Understanding the effect of H_(2)O adsorption on reactant activation is of great importance in heterogeneous catalysis,which remains a grand challenge particularly in oxide catalyst systems with structural complexity....Understanding the effect of H_(2)O adsorption on reactant activation is of great importance in heterogeneous catalysis,which remains a grand challenge particularly in oxide catalyst systems with structural complexity.Herein,the effect of D_(2)O adsorption on D_(2)activation over MgO nanocatalysts at different temperatures has been investigated by transmission Fourier transform infrared(FT-IR)and temperature-programmed desorption(TPD).Two sets of hydride and hydroxyl species produced from D_(2)dissociation at more active and less active Mg-O pairs can be observed by FT-IR,which all desorb via the product of D_(2)as confirmed by TPD experiments.We find that the physically adsorbed D_(2)O overlayer does not affect the dissociation of D_(2)since D_(2)may pass through the molecular layer and access the surface-active sites.When D_(2)O is partially dissociated on the MgO surface,D_(2)can only dissociate at the remaining active sites until that dissociated-ODw groups from D_(2)O occupy all active sites.These findings provide a fundamental understanding of the effect of water adsorption on D_(2)activation on oxide catalysts.展开更多
Semiconductor photocatalysis holds great promise for breaking the inert chemical bonds under mild condition;however,the photoexcitation-induced modulation mechanism has not been well understood at the atomic level.Her...Semiconductor photocatalysis holds great promise for breaking the inert chemical bonds under mild condition;however,the photoexcitation-induced modulation mechanism has not been well understood at the atomic level.Herein,by performing the DFT+U calculations,we quantitatively compare H_(2) activation on rutile TiO_(2)(110)under thermo-versus photo-catalytic condition.It is found that H2 dissociation prefers to occur via the heterolytic cleavage mode in thermocatalysis,but changes to the homolytic cleavage mode and gets evidently promoted in the presence of photoexcited hole(h^(+)).The origin can be ascribed to the generation of highly oxidative lattice O-radical(O_(br)^(·−))with a localized unoccupied O-2p state.More importantly,we identify that this photo-induced promotion effect can be practicable to another kind of important chemical bond,i.e.,C-H bond in light hydrocarbons including alkane,alkene and aromatics;an exception is the C(sp^(1))-H in alkyne(HC≡CH),which encounters inhibition effect from photoexcitation.By quantitative analysis,the origins behind these results are attributed to the interplay between two factors:C-H bond energy(E_(bond))and the acidity.Owing to the relatively high E_(bond) and acidity,it favors the C(sp^(1))-H bond to proceed with the heterolytic cleavage mode in both thermo-and photo-catalysis,and the photoexcited O_(br)^(·−)is adverse to receiving the transferred proton.By contrast,for the other hydrocarbons with moderate/low E_(bond),the O_(br)^(·−)would enable to change their activation mode to a more favored homolytic one and evidently decrease the C-H activation barrier.This work may provide a general picture for understanding the photocatalytic R-H(R=H,C)bond activation over the semiconductor catalyst.展开更多
基金This work was financially supported by the National Key R&D Program of China(Nos.2021YFA1502800,2022YFA1504800 and 2022YFA1504500)the National Natural Science Foundation of China(Nos.91945302,22272162,22288201 and 21825203).
文摘Understanding the effect of H_(2)O adsorption on reactant activation is of great importance in heterogeneous catalysis,which remains a grand challenge particularly in oxide catalyst systems with structural complexity.Herein,the effect of D_(2)O adsorption on D_(2)activation over MgO nanocatalysts at different temperatures has been investigated by transmission Fourier transform infrared(FT-IR)and temperature-programmed desorption(TPD).Two sets of hydride and hydroxyl species produced from D_(2)dissociation at more active and less active Mg-O pairs can be observed by FT-IR,which all desorb via the product of D_(2)as confirmed by TPD experiments.We find that the physically adsorbed D_(2)O overlayer does not affect the dissociation of D_(2)since D_(2)may pass through the molecular layer and access the surface-active sites.When D_(2)O is partially dissociated on the MgO surface,D_(2)can only dissociate at the remaining active sites until that dissociated-ODw groups from D_(2)O occupy all active sites.These findings provide a fundamental understanding of the effect of water adsorption on D_(2)activation on oxide catalysts.
基金supported by the National Key R&D Program of China(2017YFA0700104 and 2018YFA0702001)the National Natural Science Foundation of China(21871238)+2 种基金the Fundamental Research Funds for the Central Universities(WK2060000016)Natural Science Foundation of Anhui Province(2208085J09)USTC Tang Scholar。
基金supported by National Nature Science Foundation of China(Nos.21873028.91945302)National Ten Thousand Talent Program for Young Top-notch Talents in China,Shanghai Shu-Guang project(No.17SG30)the Fundamental Research Fundsfor the Central Universities.
文摘Semiconductor photocatalysis holds great promise for breaking the inert chemical bonds under mild condition;however,the photoexcitation-induced modulation mechanism has not been well understood at the atomic level.Herein,by performing the DFT+U calculations,we quantitatively compare H_(2) activation on rutile TiO_(2)(110)under thermo-versus photo-catalytic condition.It is found that H2 dissociation prefers to occur via the heterolytic cleavage mode in thermocatalysis,but changes to the homolytic cleavage mode and gets evidently promoted in the presence of photoexcited hole(h^(+)).The origin can be ascribed to the generation of highly oxidative lattice O-radical(O_(br)^(·−))with a localized unoccupied O-2p state.More importantly,we identify that this photo-induced promotion effect can be practicable to another kind of important chemical bond,i.e.,C-H bond in light hydrocarbons including alkane,alkene and aromatics;an exception is the C(sp^(1))-H in alkyne(HC≡CH),which encounters inhibition effect from photoexcitation.By quantitative analysis,the origins behind these results are attributed to the interplay between two factors:C-H bond energy(E_(bond))and the acidity.Owing to the relatively high E_(bond) and acidity,it favors the C(sp^(1))-H bond to proceed with the heterolytic cleavage mode in both thermo-and photo-catalysis,and the photoexcited O_(br)^(·−)is adverse to receiving the transferred proton.By contrast,for the other hydrocarbons with moderate/low E_(bond),the O_(br)^(·−)would enable to change their activation mode to a more favored homolytic one and evidently decrease the C-H activation barrier.This work may provide a general picture for understanding the photocatalytic R-H(R=H,C)bond activation over the semiconductor catalyst.
