Ethylene(C_(2)H_(4))in vehicle exhaust is a highly reactive volatile organic compound(VOC).Its photooxidative reaction with NOx contributes to the formation of O3 and secondary organic aerosols(SOA),the latter being a...Ethylene(C_(2)H_(4))in vehicle exhaust is a highly reactive volatile organic compound(VOC).Its photooxidative reaction with NOx contributes to the formation of O3 and secondary organic aerosols(SOA),the latter being a key precursor of PM_(2.5).In this study,a novel MgO-supported Ag-Cu bimetallic catalyst was designed and investigated using density functional theory(DFT).The effects of Ag and Cu loading on the geometric structure,stability,and reactant adsorption characteristics of the catalyst were analyzed,and the catalytic oxidation pathways of C_(2)H_(4)over AgCu-MgO was elucidated.The results indicate that loading Ag significantly enhances the adsorption of C_(2)H_(4).The incorporation of Cu into Ag-MgO to form a AgCu-MgO bimetallic catalyst(dual atom catalyst,DACS)further improves the oxidative activity toward C_(2)H_(4).Based on the binding energies of the Ag and Cu bimetallic sites and the adsorption energies of C_(2)H_(4)and O_(2),three representative configurations were selected for detailed reaction pathway analysis.Among them,Configuration 6 of AgCu-MgO exhibited the highest catalytic oxidation performance.This study provides new atomic-scale insights for the rational design of efficient catalysts targeting olefinic pollutants in automotive emissions and offers valuable guidance for advancing exhaust after-treatment technologies.展开更多
Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO-C refractory and the steel with and without the lanthanum(La)addition.Following a reaction ...Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO-C refractory and the steel with and without the lanthanum(La)addition.Following a reaction time of 50 min,a reaction layer comprised MgO and CaS with a thickness of 30μm was observed at the interface between the La-free steel and refractory.The MgO layer was observed in La-bearing steel after just 10 min of reaction.The addition of La to the steel accelerated the formation of the MgO layer.As the reaction time increased,a La-containing layer was formed at the La-bearing steel/refractory interface.This La-containing layer progressed through stages from La_(2)O_(2)S+La2O3→La-Ca-O-S→La-Ca-O→La-Ca-Al-O.Furthermore,the evolution of oxide inclusions in the La-free steel followed the sequence of MgO⋅Al_(2)O_(3),Ti-Ca-Al-O and Ti-Mg-Al-O→MgO·Al_(2)O_(3)and MgO with increasing the reaction time.In contrast,the sequence for the La-bearing steel was:La_(2)O_(2)S and La2O3→La_(2)O_(2)S and La-Ti-Al-Mg-O→La-Ti-Al-Mg-O,MgO and MgO·Al_(2)O_(3).The average penetration depth of the La-bearing steel into the refractory was notably lower than that of the La-free steel,revealing that the incorporation of rare earth element La in steel exhibits a significant inhibitory effect on the penetration of molten steel into the MgO-C refractory.展开更多
文摘为抑制碱激发胶凝材料(AASM)因水化反应集中、孔隙失水引起的显著自收缩,本文提出采用MgO与Na_(2)SiO_(3)复配为复合激发剂,系统研究其对AASM凝结行为、水化产物组成、孔结构特征、强度发展与自收缩性能的影响规律。通过XRD(X-ray diffraction)与NMR(nuclear magnetic resonance)等手段表征发现:随着复合激发剂中MgO比例的增加,体系内类水滑石相生成显著增多,同时最可几孔径向10~20 nm区间集中,孔隙率有所上升。上述微观结构演变导致以下宏观性能变化:一方面,MgO的弱碱性质延缓了矿渣的水化进程,凝结时间延长,抗压强度随其掺量增加而降低;另一方面,类水滑石相的体积膨胀效应与孔隙率的提高共同缓解了毛细孔应力,使AASM的自收缩显著减小。研究表明,MgO与Na_(2)SiO_(3)在调控反应进程与水化产物组成方面具有协同作用。Na_(2)SiO_(3)提供强碱性环境以保障早期强度发展,而MgO则通过促进膨胀性产物生成,优化孔隙结构,有效抑制收缩开裂。该复合激发策略为兼顾AASM力学性能与体积稳定性提供了可行途径。
基金Supported by the National Natural Science Foundation of China Project(22362018)the Yunnan Fundamental Research Projects(202401AS070102)。
文摘Ethylene(C_(2)H_(4))in vehicle exhaust is a highly reactive volatile organic compound(VOC).Its photooxidative reaction with NOx contributes to the formation of O3 and secondary organic aerosols(SOA),the latter being a key precursor of PM_(2.5).In this study,a novel MgO-supported Ag-Cu bimetallic catalyst was designed and investigated using density functional theory(DFT).The effects of Ag and Cu loading on the geometric structure,stability,and reactant adsorption characteristics of the catalyst were analyzed,and the catalytic oxidation pathways of C_(2)H_(4)over AgCu-MgO was elucidated.The results indicate that loading Ag significantly enhances the adsorption of C_(2)H_(4).The incorporation of Cu into Ag-MgO to form a AgCu-MgO bimetallic catalyst(dual atom catalyst,DACS)further improves the oxidative activity toward C_(2)H_(4).Based on the binding energies of the Ag and Cu bimetallic sites and the adsorption energies of C_(2)H_(4)and O_(2),three representative configurations were selected for detailed reaction pathway analysis.Among them,Configuration 6 of AgCu-MgO exhibited the highest catalytic oxidation performance.This study provides new atomic-scale insights for the rational design of efficient catalysts targeting olefinic pollutants in automotive emissions and offers valuable guidance for advancing exhaust after-treatment technologies.
基金the support from the National Key R&D Program(No.2023YFB3709900)the National Key R&D Program(No.2023YFB3709901)+2 种基金the National Natural Science Foundation of China(Grant No.U22A20171)the Hebei Natural Science Foundation(Grant No.52304340)the High Steel Center(HSC)at North China University of Technology.
文摘Laboratory experiments and thermodynamic calculations were performed to investigate the interfacial reactions between the MgO-C refractory and the steel with and without the lanthanum(La)addition.Following a reaction time of 50 min,a reaction layer comprised MgO and CaS with a thickness of 30μm was observed at the interface between the La-free steel and refractory.The MgO layer was observed in La-bearing steel after just 10 min of reaction.The addition of La to the steel accelerated the formation of the MgO layer.As the reaction time increased,a La-containing layer was formed at the La-bearing steel/refractory interface.This La-containing layer progressed through stages from La_(2)O_(2)S+La2O3→La-Ca-O-S→La-Ca-O→La-Ca-Al-O.Furthermore,the evolution of oxide inclusions in the La-free steel followed the sequence of MgO⋅Al_(2)O_(3),Ti-Ca-Al-O and Ti-Mg-Al-O→MgO·Al_(2)O_(3)and MgO with increasing the reaction time.In contrast,the sequence for the La-bearing steel was:La_(2)O_(2)S and La2O3→La_(2)O_(2)S and La-Ti-Al-Mg-O→La-Ti-Al-Mg-O,MgO and MgO·Al_(2)O_(3).The average penetration depth of the La-bearing steel into the refractory was notably lower than that of the La-free steel,revealing that the incorporation of rare earth element La in steel exhibits a significant inhibitory effect on the penetration of molten steel into the MgO-C refractory.
