The design of efficient iron-based catalysts remains a great challenge for selective cyclohexane oxidation to cyclohexanone under mild conditions.Because of the complex distribution of iron location on the support,the...The design of efficient iron-based catalysts remains a great challenge for selective cyclohexane oxidation to cyclohexanone under mild conditions.Because of the complex distribution of iron location on the support,the selectivity is always low.Here,we report a general strategy to selectively deposit highly-dispersed FeO_(x) into the micropore of ZSM-5 by atomic layer deposition(ALD).The framework of ZSM-5 and the Bronsted acid sites are intact during ALD,and the Fe species are selectively deposited onto the defect and Lewis acid sites of ZSM-5.Besides,more Fe–O–Si bonds are formed over FeO_(x)/ZSM-5 with a low loading of Fe,while FeO_(x) nanoparticles are generated at high Fe loading.They cannot be realized by the traditional solution method.The obtained FeO_(x)/ZSM-5 catalysts perform high selectivity of cyclohexanone(92%–97%),and ALD cycle numbers of FeO_(x) control the activity.Compared with the Fe nanoparticles,the Fe–O–Si species performs higher turnover frequency and stability in the oxidation reaction.展开更多
of main observation and conclusion The mechanism of Rh-catalyzed C(sp^3)—H amination has been computationally investigated.The reaction mechanism mainly involves sequential C(sp^3)—H activation,decarboxylation,nitre...of main observation and conclusion The mechanism of Rh-catalyzed C(sp^3)—H amination has been computationally investigated.The reaction mechanism mainly involves sequential C(sp^3)—H activation,decarboxylation,nitrene migration insertion,and protonation steps.Competitive concerted metalation deprotonation(CMD)and external base assisted deprotonation(EBAD)pathways are found for the involved C(sp^3)—H activation in both Rh and Co analogous systems.This is different from the previously reported C(sp^2)—H activation,where the CMD is dominant.The key mechanistic difference between the two systems is found to be in the C(sp^3)—H activation step.In comparison with Rh species,the lower activity of Co complex toward the C(sp^3)—H activation could be ascribed to smaller atomic size of Co and thus larger steric repulsion between ancillary ligand and substrate along with the CMD pathway.In view of the EBAD pathway,however,the lower activity of Co species could be imputed to the triplet nature of Co center,which is against the electron transfer from the electron-rich carbon atom of the deprotonating C(sp^3)—H bond to the Co center.As to the subsequent decarboxylation and nitrene insertion steps,compared with the Co system,the relatively lower reactivity of Rh species is partially due to the stronger Rh—N bond,and the higher Ti(Rh—N)and n^*(Rh—N)orbital energies of the corresponding transition state structure.展开更多
基金supported by the National Natural Science Foundation of China(21872160,U1832208)the National Science Fund for Distinguished Young Scholars(21825204)+2 种基金the National Key R&D Program of China(2017YFA0700101 and 2018YFB1501602)the Youth Innovation Promotion Association CAS(2017204)Natural Science Foundation of Shanxi Province(201901D211591)。
文摘The design of efficient iron-based catalysts remains a great challenge for selective cyclohexane oxidation to cyclohexanone under mild conditions.Because of the complex distribution of iron location on the support,the selectivity is always low.Here,we report a general strategy to selectively deposit highly-dispersed FeO_(x) into the micropore of ZSM-5 by atomic layer deposition(ALD).The framework of ZSM-5 and the Bronsted acid sites are intact during ALD,and the Fe species are selectively deposited onto the defect and Lewis acid sites of ZSM-5.Besides,more Fe–O–Si bonds are formed over FeO_(x)/ZSM-5 with a low loading of Fe,while FeO_(x) nanoparticles are generated at high Fe loading.They cannot be realized by the traditional solution method.The obtained FeO_(x)/ZSM-5 catalysts perform high selectivity of cyclohexanone(92%–97%),and ALD cycle numbers of FeO_(x) control the activity.Compared with the Fe nanoparticles,the Fe–O–Si species performs higher turnover frequency and stability in the oxidation reaction.
基金This work was supported by the National Natural Science Foundation of China(No.21674014)Y.L.thanks the FundamentalResearch Funds for the Central Universities(DUT18GJ201)The authors also thank the Network and lnformation Center of Dalian University of Technology and the High-performance Computing Platform of Anhui University for part of computational resources.
文摘of main observation and conclusion The mechanism of Rh-catalyzed C(sp^3)—H amination has been computationally investigated.The reaction mechanism mainly involves sequential C(sp^3)—H activation,decarboxylation,nitrene migration insertion,and protonation steps.Competitive concerted metalation deprotonation(CMD)and external base assisted deprotonation(EBAD)pathways are found for the involved C(sp^3)—H activation in both Rh and Co analogous systems.This is different from the previously reported C(sp^2)—H activation,where the CMD is dominant.The key mechanistic difference between the two systems is found to be in the C(sp^3)—H activation step.In comparison with Rh species,the lower activity of Co complex toward the C(sp^3)—H activation could be ascribed to smaller atomic size of Co and thus larger steric repulsion between ancillary ligand and substrate along with the CMD pathway.In view of the EBAD pathway,however,the lower activity of Co species could be imputed to the triplet nature of Co center,which is against the electron transfer from the electron-rich carbon atom of the deprotonating C(sp^3)—H bond to the Co center.As to the subsequent decarboxylation and nitrene insertion steps,compared with the Co system,the relatively lower reactivity of Rh species is partially due to the stronger Rh—N bond,and the higher Ti(Rh—N)and n^*(Rh—N)orbital energies of the corresponding transition state structure.
