随着低碳烯烃需求量的增加,甲醇制烯烃(MTO)成为由非石油资源制取低碳烯烃的关键技术,其中沸石由于具有可调节的酸度、有序的微孔结构和较好的择型性能而被广泛用作MTO反应催化剂.ITQ-13沸石(ITH拓扑结构)由于其独特的九元环结构在MTO...随着低碳烯烃需求量的增加,甲醇制烯烃(MTO)成为由非石油资源制取低碳烯烃的关键技术,其中沸石由于具有可调节的酸度、有序的微孔结构和较好的择型性能而被广泛用作MTO反应催化剂.ITQ-13沸石(ITH拓扑结构)由于其独特的九元环结构在MTO反应中表现出较好的丙烯选择性和反应寿命,引起了广泛关注.研究表明,分子筛的酸中心分布与MTO反应性能密切相关,因此,研究ITQ-13沸石中铝分布与MTO反应性能的关系,对进一步提升其MTO催化性能具有重要意义.本文分别以与ITH具有共同基本结构单元(双四元环,D4Rs)的LTA沸石(LTA-ITH)和薄水铝石(C-ITH)为铝源,合成了两类铝硅酸盐ITH沸石.X射线衍射、扫描电子显微镜以及氮气吸脱附表征结果表明,这两类分子筛具有相似的片状形貌和微孔性质.氨气程序升温脱附结果表明,具有相近硅铝比的两类ITH沸石具有相近的酸量.进一步采用27Al魔角旋转核磁共振(MAS NMR)、密度泛函理论计算和1-己烯裂解反应对两类ITH分子筛的铝分布进行研究.结果表明,两类分子筛具有不同的铝分布,LTA-ITH中有更多的铝进入ITH的正弦孔道与直孔道,而C-ITH中有更多的铝分布在交叉孔道.当前,研究者普遍认为MTO反应过程遵循双循环烃池机理,ITH交叉孔道由于具有较大的空间,相比于正弦孔道和直孔道,更有利于芳烃循环中间体的产生,从而有利于形成芳烃循环产物(乙烯),而正弦孔道和直孔道却更有利于烯烃循环过程,导致产生更多的丙烯.对两类ITH进行了MTO催化性能测试,结果表明,LTA-ITH比C-ITH表现出更高的丙烯选择性,并且表现出更高的丙烯与乙烯的比率,表明其烯烃循环过程得到加强,这与^(27)Al MAS NMR以及1-己烯裂解反应得到的结论一致,进一步证明ITH分子筛的铝分布得到有效调控.综上,本文阐明了ITH沸石中铝分布与其反应性能的关系,为调整沸石骨架中的Al位点提供一种新策略,为未来制备高效的MTO沸石基催化剂提供参考.展开更多
DEAR EDITOR,Three new genera and 46 new species of phrurolithid spiders(Araneae,Phrurolithidae)are described from Jiangxi Province,southern China.These results support our hypothesis that a large percentage of China’...DEAR EDITOR,Three new genera and 46 new species of phrurolithid spiders(Araneae,Phrurolithidae)are described from Jiangxi Province,southern China.These results support our hypothesis that a large percentage of China’s species remain unknown(Li,2020).Some 250 years after Swedish biologist Carl Linnaeus devised a formal system for classifying the diversity of nature.展开更多
The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions（e.g.temperature, p H, duration） of acidic leaching was shown. While the growth of the temperature of acid treatmen...The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions（e.g.temperature, p H, duration） of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80 ℃, the mesopore volume in ITH（Si/Ge = 3.4 and 5.8） and IWW（Si/Ge = 3.3） zeolites changed with the duration of the treatment（p H = 2; T = 80 ℃） as follows： 96 h 〈 1 h 〈 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at p H = 2–7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to p H = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity（i.e. number of reactant molecules converted per active site） of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.展开更多
This paper deals with estimating parameters under simple order when samples come from location models. Based on the idea of Hodges and Lehmann estimator (H-L estimator), a new approach to estimate parameters is propos...This paper deals with estimating parameters under simple order when samples come from location models. Based on the idea of Hodges and Lehmann estimator (H-L estimator), a new approach to estimate parameters is proposed, which is difference with the classical L1 isotonic regression and L2 isotonic regression. An algorithm to compute estimators is given. Simulations by the Monte-Carlo method is applied to compare the likelihood functions with respect to L1 estimators and weighted isotonic H-L estimators.展开更多
THE year 1995 was very special for Cai Shuzhen. In addition to having net earnings of 400,000 yuan, Cai retired an outstanding loan and invested 780,000 yuan in farm machinery. Local villagers found these achievements...THE year 1995 was very special for Cai Shuzhen. In addition to having net earnings of 400,000 yuan, Cai retired an outstanding loan and invested 780,000 yuan in farm machinery. Local villagers found these achievements surprising, for Cai had over the past years become notorious for undertakings which failed despite展开更多
文摘随着低碳烯烃需求量的增加,甲醇制烯烃(MTO)成为由非石油资源制取低碳烯烃的关键技术,其中沸石由于具有可调节的酸度、有序的微孔结构和较好的择型性能而被广泛用作MTO反应催化剂.ITQ-13沸石(ITH拓扑结构)由于其独特的九元环结构在MTO反应中表现出较好的丙烯选择性和反应寿命,引起了广泛关注.研究表明,分子筛的酸中心分布与MTO反应性能密切相关,因此,研究ITQ-13沸石中铝分布与MTO反应性能的关系,对进一步提升其MTO催化性能具有重要意义.本文分别以与ITH具有共同基本结构单元(双四元环,D4Rs)的LTA沸石(LTA-ITH)和薄水铝石(C-ITH)为铝源,合成了两类铝硅酸盐ITH沸石.X射线衍射、扫描电子显微镜以及氮气吸脱附表征结果表明,这两类分子筛具有相似的片状形貌和微孔性质.氨气程序升温脱附结果表明,具有相近硅铝比的两类ITH沸石具有相近的酸量.进一步采用27Al魔角旋转核磁共振(MAS NMR)、密度泛函理论计算和1-己烯裂解反应对两类ITH分子筛的铝分布进行研究.结果表明,两类分子筛具有不同的铝分布,LTA-ITH中有更多的铝进入ITH的正弦孔道与直孔道,而C-ITH中有更多的铝分布在交叉孔道.当前,研究者普遍认为MTO反应过程遵循双循环烃池机理,ITH交叉孔道由于具有较大的空间,相比于正弦孔道和直孔道,更有利于芳烃循环中间体的产生,从而有利于形成芳烃循环产物(乙烯),而正弦孔道和直孔道却更有利于烯烃循环过程,导致产生更多的丙烯.对两类ITH进行了MTO催化性能测试,结果表明,LTA-ITH比C-ITH表现出更高的丙烯选择性,并且表现出更高的丙烯与乙烯的比率,表明其烯烃循环过程得到加强,这与^(27)Al MAS NMR以及1-己烯裂解反应得到的结论一致,进一步证明ITH分子筛的铝分布得到有效调控.综上,本文阐明了ITH沸石中铝分布与其反应性能的关系,为调整沸石骨架中的Al位点提供一种新策略,为未来制备高效的MTO沸石基催化剂提供参考.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB31000000)National Natural Science Foundation of China(32100363,31970396)。
文摘DEAR EDITOR,Three new genera and 46 new species of phrurolithid spiders(Araneae,Phrurolithidae)are described from Jiangxi Province,southern China.These results support our hypothesis that a large percentage of China’s species remain unknown(Li,2020).Some 250 years after Swedish biologist Carl Linnaeus devised a formal system for classifying the diversity of nature.
基金the Czech Science Foundation for the support (1430898P)
文摘The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions（e.g.temperature, p H, duration） of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80 ℃, the mesopore volume in ITH（Si/Ge = 3.4 and 5.8） and IWW（Si/Ge = 3.3） zeolites changed with the duration of the treatment（p H = 2; T = 80 ℃） as follows： 96 h 〈 1 h 〈 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at p H = 2–7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to p H = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity（i.e. number of reactant molecules converted per active site） of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.
文摘This paper deals with estimating parameters under simple order when samples come from location models. Based on the idea of Hodges and Lehmann estimator (H-L estimator), a new approach to estimate parameters is proposed, which is difference with the classical L1 isotonic regression and L2 isotonic regression. An algorithm to compute estimators is given. Simulations by the Monte-Carlo method is applied to compare the likelihood functions with respect to L1 estimators and weighted isotonic H-L estimators.
文摘THE year 1995 was very special for Cai Shuzhen. In addition to having net earnings of 400,000 yuan, Cai retired an outstanding loan and invested 780,000 yuan in farm machinery. Local villagers found these achievements surprising, for Cai had over the past years become notorious for undertakings which failed despite
