The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted t...The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted the concept of Eappand combined it with the Butler-Volmer theory.Certain observations though,such as potential-dependent fluctuations of Eapp,are yet surprising because they conflict with the proposed linear decrease in Eappwith increasing overpotential.The most common explanation for this finding refers to coverage changes upon alterations in the temperature or the applied electrode potential.In the present contribution,it is demonstrated that the modulation of surface coverages cannot entirely explain potential-dependent oscillations of Eapp,and rather the impact of entropic contributions of the transition states has been overlooked so far.In the case of a nearly constant surface coverage,these entropic contributions can be extracted by a dedicated combination of Tafel plots and temperature-dependent experiments.展开更多
Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the...Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the wellknown carbenium ion chemistry, hydride transfer forming and consuming allylic carbenium ions in the aromatization of cycloparaffins are further investigated and differentiated. The reversibility of endocyclic β-scission and cyclization reactions is refined by accounting explicitly for the reacting olefins and resulting cycloparaffins in the corresponding thermodynamics. 24 activation energies for the reactions involved in the cracking of cycloparaffins are obtained by the regression of 15 sets of experimental data upon taking the resulting 37 main cracking products, i. e., responses into account. The enhanced SEMK model can adequately describe the catalytic behavior of 37 main products with conversion and temperature.展开更多
The developed SEMK model is used to provide an insight into the contribution of individual reactions in the cracking of methylcyclohexane as well as the site coverage by various carbenium ions. The preferred reaction ...The developed SEMK model is used to provide an insight into the contribution of individual reactions in the cracking of methylcyclohexane as well as the site coverage by various carbenium ions. The preferred reaction pathways for the conversion of methylcyclohexane are hydride transfer reactions followed by PCP-isomerizations, deprotonation and endocyclic β-scission, accounting for 61%, 22% and 12% of its disappearance, respectively, at 693 K and 30% conversion of methylcyclohexane. Protolysis plays a minor role in the cracking of methylcyclohexane. Once cyclic diolefins are formed, all of them can be instantaneously transformed to aromatics, which are easily interconverted via disproportionation. Judging from the carbenium ion concentrations it is evident that, at the investigated operating conditions, less than 5% of the acid sites are covered by carbenium ions, less than 2% of which corresponds to cyclic type species including allylic ones.展开更多
First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO2 on Cu(221)and CuZn(221)surfaces.It is found that regardless of surface structure,the carbon consumption ra...First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO2 on Cu(221)and CuZn(221)surfaces.It is found that regardless of surface structure,the carbon consumption rate follows the order:CO hydrogenation>CO/CO2 hydrogenation>CO2 hydrogenation.The superior CO hydrogenation activity mainly arises from the lower barriers of elementary reactions than CO2 hydrogenation.Compared to Cu(221),the introduction of Zn greatly lowers the activity of methanol synthesis,in particularly for CO hydrogenation.For a mixed CO/CO2 hydrogenation,CO acts as the carbon source on Cu(221)while both CO and CO2 contribute to carbon conversion on CuZn(221).The degree of rate control studies show that the key steps that determine the reaction activity of CO/CO2 hydrogenation are HCO and HCOO hydrogenation on Cu(221),instead of HCOOH hydrogenation on CuZn(221).The present work highlights the effect of the Zn doping and feed gas composition on methanol synthesis.展开更多
Our recent theoretical studies have screened out CuCs-doped Ag-based promising catalysts for ethylene epoxidation[ACS Catal.11,3371(2021)].The theoretical results were based on surface modeling,while in the actual rea...Our recent theoretical studies have screened out CuCs-doped Ag-based promising catalysts for ethylene epoxidation[ACS Catal.11,3371(2021)].The theoretical results were based on surface modeling,while in the actual reaction process Ag catalysts are particle shaped.In this work,we combine density functional theory(DFT),Wulff construction theory,and micro kinetic analysis to study the catalytic performance of Ag catalysts at the particle model.It demonstrates that the CuCs-doped Ag catalysts are superior to pure Ag catalysts in terms of selectivity and activity,which is further proved by experimental validation.The characterization analysis finds that both Cu and Cs dopant promote particle growth as well as particle dispersion,resulting in a grain boundary-rich Ag particle.Besides,CuCs also facilitate electrophilic atomic oxygen formation on catalyst surface,which is benefitial for ethylene oxide formation and desorption.Our work provides a case study for catalyst design by combining theory and experiment.展开更多
Various scaling relations have long been established in the field of heterogeneous catalysis,but the resultant volcano curves inherently limit the catalytic performance of catalyst candidates.On the other hand,it is s...Various scaling relations have long been established in the field of heterogeneous catalysis,but the resultant volcano curves inherently limit the catalytic performance of catalyst candidates.On the other hand,it is still very challenging to develop universal descriptors that can be used in various types of catalysts and reaction systems.For these reasons,several strategies have recently been proposed to break and rebuild scaling relations to go beyond the top of volcanoes.In this review,some previously proposed descriptors have been briefly introduced.Then,the strategies for breaking known and establishing new and more generalized scaling relations in complex catalytic systems have been summarized.Finally,the application of machine-learning techniques in identifying universal descriptors for future computational design and high-throughput screening of heterogeneous catalysts has been discussed.展开更多
Cr_(2)O_(3) has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate,e.g.,methanol,from syngas.By combining density functional theory calculations and microkinetic modeli...Cr_(2)O_(3) has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate,e.g.,methanol,from syngas.By combining density functional theory calculations and microkinetic modeling,we computationally studied the surface structures and catalytic activities of bare Cr_(2)O_(3)(001)and(012)surfaces,and two reduced(012)surfaces covered with dissociative hydrogens or oxygen vacancies.The reduction of(001)surface is much more difficult than that of(012)surface.The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion,and the hydrogenation of CO or CHO is identified as rate-determining step.Microkinetic modeling reveals that(001)surface is inactive for the reaction,and the rates of both reduced(012)surfaces(25−28 s^(-1))are about five times higher than bare(012)surface(4.3 s^(-1))at 673 K.These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.展开更多
The direct synthesis of hydrogen peroxide(H_(2)O_(2))via a two‐electron oxygen reduction reaction(2e‐ORR)in acidic media has emerged as a green process for the production of this valuable chemical.However,such an ap...The direct synthesis of hydrogen peroxide(H_(2)O_(2))via a two‐electron oxygen reduction reaction(2e‐ORR)in acidic media has emerged as a green process for the production of this valuable chemical.However,such an approach employs expensive noble‐metal‐based electrocatalysts,which severely undermines its feasibility when implemented on an industrial scale.Herein,based on density functional theory computations and microkinetic modeling,we demonstrate that a novel two‐dimensional(2D)material,namely a 1T′‐MoTe_(2)monolayer,can serve as an efficient non‐precious electrocatalyst to facilitate the 2e‐ORR.The 1T′‐MoTe_(2)monolayer is a stable 2D crystal that can be easily produced through exfoliation techniques.The surface‐exposed Te sites of the 1T′‐MoTe_(2)monolayer exhibit a favorable OOH*binding energy of 4.24 eV,resulting in a rather high basal plane activity toward the 2e‐ORR.Importantly,kinetic computations indicate that the 1T'‐MoTe_(2)monolayer preferentially promotes the formation of H_(2)O_(2)over the competing four‐electron ORR step.These desirable characteristics render 1T′‐MoTe_(2)a promising candidate for catalyzing the electrochemical reduction of O_(2)to H_(2)O_(2).展开更多
We study the carbon dioxide reduction reaction(CO_(2)RR)activity and selectivity of Fe single-atom catalyst(Fe-SAC)and Fe dual-atom catalyst(Fe-DAC)active sites at the interior of graphene and the edges of graphitic n...We study the carbon dioxide reduction reaction(CO_(2)RR)activity and selectivity of Fe single-atom catalyst(Fe-SAC)and Fe dual-atom catalyst(Fe-DAC)active sites at the interior of graphene and the edges of graphitic nanopore by using a combination of DFT calculations and microkinetic simulations.The trend of limiting potentials for CO_(2)RR to produce CO can be described by using either the adsorption energy of COOH,CO,or their combination.CO_(2)RR process with reasonable reaction rates can be achieved only on the active site configurations with weak tendencies toward CO poisoning.The efficiency of CO_(2)RR on a catalyst depends on its ability to suppress the parasitic hydrogen evolution reaction(HER),which is directly related to the behavior of H adsorption on the catalyst’s active site.We find that the edges of the graphitic nanopore can act as potential adsorption sites for an H atom,and in some cases,the edge site can bind the H atom much stronger than the main Fe site.The linear scaling between CO and H adsorptions is broken if this condition is met.This condition also allows some edge active site configurations to have their CO_(2)RR limiting potential lower than the HER process favoring CO production over H2 production.展开更多
Designing catalyst to achieve ammonia synthesis at mild conditions is a meaningful challenge in catalysis community.Defective g-C_(3)N_(4)nanosheet supported single-cluster ruthenium and iron catalysts were investigat...Designing catalyst to achieve ammonia synthesis at mild conditions is a meaningful challenge in catalysis community.Defective g-C_(3)N_(4)nanosheet supported single-cluster ruthenium and iron catalysts were investigated for their ammonia synthesis performance.Based on density functional theory(DFT)calculations and microkinetic simulations,Ru_(3)single-cluster anchored on defective g-C3N4 nanosheet(Ru_(3)/Nv-g-C_(3)N_(4))has a turnover frequency(TOF)5.8 times higher than the Ru(0001)step surface at industrial reaction conditions of 673 K and 100 bar for ammonia synthesis.In other words,similar TOFs could be achieved on Ru_(3)/Nv-g-C_(3)N_(4)at much milder conditions(623 K,30 bar)than on Ru(0001)(673 K,100 bar).Our computations reveal the reaction proceeds parallelly on Ru_(3)/Nv-g-C_(3)N_(4)through both dissociative and alternative associative mechanisms at typical reaction conditions(600–700 K,10–100 bar);N–N bond cleavage of*N2 and*NNH from the two respective pathways controls the reaction collectively.With increasing temperatures or decreasing pressures,the dissociative mechanism gradually prevails and associative mechanism recedes.In comparison,Fe_(3)/Nv-g-C_(3)N_(4)catalyst shows a much lower catalytic activity than Ru3/Nv-g-C_(3)N_(4)by two orders of magnitude and the reaction occurs solely through the dissociative pathway.The finding provides a prospective candidate and deepens the mechanistic understanding for ammonia synthesis catalyzed by single-cluster catalysts(SCCs).展开更多
Reverse water gas shift(RWGS)catalysis,a prominent technology for converting CO2 to CO,is emerging to meet the growing demand of global environment.However,the fundamental understanding of the reaction mechanism is hi...Reverse water gas shift(RWGS)catalysis,a prominent technology for converting CO2 to CO,is emerging to meet the growing demand of global environment.However,the fundamental understanding of the reaction mechanism is hindered by the complex nature of the reaction.Herein,microkinetic modeling of RWGS on different metals(i.e.,Co,Ru,Fe,Ni,Cu,Rh,Pd,and Pt)was performed based on the DFT results to provide the mechanistic insights and achieve the catalyst screening.Adsorption energies of the carbon-based species and the oxygen-based species can be correlated to the adsorption energy of carbon and oxygen,respectively.Moreover,oxygen adsorption energy is an excellent descriptor for the barrier of CO2 and CO direct dissociation and the difference in reaction barrier between CO2(or CO)dissociation and hydrogenation.The reaction mechanism varies on various metals.Direct CO2 dissociation is the dominating route on Co,Fe,Ru,Rh,Cu,and Ni,while it competes with the COOH-mediated path on Pt and Pd surface.The eights metals can be divided into two groups based on the degree of rate control analysis for CO production,where CO–O bond cleavage is rate relevant on Pt,Pd,and Cu,and OH–H binding is rate-controlling on Co,Fe,Ru,Ni,and Rh.Both CO-direct dissociation and hydrogen-assisted route to CH4 contribute to the methane formation on Co,Fe,Pt,Pd,Ru,and Rh,despite the significant barrier difference between the two routes.Besides,the specific rate-relevant transition states and intermediates are suggested for methane formation,and thus,the selectivity can be tuned by adjusting the energy.The descriptor(C-and O-formation energy)based microkinetic modeling proposed that the activity trend is Rh~Ni>Pt~Pd>Cu>Co>Ru>Fe,where Fe,Co,Ru,and Ni tends to be oxidized.The predicted activity trend is well consistent with those obtained experimentally.The interpolation concept of adsorption energy was used to identify bimetallic materials for highly active catalysts for RWGS.展开更多
Ammonia borane(NH_(3)BH_(3),AB)has been considered to be a promising chemical hydrogen storage material.Based on density functional theory,a series of transition metal atoms supported P_(3)C(P_(3)C_O)sheet is systemat...Ammonia borane(NH_(3)BH_(3),AB)has been considered to be a promising chemical hydrogen storage material.Based on density functional theory,a series of transition metal atoms supported P_(3)C(P_(3)C_O)sheet is systematically investigated to screen out the most promising catalyst for dehydrogenation of AB.The results indicate that the Os/P_(3)C and Os/P_(3)C_O could be an efficient single atom catalyst(SACs)and the stepwise reaction pathway with free energy barrier of 2.07 and 1.54 e V respectively.Remarkably,the rate constant further quantitatively confirmed the real situation of the first step of dehydrogenation of AB on the Os/P_(3)C and Os/P_(3)C_O substrates.We found that k_(f1)at 400 K is equivalent to k_(f2)at 800 K,which greatly improves the temperature of the first step of AB dehydrogenation on P_(3)C_O.We hope this work can provide a promising method for the design of catalysts for AB dehydrogenation reactions on the surface of two-dimensional materials(2D).展开更多
The hydrogenation of carbon dioxide(CO2)is one of important processes to effectively convert and utilize CO2,which is also regarded as the key step at the industrial methanol synthesis.Water is likely to play an impor...The hydrogenation of carbon dioxide(CO2)is one of important processes to effectively convert and utilize CO2,which is also regarded as the key step at the industrial methanol synthesis.Water is likely to play an important role in this process,but it still remains elusive.To systematically understand its influence,here we computationally compare the reaction mechanisms of CO2 hydrogenation over the stepped Cu(211)surface between in the absence and presence of water based on microkinetic simulations upon density functional theory(DFT)calculations.The effects of water on each hydrogenation step and the whole activity and selectivity are checked and its physical origin is discussed.It is found that the water could kinetically accelerate the hydrogenation on CO2 to COOH,promoting the reverse water gas shift reaction to produce carbon monoxide(CO).It hardly influences the CO2 hydrogenation to methanol kinetically.In addition,the too high initial partial pressure of water will thermodynamically inhibit the CO2 conversion.展开更多
基金funding by the Ministry of Culture and Science of the Federal State of North Rhine-Westphalia (NRW Return Grant)CRC/TRR247:"Heterogeneous Oxidation Catalysis in the Liquid Phase"(388390466-TRR247),the RESOLV Cluster of Excellence,funded by the Deutsche Forschungsgemeinschaft under Germany’s Excellence StrategyEXC 2033-390677874-RESOLV+1 种基金the Center for Nanointegration (CENIDE)supported by COST (European Cooperation in Science and Technology)。
文摘The apparent activation energy,Eapp,is a common measure in thermal catalysis to discuss the activity and limiting steps of catalytic processes on solid-state materials.Recently,the electrocatalysis community adopted the concept of Eappand combined it with the Butler-Volmer theory.Certain observations though,such as potential-dependent fluctuations of Eapp,are yet surprising because they conflict with the proposed linear decrease in Eappwith increasing overpotential.The most common explanation for this finding refers to coverage changes upon alterations in the temperature or the applied electrode potential.In the present contribution,it is demonstrated that the modulation of surface coverages cannot entirely explain potential-dependent oscillations of Eapp,and rather the impact of entropic contributions of the transition states has been overlooked so far.In the case of a nearly constant surface coverage,these entropic contributions can be extracted by a dedicated combination of Tafel plots and temperature-dependent experiments.
基金financial support from the China Scholarship Councilthe Long Term Structural Methusalem Funding by the Flemish Government
文摘Single-event microkinetic(SEMK) model of the catalytic cracking of methylcyclohexane admixed with 1-octene over REUSY zeolites at 693 K—753 K in the absence of coke formation is enhanced. To keep consistency with the wellknown carbenium ion chemistry, hydride transfer forming and consuming allylic carbenium ions in the aromatization of cycloparaffins are further investigated and differentiated. The reversibility of endocyclic β-scission and cyclization reactions is refined by accounting explicitly for the reacting olefins and resulting cycloparaffins in the corresponding thermodynamics. 24 activation energies for the reactions involved in the cracking of cycloparaffins are obtained by the regression of 15 sets of experimental data upon taking the resulting 37 main cracking products, i. e., responses into account. The enhanced SEMK model can adequately describe the catalytic behavior of 37 main products with conversion and temperature.
基金the financial support from the China Scholarship Councilthe Long Term Structural Methusalem Funding by the Flemish Government
文摘The developed SEMK model is used to provide an insight into the contribution of individual reactions in the cracking of methylcyclohexane as well as the site coverage by various carbenium ions. The preferred reaction pathways for the conversion of methylcyclohexane are hydride transfer reactions followed by PCP-isomerizations, deprotonation and endocyclic β-scission, accounting for 61%, 22% and 12% of its disappearance, respectively, at 693 K and 30% conversion of methylcyclohexane. Protolysis plays a minor role in the cracking of methylcyclohexane. Once cyclic diolefins are formed, all of them can be instantaneously transformed to aromatics, which are easily interconverted via disproportionation. Judging from the carbenium ion concentrations it is evident that, at the investigated operating conditions, less than 5% of the acid sites are covered by carbenium ions, less than 2% of which corresponds to cyclic type species including allylic ones.
基金This work was supported by the National Key R&D Program of China(No.2017YFB0602205,No.2017YFA0204800),the National Natural Science Foundation of China(No.91645202,No.91421315),the Chinese Academy of Sciences(No.QYZDJ-SSWSLH054,No.XDA09030101).
文摘First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO2 on Cu(221)and CuZn(221)surfaces.It is found that regardless of surface structure,the carbon consumption rate follows the order:CO hydrogenation>CO/CO2 hydrogenation>CO2 hydrogenation.The superior CO hydrogenation activity mainly arises from the lower barriers of elementary reactions than CO2 hydrogenation.Compared to Cu(221),the introduction of Zn greatly lowers the activity of methanol synthesis,in particularly for CO hydrogenation.For a mixed CO/CO2 hydrogenation,CO acts as the carbon source on Cu(221)while both CO and CO2 contribute to carbon conversion on CuZn(221).The degree of rate control studies show that the key steps that determine the reaction activity of CO/CO2 hydrogenation are HCO and HCOO hydrogenation on Cu(221),instead of HCOOH hydrogenation on CuZn(221).The present work highlights the effect of the Zn doping and feed gas composition on methanol synthesis.
基金This work is supported by PetroChina Innovation Foundation(2019D-5007-0403).
文摘Our recent theoretical studies have screened out CuCs-doped Ag-based promising catalysts for ethylene epoxidation[ACS Catal.11,3371(2021)].The theoretical results were based on surface modeling,while in the actual reaction process Ag catalysts are particle shaped.In this work,we combine density functional theory(DFT),Wulff construction theory,and micro kinetic analysis to study the catalytic performance of Ag catalysts at the particle model.It demonstrates that the CuCs-doped Ag catalysts are superior to pure Ag catalysts in terms of selectivity and activity,which is further proved by experimental validation.The characterization analysis finds that both Cu and Cs dopant promote particle growth as well as particle dispersion,resulting in a grain boundary-rich Ag particle.Besides,CuCs also facilitate electrophilic atomic oxygen formation on catalyst surface,which is benefitial for ethylene oxide formation and desorption.Our work provides a case study for catalyst design by combining theory and experiment.
基金supported by the National Natural Science Founda-tion of China(21473053,91645122,and 22073027)the Natural Science Foundation of Shanghai(20ZR1415800)the Funda-mental Research Funds for the Central Universities(222201718003).
文摘Various scaling relations have long been established in the field of heterogeneous catalysis,but the resultant volcano curves inherently limit the catalytic performance of catalyst candidates.On the other hand,it is still very challenging to develop universal descriptors that can be used in various types of catalysts and reaction systems.For these reasons,several strategies have recently been proposed to break and rebuild scaling relations to go beyond the top of volcanoes.In this review,some previously proposed descriptors have been briefly introduced.Then,the strategies for breaking known and establishing new and more generalized scaling relations in complex catalytic systems have been summarized.Finally,the application of machine-learning techniques in identifying universal descriptors for future computational design and high-throughput screening of heterogeneous catalysts has been discussed.
基金This work was supported by the National Natural Science Foundation of China(No.92045303)the China Postdoctoral Science Foundation(No.2020M681444).The computational resources from Sinopec Geophysical Research Institute are acknowledged.
文摘Cr_(2)O_(3) has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate,e.g.,methanol,from syngas.By combining density functional theory calculations and microkinetic modeling,we computationally studied the surface structures and catalytic activities of bare Cr_(2)O_(3)(001)and(012)surfaces,and two reduced(012)surfaces covered with dissociative hydrogens or oxygen vacancies.The reduction of(001)surface is much more difficult than that of(012)surface.The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion,and the hydrogenation of CO or CHO is identified as rate-determining step.Microkinetic modeling reveals that(001)surface is inactive for the reaction,and the rates of both reduced(012)surfaces(25−28 s^(-1))are about five times higher than bare(012)surface(4.3 s^(-1))at 673 K.These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.
文摘The direct synthesis of hydrogen peroxide(H_(2)O_(2))via a two‐electron oxygen reduction reaction(2e‐ORR)in acidic media has emerged as a green process for the production of this valuable chemical.However,such an approach employs expensive noble‐metal‐based electrocatalysts,which severely undermines its feasibility when implemented on an industrial scale.Herein,based on density functional theory computations and microkinetic modeling,we demonstrate that a novel two‐dimensional(2D)material,namely a 1T′‐MoTe_(2)monolayer,can serve as an efficient non‐precious electrocatalyst to facilitate the 2e‐ORR.The 1T′‐MoTe_(2)monolayer is a stable 2D crystal that can be easily produced through exfoliation techniques.The surface‐exposed Te sites of the 1T′‐MoTe_(2)monolayer exhibit a favorable OOH*binding energy of 4.24 eV,resulting in a rather high basal plane activity toward the 2e‐ORR.Importantly,kinetic computations indicate that the 1T'‐MoTe_(2)monolayer preferentially promotes the formation of H_(2)O_(2)over the competing four‐electron ORR step.These desirable characteristics render 1T′‐MoTe_(2)a promising candidate for catalyzing the electrochemical reduction of O_(2)to H_(2)O_(2).
基金supported by the Ministry of Education,Culture,Research,and Technology of the Republic of Indonesia through the‘WCR 2022’program under contract number 007/E5/PG.02.00.PT/2022.
文摘We study the carbon dioxide reduction reaction(CO_(2)RR)activity and selectivity of Fe single-atom catalyst(Fe-SAC)and Fe dual-atom catalyst(Fe-DAC)active sites at the interior of graphene and the edges of graphitic nanopore by using a combination of DFT calculations and microkinetic simulations.The trend of limiting potentials for CO_(2)RR to produce CO can be described by using either the adsorption energy of COOH,CO,or their combination.CO_(2)RR process with reasonable reaction rates can be achieved only on the active site configurations with weak tendencies toward CO poisoning.The efficiency of CO_(2)RR on a catalyst depends on its ability to suppress the parasitic hydrogen evolution reaction(HER),which is directly related to the behavior of H adsorption on the catalyst’s active site.We find that the edges of the graphitic nanopore can act as potential adsorption sites for an H atom,and in some cases,the edge site can bind the H atom much stronger than the main Fe site.The linear scaling between CO and H adsorptions is broken if this condition is met.This condition also allows some edge active site configurations to have their CO_(2)RR limiting potential lower than the HER process favoring CO production over H2 production.
基金supported financially by the National Natural Science Foundation of China(Nos.91961125 and 22002085)supported by the“Fundamental Research Funds for the Central Universities”(No.2018JBZ107)+4 种基金Guangdong Basic and Applied Basic Research Foundation(No.2020A1515110832)“Key Program for International S&T Cooperation Projects of China”from the Ministry of Science and Technology of China(No.2018YFE0124600)Chemistry and Chemical Engineering Guangdong Laboratory(No.1932004)Science and Technology Project of Guangdong Province(No.2020B0101370001)the Project from China Petrochemical Corporation(No.S20L00151).
文摘Designing catalyst to achieve ammonia synthesis at mild conditions is a meaningful challenge in catalysis community.Defective g-C_(3)N_(4)nanosheet supported single-cluster ruthenium and iron catalysts were investigated for their ammonia synthesis performance.Based on density functional theory(DFT)calculations and microkinetic simulations,Ru_(3)single-cluster anchored on defective g-C3N4 nanosheet(Ru_(3)/Nv-g-C_(3)N_(4))has a turnover frequency(TOF)5.8 times higher than the Ru(0001)step surface at industrial reaction conditions of 673 K and 100 bar for ammonia synthesis.In other words,similar TOFs could be achieved on Ru_(3)/Nv-g-C_(3)N_(4)at much milder conditions(623 K,30 bar)than on Ru(0001)(673 K,100 bar).Our computations reveal the reaction proceeds parallelly on Ru_(3)/Nv-g-C_(3)N_(4)through both dissociative and alternative associative mechanisms at typical reaction conditions(600–700 K,10–100 bar);N–N bond cleavage of*N2 and*NNH from the two respective pathways controls the reaction collectively.With increasing temperatures or decreasing pressures,the dissociative mechanism gradually prevails and associative mechanism recedes.In comparison,Fe_(3)/Nv-g-C_(3)N_(4)catalyst shows a much lower catalytic activity than Ru3/Nv-g-C_(3)N_(4)by two orders of magnitude and the reaction occurs solely through the dissociative pathway.The finding provides a prospective candidate and deepens the mechanistic understanding for ammonia synthesis catalyzed by single-cluster catalysts(SCCs).
基金support from the Centre for Industrial Catalysis Science and Innovation(iCSI),which receives financial support from the NO237922.
文摘Reverse water gas shift(RWGS)catalysis,a prominent technology for converting CO2 to CO,is emerging to meet the growing demand of global environment.However,the fundamental understanding of the reaction mechanism is hindered by the complex nature of the reaction.Herein,microkinetic modeling of RWGS on different metals(i.e.,Co,Ru,Fe,Ni,Cu,Rh,Pd,and Pt)was performed based on the DFT results to provide the mechanistic insights and achieve the catalyst screening.Adsorption energies of the carbon-based species and the oxygen-based species can be correlated to the adsorption energy of carbon and oxygen,respectively.Moreover,oxygen adsorption energy is an excellent descriptor for the barrier of CO2 and CO direct dissociation and the difference in reaction barrier between CO2(or CO)dissociation and hydrogenation.The reaction mechanism varies on various metals.Direct CO2 dissociation is the dominating route on Co,Fe,Ru,Rh,Cu,and Ni,while it competes with the COOH-mediated path on Pt and Pd surface.The eights metals can be divided into two groups based on the degree of rate control analysis for CO production,where CO–O bond cleavage is rate relevant on Pt,Pd,and Cu,and OH–H binding is rate-controlling on Co,Fe,Ru,Ni,and Rh.Both CO-direct dissociation and hydrogen-assisted route to CH4 contribute to the methane formation on Co,Fe,Pt,Pd,Ru,and Rh,despite the significant barrier difference between the two routes.Besides,the specific rate-relevant transition states and intermediates are suggested for methane formation,and thus,the selectivity can be tuned by adjusting the energy.The descriptor(C-and O-formation energy)based microkinetic modeling proposed that the activity trend is Rh~Ni>Pt~Pd>Cu>Co>Ru>Fe,where Fe,Co,Ru,and Ni tends to be oxidized.The predicted activity trend is well consistent with those obtained experimentally.The interpolation concept of adsorption energy was used to identify bimetallic materials for highly active catalysts for RWGS.
基金funded by the National Natural Science Foundation of China (No. 21603109)the Henan Joint Fund of the National Natural Science Foundation of China (No. U1404216)+2 种基金the Special Fund of Tianshui Normal University, China (No. CXJ2020-08)the Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 20JK0676)partially supported by the postgraduate research opportunities program of HZWTECH (HZWTECH-PROP).
文摘Ammonia borane(NH_(3)BH_(3),AB)has been considered to be a promising chemical hydrogen storage material.Based on density functional theory,a series of transition metal atoms supported P_(3)C(P_(3)C_O)sheet is systematically investigated to screen out the most promising catalyst for dehydrogenation of AB.The results indicate that the Os/P_(3)C and Os/P_(3)C_O could be an efficient single atom catalyst(SACs)and the stepwise reaction pathway with free energy barrier of 2.07 and 1.54 e V respectively.Remarkably,the rate constant further quantitatively confirmed the real situation of the first step of dehydrogenation of AB on the Os/P_(3)C and Os/P_(3)C_O substrates.We found that k_(f1)at 400 K is equivalent to k_(f2)at 800 K,which greatly improves the temperature of the first step of AB dehydrogenation on P_(3)C_O.We hope this work can provide a promising method for the design of catalysts for AB dehydrogenation reactions on the surface of two-dimensional materials(2D).
基金supported by the National Key Research and Development Program of China(2018YFA0208600)the National Natural Science Foundation of China(21673072,21333003,91845111)Program of Shanghai Subject Chief Scientist(17XD1401400)
文摘The hydrogenation of carbon dioxide(CO2)is one of important processes to effectively convert and utilize CO2,which is also regarded as the key step at the industrial methanol synthesis.Water is likely to play an important role in this process,but it still remains elusive.To systematically understand its influence,here we computationally compare the reaction mechanisms of CO2 hydrogenation over the stepped Cu(211)surface between in the absence and presence of water based on microkinetic simulations upon density functional theory(DFT)calculations.The effects of water on each hydrogenation step and the whole activity and selectivity are checked and its physical origin is discussed.It is found that the water could kinetically accelerate the hydrogenation on CO2 to COOH,promoting the reverse water gas shift reaction to produce carbon monoxide(CO).It hardly influences the CO2 hydrogenation to methanol kinetically.In addition,the too high initial partial pressure of water will thermodynamically inhibit the CO2 conversion.
