In the paper, we have studied the mixed-valence isopolyanion by cyclic voltammogram, in-situ UV-Visible-Near-IR and FTIR spectroelectrochemical methods in aprotic medium,such as methylene chloride.A number of hetero-...In the paper, we have studied the mixed-valence isopolyanion by cyclic voltammogram, in-situ UV-Visible-Near-IR and FTIR spectroelectrochemical methods in aprotic medium,such as methylene chloride.A number of hetero-- and iso--polyanions of molybdenum are re(luci})leto a series of mixed-valeDce compounds containing Mow and Mo t'. f 1 1These species exhibit intervalence transfer bands. This description ofthe electronic structure corresponds to cia88 H syetems in Robinand Day'8 classification of mixed--valence compounds t21. The electrochemical methods can prepare the mixed--valence compounds in which laceetructure of the parent oxidized form is generally retained. [31 In--situepectroelectrochemical studies have many advantages for product identification and for mechanistic studies of transition metal complexes in solution. t.1 Among theme are small electrolysis volumee that yield shortelectrolysis times, rapid time response for the measurement or kineticparameters, and the rapid in--situ generation of reactive species withBtable properties that preclude isolation [51.The cyclic voltammogram indicates that the (TBA).Mo.O.. undergoestwo reductione, which are labeled ac reactions 1--2 and corre6pond tothe electron transfers given in eq. 1-- 2.Mo.O.g-- + e * Mo.O.g--' E./2=--0.690V -----------------------------(1)Mo.O.S-- + e - Mo.O.:-- ac- other products E.,.=--1.650V------(2)展开更多
The mixed-valence heteropolyanion VMo12O40 n-(where n=4,5,6) in aprotic media wasinvestigated by cyclic voltammatry and in-situ FTIR and UV-visible-near-lRspectroelectrochemical methods. The results indicate that the...The mixed-valence heteropolyanion VMo12O40 n-(where n=4,5,6) in aprotic media wasinvestigated by cyclic voltammatry and in-situ FTIR and UV-visible-near-lRspectroelectrochemical methods. The results indicate that the heteropolyanion VMo12O403-undergoes three reversible one electron transfer reductions and the mixed-valenceheteropolyanion VMo12O40n-(where n=4,5,6) was formed after electroreduction. The spectraof the aforementioned mixed-valence compounds were characterized by in-situspectroelectrochemical mathods展开更多
Intramolecular cyclization of A catalyzed by IDA in benzene or THF yields two γ-lactams through C-alkylation and one δ-and one 7-membered lactam by O-alkylation.
The enantioselectivity of α-chymotrypsin in the esterification of N-acetyl-tryptophan with ethanol was examined in aprotic ionic liquids. The enantioselectivity was found to be strongly affected by a kind of solvent,...The enantioselectivity of α-chymotrypsin in the esterification of N-acetyl-tryptophan with ethanol was examined in aprotic ionic liquids. The enantioselectivity was found to be strongly affected by a kind of solvent, water content, and reaction temperature. The (kcatKM)L/(kcat/KM)D ratio in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([C2mim][FSI]) containing 1.0% (v/v) water at 25°C exhibits 32,000, while that in 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) containing 1.0% (v/v) water at 25°C shows 190. The (kcat/KM)L/(kcat/KM)D ratio in [C2mim] [BF4] at 25°C varies from 190 at 1.0% (v/v) water to 65000 at 5.0% (v/v) water. Moreover, the (kcat/KM)L/ (kcat/KM)展开更多
A series of mesoporous nanocrystalline silicoaluminophosphate (SAPO)zeolites (SAPO-34)were synthesized via an ultrasonic and microwave-assisted hydrothermal method in the presence of [3- (trimethoxysilyl)propyl]octade...A series of mesoporous nanocrystalline silicoaluminophosphate (SAPO)zeolites (SAPO-34)were synthesized via an ultrasonic and microwave-assisted hydrothermal method in the presence of [3- (trimethoxysilyl)propyl]octadecyldimethylammonium chloride and cetyltrimethylammonium bromide surfactants as soft templates.Nickel and cerium were then doped on SAPO-34using incorporation and impregnation methods,and all the catalysts were applied to the methanol-to-olefin (MTO)reaction. The catalysts were characterized using X-ray diffraction,field-emission scanning electron microcopy, inductively coupled plasma-atomic emission spectroscopy,transmission electron microscopy,Fourier- transform infrared spectroscopy,Brunauer-Emmett-Teller analysis,NH3temperature-programmed desorption analysis,and thermogravimetric analysis.For the impregnation method,the effect of using protic or aprotic solvents as impregnation media on the physico-chemical properties of the metal-based SAPO-34was investigated.Water and N,N-dimethylformamide (DMF)were employed as the protic and aprotic solvents,respectively.The catalyst prepared using the aprotic DMF solvent exhibited higher dispersion and lower aggregation of metal species compared with that prepared using the protic water solvent.Furthermore,the sample synthesized using the incorporation method exhibited good catalytic performance;however,the Ni-Ce[SAPO-34 sample prepared using the impregnation method and aprotic DMF solvent exhibited superior catalytic performance in the MTO reaction.展开更多
Aprotic Li-O2 battery has attracted a great deal of interest because of its high theoretical energy density that is far beyond what the best Li-ion technologies can achieve.However, the present Li-O2 batteries suffer ...Aprotic Li-O2 battery has attracted a great deal of interest because of its high theoretical energy density that is far beyond what the best Li-ion technologies can achieve.However, the present Li-O2 batteries suffer from the low energy efficiency that is limited mainly by the high overpotentials required to re-oxidize Li2O2, the discharge product. Over the past few years, considerable research efforts have been devoted to the understanding of the Li2O2 oxidation reactions. Here, we summarize the results obtained from the fundamental study of the Li2O2 oxidation, including its morphology, reaction route, kinetics, the initial location upon oxidation and the charge transport within Li2O2. A better mechanistic understanding of the Li2O2 oxidation reaction will provide a solid foundation for the realization of practical Li-O2 cells with a higher energy efficiency.展开更多
Microcrystalline cellulose (avicel) is treated in hot-compressed aprotic solvents, sulfolane and 1,4-dioxane, using a batch-type reaction system with a molten tin bath in a range from 290 to 390°C. The correspond...Microcrystalline cellulose (avicel) is treated in hot-compressed aprotic solvents, sulfolane and 1,4-dioxane, using a batch-type reaction system with a molten tin bath in a range from 290 to 390°C. The corresponding densities of the solvent are 0.25–1.26 g/cm3 and 0.21–1.03 g/cm3 for sulfolane and 1,4-dioxane, respectively. As a result, in both solvents, more than 90% of cellulose is found to be decomposed to the solvent-soluble portion in which levoglucosan is the main component with the highest yield of about 35% on original cellulose basis. The decomposition rate to levoglucosan is, however, faster in sulfolane than in 1,4-dioxane, while levoglucosan is more stable in 1,4-dioxane. In addition, its yield is found to be solvent-density dependent to be highest around 0.4–0.5 g/cm3 for both solvents. To elucidate these decomposition behaviors, the results obtained in this study with aprotic solvents are compared with protic solvents such as water and methanol in previous works.展开更多
Binary mixtures of alcohols(ethyl,n-butyl and n-amyl)with several aprotic sol- vents,such as acetone,dioxane,THF,DMSO and DMF have been studied systematically by ~1H,^(13)C,^(15)N and ^(17)O NMR measurements.The conce...Binary mixtures of alcohols(ethyl,n-butyl and n-amyl)with several aprotic sol- vents,such as acetone,dioxane,THF,DMSO and DMF have been studied systematically by ~1H,^(13)C,^(15)N and ^(17)O NMR measurements.The concentration dependence of chemical shift of the solvent was used to evaluate equilibrium constants of the complexation of alcohols with the solvents.A relationship between the proton shift of alcohol uncombined with the solvent and its concentration was found,and the fraction of unassociated hydroxyl groups was thus quantitatively described.The effect of solvent on self association and complexation of the alcohol is discussed on the basis of the electron donicity of the solvents.展开更多
When aprotic Li-O2 batteries recharge, the solid Li2O2 in the positive electrode is oxidized, which often exhibits a continuous or step increase in the charging potential as a function of the charging capacity, and it...When aprotic Li-O2 batteries recharge, the solid Li2O2 in the positive electrode is oxidized, which often exhibits a continuous or step increase in the charging potential as a function of the charging capacity, and its origin remains incompletely understood. Here, we report a model study of electro-oxidation of a Li2O2 film on an Au electrode using voltammetry coupled with in situ Raman spectroscopy. It was found that the charging reaction initializes at the positive electrodelLizO2 interface, instead of the previously presumed Li2O2 surface, and consists of two temporally and spatially separated Li2O2 oxidation processes, accounting for the potential rise during charging of Li-O2 batteries. Moreover, the electrode surface-initialized oxidation can disintegrate the Li2O2 film resulting in a loss of Li2O2 into electrolyte solution, which drastically decreases the charging efficiency and highlights the importance of using soluble electro-catalyst for the complete charging of Li-02 batteries.展开更多
Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from f...Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from four solvents under diverse conditions were analyzed in detail and their formation process was studied.Maltese cross is shown by PhgTS spherulites obtained from aprotic solvents via polarized optical microscopy.In comparison,no Maltese cross can be observed from branch-like crystals formed from protic solvents.Independent on the micro-scaled morphology,lamellae were found to be the basic blocks constructing both PhgTS spherulites and branch-like crystals,which were formed predominantly by stacked PhgTS molecules.Although differential characters of the solvents did not affect the formation of lamellas,the solvents played a crucial role in the formation of self-assembled microscaled morphologies.In particular,the morphologies of spherulites were strongly affected by the concentration of PhgTS solutions,surrounding tempera-ture and evaporation rate of solvents.Generally,a higher concentration of PhgTS led to more homogeneous spherulites,a lower evaporation rate resulted in more compact spherulites,and a higher surounding temperature generated preferentially more ring-banded spherulites of PhgTS.展开更多
文摘In the paper, we have studied the mixed-valence isopolyanion by cyclic voltammogram, in-situ UV-Visible-Near-IR and FTIR spectroelectrochemical methods in aprotic medium,such as methylene chloride.A number of hetero-- and iso--polyanions of molybdenum are re(luci})leto a series of mixed-valeDce compounds containing Mow and Mo t'. f 1 1These species exhibit intervalence transfer bands. This description ofthe electronic structure corresponds to cia88 H syetems in Robinand Day'8 classification of mixed--valence compounds t21. The electrochemical methods can prepare the mixed--valence compounds in which laceetructure of the parent oxidized form is generally retained. [31 In--situepectroelectrochemical studies have many advantages for product identification and for mechanistic studies of transition metal complexes in solution. t.1 Among theme are small electrolysis volumee that yield shortelectrolysis times, rapid time response for the measurement or kineticparameters, and the rapid in--situ generation of reactive species withBtable properties that preclude isolation [51.The cyclic voltammogram indicates that the (TBA).Mo.O.. undergoestwo reductione, which are labeled ac reactions 1--2 and corre6pond tothe electron transfers given in eq. 1-- 2.Mo.O.g-- + e * Mo.O.g--' E./2=--0.690V -----------------------------(1)Mo.O.S-- + e - Mo.O.:-- ac- other products E.,.=--1.650V------(2)
文摘The mixed-valence heteropolyanion VMo12O40 n-(where n=4,5,6) in aprotic media wasinvestigated by cyclic voltammatry and in-situ FTIR and UV-visible-near-lRspectroelectrochemical methods. The results indicate that the heteropolyanion VMo12O403-undergoes three reversible one electron transfer reductions and the mixed-valenceheteropolyanion VMo12O40n-(where n=4,5,6) was formed after electroreduction. The spectraof the aforementioned mixed-valence compounds were characterized by in-situspectroelectrochemical mathods
文摘Intramolecular cyclization of A catalyzed by IDA in benzene or THF yields two γ-lactams through C-alkylation and one δ-and one 7-membered lactam by O-alkylation.
文摘The enantioselectivity of α-chymotrypsin in the esterification of N-acetyl-tryptophan with ethanol was examined in aprotic ionic liquids. The enantioselectivity was found to be strongly affected by a kind of solvent, water content, and reaction temperature. The (kcatKM)L/(kcat/KM)D ratio in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([C2mim][FSI]) containing 1.0% (v/v) water at 25°C exhibits 32,000, while that in 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) containing 1.0% (v/v) water at 25°C shows 190. The (kcat/KM)L/(kcat/KM)D ratio in [C2mim] [BF4] at 25°C varies from 190 at 1.0% (v/v) water to 65000 at 5.0% (v/v) water. Moreover, the (kcat/KM)L/ (kcat/KM)
文摘A series of mesoporous nanocrystalline silicoaluminophosphate (SAPO)zeolites (SAPO-34)were synthesized via an ultrasonic and microwave-assisted hydrothermal method in the presence of [3- (trimethoxysilyl)propyl]octadecyldimethylammonium chloride and cetyltrimethylammonium bromide surfactants as soft templates.Nickel and cerium were then doped on SAPO-34using incorporation and impregnation methods,and all the catalysts were applied to the methanol-to-olefin (MTO)reaction. The catalysts were characterized using X-ray diffraction,field-emission scanning electron microcopy, inductively coupled plasma-atomic emission spectroscopy,transmission electron microscopy,Fourier- transform infrared spectroscopy,Brunauer-Emmett-Teller analysis,NH3temperature-programmed desorption analysis,and thermogravimetric analysis.For the impregnation method,the effect of using protic or aprotic solvents as impregnation media on the physico-chemical properties of the metal-based SAPO-34was investigated.Water and N,N-dimethylformamide (DMF)were employed as the protic and aprotic solvents,respectively.The catalyst prepared using the aprotic DMF solvent exhibited higher dispersion and lower aggregation of metal species compared with that prepared using the protic water solvent.Furthermore,the sample synthesized using the incorporation method exhibited good catalytic performance;however,the Ni-Ce[SAPO-34 sample prepared using the impregnation method and aprotic DMF solvent exhibited superior catalytic performance in the MTO reaction.
基金supported by the Recruitment Program of Global Youth Experts of Chinathe Strategic Priority Research Program of the Chinese Academy of Sciences(XDA09010401)the Science and Technology Development Program of the Jilin Province(20150623002TC)
文摘Aprotic Li-O2 battery has attracted a great deal of interest because of its high theoretical energy density that is far beyond what the best Li-ion technologies can achieve.However, the present Li-O2 batteries suffer from the low energy efficiency that is limited mainly by the high overpotentials required to re-oxidize Li2O2, the discharge product. Over the past few years, considerable research efforts have been devoted to the understanding of the Li2O2 oxidation reactions. Here, we summarize the results obtained from the fundamental study of the Li2O2 oxidation, including its morphology, reaction route, kinetics, the initial location upon oxidation and the charge transport within Li2O2. A better mechanistic understanding of the Li2O2 oxidation reaction will provide a solid foundation for the realization of practical Li-O2 cells with a higher energy efficiency.
基金the National Natural Science Foundation of China (Grant No. 90610035)
文摘Microcrystalline cellulose (avicel) is treated in hot-compressed aprotic solvents, sulfolane and 1,4-dioxane, using a batch-type reaction system with a molten tin bath in a range from 290 to 390°C. The corresponding densities of the solvent are 0.25–1.26 g/cm3 and 0.21–1.03 g/cm3 for sulfolane and 1,4-dioxane, respectively. As a result, in both solvents, more than 90% of cellulose is found to be decomposed to the solvent-soluble portion in which levoglucosan is the main component with the highest yield of about 35% on original cellulose basis. The decomposition rate to levoglucosan is, however, faster in sulfolane than in 1,4-dioxane, while levoglucosan is more stable in 1,4-dioxane. In addition, its yield is found to be solvent-density dependent to be highest around 0.4–0.5 g/cm3 for both solvents. To elucidate these decomposition behaviors, the results obtained in this study with aprotic solvents are compared with protic solvents such as water and methanol in previous works.
文摘Binary mixtures of alcohols(ethyl,n-butyl and n-amyl)with several aprotic sol- vents,such as acetone,dioxane,THF,DMSO and DMF have been studied systematically by ~1H,^(13)C,^(15)N and ^(17)O NMR measurements.The concentration dependence of chemical shift of the solvent was used to evaluate equilibrium constants of the complexation of alcohols with the solvents.A relationship between the proton shift of alcohol uncombined with the solvent and its concentration was found,and the fraction of unassociated hydroxyl groups was thus quantitatively described.The effect of solvent on self association and complexation of the alcohol is discussed on the basis of the electron donicity of the solvents.
基金supported by the National Natural Science Foundation of China (91545129, 21575135, 21605136)the “Strategic Priority Research Program” of the Chinese Academy of Science (XDA09010401)+1 种基金the National Key Technology Research and Development Program of China (2016YBF0100100)the Science and Technology Development Program of the Jilin Province (20150623002TC, 20160414034GH)
文摘When aprotic Li-O2 batteries recharge, the solid Li2O2 in the positive electrode is oxidized, which often exhibits a continuous or step increase in the charging potential as a function of the charging capacity, and its origin remains incompletely understood. Here, we report a model study of electro-oxidation of a Li2O2 film on an Au electrode using voltammetry coupled with in situ Raman spectroscopy. It was found that the charging reaction initializes at the positive electrodelLizO2 interface, instead of the previously presumed Li2O2 surface, and consists of two temporally and spatially separated Li2O2 oxidation processes, accounting for the potential rise during charging of Li-O2 batteries. Moreover, the electrode surface-initialized oxidation can disintegrate the Li2O2 film resulting in a loss of Li2O2 into electrolyte solution, which drastically decreases the charging efficiency and highlights the importance of using soluble electro-catalyst for the complete charging of Li-02 batteries.
基金Y.Y.thanks the China Scholarship Council(CSC)for financial support.K.Z.thanks Georg-August-University of Goettingen for the Anschubfinanzierung(Funding for the Promotion of Young Academics of University of Goettingen)and Fonds der Chemischen Industrie(FCI)for the financial support.The authors declare no conflicts of interest.
文摘Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from four solvents under diverse conditions were analyzed in detail and their formation process was studied.Maltese cross is shown by PhgTS spherulites obtained from aprotic solvents via polarized optical microscopy.In comparison,no Maltese cross can be observed from branch-like crystals formed from protic solvents.Independent on the micro-scaled morphology,lamellae were found to be the basic blocks constructing both PhgTS spherulites and branch-like crystals,which were formed predominantly by stacked PhgTS molecules.Although differential characters of the solvents did not affect the formation of lamellas,the solvents played a crucial role in the formation of self-assembled microscaled morphologies.In particular,the morphologies of spherulites were strongly affected by the concentration of PhgTS solutions,surrounding tempera-ture and evaporation rate of solvents.Generally,a higher concentration of PhgTS led to more homogeneous spherulites,a lower evaporation rate resulted in more compact spherulites,and a higher surounding temperature generated preferentially more ring-banded spherulites of PhgTS.
