The reaction of methylene radicals in their 3 B1 electronic ground state with molecular NO was studied. Pure CH2(X 3 B1 ) radicals were prodced by UV photolysis of ketene at 351 nm.The products were measured by Time-R...The reaction of methylene radicals in their 3 B1 electronic ground state with molecular NO was studied. Pure CH2(X 3 B1 ) radicals were prodced by UV photolysis of ketene at 351 nm.The products were measured by Time-Resolved Fourier Transform Infrard (TR-FTIR) spectrometer. CO.OH .NH2 and HOCN or its isomer HNCO were found as primary prodcts and several possible channels of this reaction were suggested.展开更多
The spatial variability in the atmospheric CO_(2)and CH_(4)concentrations in urban land is affected by the source type,source distribution,and emission intensity in the cityscape.In this study,we analyzed vehicle-moun...The spatial variability in the atmospheric CO_(2)and CH_(4)concentrations in urban land is affected by the source type,source distribution,and emission intensity in the cityscape.In this study,we analyzed vehicle-mounted measurements of street-level CO_(2)and CH_(4)concentrations in Hangzhou—a large metropolitan area in the Yangtze River Delta in eastern China.The results revealed that CO_(2)and CH_(4)emission hotspots did not overlap geographically,with the former occurring as linear features at elevated road intersections and expressways and the latter occurring at waste treatment facilities(sewage treatment plants and landfills).The CH_(4):CO_(2)emission ratios(ppb ppm^(-1))were ranked in increasing order as follows:traffic(1.01±1.82;mean±1 SD);overall(3.46±2.71);sewage treatment(12.76±2.50);and landfill(36.50±10.15).Waste treatment was largely responsible for the increased overall emission ratio,supporting this source category as a major contributor to the CH_(4)budget in this city and suggesting a negligible role of domestic appliances(cookstoves and water heaters).A two-source mixing model calculation indicated that 99.9%of nonelectric vehicles in Hangzhou were gasoline-powered,revealing a recent shift in vehicle fuel composition from gasoline/natural gas to gasoline/electricity.The methodology established in this study is applicable to cities elsewhere.展开更多
Heterogeneous solid frustrated-Lewis-pair(FLP)catalyst is of great promise in practical hydrogenation applications.It has been found that all-solid FLPs can be created on ceria via surface oxygen vacancy regulation.Co...Heterogeneous solid frustrated-Lewis-pair(FLP)catalyst is of great promise in practical hydrogenation applications.It has been found that all-solid FLPs can be created on ceria via surface oxygen vacancy regulation.Consequently,it is desired to investigate the mechanisms of the FLP-catalyzed hydrogenation of C=C and C=O and provide insight into the modification of CeO_(2)catalysts for the selective hydrogenation.In this work,the reaction mechanism of the hydrogenation of CH_(2)=CH_(2)and CH_(3)CH=O at the FLP sites constructed on CeO_(2)(110)surface was investigated by density functional theory(DFT),with the classical Lewis acid-base pairs(CLP)site as the reference.The results illustrate that at the CLP site,the dissociated hydride(H^(δ−))forms a stable H−O bond with the surface O atom,while at the FLP site,H^(δ−)is stabilized by Ce,displaying higher activity on the one hand.On the other hand,the electron cloud density of the Ce atom at the FLP site is higher,which can transfer more electrons to the adsorbed C_(C=C)and O_(C=O)atoms,leading to a higher degree of activation for C=C and C=O bonds,as indicated by the Bader charge analysis.Therefore,compared to the CLP site,the FLP site exhibits higher hydrogenation activity for CH_(2)=CH_(2)and CH_(3)CH=O.Furthermore,at the FLP sites,it demonstrates high efficiency in catalyzing the hydrogenation of CH_(2)=CH_(2)with the rate-determining barrier of 1.04 eV,but it shows limited activity for the hydrogenation of CH_(3)CH=O with the rate-determining barrier of 1.94 eV.It means that the selective hydrogenation of C=C can be effectively achieved at the FLP sites concerning selective hydrogenation catalysis.The insights shown in this work help to clarify the reaction mechanism of the hydrogenation of C=C and C=O at FLP site on CeO_(2)(110)and reveal the relationship between the catalytic performance and the nature of the active site,which is of great benefit to development of rational design of heterogeneous FLP catalysts.展开更多
文摘The reaction of methylene radicals in their 3 B1 electronic ground state with molecular NO was studied. Pure CH2(X 3 B1 ) radicals were prodced by UV photolysis of ketene at 351 nm.The products were measured by Time-Resolved Fourier Transform Infrard (TR-FTIR) spectrometer. CO.OH .NH2 and HOCN or its isomer HNCO were found as primary prodcts and several possible channels of this reaction were suggested.
基金supported by the National Natural Science Foundation of China(Grant Nos.U24A20590,42021004)the Joint funds of the Zhejiang Provincial NaturalScienceFoundationofChina(GrantNo.LZJMZ23D050002)+2 种基金the 333 Project of Jiangsu Province(Grant No.BRA2022023)the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars(Grant No.BK20220055)the Key Laboratory of Ecosystem Carbon Source and Sink,China Meteorological Administration(Grant No.ECSS-CMA202302)。
文摘The spatial variability in the atmospheric CO_(2)and CH_(4)concentrations in urban land is affected by the source type,source distribution,and emission intensity in the cityscape.In this study,we analyzed vehicle-mounted measurements of street-level CO_(2)and CH_(4)concentrations in Hangzhou—a large metropolitan area in the Yangtze River Delta in eastern China.The results revealed that CO_(2)and CH_(4)emission hotspots did not overlap geographically,with the former occurring as linear features at elevated road intersections and expressways and the latter occurring at waste treatment facilities(sewage treatment plants and landfills).The CH_(4):CO_(2)emission ratios(ppb ppm^(-1))were ranked in increasing order as follows:traffic(1.01±1.82;mean±1 SD);overall(3.46±2.71);sewage treatment(12.76±2.50);and landfill(36.50±10.15).Waste treatment was largely responsible for the increased overall emission ratio,supporting this source category as a major contributor to the CH_(4)budget in this city and suggesting a negligible role of domestic appliances(cookstoves and water heaters).A two-source mixing model calculation indicated that 99.9%of nonelectric vehicles in Hangzhou were gasoline-powered,revealing a recent shift in vehicle fuel composition from gasoline/natural gas to gasoline/electricity.The methodology established in this study is applicable to cities elsewhere.
基金supported by the National Natural Science Foundation of China(22302115,22072079)the Fundamental Research Program of Shanxi Province(202303021221056).
文摘Heterogeneous solid frustrated-Lewis-pair(FLP)catalyst is of great promise in practical hydrogenation applications.It has been found that all-solid FLPs can be created on ceria via surface oxygen vacancy regulation.Consequently,it is desired to investigate the mechanisms of the FLP-catalyzed hydrogenation of C=C and C=O and provide insight into the modification of CeO_(2)catalysts for the selective hydrogenation.In this work,the reaction mechanism of the hydrogenation of CH_(2)=CH_(2)and CH_(3)CH=O at the FLP sites constructed on CeO_(2)(110)surface was investigated by density functional theory(DFT),with the classical Lewis acid-base pairs(CLP)site as the reference.The results illustrate that at the CLP site,the dissociated hydride(H^(δ−))forms a stable H−O bond with the surface O atom,while at the FLP site,H^(δ−)is stabilized by Ce,displaying higher activity on the one hand.On the other hand,the electron cloud density of the Ce atom at the FLP site is higher,which can transfer more electrons to the adsorbed C_(C=C)and O_(C=O)atoms,leading to a higher degree of activation for C=C and C=O bonds,as indicated by the Bader charge analysis.Therefore,compared to the CLP site,the FLP site exhibits higher hydrogenation activity for CH_(2)=CH_(2)and CH_(3)CH=O.Furthermore,at the FLP sites,it demonstrates high efficiency in catalyzing the hydrogenation of CH_(2)=CH_(2)with the rate-determining barrier of 1.04 eV,but it shows limited activity for the hydrogenation of CH_(3)CH=O with the rate-determining barrier of 1.94 eV.It means that the selective hydrogenation of C=C can be effectively achieved at the FLP sites concerning selective hydrogenation catalysis.The insights shown in this work help to clarify the reaction mechanism of the hydrogenation of C=C and C=O at FLP site on CeO_(2)(110)and reveal the relationship between the catalytic performance and the nature of the active site,which is of great benefit to development of rational design of heterogeneous FLP catalysts.
