Ru single atoms dispersed on nitrogen-doped ultra-thin carbon nanosheets(Ru_(1)Co SAA/NC).The prepared electrocatalyst exhibits superior OER activity and superb stability,demonstrating an overpotential of 238 mV for OER with a current density of 10 mA·cm^(-2) in 0.5 mol/L H_(2)SO_(4).And we also utilized in-situ XAS to detect the oxidation state of Ru sites during OER.All in all,this method achieves cost reductions and efficiency improvements through the design of SAAs,offering new prospects for the structural transformation of clean energy.

Efficient and stable PtFe alloy catalyst for electrocatalytic methanol oxidation with high resistance to CO

Direct methanol fuel cells(DMFC) are widely considered to be an ideal green energy conversion device but their widespread applications are limited by the high price of the Pt-based catalysts and the instability in terms of surface CO toxicity in long-term operation.Herein,the PtFe alloy nanoparticles(NPs) with small particle size(~4.12 nm) supported on carbon black catalysts with different Pt/Fe atomic ratios(Pt_(1)Fe_(2)/C,Pt_(3)Fe_(4)/C,Pt_(1)Fe_(1)/C,and Pt_(2)Fe_(1)/C) are successfully prepared for enhanced anti-CO poisoning during methanol oxidation reaction(MOR).The optimal atomic ratio of Pt/Fe for the MOR is 1:2,and the mass activity of Pt_(1)Fe_(2)/C(5.40 A mg_(Pt)^(-1)) is 13.5 times higher than that of conventional commercial Pt/C(Pt/C-JM)(0.40 A mg_(Pt)^(-1)).The introduction of Fe into the Pt lattice forms the PtFe alloy phase,and the electron density of Pt is reduced after forming the PtFe alloy.In-situ Fourier transform infrared results indicate that the addition of oxyphilic metal Fe has reduced the adsorption of reactant molecules on Pt during the MOR.The doping of Fe atoms helps to desorb toxic intermediates and regenerate Pt active sites,promoting the cleavage of C-O bonds with good selectivity of CO_(2)(58.1%).Moreover,the Pt_(1)Fe_(2)/C catalyst exhibits higher CO tolerance,methanol electrooxidation activity,and long-term stability than other Pt_(x)Fe_(y)/C catalysts.

Rational design of copper-based single-atom alloy catalysts for electrochemical CO_(2)reduction

Electrochemical CO_(2)-reduction reaction(CO_(2)RR)is a promising way to alleviate energy crisis and excessive carbon emission.The Cu-based electrocatalysts have been considered for CO_(2)RR to generate hydrocarbons and alcohols.However,the application of Cu electrocatalysts has been restricted by a high onset potential for CO_(2)RR and low selectivity.In this study,we have designed a series of Cu-based single-atom alloy catalysts(SAAs),denoted as TM1/Cu(111),by doping isolated 3dtransition metal(TM)atom onto the Cu(111)surface.We theoretically evaluated their stability and investigated the activity and selectivity toward CO_(2)RR.Compared to the pure Cu catalyst,the majority TM1/Cu(111)catalysts are more favorable for hydrogenating CO_(2)and can efficiently avoid the hydrogen-evolution reaction due to the strong binding of carbonaceous intermediates.Based on the density functional theory calculations,instead of the HCOOH or CO products,the initial hydrogenation of CO_(2)on SAAs would form the*CO intermediate,which could be further hydrogenated to produce methane.In addition,we have identified the bond angle of adsorbed*CO_(2)can describe the CO_(2)activation ability of TM1/Cu(111)and the binding energy of*OH can describe the CO_(2)RR activity of TM1/Cu(111).We speculated that the V/Cu(111)can show the best activity and selectivity for CO_(2)RR among all the 3d-TM-doped TM1/Cu(111).This work could provide a rational guide to the design of new type of single-atom catalysts for efficient CO_(2)RR.

Engineering nanoporous and solid core-shell architectures of lowplatinum alloy catalysts for high power density PEM fuel cells

Low-platinum(Pt)alloy catalysts hold promising application in oxygen reduction reaction(ORR)electrocatalysis of protonexchange-membrane fuel cells(PEMFCs).Although significant progress has been made to boost the kinetic ORR mass activity at low current densities in liquid half-cells,little attention was paid to the performance of Pt-based catalysts in realistic PEMFCs particularly at high current densities for high power density,which remains poorly understood.In this paper,we show that,regardless of the kinetic mass activity at the low current density region,the high current density performance of the low-Pt alloy catalysts is dominantly controlled by the total Pt surface area,particularly in low-Pt-loading H_(2)–air PEMFCs.To this end,we propose two different strategies to boost the specific Pt surface area,the post-15-nm dealloyed nanoporous architecture and the sub-5-nm solid core–shell nanoparticles(NPs)through fluidic-bed synthesis,both of which bring in comparably high mass activity and high Pt surface area for large-current-density performance.At medium current density,the dealloyed porous NPs provide substantially higher H_(2)–air PEMFC performance compared to solid core–shell catalysts,despite their similar mass activity in liquid half-cells.Scanning transmission electron microscopy images combined with electron energy loss spectroscopic imaging evidence a previously unreported“semi-immersed nanoporous-Pt/ionomer”structure in contrast to a“fully-immersed core–shellPt/ionomer”structure,thus favoring O_(2) transport and improving the fuel cell performance.Our results provide new insights into the role of Pt nanostructures in concurrently optimizing the mass activity,Pt surface area and Pt/Nafion interface for high power density fuel cells.

Ru-Ni alloy nanosheets as tandem catalysts for electrochemical reduction of nitrate to ammonia

Developing electrocatalysts that exhibit both high activity and ammonia selectivity for nitrate reduction is a significant and demanding challenge,primarily due to the complex nature of the multiple-electron reduction process involved.An encouraging approach involves coupling highly active precious metals with transition metals to enhance catalytic performance through synergy.Here,we report a ruthenium-nickel alloy catalyst with nanosheets(Ru-Ni NSs)structure that achieves a remarkable ammonia Faradaic efficiency of approximately 95.93%,alongside a yield rate of up to 6.11 g·h^(−1)·cm^(−2).Moreover,the prepared Ru-Ni NSs exhibit exceptional stability during continuous nitrate reduction in a flow reactor for 100 h,maintaining a Faradaic efficiency of approximately 90%and an ammonia yield of 37.4 mg·L^(−1)·h^(−1)using 0.05 M nitrate alkaline electrolyte.Mechanistic studies reveal that the catalytic process follows a two-step pathway,in which HONO serves as a migration intermediate.The presence of a partially oxidized Ru(002)surface enhances the adsorption of nitrate and facilitates the release of the migration intermediate by adjusting the strength of the electrostatic and covalent interactions between the adsorbate and the surface,respectively.On the other hand,the Ni(111)surface promotes the utilization of the migration intermediate and requires less energy for NH_(3)desorption.This tandem process contributes to a high catalytic activity of Ru-Ni NSs towards nitrate reduction.

Effect of Lanthanum on Performance of RuB Amorphous Alloy Catalyst for Benzene Selective Hydrogenation

The effect of La on the performance of a supported RuB amorphous alloy catalyst for benzene selective hydrogenation was studied by means of activity and selectivity tests, such as HRTEM, SAED, XPS, and XRD. The results show that the addition of La to RuB amorphous alloy catalyst can evidently increase the activity and improve the thermal stability of RuB amorphous alloy to refrain its crystallization. The promoting effect of La on the activity of RuB amorphous alloy catalyst is because of the high dispersion of the active components.

Scission of C–O and C–C linkages in lignin over RuRe alloy catalyst

The performance of lignin depolymerization is basically determined by the interunit C–O and C–C bonds.Numerous C–O bond cleavage strategies have been developed, while the cleavage of C–C bond between the primary aromatic units remains a challenging task due to the high dissociation energy of C–C bond.Herein, a multifunctional Ru Re alloy catalyst was designed, which exhibited exceptional catalytic activity for the cleavage of both C–O and C–C linkages in a broad range of lignin model compounds(β-1, a-5, 5–5,β-O-4, 4-O-5) and two stubborn lignins(kraft lignin and alkaline lignin), affording 97.5% overall yield of monocyclic compounds from model compounds and up to 129% of the maximum theoretical yield of monocyclic products based on C–O bonds cleavage from realistic lignin. Scanning transmission electron microscopy(STEM) characterization showed that Ru Re(1:1) alloy particles with hexagonal close-packed structure were homogeneously dispersed on the support. Quasi-in situ X-ray photoelectron spectroscopy(XPS), and X-ray absorption spectroscopy(XAS) indicate that Ru species were predominantly metallic state, whereas Re species were partially oxidized;meanwhile, there was a strong interaction between Ru and Re, where the electron transfer from Re to Ru was occurred, resulting in great improvement on the capability of C–O and C–C bonds cleavage in lignin conversion.

Synthesis and Characterization of ZnO Bicrystalline Nanosheets Grown via Ag-Au Alloy Catalyst

ZnO bicrystalline nanosheets have been synthesized by using Ax=AU1-x alloy catalyst via the vapor transport and condensation method at 650 ℃. High resolution transmission electron microscopy characterization reveals a twin boundary with {01-13} plane existing in the bicrystalline. A series of control experiments show that both AgxAu1-x alloy catalyst and high supersaturation of Zn vapor are prerequisites for the formation of ZnO bicrystalline nanosheet. Moreover, it is found that the density of ZnO bicrytalline nanosheets can be tuned through varying the ratio of Ag to Au in the alloy catalyst. The result demonstrates that new complicated nanostructures can be produced controllably with appropriate alloy catalyst.

Preparation of Uniform Ni-B Amorphous Alloy Catalyst on CNTs and its Performance for Acetylene Selective Hydrogenation

Uniform Ni-B amorphous alloys about 14 nm have been prepared on CNTs-A support,named Ni-B/CNTs-A. In comparison with the Ni-B/CNTs amorphous catalyst, Ni-B/CNTs-A showed higher nickel loading, determined by ICP and better catalytic activity and ethylene selectivity in the acetylene hydrogenation reaction.

Kinetics Research on In-situ Rapid Dechlorination of 1,4-dichlorobenzene by Microwave-assisted Raney Ni-Al Alloy Catalyst

[Objective]The research aimed to study rapid dechlodnation kinetics of 1,4-dichlorobenzene （1,4-DCB） by microwave-assisted Raney Ni -AI alloy catalyst. [ Method] Microwave-assisted Raney Ni -AI alloy catalyst was used for dechlorination of chlorobenzene （CB） and 1,4-DCB to analyze dechlorination kinetics of 1,4-DCB. [ Result] Reductive dechlorination reaction of 1,4-DCB by microwave-assisted Raney Ni- AI alloy catalyst was in accordance of the two-order reaction kinetics. Reaction rate constants of 1,4-DCB dechlorination at 35 and 50 ℃ were 0.037 6 and 0.151 mol/（ L . min）, and the activation energy was 76.66 kJ/mol. By microwave-assisted Raney Ni - AI alloy catalyst, dechlorination rate of 1,4- DCB reached 90% at 10 rain and 35 ℃. Moreover, two chlorine atoms were removed simultaneously, reaching the target of efficient dechlorination. [ Condusion] Oechlodnation of polychlodnated organic compounds by microwave-assisted Raney Ni- AI alloy catalyst obtained good effect .

Iron-nickel alloy particles with N-doped carbon “armor” as a highly selective and long-lasting catalyst for the synthesis of Nbenzylaniline molecules

A scalable strategy for the convenient and rapid preparation of nitrogen-doped carbon-coated iron-based alloy catalysts was developed.By controlling the type and amount of metal salts in the precursor,various types of nitrogen-doped carbon-coated alloy catalysts can be prepared in a targeted manner.Fe_(2)Ni2@CN materials with small particle sizes and relatively homogeneous basic sites showed promising results in the N-alkylation reaction of benzyl alcohol with aniline(optimum yield:99%).It is worth noting that the catalyst can also be magnetically separated and recovered after the reaction,and its performance can be regenerated through simple calcination.Furthermore,it was confirmed by kinetic experiments that the activation of C–H at the benzyl alcohol benzylic position is the rate-determining step(RDS).According to density flooding theory calculations,Fe_(2)Ni2@CN catalysts require less energy than other materials(Fe@CN and Ni@CN)for the RDS(dehydrogenation reaction)process.Therefore N-alkylation reactions are more easily carried out on Fe_(2)Ni2@CN catalysts,which may be the reason for the best catalytic activity of Fe-Ni alloy materials.These carbon-coated alloy materials will show great potential in more types of heterogeneous catalysis.

Enhancement of oxygen reduction activity and stability via introducing acid-resistant refractory Mo and regulating the near-surface Pt content

Although Pt Ni catalyst possesses good oxygen reduction activity, its poor stability is the main obstacle for the commercialization of proton exchange membrane fuel cells(PEMFCs). In this work, we introduce the acid-resistant refractory Mo to enhance the structure stability and modify the electronic structure of Pt in the prepared PtNi catalyst, improving the catalytic activity for oxygen reduction reaction(ORR). In addition, near-surface Pt content in the nanoparticle is also optimized to balance the ORR activity and stability. The electrochemical results show that the alloy formed by Mo and Pt Ni is obviously more stable than the PtNi alloy alone, because the acid-resistant Mo and its oxides effectively prevent the dissolution of Pt. Especially, the Pt3 Ni3 MoN/C exhibits the optimal ORR catalytic performance in O2-saturated 0.1 mol L^(-1) HClO4 aqueous solutions, with mass activity(MA) of 900 m A mg^(-1) Pt at 0.90 V vs. RHE, which is 3.75 times enhancement compared with the commercial Pt/C(240 mA mg^(-1) Pt). After 30 k accelerated durability tests, its MA(690 m A mg^(-1) Pt) is still 2.88 times higher than the pristine Pt/C. This study thus provides a valuable method to design stable ORR catalysts with high efficiency and has great significance for the commercialization of PEMFCs.

Effect of Metallic Additives on Structure and Catalytic Properties of Supported NiPB/SiO_2 Catalyst

A new preparation method was proposed to deposit amorphous alloys alloys containing NiPand metallic metallic additives such as Fe.Co. and Cu.The different effects of metallic additive onstructure and catalytic properties of supported amorphous NiMPB/SiO2 (M=Fe, Co. Cu) cafalysts were observed,and the improvement of catalytic activity due to heating pretreatment in hydrogenwas found.

High-entropy alloy stabilized and activated Pt clusters for highly efficient electrocatalysis

Although Pt and other noble metals are the state-of-the-art catalysts for various energy conversion applications,their low reserve,high cost,and instability limit their large-scale utilization.Herein,we report a hybrid catalysts design featuring noble metal clusters(e.g.,Pt)uniformly dispersed and stabilized on high-entropy alloy nanoparticles(HEA,e.g.,FeCoNiCu),denoted as HEA@Pt,which is prepared via ultra-fast shock synthesis(∼300 ms)for HEA alloying combined with Pt galvanic replacement for surface anchoring.In our design,the HEA core critically ensures high dispersity,stability,and tunability of the surface Pt clusters through high entropy stabilization and core-shell interactions.As an example in the hydrogen evolution reaction,HEA@Pt achieved a significant mass activity of 235 A/gPt,which is 9.4,3.6,and 1.9-times higher compared to that of homogeneous FeCoNiCuPt(HEA-Pt),Pt,and commercial Pt/C,respectively.We also demonstrated noble Ir stabilized on FeCoNiCrMn nanoparticles(HEA-5@Ir),achieving excellent anodic oxygen evolution performance and highly efficient overall water splitting when combined with the cathodic HEA@Pt.Therefore,our work developed a general catalysts design strategies by using high entropy nanoparticles for effective dispersion,stabilization,and modulation of surface active sites,achieving a harmonious combination of high activity,stability,and low cost.

Electrochemical converting ethanol to hydrogen and acetic acid for large scale green hydrogen production

Electrochemical coupling hydrogen evolution with biomass reforming reaction(named electrochemical hydrogen and chemical cogeneration(EHCC)),which realizes green hydrogen production and chemical upgrading simultaneously,is a promising method to build a carbon-neutral society.Herein,we analyze the EHCC process by considering the market assessment.The ethanol to acetic acid and hydrogen approach is the most feasible for large-scale hydrogen production.We develop AuCu nanocatalysts,which can selectively oxidize ethanol to acetic acid(>97%)with high long-term activity.The isotopic and in-situ infrared experiments reveal that the promoted water dissociation step by alloying contributes to the enhanced activity of the partial oxidation reaction path.A flow-cell electrolyzer equipped with the AuCu anodic catalyst achieves the steady production of hydrogen and acetic acid simultaneously in both high selectivity(>90%),demonstrating the potential scalable application for green hydrogen production with low energy consumption and high profitability.

Magnetically stabilized bed reactor for selective hydrogenation of olefins in reformate with amorphous nickel alloy catalyst

A magnetically stabilized bed （MSB） reactor for selective hydrogenation of olefins in reformate was developed by combining the advantages of MSB and amorphous nickel alloy catalyst. The effects of operating conditions, such as temperature, pressure, liquid space velocity, hydrogen-to-oil ratio, and magnetic field intensity on the reaction were studied. A mathematical model of MSB reactor for hydrogenation of olefins in reformate was established. A reforming flow scheme with a post-hydrogenation MSB reactor was proposed. Finally, MSB hydrogenation was compared with clay treatment and conventional post-hydrogenation.

Promoting the methanol oxidation catalytic activity by introducing surface nickel on platinum nanoparticles

High performance methanol oxidation reaction （MOR） catalysts are critical to the performance of attractive, direct methanol fuel cells. Here, we use surface controlled PtNi alloy nanoparticles as model catalysts to study the MOR mechanism and give further guidance to the design of new high performance MOR catalysts. The enhanced MOR activity of PtNi alloy was mainly attributed to the enhanced OH adsorption owing to surface Ni sites. This suggests that the MOR undergoes the Langmuir-Hinshelwood mechanism, whereby adsorbed CO is removed with the assistance of adsorbed OH. Within the PtNi catalyst, Pt provides methanol adsorption sites （in which methanol is converted to adsorbed CO） and Ni provides OH adsorption sites. The optimized Pt-Ni ratio for MOR was found to be 1：1. This suggests that bifunctional catalysts with both CO and OH adsorption sites can lead to highly active MOR catalysts.

Concurrent catalytic removal of typical volatile organic compound mixtures over Au-Pd/α-MnO2 nanotubes

α-MnO2 nanotubes and their supported Au-Pd alloy nanocatalysts were prepared using hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Their catalytic activity for the oxidation of toluene/m-xylene, acetone/ethyl acetate, acetone/m-xylene and ethyl acetate/m-xylene mixtures was evaluated. It was found that the interaction between Au-Pd alloy nanoparticles and α-MnO2 nanotubes significantly improved the reactivity of lattice oxygen, and the 0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst outperformed the α-MnO2 nanotube catalyst in the oxidation of toluene, m-xylene, ethyl acetate and acetone. Over the0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst,（i） toluene oxidation was greatly inhibited in the toluene/m-xylene mixture, while m-xylene oxidation was not influenced;（ii） acetone and ethyl acetate oxidation suffered a minor impact in the acetone/ethyl acetate mixture; and（iii） m-xylene oxidation was enhanced whereas the oxidation of the oxygenated VOCs（volatile organic compounds） was suppressed in the acetone/m-xylene or ethyl acetate/m-xylene mixtures. The competitive adsorption of these typical VOCs on the catalyst surface induced an inhibitive effect on their oxidation, and increasing the temperature favored the oxidation of the VOCs. The mixed VOCs could be completely oxidized into CO2 and H2 O below 320°C at a space velocity of 40,000 m L/（g·hr）. The 0.91 wt.% Au0.48 Pd/α-MnO2 nanotube catalyst exhibited high catalytic stability as well as good tolerance to water vapor and CO2 in the oxidation of the VOC mixtures. Thus, the α-MnO2 nanotube-supported noble metal alloy catalysts hold promise for the efficient elimination of VOC mixtures.

Hydrogenation of cinnamaldehyde over bimetallic Au-Cu/CeO_2 catalyst under a mild condition

Bimetallic Au_xCu_y/CeO_2（x/y = 3/1,1/1,and 1 /3） catalysts were prepared by direct anion exchange（DAE）,following impregnation（IMP） methods,and used for selective hydrogenation of cinnamaldehyde.The effects of pretreatments,such as calcination or reduction on the catalytic activities of these catalysts were investigated.XRD and HRTEM showed that for the reduced catalysts,there is the formation of an Au-Cu alloy.HAADF-STEM displayed that reduction pretreatment leads to a very homogenous distribution of Au and Cu on the external catalyst surface.Reaction parameters,such as CAL concentration,the stirring speed,nature of the solvent influence the catalytic activities.Pretreatments lead to a major effect on CAL conversion and HCAL selectivity.Catalysts Au_xCu_y/CeO_2 pretreated under reduction display higher CAL conversion and HCAL selectivity than that of under calcination mainly due to the synergistic effect resulting in a formation of Au-Cu alloy.