The efficient conversion of lignin into mono-cycloalkanes via both C–O and C–C bonds cleavage are attractive,but challenging due to the high C–C bond dissociation energy.Previous studies have demonstrated that NbO_...The efficient conversion of lignin into mono-cycloalkanes via both C–O and C–C bonds cleavage are attractive,but challenging due to the high C–C bond dissociation energy.Previous studies have demonstrated that NbO_(x)-based catalysts exhibited exceptional capabilities for C_(Ar)–C bond cleavage and broken the limitation of lignin monomers.In this work,we presented an economical multifunctional Pt-Nb/MOR catalyst that achieved an impressive monomer yield of 147%during the depolymerization and hydrodeoxygenation of lignin into mono-cycloalkanes.Reaction pathway studies showed that unlike traditional NbO_(x)-based catalytic system,bicyclohexane was an important intermediate in this system and followed the C_(sp3)–C_(sp3)cleavage pathway after complete cyclic-hydrogenation.Deep investigations demonstrated that the doping of Nb in Pt/MOR not only enhanced the activation of hydrogen by Pt,but also increased the acidity of MOR,both of these are favor for the hydrogenolytic cleavage of C_(sp3)–C_(sp3)bonds.This work provides a low-cost catalyst to obtain high-yield monomers from lignin under relatively mild conditions and would help to design catalysts with higher activity for the valorization of lignin.展开更多
A Chinese diplomat observes Moroccan life and customs up close.MOROCCO is known as the Garden of North Africa for its beautiful scenery.Moroccans are suave,open-minded,and hospitable,especially to foreigners.During my...A Chinese diplomat observes Moroccan life and customs up close.MOROCCO is known as the Garden of North Africa for its beautiful scenery.Moroccans are suave,open-minded,and hospitable,especially to foreigners.During my work here,I have made many friends with people from all walks of life.As a result,this has given me the opportunity to visit local families and experience Moroccan hospitality first-hand.展开更多
The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of ex...The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of extra-framework aluminum(EFAl),its impact on catalytic performance requires further investigation.Herein,mordenite(MOR)zeolites with comparable acid density within the 8MR and 12MR channels but different EFAl contents were prepared,and their catalytic roles were examined in syngas conversion.Intelligent gravimetric analysis,model experiment of ethylene conversion and thermogravimetric analysis demonstrate that the existence of EFAl species can inhibit the secondary conversion of ethylene to long chain hydrocarbons(i.e.,C_(5+))as well as the over-accumulation of carbonaceous species.However,excessive EFAl species lead to rapid deactivation due to restricted space and thus severe diffusion limitation.MOR zeolite with a moderate amount of EFAl species achieves a superior ethylene selectivity and exhibits an enhanced stability in syngas conversion when combined with ZnAlOx oxide.The insights gained in this work provide important guidance for the design of more efficient zeolite-based catalysts.展开更多
采用量子力学与分子力学组合的ONIOM方法,研究了赖氨酸限域在水与MOR分子筛复合环境下的手性转变.结构分析表明:2个水分子比1个水分子助氢迁移反应的过渡态分子氢键键角显著增大。反应通道研究发现:标题反应有a、b和c三个通道,是赖氨酸...采用量子力学与分子力学组合的ONIOM方法,研究了赖氨酸限域在水与MOR分子筛复合环境下的手性转变.结构分析表明:2个水分子比1个水分子助氢迁移反应的过渡态分子氢键键角显著增大。反应通道研究发现:标题反应有a、b和c三个通道,是赖氨酸在MOR分子筛限域环境下,水助质子以氨基、羰基和羟基为桥从手性碳的一侧迁移到另一侧,实现手性转变。势能面计算表明,a是主反应通道,质子从手性碳向氨基的迁移是决速步骤,在2个水分子助决速步时,吉布斯自由能垒被降到最低值101.9 k J/mol,与裸反应、限域在MOR分子筛和限域在水环境的此通道决速步能垒252.6、229.7和123.9 k J/mol相比较,均有明显降低。结果表明:水与MOR分子筛复合环境对赖氨酸手性转变具有较好的共催化作用,左旋赖氨酸在生命体内可以缓慢地旋光异构。展开更多
文摘The efficient conversion of lignin into mono-cycloalkanes via both C–O and C–C bonds cleavage are attractive,but challenging due to the high C–C bond dissociation energy.Previous studies have demonstrated that NbO_(x)-based catalysts exhibited exceptional capabilities for C_(Ar)–C bond cleavage and broken the limitation of lignin monomers.In this work,we presented an economical multifunctional Pt-Nb/MOR catalyst that achieved an impressive monomer yield of 147%during the depolymerization and hydrodeoxygenation of lignin into mono-cycloalkanes.Reaction pathway studies showed that unlike traditional NbO_(x)-based catalytic system,bicyclohexane was an important intermediate in this system and followed the C_(sp3)–C_(sp3)cleavage pathway after complete cyclic-hydrogenation.Deep investigations demonstrated that the doping of Nb in Pt/MOR not only enhanced the activation of hydrogen by Pt,but also increased the acidity of MOR,both of these are favor for the hydrogenolytic cleavage of C_(sp3)–C_(sp3)bonds.This work provides a low-cost catalyst to obtain high-yield monomers from lignin under relatively mild conditions and would help to design catalysts with higher activity for the valorization of lignin.
文摘A Chinese diplomat observes Moroccan life and customs up close.MOROCCO is known as the Garden of North Africa for its beautiful scenery.Moroccans are suave,open-minded,and hospitable,especially to foreigners.During my work here,I have made many friends with people from all walks of life.As a result,this has given me the opportunity to visit local families and experience Moroccan hospitality first-hand.
文摘The location of aluminum within the framework or extra-framework of zeolites is a critical factor in determining its catalytic performance.Despite extensive research on the identification and formation mechanism of extra-framework aluminum(EFAl),its impact on catalytic performance requires further investigation.Herein,mordenite(MOR)zeolites with comparable acid density within the 8MR and 12MR channels but different EFAl contents were prepared,and their catalytic roles were examined in syngas conversion.Intelligent gravimetric analysis,model experiment of ethylene conversion and thermogravimetric analysis demonstrate that the existence of EFAl species can inhibit the secondary conversion of ethylene to long chain hydrocarbons(i.e.,C_(5+))as well as the over-accumulation of carbonaceous species.However,excessive EFAl species lead to rapid deactivation due to restricted space and thus severe diffusion limitation.MOR zeolite with a moderate amount of EFAl species achieves a superior ethylene selectivity and exhibits an enhanced stability in syngas conversion when combined with ZnAlOx oxide.The insights gained in this work provide important guidance for the design of more efficient zeolite-based catalysts.
文摘采用量子力学与分子力学组合的ONIOM方法,研究了赖氨酸限域在水与MOR分子筛复合环境下的手性转变.结构分析表明:2个水分子比1个水分子助氢迁移反应的过渡态分子氢键键角显著增大。反应通道研究发现:标题反应有a、b和c三个通道,是赖氨酸在MOR分子筛限域环境下,水助质子以氨基、羰基和羟基为桥从手性碳的一侧迁移到另一侧,实现手性转变。势能面计算表明,a是主反应通道,质子从手性碳向氨基的迁移是决速步骤,在2个水分子助决速步时,吉布斯自由能垒被降到最低值101.9 k J/mol,与裸反应、限域在MOR分子筛和限域在水环境的此通道决速步能垒252.6、229.7和123.9 k J/mol相比较,均有明显降低。结果表明:水与MOR分子筛复合环境对赖氨酸手性转变具有较好的共催化作用,左旋赖氨酸在生命体内可以缓慢地旋光异构。
