The efficient conversion of alkanes into high-value chemicals remains challenging due to the inert C-H bonds.Mimicking enzymes could provide a green and sustainable approach to address such demanding tasks.Here we fou...The efficient conversion of alkanes into high-value chemicals remains challenging due to the inert C-H bonds.Mimicking enzymes could provide a green and sustainable approach to address such demanding tasks.Here we found that atomically dispersed hydrophilic Fe-N-C interplayed with hydrophobic microenvironments could be leveraged for concentrating and converting aromatic alkanes using oxidants in aqueous conditions.Specifically,the hydrophilic/hydrophobic Fe-N-C catalysts give an approximate 2-fold enhancement in the turnover frequency(1,107.7 h^(-1))compared to hydrophilic counterparts(403.8 h^(-1))in terms of ethylbenzene(EB)oxidation.The hydrophobic microenvironment surrounding the Fe sites markedly diminishes the interfacial water density,which reduces the solvation-free energy of the hydrophobic substrate and promotes the activation and dissociation of tert-butyl hydroperoxide into radicals in water.Consequently,EB reactant is effectively enriched around the atomic Fe sites and is rapidly activated by the generated radicals.This work highlights the potential of engineering a single-atom catalyst microenvironment for efficient and green alkane conversion in aqueous solution.展开更多
Exploring new heterogeneous catalysts to achieve efficient C-H bond oxidation is momentous in industrial chemical production.Herein,three Fe-incorporated polyoxometalate-encapsulated metal-organic frameworks(POM@MOFs)...Exploring new heterogeneous catalysts to achieve efficient C-H bond oxidation is momentous in industrial chemical production.Herein,three Fe-incorporated polyoxometalate-encapsulated metal-organic frameworks(POM@MOFs),[Fe(H_(2)O)_(3)(dtb)][Fe(dtb)_(2)][HBW_(12)O_(40)]-12H_(2)O(1),[Fe(H_(2)O)2(dtb)]_(2)[Fe(dtb)_(2)(Hdtb)][SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]·16H_(2)O(2),[Fe(H_(2)O)_(2)]_(4)(dtb)_(5)[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]_(2)·18H_(2)O(3),(dtb=1,4-di[4H-1,2,4-triazol-4-yl]-benzene),were hydrothermally synthesized for catalytic C-H bond oxidation.They exhibited three-dimensional(3-D)POM-based metal-organic host-vip frameworks with diverse cages.In compound 1,cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(6)(H_(2)O)_(2)]^(4+)clusters and dtb ligands present a pcu alpha-Po primitive cubic topological net and abundant twisted quadrangular prism-shaped cages,in which the monoprotonated[HBW_(12)O_(40)]^(4-)polyoxoanions are encapsulated.In compound 2,two-dimensional(2-D)cationic metal-organic layers constructed by trinuclear[Fe_(3)(dtb)_(6)(H_(2)O)_(4)]^(6+)clusters and dtb ligands display a sql/Shubnikov tetragonal plane net topology,in which the rhomboid-shaped metal-organic windows in adjacent parallel-arranged 2-D layers are enclosed to form an open parallelepiped cage.The[SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]^(7-)poly-oxoanions locate in the parallelepiped cages between 2-D bilayers.In compound 3,the 3-D cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(3)(H_(2)O)_(4)]^(4+)clusters and dtb ligands possess a bnn hexagonal BN topology,in which the hexagonal prismatic metal-organic cages accommodate four[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)poly-oxoanions.Employing diphenylmethane(DPM)oxidation as C-H bond oxidation model reaction,compounds 1-3 displayed distinct catalytic activities owing to the synergistic effect of polynuclear Fe nodes and poly-oxoanions.Among them,[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)-contained compound 3 exhibited higher catalytic activity than polyoxotungstate-based compounds 1-2 with 99%DPM conversion and 99%benzophenone(BP)selectivity within 6 h as well as good recyclability and structural stability.展开更多
A comparative study was conducted on the oxidation behavior of four different bond coat structures:single-layer air plasma spraying(APS),single-layer high-velocity oxygen fuel(HVOF),double-layer APS+HVOF,and double-la...A comparative study was conducted on the oxidation behavior of four different bond coat structures:single-layer air plasma spraying(APS),single-layer high-velocity oxygen fuel(HVOF),double-layer APS+HVOF,and double-layer HVOF+HVOF in a high-temperature and high-water vapor environment.The oxidation resistance and surface mixed oxide(MO)growth behavior and formation mechanisms of different structures in this environment were analyzed.The results indicate that CoNiCrAlY bond coats with different structures exhibit distinct oxidation behaviors in a high-temperature,high-water vapor environment.The growth of the MO phase is significantly influenced by the bond coat structure,and the high-water vapor environment promotes the nucleation and growth of bulk MO phase,resulting in a multilayer internal structure.Among these,the double-layer HVOF bond coat structure demonstrates superior resistance to water vapor corrosion,with fewer surface MO formations.These findings suggest that proper structural design can enhance the water vapor corrosion resistance of MCrAlY bond coats,providing theoretical foundations and technical support for optimizing their applications in high-temperature,high-water vapor environments.展开更多
Photocatalytic activation of C-H bonds is versatile but challenging for undergoing oriented conversion processes.Herein,a spatially site-isolated heterojunction(ZS-Vs/ZIS)of ZnIn2S4 with strong Lewis acidity(ZIS)and Z...Photocatalytic activation of C-H bonds is versatile but challenging for undergoing oriented conversion processes.Herein,a spatially site-isolated heterojunction(ZS-Vs/ZIS)of ZnIn2S4 with strong Lewis acidity(ZIS)and ZnS with S-vacancy(ZS-Vs)is constructed for activating α-C‒H bond and forming·O_(2)^(-)to cleave the C-H bond,respectively.ZS-Vs/ZIS displays outstanding performance in visible-light partial photooxidation of bio-based 5-hydroxymethylfurfural(HMF)to 2,5-diformylfuran(DFF)in an unprecedented yield of 95.7%at 25°C.In-situ experiments and calculations reveal that Zn sites of ZIS serve as hole enrichment to adsorb HMF for α-C‒H activation via ligand-to-metal charge transfer.Shallow trap states introduced by S-vacancy in ZS-Vs act as an electron pool to realize directed O_(2) activation into·O_(2)^(-)for breaking pre-activated α-C‒H bond in HMF to exclusively give DFF.Moreover,ZS-Vs/ZIS has good recyclability and universality in the photooxidation of various alcohols to carbonyls(86.4-95.6%yields).The synergistic C-H activation/breaking strategy exhibits high potential in targeted photocatalytic transformations.展开更多
The oxidation of lignin model compounds to esters via C-C bond cleavage has attracted considerable attention,as esters could be used as important polymer precursors and pharmaceutical intermediates.However,most studie...The oxidation of lignin model compounds to esters via C-C bond cleavage has attracted considerable attention,as esters could be used as important polymer precursors and pharmaceutical intermediates.However,most studies focus on designing homogeneous or noble metal catalysts and conducting the reactions under basic conditions.Here,we report an efficient process for the C-C bond cleavage of lignin model compounds and selectively producing esters over different shaped CeO_(2)(i.e.,nanospheres(S),nanorods(R),nanoparticles(P),and nanocubes(C))under base-free conditions.Specifically,the yield of methyl anisate from the aerobic oxidation of l-(4-methoxyphenyl)ethanol reaches 77.6%over CeO_(2)-S in one hour(91%in 9 h),exhibiting higher performance compared to other evaluated CeO_(2)catalysts(6.4%-40.2%).Extensivecharacterizations and experimental investigations reveal that the density of weak base sites and oxygen vacancies on the CeO_(2)surface is positively correlated with the yield of methyl esters.Furthermore,the reaction pathway is investigated,which confirms that 1-(4-methoxyphenyl)ethanol first undergoes two reactions(i.e.,etherification and dehydrogenation)to produce intermediates of1-methoxy-4-(1-methoxy-ethyl)-benzene and 1-(4-methoxyphenyl)ethanone,respectively,followed by a series of functional group transformations to generate the targeted methyl anisate ultimately.展开更多
Novel reusable MnOx‐N@C catalyst has been developed for the direct oxidation of N‐heterocycles under solvent‐free conditions using TBHP as benign oxidant to give the corresponding N‐heterocyclic ketones. The catal...Novel reusable MnOx‐N@C catalyst has been developed for the direct oxidation of N‐heterocycles under solvent‐free conditions using TBHP as benign oxidant to give the corresponding N‐heterocyclic ketones. The catalytic system exhibited a broad substrate scope and excellent regi‐oselectivity, as well as being amenable to gram‐scale synthesis. This MnOx‐N@C catalyst also showed good reusability and was successfully recycled six times without any significant loss of activity.展开更多
Hexagonal boron nitride(h-BN)is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes.Despite intense recent research effort,many aspects of the reaction mecha...Hexagonal boron nitride(h-BN)is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes.Despite intense recent research effort,many aspects of the reaction mechanism,such as the observed supra-linear reaction order of alkanes,remain unresolved.In this work,we show that the introduction of a low concentration of propane in the feed of ethane oxidative dehydrogenation is able to enhance the C_(2)H_(6) conversion by 47%,indicating a shared reaction intermediate in the activation of ethane and propane.The higher activity of propane makes it the dominant radical generator in the oxidative co-dehydrogenation of ethane and propane(ODEP).This unique feature of the ODEP renders propane an effective probe molecule to deconvolute the two roles of alkanes in the dehydrogenation chemistry,i.e.,radical generator and substrate.Kinetic studies indicate that both the radical generation and the dehydrogenation pathways exhibit a first order kinetics toward the alkane partial pressure,leading to the observed second order kinetics of the overall oxidative dehydrogenation rate.With the steady-state approximation,a radical chain reaction mechanism capable of rationalizing observed reaction behaviors is proposed based on these insights.This work demonstrates the potential of ODEP as a strategy of both activating light alkanes in oxidative dehydrogenation on BN and mechanistic investigations.展开更多
Mn-based layered oxides(KMO)have emerged as one of the promising low-cost cathodes for potassiumion batteries(PIBs).However,due to the multiple-phase transitions and the distortion in the MnO6structure induced by the ...Mn-based layered oxides(KMO)have emerged as one of the promising low-cost cathodes for potassiumion batteries(PIBs).However,due to the multiple-phase transitions and the distortion in the MnO6structure induced by the Jahn-Teller(JT)effect associated with Mn-ion,the cathode exhibits poor structural stability.Herein,we propose a strategy to enhance structural stability by introducing robust metal-oxygen(M-O)bonds,which can realize the pinning effect to constrain the distortion in the transition metal(TM)layer.Concurrently,all the elements employed have exceptionally high crustal abundance.As a proof of concept,the designed K_(0.5)Mn_(0.9)Mg_(0.025)Ti_(0.025)Al_(0.05)O_(2)cathode exhibited a discharge capacity of approximately 100 mA h g^(-1)at 20 mA g^(-1)with 79%capacity retention over 50 cycles,and 73%capacity retention over 200 cycles at 200 mA g^(-1),showcased much better battery performance than the designed cathode with less robust M-O bonds.The properties of the formed M-O bonds were investigated using theoretical calculations.The enhanced dynamics,mitigated JT effect,and improved structural stability were elucidated through the in-situ X-ray diffractometer(XRD),in-situ electrochemical impedance spectroscopy(EIS)(and distribution of relaxation times(DRT)method),and ex-situ X-ray absorption fine structure(XAFS)tests.This study holds substantial reference value for the future design of costeffective Mn-based layered cathodes for PIBs.展开更多
Al/steel composite plate has a wide application prospect,but great differences in properties between Al and steel are observed.It is difficult to obtain high bonding strength by the traditional cold roll bonding proce...Al/steel composite plate has a wide application prospect,but great differences in properties between Al and steel are observed.It is difficult to obtain high bonding strength by the traditional cold roll bonding process.Al/steel composite plate was thus prepared by cold roll bonding at a reduction rate of 60%after oxidation treatment on the surface to be composited on the steel side.The heat treatment of holding at 400℃ for 1 h and cooling with the furnace was then adopted.The bonding strength,microstructure,and properties of the Al/steel composite plate before and after annealing were analysed and compared through shear test,bending test,tensile test,and micro-characterization.Results show that the shear strengths of the interface before and after annealing are 100 and 80 MPa,respectively.Although the shear strength of the annealed Al/steel composite plate decreases,the bending and overall tensile properties of the composite plate are improved,showing better mechanical properties.展开更多
A molecular [Ru(bda)]-type(bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand(Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylben...A molecular [Ru(bda)]-type(bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand(Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylbenzene(3 F) or styrene(St) blocking units on the surface of glassy carbon(GC) electrodes by electrochemical polymerization, in order to prepare the corresponding poly-1@GC, poly-1+P3 F@GC, and poly-1+PSt@GC functional electrodes. Kinetic measurements of the electrode surface reaction revealed that [Ru(bda)] triggers the O–O bond formation via(1) the radical coupling interaction between the two metallo-oxyl radicals(I2 M) in the homo-coupling polymer(poly-1), and(2) the water nucleophilic attack(WNA) pathway in poly-1+P3 F and poly-1+PSt copolymers. The comparison of the three electrodes revealed that the second coordination sphere of the water oxidation catalysts plays vital roles in stabilizing their reaction intermediates, tuning the O–O bond formation pathways and improving the water oxidation reaction kinetics without changing the first coordination structures.展开更多
Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that t...Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in Au Pd nanoparticles.It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation.Remarkably,the catalyst with the most electron-rich Pd sites(binding energy downshift:1.0 e V)exhibits an extremely high turnover frequency(~500000 h-1 vs 12000 h-1 for that with net Pd atoms)for solvent-free selective oxidation of benzyl alcohol,which is,to the best of our knowledge,the highest value ever reported.Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage,as indicated by the significant reduction in the activation energy as compared to net Pd atoms.展开更多
A blue light-induced formal insertion reaction ofα-siloxy carbene into the C—H bond of 1,3-diketones has been reported.Under the irradiation of blue light,acylsilane converts toα-siloxy carbene,which then undergoes...A blue light-induced formal insertion reaction ofα-siloxy carbene into the C—H bond of 1,3-diketones has been reported.Under the irradiation of blue light,acylsilane converts toα-siloxy carbene,which then undergoes formal C—H bond insertion reaction with the enol form of 1,3-diketone.This method uses readily available and relative stable acylsilane as car-bene precursor,which features a simple and metal-free approach under mild conditions.Moreover,the synthetic potential of this protocol has been demonstrated by performing the reaction on a gram scale with comparable high yield.展开更多
The methylene-selective oxidation of simple alkanes catalyzed by a nonheme iron(Ⅲ)-monoamidate complex using H_(2)O_(2)as the terminal oxidant is reported.Mechanistic studies suggest that iron(V)-oxo species is the a...The methylene-selective oxidation of simple alkanes catalyzed by a nonheme iron(Ⅲ)-monoamidate complex using H_(2)O_(2)as the terminal oxidant is reported.Mechanistic studies suggest that iron(V)-oxo species is the active intermediate,undergoing hydrogen atom abstraction(HAA)as the rate-determining step to initiate C-H bond activation.展开更多
Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD a...Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD and SEM.The results show that Si3N4 and Si2N2O bonded SiC refractory presents better steam oxidation resistance than SiAlON bonded SiC.For Si3N4 and Si2N2O bonded SiC,the oxidation speed is higher with more pronounced volume expansion in the early 100 h;afterwards,the volume expansion slows down gradually and starts to level off after 300 h.It is considered that the high silica glass phase formed during the oxidation covers Si3N4 and Si2N2O,and SiC as a protective layer and fills the open pores.But for SiAlON bonded SiC,the volume expands gradually and constantly with the increasing oxidation duration even after 500 h,due to the continuous formation of mullite transformed from oxidation products and Al2O3 in SiAlON.展开更多
Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earthabundant metals...Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earthabundant metals.This work reports the synthesis,characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda(H2 bnda=2,2’-bi(nicotinic acid)-6,6’-dicarboxylic acid)featuring steric hindrance and enhanced hydrophilicity on the backbone.Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda(H_(2)bda=2,2’-bipyridine-6,6’-dicarboxylic acid),Ru-pda(H_(2)pda=1,10-phenanthroline-2,9-dicarboxylic acid),and Ru-biqa(H_(2)biqa=(1,1’-biisoquinoline)-3,3’-dicarboxylic acid),we emphasized that seven coordination clearly determines presence of Ru^(Ⅴ)=O with high spin density on the ORu^(Ⅴ)=O atom,i.e.oxo with radical properties,which is one of the necessary conditions for reacting through the O-O coupling pathway.However,an additional factor to make the condition sufficient is the favorable intermolecular faceto-face interaction for the generation of the pre-reactive[Ru^(Ⅴ)=O…O=Ru^(Ⅴ)],which may be significantly influenced by the secondary coordination environments.This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O-O bond formation.展开更多
The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis（CPE）. After modification, a re-melted layer without obvious pores and oxide stringers is formed,the gain s...The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis（CPE）. After modification, a re-melted layer without obvious pores and oxide stringers is formed,the gain size of re-melted layer is approximately 80–120 nm. It is shown, from cyclic oxidation at 1100℃,that a thin oxide scale mainly composed of α-Al;O;has been formed on the modified bond-coat and the oxidation resistance of the modified bond-coat has been significantly improved. Such beneficial result can be attributed to following effects: during CPE process, the plasma discharges with high temperature take place on the bond-coat surface. With plasma discharge treatment, the surface is melted and quickly re-solidified, the grain size decreases, and the pores and oxide stringers disappear. During cyclic oxidation, owing to the above modification of surface properties, the critical content of Al for selective oxidation is significantly decreased. Therefore, a continuous Al;O;scale is formed.展开更多
The steam oxidation of Si3N4-bonded SiC was determined at 1000℃for 50,100,150,200,250 and 300 h,respectively,according to ASTM C863-2000.The evolution of the phase composition and the microstructure as well as their ...The steam oxidation of Si3N4-bonded SiC was determined at 1000℃for 50,100,150,200,250 and 300 h,respectively,according to ASTM C863-2000.The evolution of the phase composition and the microstructure as well as their relationship was investigated by XRD and SEM.The results show that the oxidation rate of Si3N4-bonded SiC is periodic.The presence of nitrogen element can impede the crystallization of SiO2 glass;the local enrichment of CaO impurities is unfavorable for the existence of fibrous SiO2.SiO2 mainly exists as cristobalite when the CaO/SiO2 ratio reaches a suitable level,but gradually transforms to quartz along with the oxidation time when the SiO2 content increases,or the CaO/SiO2 ratio decreases,due to the insufficient mineralization of CaO.The crystallization of SiO2 glass,especially the formation of quartz is the key factor leading to the volume expansion and structural stress.When the cracks extend and reach the surface,the degradation of the material accelerates.展开更多
An innovative method of hot compression bonding is proposed in this work for the joining of 9Cr oxide dispersion strengthened(ODS)alloy and 9Cr reduced-activation ferritic/martensitic(RAFM)alloy.The microstructural ev...An innovative method of hot compression bonding is proposed in this work for the joining of 9Cr oxide dispersion strengthened(ODS)alloy and 9Cr reduced-activation ferritic/martensitic(RAFM)alloy.The microstructural evolution of the bonding interface was investigated by scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD),and transmission electron microscopy(TEM).The results verify that the pinning effect of nano-oxides particles(NPs)in 9Cr ODS alloy significantly enhances its dynamic recrystallization(DRX)temperature and deformation resistance.Continuous DRX(CDRX)first occurred on the 9Cr RAFM alloy side,and the areas near the bonding interface were composed of recrystallized grains.With increasing strain,CDRX also showed up on the 9Cr ODS alloy side.Inevitable slight oxidation occurred at the bonding interface during the hot compression bonding(HCB)process,and the interfacial oxides transformed from initial coarse CrO to TiO and finally to Y-Ti-O nanoparticles with sizes comparable to pre-existing NPs dispersed in the 9Cr ODS alloy matrix.It is believed that interfacial oxide transformation and grain structure consistency contributed to the excellent interface healing of the two dissimilar alloy pieces.The effectiveness of the bonding was tested by tensile tests and fractography analysis,revealing that ideal metallurgical bonding could be achieved under a controlled strain level of 10%at 800℃ followed by soaking at 1000℃ for 4 h.展开更多
The methane selective oxidation was a"holy grail"reaction.However,peroxidation and low selectivity limited the application.Herein,we combined three Au contents with TiO_(2)in both encapsulation(xAu@TiO_(2))a...The methane selective oxidation was a"holy grail"reaction.However,peroxidation and low selectivity limited the application.Herein,we combined three Au contents with TiO_(2)in both encapsulation(xAu@TiO_(2))and surface-loaded(xAu/TiO_(2))ways by MOF derivation strategy,reported a catalyst 0.5Au@TiO_(2)exhibited a CH_(3)OH yield of 32.5μmol·g^(-1)·h^(-1)and a CH_(3)OH selectivity of 80.6%under catalytic conditions of only CH_(4),O_(2),and H_(2)O.Mechanically speaking,the catalytic activity was controlled by both electron-hole separation efficiency and core-shell structure.The interfacial contact between Au nanoparticles and TiO_(2)in xAu@TiO_(2)and xAu/TiO_(2)induced the formation of oxygen vacancies,with 0.5 Au content showing the highest oxygen vacancy concentration.At the same Au content,xAu@TiO_(2)generated more oxygen vacancies than xAu/TiO_(2).The oxygen vacancy acted as an effective electron cold trap,which enhanced the photogenerated carrier separation efficiency and thereby improved the catalytic activity.In-situ DRIFTs revealed that the isolated OH(non-hydrogen bond adsorption)were key species for the methane selective oxidation,playing a role in the activation of CH_(4)to^(*)CH_(3).However,an overabundance of isolated OH led to severe overoxidation.Fortunately,the core-shell structure over xAu@TiO_(2)provided a slow-release environment for isolated OH through the intermediate state of^(*)OH(hydrogen bond adsorption)to balance the formation rate and consumption rate of isolated OH,doubling the methanol yield and increasing the>29%selectivity.These results showed a new strategy for the control of the overoxidation rate via a strategy of MOF encapsulation followed by pyrolytic derivation for methane selective oxidation.展开更多
The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050,1100 and 1150°C,and compared with a conve...The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050,1100 and 1150°C,and compared with a conventional NiCoCrAlY coating deposited on the same substrate.The AlCoCrFeNiY bond coat exhibits lower oxide growth rates due to its large columnar grains and low Al activity at the oxide scale/bond coat interface.Meanwhile,AlCoCrFeNiY has higher resistance to oxide spallation than NiCoCrAlY,which is attributed to the formation of a clean and defect-free metal/oxide interface.Significant interdiffusion occurs across the AlCoCrFeNiY/superalloy substrate interface.Our experimental evidence and thermody-namic modelling suggest that Fe accelerates interdiffusion and destabilizes theγ’phase,thereby causing the formation of a thick andγ’-depleted interdiffusion zone.In addition,the AlCoCrFeNiY bond coat un-dergoes more Al depletion and subsequentβtoγtransformation compared with NiCoCrAlY.Based on the findings in this work,a novel AlCoCrFeNiY/NiCoCrAlY double-layer bond coat was designed,tested and validated to achieve optimal balance between oxidation and interdiffusion.展开更多
基金supported by the National Natural Science Foundation of China(22478214,22175104)the Natural Science Foundation of Shandong Province(ZR2021YQ09,ZR2019ZD47,2024CXPT033)+3 种基金the China Postdoctoral Science Foundation(2022M723259)the Qingdao Postdoctoral Science Foundation(QDBSH20220201007)the Education Department of Shandong Province(2019KJC006)the Taishan Scholars Program.
文摘The efficient conversion of alkanes into high-value chemicals remains challenging due to the inert C-H bonds.Mimicking enzymes could provide a green and sustainable approach to address such demanding tasks.Here we found that atomically dispersed hydrophilic Fe-N-C interplayed with hydrophobic microenvironments could be leveraged for concentrating and converting aromatic alkanes using oxidants in aqueous conditions.Specifically,the hydrophilic/hydrophobic Fe-N-C catalysts give an approximate 2-fold enhancement in the turnover frequency(1,107.7 h^(-1))compared to hydrophilic counterparts(403.8 h^(-1))in terms of ethylbenzene(EB)oxidation.The hydrophobic microenvironment surrounding the Fe sites markedly diminishes the interfacial water density,which reduces the solvation-free energy of the hydrophobic substrate and promotes the activation and dissociation of tert-butyl hydroperoxide into radicals in water.Consequently,EB reactant is effectively enriched around the atomic Fe sites and is rapidly activated by the generated radicals.This work highlights the potential of engineering a single-atom catalyst microenvironment for efficient and green alkane conversion in aqueous solution.
基金supported by National Natural Science Foundation of China(Grants 21901060,21871076)Natural Science Foundation of Hebei Province(Grants B2022205005,B2019205074,B2020205008 and B2016205051)+3 种基金Science and Technology Project of Hebei Education Department(Grants BJ2020037 and QN2023049)the China Postdoctoral Science Foundation funded project(No.2021TQ0095)Science Foundation of Hebei Normal University(L2019B15)the Innovation Capability Improvement Plan Project of Hebei Province(22567604H).
文摘Exploring new heterogeneous catalysts to achieve efficient C-H bond oxidation is momentous in industrial chemical production.Herein,three Fe-incorporated polyoxometalate-encapsulated metal-organic frameworks(POM@MOFs),[Fe(H_(2)O)_(3)(dtb)][Fe(dtb)_(2)][HBW_(12)O_(40)]-12H_(2)O(1),[Fe(H_(2)O)2(dtb)]_(2)[Fe(dtb)_(2)(Hdtb)][SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]·16H_(2)O(2),[Fe(H_(2)O)_(2)]_(4)(dtb)_(5)[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]_(2)·18H_(2)O(3),(dtb=1,4-di[4H-1,2,4-triazol-4-yl]-benzene),were hydrothermally synthesized for catalytic C-H bond oxidation.They exhibited three-dimensional(3-D)POM-based metal-organic host-vip frameworks with diverse cages.In compound 1,cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(6)(H_(2)O)_(2)]^(4+)clusters and dtb ligands present a pcu alpha-Po primitive cubic topological net and abundant twisted quadrangular prism-shaped cages,in which the monoprotonated[HBW_(12)O_(40)]^(4-)polyoxoanions are encapsulated.In compound 2,two-dimensional(2-D)cationic metal-organic layers constructed by trinuclear[Fe_(3)(dtb)_(6)(H_(2)O)_(4)]^(6+)clusters and dtb ligands display a sql/Shubnikov tetragonal plane net topology,in which the rhomboid-shaped metal-organic windows in adjacent parallel-arranged 2-D layers are enclosed to form an open parallelepiped cage.The[SiW^(Ⅵ)_(9)W^(Ⅴ)_(3)O_(40)]^(7-)poly-oxoanions locate in the parallelepiped cages between 2-D bilayers.In compound 3,the 3-D cationic metal-organic frameworks constructed by binuclear[Fe_(2)(dtb)_(3)(H_(2)O)_(4)]^(4+)clusters and dtb ligands possess a bnn hexagonal BN topology,in which the hexagonal prismatic metal-organic cages accommodate four[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)poly-oxoanions.Employing diphenylmethane(DPM)oxidation as C-H bond oxidation model reaction,compounds 1-3 displayed distinct catalytic activities owing to the synergistic effect of polynuclear Fe nodes and poly-oxoanions.Among them,[PMo^(Ⅵ)_(11)Mo^(Ⅴ)O_(40)]^(4-)-contained compound 3 exhibited higher catalytic activity than polyoxotungstate-based compounds 1-2 with 99%DPM conversion and 99%benzophenone(BP)selectivity within 6 h as well as good recyclability and structural stability.
基金financially supported by the Funds of Science Center for Gas Turbine Project(No.P2022–B-Ⅳ-009–001)Beijing Natural Science Foundation(No.22B20116),Zhejiang Provincial Natural Science Foundation of China(No.LZ23E020005)+1 种基金University-Industry Cooperation Projects(No.HFZL2021CXY016)the Key R&D Program of Zhejiang(No.2024SSYS0075).
文摘A comparative study was conducted on the oxidation behavior of four different bond coat structures:single-layer air plasma spraying(APS),single-layer high-velocity oxygen fuel(HVOF),double-layer APS+HVOF,and double-layer HVOF+HVOF in a high-temperature and high-water vapor environment.The oxidation resistance and surface mixed oxide(MO)growth behavior and formation mechanisms of different structures in this environment were analyzed.The results indicate that CoNiCrAlY bond coats with different structures exhibit distinct oxidation behaviors in a high-temperature,high-water vapor environment.The growth of the MO phase is significantly influenced by the bond coat structure,and the high-water vapor environment promotes the nucleation and growth of bulk MO phase,resulting in a multilayer internal structure.Among these,the double-layer HVOF bond coat structure demonstrates superior resistance to water vapor corrosion,with fewer surface MO formations.These findings suggest that proper structural design can enhance the water vapor corrosion resistance of MCrAlY bond coats,providing theoretical foundations and technical support for optimizing their applications in high-temperature,high-water vapor environments.
基金supported by the National Natural Science Foundation of China(22478087,22368014)Guizhou Provincial S&T Project(GCC[2023]011,ZK[2022]011)Guizhou Provincial Higher Education Institution Program(Qianjiaoji[2023]082).
文摘Photocatalytic activation of C-H bonds is versatile but challenging for undergoing oriented conversion processes.Herein,a spatially site-isolated heterojunction(ZS-Vs/ZIS)of ZnIn2S4 with strong Lewis acidity(ZIS)and ZnS with S-vacancy(ZS-Vs)is constructed for activating α-C‒H bond and forming·O_(2)^(-)to cleave the C-H bond,respectively.ZS-Vs/ZIS displays outstanding performance in visible-light partial photooxidation of bio-based 5-hydroxymethylfurfural(HMF)to 2,5-diformylfuran(DFF)in an unprecedented yield of 95.7%at 25°C.In-situ experiments and calculations reveal that Zn sites of ZIS serve as hole enrichment to adsorb HMF for α-C‒H activation via ligand-to-metal charge transfer.Shallow trap states introduced by S-vacancy in ZS-Vs act as an electron pool to realize directed O_(2) activation into·O_(2)^(-)for breaking pre-activated α-C‒H bond in HMF to exclusively give DFF.Moreover,ZS-Vs/ZIS has good recyclability and universality in the photooxidation of various alcohols to carbonyls(86.4-95.6%yields).The synergistic C-H activation/breaking strategy exhibits high potential in targeted photocatalytic transformations.
基金financially supported by the National Key Research and Development Program of China(No.2023YFD2200505)the National Natural Science Foundation of China(No.22202105)+3 种基金the Natural Science Foundation of Jiangsu Higher Education Institutions of China(No.21KJA150003)the Innovation and Entrepreneurship Team Program of Jiangsu Province(No.JSSCTD202345)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX23_1163)the China Postdoctoral Science Foundation(Nos.2023M731703 and 2024T170415)
文摘The oxidation of lignin model compounds to esters via C-C bond cleavage has attracted considerable attention,as esters could be used as important polymer precursors and pharmaceutical intermediates.However,most studies focus on designing homogeneous or noble metal catalysts and conducting the reactions under basic conditions.Here,we report an efficient process for the C-C bond cleavage of lignin model compounds and selectively producing esters over different shaped CeO_(2)(i.e.,nanospheres(S),nanorods(R),nanoparticles(P),and nanocubes(C))under base-free conditions.Specifically,the yield of methyl anisate from the aerobic oxidation of l-(4-methoxyphenyl)ethanol reaches 77.6%over CeO_(2)-S in one hour(91%in 9 h),exhibiting higher performance compared to other evaluated CeO_(2)catalysts(6.4%-40.2%).Extensivecharacterizations and experimental investigations reveal that the density of weak base sites and oxygen vacancies on the CeO_(2)surface is positively correlated with the yield of methyl esters.Furthermore,the reaction pathway is investigated,which confirms that 1-(4-methoxyphenyl)ethanol first undergoes two reactions(i.e.,etherification and dehydrogenation)to produce intermediates of1-methoxy-4-(1-methoxy-ethyl)-benzene and 1-(4-methoxyphenyl)ethanone,respectively,followed by a series of functional group transformations to generate the targeted methyl anisate ultimately.
基金supported by the National Basic research Program of China (973 Program,2009CB623505)the National Natural Science Foundation of China (21273225)~~
文摘Novel reusable MnOx‐N@C catalyst has been developed for the direct oxidation of N‐heterocycles under solvent‐free conditions using TBHP as benign oxidant to give the corresponding N‐heterocyclic ketones. The catalytic system exhibited a broad substrate scope and excellent regi‐oselectivity, as well as being amenable to gram‐scale synthesis. This MnOx‐N@C catalyst also showed good reusability and was successfully recycled six times without any significant loss of activity.
文摘Hexagonal boron nitride(h-BN)is a highly selective catalyst for oxidative dehydrogenation of light alkanes to produce the corresponding alkenes.Despite intense recent research effort,many aspects of the reaction mechanism,such as the observed supra-linear reaction order of alkanes,remain unresolved.In this work,we show that the introduction of a low concentration of propane in the feed of ethane oxidative dehydrogenation is able to enhance the C_(2)H_(6) conversion by 47%,indicating a shared reaction intermediate in the activation of ethane and propane.The higher activity of propane makes it the dominant radical generator in the oxidative co-dehydrogenation of ethane and propane(ODEP).This unique feature of the ODEP renders propane an effective probe molecule to deconvolute the two roles of alkanes in the dehydrogenation chemistry,i.e.,radical generator and substrate.Kinetic studies indicate that both the radical generation and the dehydrogenation pathways exhibit a first order kinetics toward the alkane partial pressure,leading to the observed second order kinetics of the overall oxidative dehydrogenation rate.With the steady-state approximation,a radical chain reaction mechanism capable of rationalizing observed reaction behaviors is proposed based on these insights.This work demonstrates the potential of ODEP as a strategy of both activating light alkanes in oxidative dehydrogenation on BN and mechanistic investigations.
基金financially supported by the National Natural Science Foundation of China(NSFC)(52274295)the Natural Science Foundation of Hebei Province(E2021501029)+3 种基金the Fundamental Research Funds for the Central Universities(N2423051,N2423053,N2302016,N2423019,N2323013,N2423005)the Science and Technology Project of Hebei Education Department(QN2024238)the Basic Research Program Project of Shijiazhuang City for Universities Stationed in Hebei Province(241790937A)the Science and Technology Project of Qinhuangdao City in 2023.
文摘Mn-based layered oxides(KMO)have emerged as one of the promising low-cost cathodes for potassiumion batteries(PIBs).However,due to the multiple-phase transitions and the distortion in the MnO6structure induced by the Jahn-Teller(JT)effect associated with Mn-ion,the cathode exhibits poor structural stability.Herein,we propose a strategy to enhance structural stability by introducing robust metal-oxygen(M-O)bonds,which can realize the pinning effect to constrain the distortion in the transition metal(TM)layer.Concurrently,all the elements employed have exceptionally high crustal abundance.As a proof of concept,the designed K_(0.5)Mn_(0.9)Mg_(0.025)Ti_(0.025)Al_(0.05)O_(2)cathode exhibited a discharge capacity of approximately 100 mA h g^(-1)at 20 mA g^(-1)with 79%capacity retention over 50 cycles,and 73%capacity retention over 200 cycles at 200 mA g^(-1),showcased much better battery performance than the designed cathode with less robust M-O bonds.The properties of the formed M-O bonds were investigated using theoretical calculations.The enhanced dynamics,mitigated JT effect,and improved structural stability were elucidated through the in-situ X-ray diffractometer(XRD),in-situ electrochemical impedance spectroscopy(EIS)(and distribution of relaxation times(DRT)method),and ex-situ X-ray absorption fine structure(XAFS)tests.This study holds substantial reference value for the future design of costeffective Mn-based layered cathodes for PIBs.
基金the National Key Research and Development Program of China(Grant No.2018YFA0707300)the National Natural Science Foundation of China(Grant Nos.52075472 and 52004242)the National Science Foundation of Hebei Province(Grant No.E2020203001).
文摘Al/steel composite plate has a wide application prospect,but great differences in properties between Al and steel are observed.It is difficult to obtain high bonding strength by the traditional cold roll bonding process.Al/steel composite plate was thus prepared by cold roll bonding at a reduction rate of 60%after oxidation treatment on the surface to be composited on the steel side.The heat treatment of holding at 400℃ for 1 h and cooling with the furnace was then adopted.The bonding strength,microstructure,and properties of the Al/steel composite plate before and after annealing were analysed and compared through shear test,bending test,tensile test,and micro-characterization.Results show that the shear strengths of the interface before and after annealing are 100 and 80 MPa,respectively.Although the shear strength of the annealed Al/steel composite plate decreases,the bending and overall tensile properties of the composite plate are improved,showing better mechanical properties.
文摘A molecular [Ru(bda)]-type(bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand(Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylbenzene(3 F) or styrene(St) blocking units on the surface of glassy carbon(GC) electrodes by electrochemical polymerization, in order to prepare the corresponding poly-1@GC, poly-1+P3 F@GC, and poly-1+PSt@GC functional electrodes. Kinetic measurements of the electrode surface reaction revealed that [Ru(bda)] triggers the O–O bond formation via(1) the radical coupling interaction between the two metallo-oxyl radicals(I2 M) in the homo-coupling polymer(poly-1), and(2) the water nucleophilic attack(WNA) pathway in poly-1+P3 F and poly-1+PSt copolymers. The comparison of the three electrodes revealed that the second coordination sphere of the water oxidation catalysts plays vital roles in stabilizing their reaction intermediates, tuning the O–O bond formation pathways and improving the water oxidation reaction kinetics without changing the first coordination structures.
文摘Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in Au Pd nanoparticles.It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation.Remarkably,the catalyst with the most electron-rich Pd sites(binding energy downshift:1.0 e V)exhibits an extremely high turnover frequency(~500000 h-1 vs 12000 h-1 for that with net Pd atoms)for solvent-free selective oxidation of benzyl alcohol,which is,to the best of our knowledge,the highest value ever reported.Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage,as indicated by the significant reduction in the activation energy as compared to net Pd atoms.
文摘A blue light-induced formal insertion reaction ofα-siloxy carbene into the C—H bond of 1,3-diketones has been reported.Under the irradiation of blue light,acylsilane converts toα-siloxy carbene,which then undergoes formal C—H bond insertion reaction with the enol form of 1,3-diketone.This method uses readily available and relative stable acylsilane as car-bene precursor,which features a simple and metal-free approach under mild conditions.Moreover,the synthetic potential of this protocol has been demonstrated by performing the reaction on a gram scale with comparable high yield.
文摘The methylene-selective oxidation of simple alkanes catalyzed by a nonheme iron(Ⅲ)-monoamidate complex using H_(2)O_(2)as the terminal oxidant is reported.Mechanistic studies suggest that iron(V)-oxo species is the active intermediate,undergoing hydrogen atom abstraction(HAA)as the rate-determining step to initiate C-H bond activation.
文摘Steam oxidation resistance of Si3N4 and Si2N2O as well as SiAlON bonded SiC refractories at 900℃was tested according to ASTM-C863.Phase composition and microstructure before and after oxidation were analyzed by XRD and SEM.The results show that Si3N4 and Si2N2O bonded SiC refractory presents better steam oxidation resistance than SiAlON bonded SiC.For Si3N4 and Si2N2O bonded SiC,the oxidation speed is higher with more pronounced volume expansion in the early 100 h;afterwards,the volume expansion slows down gradually and starts to level off after 300 h.It is considered that the high silica glass phase formed during the oxidation covers Si3N4 and Si2N2O,and SiC as a protective layer and fills the open pores.But for SiAlON bonded SiC,the volume expands gradually and constantly with the increasing oxidation duration even after 500 h,due to the continuous formation of mullite transformed from oxidation products and Al2O3 in SiAlON.
基金the financial support from the Swedish Research Council(2017-00935)Swedish Energy Agency+3 种基金the Knut and Alice Wallenberg Foundationthe National Natural Science Foundation of China(21120102036)the National Basic Research Program of China(973 program,2014CB239402)the China Scholarship Council(CSC)。
文摘Understanding the seven coordination and O-O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earthabundant metals.This work reports the synthesis,characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda(H2 bnda=2,2’-bi(nicotinic acid)-6,6’-dicarboxylic acid)featuring steric hindrance and enhanced hydrophilicity on the backbone.Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda(H_(2)bda=2,2’-bipyridine-6,6’-dicarboxylic acid),Ru-pda(H_(2)pda=1,10-phenanthroline-2,9-dicarboxylic acid),and Ru-biqa(H_(2)biqa=(1,1’-biisoquinoline)-3,3’-dicarboxylic acid),we emphasized that seven coordination clearly determines presence of Ru^(Ⅴ)=O with high spin density on the ORu^(Ⅴ)=O atom,i.e.oxo with radical properties,which is one of the necessary conditions for reacting through the O-O coupling pathway.However,an additional factor to make the condition sufficient is the favorable intermolecular faceto-face interaction for the generation of the pre-reactive[Ru^(Ⅴ)=O…O=Ru^(Ⅴ)],which may be significantly influenced by the secondary coordination environments.This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O-O bond formation.
基金financially supported by the National Natural Science Foundation of China (Grant No. 51271030)
文摘The surface properties of the air-plasma sprayed bond-coat have been modified by cathode plasma electrolysis（CPE）. After modification, a re-melted layer without obvious pores and oxide stringers is formed,the gain size of re-melted layer is approximately 80–120 nm. It is shown, from cyclic oxidation at 1100℃,that a thin oxide scale mainly composed of α-Al;O;has been formed on the modified bond-coat and the oxidation resistance of the modified bond-coat has been significantly improved. Such beneficial result can be attributed to following effects: during CPE process, the plasma discharges with high temperature take place on the bond-coat surface. With plasma discharge treatment, the surface is melted and quickly re-solidified, the grain size decreases, and the pores and oxide stringers disappear. During cyclic oxidation, owing to the above modification of surface properties, the critical content of Al for selective oxidation is significantly decreased. Therefore, a continuous Al;O;scale is formed.
基金The project is supported by Municipal Science&Technology Program(No.1901001A),Luoyang,China.
文摘The steam oxidation of Si3N4-bonded SiC was determined at 1000℃for 50,100,150,200,250 and 300 h,respectively,according to ASTM C863-2000.The evolution of the phase composition and the microstructure as well as their relationship was investigated by XRD and SEM.The results show that the oxidation rate of Si3N4-bonded SiC is periodic.The presence of nitrogen element can impede the crystallization of SiO2 glass;the local enrichment of CaO impurities is unfavorable for the existence of fibrous SiO2.SiO2 mainly exists as cristobalite when the CaO/SiO2 ratio reaches a suitable level,but gradually transforms to quartz along with the oxidation time when the SiO2 content increases,or the CaO/SiO2 ratio decreases,due to the insufficient mineralization of CaO.The crystallization of SiO2 glass,especially the formation of quartz is the key factor leading to the volume expansion and structural stress.When the cracks extend and reach the surface,the degradation of the material accelerates.
基金supported by the National Natural Science Foundation of China(Grant Nos.52233017,51774265,52301032,and 52173305)the National Key Research and Development Program(Grant No.2018YFA0702900)+2 种基金the National Science and Technology Major Project of China(Grant No.2019ZX06004010)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC04000000)the LingChuang Research Project of China National Nuclear Corporation,CNNC Science Fund for Talented Young Scholars,the Program of CAS Interdisciplinary Innovation Team,and the Youth Innovation Promotion Association,CAS.
文摘An innovative method of hot compression bonding is proposed in this work for the joining of 9Cr oxide dispersion strengthened(ODS)alloy and 9Cr reduced-activation ferritic/martensitic(RAFM)alloy.The microstructural evolution of the bonding interface was investigated by scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD),and transmission electron microscopy(TEM).The results verify that the pinning effect of nano-oxides particles(NPs)in 9Cr ODS alloy significantly enhances its dynamic recrystallization(DRX)temperature and deformation resistance.Continuous DRX(CDRX)first occurred on the 9Cr RAFM alloy side,and the areas near the bonding interface were composed of recrystallized grains.With increasing strain,CDRX also showed up on the 9Cr ODS alloy side.Inevitable slight oxidation occurred at the bonding interface during the hot compression bonding(HCB)process,and the interfacial oxides transformed from initial coarse CrO to TiO and finally to Y-Ti-O nanoparticles with sizes comparable to pre-existing NPs dispersed in the 9Cr ODS alloy matrix.It is believed that interfacial oxide transformation and grain structure consistency contributed to the excellent interface healing of the two dissimilar alloy pieces.The effectiveness of the bonding was tested by tensile tests and fractography analysis,revealing that ideal metallurgical bonding could be achieved under a controlled strain level of 10%at 800℃ followed by soaking at 1000℃ for 4 h.
文摘The methane selective oxidation was a"holy grail"reaction.However,peroxidation and low selectivity limited the application.Herein,we combined three Au contents with TiO_(2)in both encapsulation(xAu@TiO_(2))and surface-loaded(xAu/TiO_(2))ways by MOF derivation strategy,reported a catalyst 0.5Au@TiO_(2)exhibited a CH_(3)OH yield of 32.5μmol·g^(-1)·h^(-1)and a CH_(3)OH selectivity of 80.6%under catalytic conditions of only CH_(4),O_(2),and H_(2)O.Mechanically speaking,the catalytic activity was controlled by both electron-hole separation efficiency and core-shell structure.The interfacial contact between Au nanoparticles and TiO_(2)in xAu@TiO_(2)and xAu/TiO_(2)induced the formation of oxygen vacancies,with 0.5 Au content showing the highest oxygen vacancy concentration.At the same Au content,xAu@TiO_(2)generated more oxygen vacancies than xAu/TiO_(2).The oxygen vacancy acted as an effective electron cold trap,which enhanced the photogenerated carrier separation efficiency and thereby improved the catalytic activity.In-situ DRIFTs revealed that the isolated OH(non-hydrogen bond adsorption)were key species for the methane selective oxidation,playing a role in the activation of CH_(4)to^(*)CH_(3).However,an overabundance of isolated OH led to severe overoxidation.Fortunately,the core-shell structure over xAu@TiO_(2)provided a slow-release environment for isolated OH through the intermediate state of^(*)OH(hydrogen bond adsorption)to balance the formation rate and consumption rate of isolated OH,doubling the methanol yield and increasing the>29%selectivity.These results showed a new strategy for the control of the overoxidation rate via a strategy of MOF encapsulation followed by pyrolytic derivation for methane selective oxidation.
基金financially supported by the National Natural Science Foundation of China(Nos.52201082 and 51971139)the Science Center for Gas Turbine Project(No.P2022-A-I-002-001)+1 种基金the Shanghai Sailing Program(No.22YF1419200)sponsored by the Chenguang Program supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission(No.21CGA10).
文摘The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050,1100 and 1150°C,and compared with a conventional NiCoCrAlY coating deposited on the same substrate.The AlCoCrFeNiY bond coat exhibits lower oxide growth rates due to its large columnar grains and low Al activity at the oxide scale/bond coat interface.Meanwhile,AlCoCrFeNiY has higher resistance to oxide spallation than NiCoCrAlY,which is attributed to the formation of a clean and defect-free metal/oxide interface.Significant interdiffusion occurs across the AlCoCrFeNiY/superalloy substrate interface.Our experimental evidence and thermody-namic modelling suggest that Fe accelerates interdiffusion and destabilizes theγ’phase,thereby causing the formation of a thick andγ’-depleted interdiffusion zone.In addition,the AlCoCrFeNiY bond coat un-dergoes more Al depletion and subsequentβtoγtransformation compared with NiCoCrAlY.Based on the findings in this work,a novel AlCoCrFeNiY/NiCoCrAlY double-layer bond coat was designed,tested and validated to achieve optimal balance between oxidation and interdiffusion.
