To consider the reliability and performance of electronic devices based on polyimide derivatives, dynamic water sorption and diffusion behavior in a polyimide derivative： poly（4＇4 oxydiphenylene pyromellitimide） ...To consider the reliability and performance of electronic devices based on polyimide derivatives, dynamic water sorption and diffusion behavior in a polyimide derivative： poly（4＇4 oxydiphenylene pyromellitimide） （PMDA-ODA）/silica nanocomposite was investigated by two-dimensional ATR-FTIR spectroscopy, by which three states of water molecules owning different H-bonding strength were distinguished. The amounts and strength of H-bonding also played a significant role in determining the diffusion rate of the different states of water molecules. The type of aggregated water molecules which also formed H-bonding with silicic acid （residues） or polyimide system was the last one diffusing to the polymer side in contact with the ATR crystal element because the polymeric matrix blocked their diffusion to a great extent. The diffusion coefficient was also estimated to gain the information of the dynamic diffusion behavior.展开更多
Single-atom catalysis,the catalysis by single-atom catalysts(SACs),has attracted considerable attention in recent years as a new frontier in the heterogeneous catalysis field.SACs have the advantages of both homogeneo...Single-atom catalysis,the catalysis by single-atom catalysts(SACs),has attracted considerable attention in recent years as a new frontier in the heterogeneous catalysis field.SACs have the advantages of both homogeneous catalysts(isolated active sites)and heterogeneous catalysts(stable and easy to separate),and are thus predicted to be able to bridge the homo-and heterogeneous catalysis.This prediction was first experimentally demonstrated in 2016.In this mini-review,we summarize the few homogeneous catalysis progresses reported recently where SACs have exhibited promising application:a)Rh/ZnO and Rh/CoO SAC have been used successfully in hydroformylation of olefin of which the activity are comparable to the homogeneous Wilkinson’s catalyst;b)a Pt/Al2O3 SAC has shown excellent performance in hydrosilylation reaction;and c)M-N-C SACs(M=Fe,Co etc.)have been applied in the activation of C–H bonds.All of these examples suggest that fabrication of suitable SACs could provide a new avenue for the heterogenization of homogeneous catalysts.These pioneering works shed new light on the recognition of single-atom catalysis in bridging the homo-and heterogeneous catalysis.展开更多
Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformati...Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.展开更多
基金supported by the National Natural Science Foundation of China(No.20573022,No.20425415)the National Basic Research Pro-gram of China(2005CB623800),the PHD Program of M0E(20050246010)the"Qimingxing"Project(No.04QM1402)of Shanghai Municipal Science and Technology Commission,and the"Shuguang"Project(No.01SG05)of the Shanghai Municipal Education Commission and Shanghai Education Development Foundation.
文摘To consider the reliability and performance of electronic devices based on polyimide derivatives, dynamic water sorption and diffusion behavior in a polyimide derivative： poly（4＇4 oxydiphenylene pyromellitimide） （PMDA-ODA）/silica nanocomposite was investigated by two-dimensional ATR-FTIR spectroscopy, by which three states of water molecules owning different H-bonding strength were distinguished. The amounts and strength of H-bonding also played a significant role in determining the diffusion rate of the different states of water molecules. The type of aggregated water molecules which also formed H-bonding with silicic acid （residues） or polyimide system was the last one diffusing to the polymer side in contact with the ATR crystal element because the polymeric matrix blocked their diffusion to a great extent. The diffusion coefficient was also estimated to gain the information of the dynamic diffusion behavior.
基金supported by National Natural Science Foundation of China(21606222,21776270)Postdoctoral Science Foundation(2017M621170,2016M601350)~~
文摘Single-atom catalysis,the catalysis by single-atom catalysts(SACs),has attracted considerable attention in recent years as a new frontier in the heterogeneous catalysis field.SACs have the advantages of both homogeneous catalysts(isolated active sites)and heterogeneous catalysts(stable and easy to separate),and are thus predicted to be able to bridge the homo-and heterogeneous catalysis.This prediction was first experimentally demonstrated in 2016.In this mini-review,we summarize the few homogeneous catalysis progresses reported recently where SACs have exhibited promising application:a)Rh/ZnO and Rh/CoO SAC have been used successfully in hydroformylation of olefin of which the activity are comparable to the homogeneous Wilkinson’s catalyst;b)a Pt/Al2O3 SAC has shown excellent performance in hydrosilylation reaction;and c)M-N-C SACs(M=Fe,Co etc.)have been applied in the activation of C–H bonds.All of these examples suggest that fabrication of suitable SACs could provide a new avenue for the heterogenization of homogeneous catalysts.These pioneering works shed new light on the recognition of single-atom catalysis in bridging the homo-and heterogeneous catalysis.
文摘Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moieties interact with kinetically relevant hydride transfer transition states.The discussed examples collectively highlight the utmost importance of hydrogen-bonding interactions and ionization of covalently bonded surface moieties as the main factors underlying the uniqueness of water-mediated interfacial acid-base chemistries and the associated solvation effects in the aqueous phase or in the presence of water.A perspective is also provided for future research in this vibrant field.
