Theoretically predicted innovative palladium stripe dopingcobalt(111) surface with excellent catalytic performance for carbonmonoxide oxidative coupling to dimethyl oxalate

Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction.In this study,we theoretically predict that Pd stripe doping Co(111)surface exhibits excellent performance than pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface,and clearly expound the catalytic mechanisms through the density functional theory(DFT)calculation and micro-reaction kinetic model analysis.It is obtained that the favorable reaction pathway is COOCH_(3)-COOCH_(3)coupling pathway over these four catalysts,while the rate-controlling step is COOCH_(3)+CO+OCH_(3)→2COOCH_(3)on Pd stripe doping Co(111)surface,which is different from the case(2COOCH_(3)→DMO)on pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface.This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.

Single atom doping induced charge-specific distribution of Cu1-TiO_(2) for selective aniline oxidation via a new mechanism

Utilizing single atom sites doping into metal oxides to modulate their intrinsic active sites,achieving precise selectivity control in complex organic reactions,is a highly desirable yet challenging endeavor.Meanwhile,identifying the active site also represents a significant obstacle,primarily due to the intricate electronic environment of single atom site doped metal oxide.Herein,a single atom Cu doped TiO_(2)catalyst(Cu_(1)-TiO_(2)) is prepared via a simple“colloid-acid treatment”strategy,which switches aniline oxidation selectivity of TiO_(2) from azoxybenzene to nitrosobenzene,without using additives or changing solvent,while other metal or nonmetal doped TiO_(2) did not possess.Comprehensive mechanistic investigations and DFT calculations unveil that Ti-O active site is responsible for triggering the aniline to form a new PhNOH intermediate,two PhNOH condense to azoxybenzene over TiO_(2) catalyst.As for Cu_(1)-TiO_(2),the charge-specific distribution between the isolated Cu and TiO_(2) generates unique Cu_(1)-O-Ti hybridization structure with nine catalytic active sites,eight of them make PhNOH take place spontaneous dissociation to produce nitrosobenzene.This work not only unveils a new mechanistic pathway featuring the PhNOH intermediate in aniline oxidation for the first time but also presents a novel approach for constructing single-atom doped metal oxides and exploring their intricate active sites.

理论和实验相结合研究NiCo_(2)O_(4)纳米片用于甘油电氧化反应机制

甘油是生物质精炼的主要副产物(约占10%),年过剩量与低利用率导致其市场价格(0.24-0.6 US kg^(-1))较低.甘油是具有三个活性羟基的多元醇,被认为是生产高价值产品的理想原料.甲酸作为甘油转化最重要的产品之一,广泛应用于农药、皮革、染料和医药行业,将甘油电氧化(EGOR)为甲酸(FA)不仅能有效避免资源过剩造成浪费,而且能满足未来对甲酸燃料电池的需求.然而甘油电催化氧化途径较为复杂,涉及反应中间产物的脱氢、吸附/解吸和C-C键裂解.本文将密度泛函理论(DFT)与实验相结合,研究了在精细构建的NiCo_(2)O_(4)纳米片上通过EGOR生产FA的反应机制.DFT计算结果表明,活性羟基(OH^(*))物种可以改变EGOR生产FA过程的决速步骤(RDS),通过调节吸附中间体的吸附能可获得理想的FA产率.其中,高度羟基化的NiCo_(2)O_(4)纳米片(311)-OH^(*)晶面上具有最低的吉布斯自由能,能显著提升反应过程动力学.在理论分析的基础上,通过简易的电沉积方法精准制备了超薄NiCo_(2)O_(4)纳米片(~1.7 nm),并采用X射线吸收精细结构谱和高分辨透射电镜对催化剂进行了结构分析.结果表明,NiCo_(2)O_(4)纳米片中四面体(A_(Td))和八面体(B_(Oh))配位具有内角共享的A_(Td)-O-B_(Oh)和边共享的B_(Oh)-O-B_(Oh)构型,金属间的协同作用有效改善了材料的电子效应,有利于提供更多的吸附位点并促进EGOR过程中的电荷转移.NiCo_(2)O_(4)纳米片在EGOR中的电荷转移电阻仅为0.94Ω,电化学活性表面积高达10.25 cm^(2).相比较电催化析氧反应,NiCo_(2)O_(4)纳米片表现出了较好的EGOR性能,在10 mA cm^(-2)的电流密度下阳极功耗降低了320 mV,在100 mA cm^(-2)的电流密度时的阳极电势仅为1.46 VRHE.此外,在120 h的稳定性测试中,甘油的转化率和FA的选择性可分别保持在89%和70%.多电位步骤实验、原位电化学阻抗谱和电子顺磁共振谱结果表明,NiCo_(2)O_(4)纳米片上原位产生的OH^(*)物种是EGOR过程中的直接活性中心,有利于将RDS从甘油酸脱氢裂解转化为甘油醛的脱氢步骤,并进一步促进C-C键的裂解.进一步结合理论预测,证实了OH^(*)物种是EGOR过程中的直接活性中心.综上,采用绿色高效的电催化手段促进甘油生产高附加值化学品是生物质链升级的重要举措,有效避免了传统的高温高压,以水为介质,原位利用OH^(*).本文为新型催化剂的未来设计和理解生物质基原料电氧化升级反应机制提供了新思路.

Formation mechanism of methane during coal evolution:A density functional theory study

The formation mechanism of methane （CH4） during coal evolution has been investigated by density functional theory （DFT） of quantum chemistry. Thermogenic gas, which is generated during the thermal evolution of medium rank coal, is the main source of coalbed methane （CBM）. Ethylbenzene （A） and 6,7-dimethyl-5,6,7,8-tetrahydro-1-hydroxynaphthalene （B） have been used as model compounds to study the pyrolysis mechanism of highly volatile bituminous coal （R）, according to the similarity of bond orders and bond lengths. All possible paths are designed for each model. It can be concluded that the activation energies for H-assisted paths are lower than others in the process of methane formation; an H radical attacking on β-C to yield CH4 is the dominant path for the formation of CH4 from highly volatile bituminous coal. In addition, the calculated results also reveal that the positions on which H radical attacks and to which intramolecular H migrates have effects on methyl cleavage.

A DFT theoretical study of CH_4 dissociation on gold-alloyed Ni(111)surface

A density-functional theory（DFT）method has been conducted to systematically investigate the adsorption of CHx（x=0～4）as well as the dissociation of CHx（x=1～4）on（111）facets of gold-alloyed Ni surface.The results have been compared with those obtained on pure Ni（111）surface.It shows that the adsorption energies of CHx（x=1～3）are lower,and the reaction barriers of CH4 dissociation are higher in the first and the fourth steps on gold-alloyed Ni（111）compared with those on pure Ni（111）.In particular,the rate-determining step for CH4 dissociation is considered as the first step of dehydrogenation on gold-alloyed Ni（111）,while it is the fourth step of dehydrogenation on pure Ni（111）.Furthermore,the activation barrier in rate-determining step is higher by 0.41 eV on gold-alloyed Ni（111）than that on pure Ni（111）.From above results,it can be concluded that carbon is not easy to form on gold-alloyed Ni（111）compared with that on pure Ni（111）.

Syngas to ethanol on MoCu(211)surface:Effect of promoter Mo on C-O bond breaking and C-C bond formation

The mechanism of syngas to ethanol on MoCu(211)surface has been researched by density functional theory(DFT)calculation,and the effects of Mo as a promoter on C-O bond breaking and C-C bond formation have been discussed.Calculations show that Cu-Mo atoms constitute the active sites on MoCu(211)surface after Mo atom being served as a promoter of Cu catalyst.Compared with Cu(211),MoCu(211)has two improvements.Firstly,CH_(3) is the most advantageous monomer on the MoCu(211)surface,which provides abundant CH_(3) intermediate for syngas to ethanol.Secondly,the C-C bond is formed mainly by inserting CHO into the abundant CH_(3),and the generated CH_(3)CHO through multiple steps of hydrogenation to generate C_(2)H_(5)OH.The key of the promoter Mo on the MoCu(211)surface also has been verified by the analysis of its electronic properties.Differential charge density shows that the massive electron transfer from Mo to Cu,projected density of states(pDOS)shows that the electron transfer from Mo to Cu makes the d-band center of MoCu(211)nearer to the Fermi level,these indicate that the MoCu(211)catalytic capacity increased.The addition of Mo in the Cu-based catalyst not only can effectively solve the problem of C-O bond breaking,but also promote C-C bond formation.About the influence of Mo content on C-O bond breaking and C-C bond formation,compared with MoCu(211),the DFT results and the d-band center of Mo_(2)Cu(211)show that the increase of Mo content could not promote the synergistic effect of Cu/Mo on the generation of ethanol more effectively.

A novel carbon cycle process assisted by Ni/La_(2)O_(3) catalyst for enhanced thermochemical CO_(2) splitting

Thermochemical two-step CO_(2) splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels.However,the harsh CO_(2) splitting conditions,the limited oxygen release kinetics and capacity of metal oxides block further promoted the CO yield and solar-to-fuel energy efficiency.Here,we propose a different carbon cycle assisted by Ni/La_(2)O_(3) via coupling methane decomposition with thermochemical CO_(2) splitting,replacing conventional metal oxides cycle.Superior performance was demonstrated with methane conversion reached around 94%with almost pure H_(2) generation.Encouragingly,CO_(2) conversion of 98%and CO yield of 6.9 mmol g^(-1) derived from CO_(2) were achieved,with peak CO evolution rate(402 mL min^(-1) g^(-1))of orders of magnitude higher than that in metal oxide process and outstanding thermodynamic solar-to-fuel energy efficiency(55.5%vs.18.5%).This was relevant to the synergistic activation of La_(2)O_(3) and Ni for CO_(2) in carbon cycle,thus improving CO_(2) splitting reaction with carbon species.

The regulating effect of doping Cu on the catalytic performance of CO oxidative coupling to DMO on Pd_(x)Cu_(y)/GDY:A DFT study

Rely on the density functional theory(DFT)calculation,the catalytic performance of Pd_(x)Cu_(y)/GDY(x=1,2,3,4;x+y≤4)for CO oxidative coupling reaction was obtained.The Pdx/GDY(x=1,2,3,4)are not ideal catalyst for dimethyl oxalate(DMO)formation because byproduct dimethyl carbonate(DMC)is easily formed on Pd_(1)/GDY and Pd_(2)/GDY,and high activation energies are needed on Pd_(3)/GDY and Pd_(4)/GDY.Therefore the second metal Cu is doped to regulate the performance of Pdx/GDY(x=1,2,3,4).Doping Cu not only improve the activity of DMO formation,but more importantly,controlling the ratio of Cu:Pd can effectively regulate the selectivity of DMO.Thus taking into account the activity and selectivity of the reaction for the preparation of DMO by CO oxidative coupling,the Pd_(1)Cu_(1)/GDY and Pd_(1)Cu_(2)/GDY with the activation energies of 105.2 and 99.2 kJ mol^(-1)to generate DMO show excellent catalytic activity and high DMO selectivity,which are considered as good catalysts for CO oxidative coupling.The differential charge density analysis shows the decrease in the charge density of metal clusters is an important reason for improving the selectivity of the catalyst.

The newly-assisted catalytic mechanism of surface hydroxyl species performed as the promoter in syngas-to-C2 species on the Cu-based bimetallic catalysts

In the conversion process of syngas-to-C_(2)species,the OH species are inevitably produced accompanying the production of key intermediates CH_(x)(x=1-3),traditionally,the function of surface OH species is generally accepted as the hydrogenating reactive species.This work for the first time proposed and confirmed the assisted catalytic mechanism of surface OH species that performed as the promoter for syngas-to-C_(2)species on Cu-based catalysts.DFT and microkinetic modeling results reveal that the produced OH species accompanying the intermediates CH_(x)production on the MCu(M=Co,Fe,Rh)catalysts can stably exist to form OH/MCu catalysts,on which the presence of surface OH species as the promoter not only presented better activity and selectivity toward CH_(x)(x=1-3)compared to MCu catalysts,but also significantly suppressed CH_(3)OH production,providing enough CH_(x)sources to favor the production of C_(2)hydrocarbons and oxygenates.Correspondingly,the electronic properties analysis revealed the essential relationship between the electronic feature of OH/MCu catalysts and catalytic performance,attributing to the unique electronic micro-environment of the catalysts under the interaction of surface OH species.This new mechanism is called as OH-assisted catalytic mechanism,which may be applied in the reaction systems related to the generation of OH species.

C_(2)H_(2)semi-hydrogenation on the Pd_(x)M_(y)cluster/graphdiyne catalysts:Effects of cluster composition and size on the activity and selectivity

C_(2)H_(2)semi-hydrogenation has been widely applied in industry to eliminate trace C_(2)H_(2)from C_(2)H_(4)feed.C_(2)H_(2)semi-hydrogenation to C_(2)H_(4)on a series of the newly designed catalysts,graphdiyne(GDY)as a new carbon allotrope supported different sizes of Pd_(x)M_(y)clusters(Pd_(x)M_(y)/GDY,M=Cu,Ag,Au,Ni;x+y=1-3),were studied using DFT calculations.The results found that C_(2)H_(2)semi-hydrogenation to C_(2)H_(4)on Pd_(x)M_(y)/GDY catalysts exhibits that both the activity and selectivity greatly depend on the composition and size of Pd_(x)M_(y)/GDY catalysts.Surprisingly,our results for the first time discovered the Pd_(1)/GDY catalyst with GDY supported the single atom Pd that presents the best selectivity and activity toward C_(2)H_(4)formation compared to the previously reported catalysts so far in C_(2)H_(2)semi-hydrogenation.This study would provide a theoretical clue for designing and screening out the potential catalysts with GDY supported small sizes of Pd_(x)M_(y)and other metal clusters in C_(2)H_(2)hydrogenation.

Bonding Interaction of Adjacent Pt and Ag Single-Atom Pairs on Carbon Nitride Efficiently Promotes Photocatalytic H_(2)Production

Dual-atom catalysts(DACs)represent an exciting advance in the field of heterogeneous catalysis.They not only retain the beneficial characteristics of single-atom catalysts(SACs),but they also harness the synergistic effects that arise from the proximity of neighboring single-metal atoms.Nevertheless,the fabrication of heteronuclear dual-atom metals positioned adjacently for use in photocatalysis remains a significant challenge.Herein,we report the atomically dispersed adjacent Pt-Ag dual-atom pairs on carbon nitride(Pt1Ag1-a/CN)by a facile hydrogen-bonding assembly strategy via pyrolysis of the hydrogen-bonding supramolecule containing melamine-Ag and cyanuric acid-Pt complexes on carbon nitride(CN),through which the light absorption depressed by deposited carbonaceous materials during the preparation of dual-atom metals via a traditional method like the pyrolysis of the metal-organic framework.Thanks to the synergism achieved by the bonding interaction of adjacent Pt and Ag single-atom pairs,the developed Pt1Ag1-a/CN with 0.21%Pt loading shows a high turnover frequency(TOF)of 1115 h^(−1)with a H_(2)evolution rate(HER)of 12,000μmol g^(−1)h^(−1)for photocatalytic water splitting under simulated solar light irradiation(325 h^(−1)of TOF with 3480μmol g^(−1)h^(−1)of HER under visible light irradiation).This strategy outperforms the previously reported SACs on CN-based semiconductors.Density functional theory(DFT)calculations demonstrate that the adjacent Ag atom acts as a coordination atom to effectively regulate the electronic structure of the Pt atom and thus brings the d-band center of Pt close to the Fermi energy level,which is beneficial for the H_(2)production.This work presents a facile and general strategy for designing diverse adjacent diatomic cocatalysts in photocatalysis without depressing light absorption by the deposited carbon during the DAC preparation via previously reported methods.

Ethane dehydrogenation over the g-C_(3)N_(4)supported metal singleatom catalysts to enhance reactivity and coking-resistance ability

Ethane dehydrogenation(EDH)to produce ethylene requires high operating temperature to achieve satisfactory ethylene yield,however,this process leads to coke formation and catalyst deactivation.Here,an active site isolation strategy was employed to inhibit side reaction and coke formation over fifteen types of metal single-atom metal/graphitic carbon nitride(M/g-C_(3)N_(4))catalysts.Density functional theory(DFT)calculations completely describe reaction network of ethane dehydrogenation.Onlattice kinetic Monte Carlo simulations were carried out to evaluate catalytic performance under the realistic conditions.The Co/g-C_(3)N_(4),Rh/g-C_(3)N_(4),Ni/g-C_(3)N_(4)catalysts were screened out to exhibit higher C_(2)H_(4)(g)formation activity and C_(2)H_(4)(g)selectivity close to or equal to 100%.The low reactant partial pressure 0%–5%at atmospheric pressure facilitates ethane dehydrogenation,and the appropriate temperatures over Co/g-C_(3)N_(4),Rh/g-C_(3)N_(4),Ni/g-C_(3)N_(4)catalysts are 673.15,723.15,723.15 K,respectively.Especially,Co/g-C_(3)N_(4)catalyst presents the highest C_(2)H_(4)(g)formation activity,attributing to the appropriate antibonding strength between C atom and metal single-atom.Further,a simple descriptor,the reaction energy of C_(2)H_(5)*dehydrogenation to C_(2)H_(4)*,was proposed to quantitatively and quickly evaluate C_(2)H_(4)(g)formation activity.The present study laid a solid foundation for efficient design and development of single-atom catalysts with high-performance for selective dehydrogenation of alkanes.

Enhanced performance of oxygen vacancies on CO_(2) adsorption and activation over different phases of ZrO_(2)

The effect of oxygen vacancies on the adsorption and activation of CO_(2) on the surface of different phases of ZrO_(2) is investigated by density functional theory(DFT)calculations.The calculations show that the oxygen vacancies contribute greatly to both the adsorption and activation of CO_(2).The adsorption energy of CO_(2) on the c-ZrO_(2),t-ZrO_(2) and,m-ZrO_(2) surfaces is enhanced to 5,4,and 3 folds with the help of oxygen vacancies,respectively.Moreover,the energy barrier of CO_(2) dissociation on the defective surfaces of c-ZrO_(2),t-ZrO_(2),and m-ZrO_(2) is reduced to 1/2,1/4,and 1/5 of the perfect surface with the assistance of oxygen vacancies.Furthermore,the activation of CO_(2) on the ZrO_(2) surface where oxygen vacancies are present,and changes from an endothermic reaction to an exothermic reaction.This finding demonstrates that the presence of oxygen vacancies promotes the activation of CO_(2) both kinetically and thermodynamically.These results could provide guidance for the high-efficient utilization of CO_(2) at an atomic scale.

Controllable Generation of Reactive Oxygen Species on Cyano-Group-Modified Carbon Nitride for Selective Epoxidation of Styrene

The controlled generation of reactive oxygen species(ROS)to selectively epoxidize styrene is a grand challenge.Herein,cyano-group-modified carbon nitrides(CNCY_(x) and CN-T_(y))are prepared,and the catalysts show better performance in regulating ROS and producing styrene oxide than the cyano-free sample.The in situ diffuse reflectance infrared and density functional theory calculation results reveal that the cyano group acts as the adsorption and activation site of oxygen.X-ray photoelectron spectroscopy and NMR spectrum results confirm that the cyano group bonds with the intact heptazine ring.This unique structure could inhibit H_(2)O_(2) and,OH formation,resulting in high selectivity of styrene oxide.Furthermore,high catalytic activity is still achieved when the system scales up to 2.7 L with 100 g styrene under solar light irradiation.The strategy of cyano group modification gives a new insight into regulating spatial configuration for tuning the utilization of oxygen-active species and shows potential applications in industry.

Depositing the PtNi nanoparticles on niobium oxide to enhance the activity and CO-tolerance for alkaline methanol electrooxidation

Direct methanol fuel cells have the advantages of simple system,convenient operation,high conversion rate and low carbon emission,which are considered as the environmental and friendly energy conversion devices.How-ever,the low activity,CO-tolerance and high cost of anode catalysts restrict the large-scale commercial appli-cations.Therefore,it is of great practical significance to design and construct the anodic catalysts with high activity,stability and low cost for methanol oxidation reaction.In this work,the PtM/Nb_(2)O_(5)-C(M=Co,Sn,Ni)catalysts are synthesized by the ethylene glycol solvothermal method using transition metal oxide Nb_(2)O_(5)as the support.The catalytic performance of different catalysts is further evaluated for alkaline MOR.The results show that the introduction of Ni(existing in Ni^(2+)and Ni^(3+))has the most obvious improvement for alkaline MOR performance.By adjusting the doped ratio of Pt:Ni,it is shown that PtNi/Nb_(2)O_(5)-C has the highest mass activity(3877.9 mA-mg_(pt)^(-1)),12 times that of the commercial Pt/C catalyst.CV,LSV,Tafel and EIS analyses show that PtNi/Nb_(2)O_(5)-C has the lowest onset potential and charge transfer resistance,and the fastest electrocatalytic oxidation rate of methanol.CA tests show that the electrochemical stability is also significantly improved with the introduction of Nb_(2)O_(5)and Ni.Combined with the structural characterization and electrochemical tests,it is found that the evident electronic effect among Pt and Ni,Nb_(2)O_(5)and the hydroxyl brought from Ni species are mainly ascribed for enhancing the activity,CO resistance and stability of PtNi/Nb_(2)O_(5)-C.