Effect of valence and spin state on ethane dehydrogenation in Fe-S-1 catalyst

Light alkanes non-oxidative dehydrogenation is an attractive non-oil route for olefins production.The alkane dehydrogenation reaction is limited by thermodynamic equilibrium,and the C-H bond cleavage is commonly considered as the rate-determined step.The valence state of metal sites in catalysts will influence the stabilization of the vital intermediate(i.e.,C_(x)H_(y)...M^(δ+)...H)during the C-H bond cleavage process,which in turn affects the catalytic reactivity.Herein,we explicitly investigated the effect of different valence states of framework-Fe in silicate-1 zeolite on ethane dehydrogenation reaction through the combination of experimental and theoretical study.Fe(Ⅱ)-S-1 and Fe(Ⅲ)-S-1 catalysts are successfully synthesized by ligand-assisted in situ crystallization method,In-situ C_(2)H_6-FTIR shows the higher coverage of hydrocarbon intermediates on Fe(Ⅱ)-S-1,Under the same evaluation co nditio n,Fe(Ⅱ)-S-1 exhibits a higher space time yield of ethylene.Density functional theory(DFT)results reveal that the more coordinate-unsaturated and electron-enriched Fe(Ⅱ)sites boost the first C-H bond activation by slight deformation and efficient electron donation with C_(2)H_(5)^(*)species.Remarkably,the second C-H bond cleavage on Fe(Ⅱ)-S-1 undergoes a spin-crossing process from quintet state to triplet state,which involves a two-electro n-two-orbital interaction,further promoting the formation of ethylene.Microkinetic analysis is consistent with the experimental and DFT results.This work could provide methodology for elucidating the effect of metal valence states on catalytic performance as well as offer guidance for designing more efficient Fe-zeolite catalysts.

Ab initio molecular dynamics simulation reveals the influence of entropy effect on Co@BEA zeolite-catalyzed dehydrogenation of ethane

The C–H bond activation in alkane dehydrogenation reactions is a key step in determining the reaction rate.To understand the impact of entropy,we performed ab initio static and molecular dynamics free energy simulations of ethane dehydrogenation over Co@BEA zeolite at different temperatures.AIMD simulations showed that a sharp decrease in free energy barrier as temperature increased.Our analysis of the temperature dependence of activation free energies uncovered an unusual entropic effect accompanying the reaction.The unique spatial structures around the Co active site at different temperatures influenced both the extent of charge transfer in the transition state and the arrangement of 3d orbital energy levels.We provided explanations consistent with the principles of thermodynamics and statistical physics.The insights gained at the atomic level have offered a fresh interpretation of the intricate long-range interplay between local chemical reactions and extensive chemical environments.

压缩学时背景下无机化学教学改革

在无机化学教学学时压缩的背景下,综合考虑我国中学化学课程改革及目前无机化学教学所面临的问题,适度调整、拓宽和深化无机化学教学内容,并基于OBE理念,采用"模块化"教学、"分层化"教学及"专题研讨式"教学,培养学生自主学习能力、解决实际问题的能力以及创新能力,形成"知识-能力"一体化的教育理念。

Tuning Atomically Dispersed Fe Sites in Metal–Organic Frameworks Boosts Peroxidase‑Like Activity for Sensitive Biosensing

Although nanozymes have been widely developed,accurate design of highly active sites at the atomic level to mimic the electronic and geometrical structure of enzymes and the exploration of underlying mechanisms still face significant challenges.Herein,two functional groups with opposite electron modulation abilities(nitro and amino)were introduced into the metal–organic frameworks(MIL-101(Fe))to tune the atomically dispersed metal sites and thus regulate the enzymelike activity.Notably,the functionalization of nitro can enhance the peroxidase(POD)-like activity of MIL-101(Fe),while the amino is poles apart.Theoretical calculations demonstrate that the introduction of nitro can not only regulate the geometry of adsorbed intermediates but also improve the electronic structure of metal active sites.Benefiting from both geometric and electronic effects,the nitro-functionalized MIL-101(Fe)with a low reaction energy barrier for the HO*formation exhibits a superior POD-like activity.As a concept of the application,a nitro-functionalized MIL-101(Fe)-based biosensor was elaborately applied for the sensitive detection of acetylcholinesterase activity in the range of 0.2–50 mU mL−1 with a limit of detection of 0.14 mU mL−1.Moreover,the detection of organophosphorus pesticides was also achieved.This work not only opens up new prospects for the rational design of highly active nanozymes at the atomic scale but also enhances the performance of nanozyme-based biosensors.

MIL-53(Al)derived single-atom Rh catalyst for the selective hydrogenation of m-chloronitrobenzene into m-chloroaniline

The catalytic hydrogenation of halonitroarenes to haloanilines is a green and sustainable process for the production of key nitrogen-containing intermediates in fine chemical industry.Chemoselective hydrogenation poses a significant challenge,which requires the rational design of the catalysts with proper hydrogenation ability for nitro group and simultaneously preventing dehalogenation of halogen group.Herein,a highly effective Rh@Al_(2)O_(3)@C single-atom catalyst(SAC)was developed for the hydrogenation of m-chloronitrobenzene(m-CNB)to m-chloroaniline(m-CAN),through an in-situ grafting of metal during the assembly of MIL-53(Al),followed by confined pyrolysis.Extensive characterizations reveal an exquisite structure of the Rh@Al_(2)O_(3)@C,containing atomically dispersed Rh sites onto Al_(2)O_(3) confined by the amorphous carbon.The five-coordinated aluminum(Al^(Ⅴ))species are essential for achieving the atomic dispersion of Rh atoms,providing the unsaturated coordinative sites for metal.Compared to the benchmark Rh/γ-Al_(2)O_(3) and Rh/C nanocatalysts,the Rh@Al_(2)O_(3)@C SAC affords an excellent turnover frequency of 2317 molm-CNB·molRh^(–1)·h^(–1),the highest value to date in heterogeneous catalyst systems for the hydrogenation of m-CNB at 313 K and 20 bar H2,together with a sustained selectivity to m-CAN(~98%)during five consecutive runs.The superior catalytic performance of the Rh@Al_(2)O_(3)@C is attributed to a proper modulation of electronic structure of hydrogenation metal by forming SAC,together with an enhanced accessibility of acid function sites.

Mechanism investigation of PtPd decorated Zn_(0.5)Cd_(0.5)S nanorods with efficient photocatalytic hydrogen production combining with kinetics and thermodynamics

Different components of PtPd bimetallic cocatalysts modified Zn_(0.5)Cd_(0.5)S nanorods have already been designed and prepared in this study.The obtained hybrid photocatalysts were tested and characterized by XPS,ICP-OES and UV-Vis spectra,TEM and EDX tools.Such characterizations can prove the formation of PtPd bimetallic alloy particles in hybrid catalysts.Under visible light illumination,an outstanding hydrogen producing rate of 9.689mmol·g^(-1)·h^(-1) and a high AQY efficiency up to 10.43%at 420 nm are achieved in this work.In addition,thermodynamics(DFT calculations)and kinetics(Photoluminescence emission,photocurrent responses,electrochemical impedance spectroscopy and surface photovoltage spectra)investigations illustrate that PtPd bimetallic alloy has similar catalytic thermodynamic properties to Pt,which can greatly boost the charge separation and speed up the charge transfer,and decrease the activation energy of H2 generation.Notably,the calculation data suggests that Pt is thermodynamically favorable,while PtPd alloy is kinetically beneficial to H_(2)production,which can be ascribed to the higher activity of PtPd/Zn_(0.5)Cd_(0.5)S than Pt/Zn_(0.5)Cd_(0.5)S.This work can propose a fresh perspective for preparing high efficiency hybrid photocatalysts.

Efficient Contact between H_(2)O and N-Coordinate Ru Nanoparticles in Three-Dimensionally Ordered Macro/Mesoporous Carbon Boosting Alkaline HER

In this study,a novel approach is proposed to achieve the uniformly dispersed Ru nanoparticles with N coordination loaded on three-dimensionally ordered macro/mesoporous carbon(3DOMMC)through simultaneous pyrolysis of Ru^(3+)and cyanamide on 33DOMMC.In an alkaline medium,the synthesized catalysts exhibit exceptional hydrogen evolution reaction(HER)performance.Specificall,Ru-N/3DOMMC demonstrates a significantly low overpotential of 13.8 mV to achieve acrent density of 10 mA.cmzandit exhibits a mass activity 17.5 times higher than that of commercial Pt/C.The outstanding performance could be attributed to the ultrahigh Ru dispersion and more efficient contact between active sites and reactant,which derived from the large specific surface area and interconnective three-dimensionally macro/mesopores of 3DOMMC.

Enhanced thermoelectric properties of Cu_(3)SbSe_(4)-based materials by synergistic modulation of carrier concentration and phonon scattering

Cu_(3)SbSe_(4),a copper-based sulfide free of rare earth elements,has received extensive attention in ther-moelectric materials.However,its low carrier concentration restricts its widespread application.In this study,a microwave-assisted solution synthesis method was used to produce samples of Cu_(3)SbSe_(4),which enabled the formation of CuSe in situ and increased the yield.Through the use of first-principles cal-culations,structural analysis,and performance evaluation,it was found that CuSe can enhance the carrier concentration and that induced nano-defects have a positive effect on reducing the lattice thermal conductivity.Moreover,doping with Sn decreases the band gap of the system and moves the Fermi level into the valence band,increasing the carrier concentration to 1.15×10^(-20)cm^(-3).Finally,the zT value of the Cu_(3)Sb_(0.98)Sn_(0.02)Se_(4)sample was achieved at 1.05 at 623 K when the theoretical yield of a single synthesis was 10 mmol.

Mesoporous MnO_(2)nanosheets for efficient electrocatalytic nitrogen reduction via high spin polarization induced by oxygen vacancy

The electrochemical N_(2)reduction reaction(NRR)represents a green and sustainable route for NH_(3)synthesis under ambient conditions.However,the mechanism of N_(2)activation in the electrocatalytic NRR remains unclear.Herein,we found that the high spin state Mn^(3+)-Mn^(3+)pairs induced by oxygen vacancy in MnO_(2)nanosheets greatly enhance the catalytic activities.The strong electron transfer between d orbital of Mn and orbital of N2 forces the N_(2)to be of radical nature,which activates the hydrogenation process and weakens the N≡N bond.Based on the density functional theory(DFT)calculation results,we precisely designed mesoporous MnO_(2)nanosheets with rich oxygen vacancies via using methyltriphenylphosphonium bromide(MPB)to induce more Mn^(3+)-Mn^(3+)pairs(Mn^(3-3)-MnO_(2)),which can achieve a fairly high ammonia yield of up to 147.2μg·h^(−1)·mgcat−1.at−0.75 V vs.reversible hydrogen electrode(RHE)and a high Faradaic efficiency(FE)of 11%.Furthermore,these mesoporous MnO_(2)nanosheets exhibit the superior durability with negligible changes in both NH3 yield and FE after a consecutive 6-recycle test and the current density electrolyzed over a 24-hour period.Our findings offer an approach to designing highly active transition metal catalysts for electrocatalytic nitrogen reduction.

Fabrication of La1-xCaxFeO3 perovskite-type oxides with macro-mesoporous structure via a dual-template method for highly efficient soot combustion

A series of three-dimensionally ordered macro-mesoporous(3DOMM)La1-xCaxFeO3(x=0-0.3)perovskite-type oxides were designed and successfully fabricated for the first time via a dual-template method.In which,PMMA and Brij-56 were employed as the hard template and soft template,respectively.It is found that 3 DOMM La1-xCaxFeO3 exhibits abundant wormlike mesoporous channels about 3 nm in diameter on macroporous skeleton walls.The excellent catalytic activity of soot combustion benefits from not only the well-designed hierarchical porous structure of catalyst,but also the redox electron pair of Fe3+/Fe4+induced by the doping of low-valent alkaline earth metal Ca to A-site of LaFeO3.3DOMM La0.8Ca0.2FeO3 exhibits superior catalytic performance for soot combustion,which shows T50 of396℃.It is 189℃lower than that without catalyst.A combination of structure and composition in the design of catalyst can be widely extended to other catalytic systems.

Atomically dispersed N-coordinated Fe-Fe dual-sites with enhanced enzyme-like activities

Replacement of enzymes with nanomaterials such as atomically dispersed metal catalysts is one of the most crucial steps in addressing the challenges in biocataiysis.Despite the breakthroughs of single-atom catalysts in enzyme-mimicking,a fundamental investigation on the development of an instructional strategy is still required for mimicking biatomic/multiatomic active sites in natural enzymes and constructing synergistically enhanced metal atom active sites.Herein,Fe_(2)NC catalysts with atomically dispersed Fe-Fe dual-sites supported by the metal-organic frameworks-derived nitrogen-doped carbon are employed as biomimetic catalysts to perform proof-of-concept investigation.The effect of Fe atom number toward typical oxidase(cytochrome C oxidase,NADH oxidase,and ascorbic acid oxidase)and peroxidase(NADH peroxidase and ascorbic acid peroxidase)activities is systematically evaluated by experimental and theoretical investigations.A peroxo-like O_(2) adsorption in Fe_(2)NC nanozymes could accelerate the O-O activation and thus achieve the enhanced enzyme-like activities.This work achieves the vivid simulation of the enzyme active sites and provides the theoretical basis for the design of high-performance nanozymes.As a concept application,a colorimetric biosensor for the detection of S^(2-) in tap water is established based on the inhibition of enzyme-like activity of Fe_(2)NC nanozymes.

Achieving high thermoelectric performance through carrier concentration optimization and energy filtering in Cu_(3)SbSe_(4)-based materials

The previous works commonly adjust the carrier concentration through acceptor doping,but at the same time,the decrease of the Seebeck coefficient limits the further improvement of electrical properties in Cu_(3)SbSe_(4)-based materials.In this work,a microwave-assisted hydrothermal synthesis method was used to synthesize Cu_(3)SbSe_(4)/TiO_(2) hollow microspheres.Part of TiO_(2) participates in the reaction,replaces the Sb site of Cu_(3)SbSe_(4) to form holes,and the rest is dispersed in the matrix in the form of the second phase.The first-principles calculations reveal that the doping of Ti significantly changes the band structure and phonon spectrum,thereby regulating carrier concentration while increasing phonon scattering.In addition,experimental results show that the energy filtering effect generated by the extra-mixed TiO_(2) nano particles,which suppresses the decrease of Seebeck coefficient by acceptor doping.Consequently,the highest average power factor 897.5 mW m^(-1) K^(-2) and the zT peak value of 0.70 can be obtained in Cu_(3)SbSe_(4)/6%TiO_(2) sample at 298e623 K.This work provides a new sight to improve the thermoelectric properties in Cu_(3)SbSe_(4) through carrier concentration regulation and nano-phase composition.

Highly stable Pt_(3)Ni ultralong nanowires tailored with trace Mo for the ethanol oxidation

Pt_(3)Ni alloy structure is an effective strategy to accelerate ethanol oxidation reaction(EOR),while the stability in acid electrolyte is the fatal weakness and the current density still needs to be enhanced.Herein,ultralong Pt_(3)Ni nanowires tailored by trace Mo(Mo/Pt_(3)Ni NWs)were successfully synthesized by surfactant free method.The specific activity of the optimized catalyst was 2.66 mA·cm^(-2),which is approximately 2.16 and 4.6-fold that of Pt_(3)Ni NWs and commercial Pt/C catalyst,respectively.Most importantly,the Mo/Pt_(3)Ni NWs catalyst showed negligible structure degradation after 3,000 cycles(42 h)of durability test in 0.1 M HClO4 and 0.5 M ethanol,as compared to severe structural collapse and Ni dissolution for the pure Pt_(3)Ni NWs.The density functional theory(DFT)calculation also confirmed that both the surface and subsurface Mo atom could form Pt-Mo and Ni-Mo bonds with Pt and Ni,which were stronger than Pt-Ni bonds,to pin the Ni atoms in the unstable position and suppress the dissolution of surface Ni.The findings of this study indicate a promising pathway for the design and engineering of durable alloy nanocatalysts for direct ethanol fuel cell applications.

Fine-Tuning Pyridinic Nitrogen in Nitrogen-Doped Porous Carbon Nanostructures for Boosted Peroxidase-Like Activity and Sensitive Biosensing

Carbon materials have been widely used as nanozymes in bioapplications,attributing to their intrinsic enzyme-like activities.Nitrogen(N)-doping has been explored as a promising way to improve the activity of carbon material-based nanozymes(CMNs).However,hindered by the intricate N dopants,the real active site of N-doped CMNs(N-CMNs)has been rarely investigated,which subsequently retards the further progress of high-performance N-CMNs.Here,a series of porous N-CMNs with well-controlled N dopants were synthesized,of which the intrinsic peroxidase(POD)like activity has a positive correlation with the pyridinic N content.Density functional theory calculations also reveal that pyridinic N boosts the intrinsic POD-like activity of N-CMNs.Pyridinic-N dopant can effectively promote the first H_(2)O desorption process in comparison with the graphitic and pyrrolic N,which is the key endothermic reaction during the catalytic process.Then,utilizing the optimized nanozymes with high pyridinic N content(NP-CMNs)and superior POD-like activity,a facile total antioxidant capacity(TAC)assay was developed,holding great promise in the quality assessment of medicine tablets and antioxidant food for healthcare and healthy diet.

Defect engineering synergistically modulates power factor and thermal conductivity of CuGaTe2 for ultra-high thermoelectric performance

The ternary chalcopyrite CuGaTe_(2)has emerged as a promising p-type thermoelectric material with its advantages of low cost,good stability,and non-toxic elements.However,its thermoelectric performance is limited by the intrinsic low electrical conductivity and high lattice thermal conductivity.In this work,A deficiency of Cu in Cu_(1–x)Ga Te_(2)semiconductors can be used to optimize the electrical properties by improving the carrier concentration and to reduce thermal conductivity through multi-scale phonon scattering,which is predicted and guided by the First-principles density functional theory calculations.The carrier concentration is increased to 1020,which compensates for the low electrical performance caused by the intrinsic low nHof CuGaTe_(2).The average power factor of Cu_(0.96)Ga Te_(2)reaches 106.3%higher than that of the original CuGaTe_(2).In addition,the lattice thermal conductivity of the defective samples is greatly reduced at high temperatures,which is mainly due to the reduction of sound speed and phonon scattering.All the above factors contribute to the highest dimensionless figure of merit(ZT)value of 1.23 at 823 K in Cu_(0.96)GaTe_(2),which is 114%higher than the pristine CuGaTe_(2),and the average ZT is 171.4%higher.

Enhanced thermoelectric performance in n-type Mg_(3.2)Sb_(1.5)Bi_(0.5) doping with lanthanides at the Mg site

Mg-based thermoelectric materials have attracted more and more attention because of their rich composition elements,green environmental protection,and lower price.In recent years,the thermoelectric properties of n-type Mg_(3)Sb_(2) materials have been optimized by doping chalcogenide elements(S,Se,and Te)at the anionic position.In this work,n-type Mg_(3.2)A_(x)Sb_(1.5)Bi_(0.5)(A=Gd,Ho;x=0.01,0.02,0.03,and 0.4)samples were prepared by the cation site doping of lanthanide elements(Gd and Ho).The research results show that Gd and Ho doped n-type Mg3.2Sb1.5Bi0.5samples are entirely comparable to the S,Se,and Te doped n-type Mg3.2Sb1.5Bi0.5samples,demonstrating more excellent thermoelectric properties.Doping with lanthanides(Gd and Ho)at the Mg site increases the carrier concentration of the material to 8.161×10^(19)cm^(-3).Doping induces the contribution of more electron,thus obtaining higher conductivity.The maximum zT value of the Mg_(3.2)Gd_(0.02)Sb_(1.5)Bi_(0.5) and the Mg_(3.2)Ho_(0.02)Sb_(1.5)Bi_(0.5) samples reaches 1.61 and 1.55,respectively.This work theoretically and experimentally demonstrates Gd and Ho are efficient n-type dopants for Mg_(3.2)Sb_(1.5)Bi_(0.5) thermoelectric material.