Direct conversion of syngas to light olefins(STO)on bifunctional catalysts has garnered significant attention,yet a comprehensive understanding of the reaction pathway and reaction kinetics remains elusive.Herein,we t...Direct conversion of syngas to light olefins(STO)on bifunctional catalysts has garnered significant attention,yet a comprehensive understanding of the reaction pathway and reaction kinetics remains elusive.Herein,we theoretically addressed the kinetics of the direct STO reaction on typical ZnAl_(2)O_(4)/zeolite catalysts by establishing a complete reaction network,consisting of methanol synthesis and conversion,water gas shift(WGS)reaction,olefin hydrogenation,and other relevant steps.The WGS reaction occurs very readily on ZnAl_(2)O_(4) surface whereas which is less active towards alkane formation via olefin hydrogenation,and the latter can be attributed to the characteristics of the H_(2) heterolytic activation and the weak polarity of olefins.The driving effect of zeolite component towards CO conversion was demonstrated by microkinetic simulations,which is sensitive to reaction conditions like space velocity and reaction temperature.Under a fixed ratio of active sites between oxide and zeolite components,the concept of the“impossible trinity”of high CO conversion,high olefin selectivity,and high space velocity can thus be manifested.This work thus provides a comprehensive kinetic picture on the direct STO conversion,offering valuable insights for the design of each component of bifunctional catalysts and the optimization of reaction conditions.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
文摘Direct conversion of syngas to light olefins(STO)on bifunctional catalysts has garnered significant attention,yet a comprehensive understanding of the reaction pathway and reaction kinetics remains elusive.Herein,we theoretically addressed the kinetics of the direct STO reaction on typical ZnAl_(2)O_(4)/zeolite catalysts by establishing a complete reaction network,consisting of methanol synthesis and conversion,water gas shift(WGS)reaction,olefin hydrogenation,and other relevant steps.The WGS reaction occurs very readily on ZnAl_(2)O_(4) surface whereas which is less active towards alkane formation via olefin hydrogenation,and the latter can be attributed to the characteristics of the H_(2) heterolytic activation and the weak polarity of olefins.The driving effect of zeolite component towards CO conversion was demonstrated by microkinetic simulations,which is sensitive to reaction conditions like space velocity and reaction temperature.Under a fixed ratio of active sites between oxide and zeolite components,the concept of the“impossible trinity”of high CO conversion,high olefin selectivity,and high space velocity can thus be manifested.This work thus provides a comprehensive kinetic picture on the direct STO conversion,offering valuable insights for the design of each component of bifunctional catalysts and the optimization of reaction conditions.
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).
