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
Constructing new Brönsted acid sites within zeolitic materials holds paramount importance for the advancement of solid-acid catalysis.Zeo-type germanosilicates,a class of metallosilicates with a neutral framework...Constructing new Brönsted acid sites within zeolitic materials holds paramount importance for the advancement of solid-acid catalysis.Zeo-type germanosilicates,a class of metallosilicates with a neutral framework composed of tetravalent Ge and Si oxygen tetrahedrons,are conventionally considered not to generate Brönsted acid sites.Herein,we disclose an abnormal phenomenon with Ge-rich IWW-type germanosilicate(IWW-A)as an example that Ge-enriched germanosilicates are featured by mild Brönsted acidity.Using the art-of-state density functional theory calculation,19F magic angle spinning nuclear magnetic resonance,microcalorimetric and ammonia infrared mass spectrometry-temperature-programmed desorption characterizations,the nature of germanosilicate's Brönsted acidity has been demonstrated to be closely related to the neighboring framework Ge-hydroxyl pairs.Besides,the contribution of Ge-OH groups to Brönsted acidity and the role of Ge-pair structure for maintaining mild acid strength have been elucidated.In catalytic cracking of n-hexane and methanol-to-olefins reaction,the IWW-A germanosilicate exhibit high light olefins selectivity,good recyclability and low carbon deposition,outperforming the benchmark zeolite catalyst,ZSM-5 aluminosilicate.展开更多
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Constructing new Brönsted acid sites within zeolitic materials holds paramount importance for the advancement of solid-acid catalysis.Zeo-type germanosilicates,a class of metallosilicates with a neutral framework composed of tetravalent Ge and Si oxygen tetrahedrons,are conventionally considered not to generate Brönsted acid sites.Herein,we disclose an abnormal phenomenon with Ge-rich IWW-type germanosilicate(IWW-A)as an example that Ge-enriched germanosilicates are featured by mild Brönsted acidity.Using the art-of-state density functional theory calculation,19F magic angle spinning nuclear magnetic resonance,microcalorimetric and ammonia infrared mass spectrometry-temperature-programmed desorption characterizations,the nature of germanosilicate's Brönsted acidity has been demonstrated to be closely related to the neighboring framework Ge-hydroxyl pairs.Besides,the contribution of Ge-OH groups to Brönsted acidity and the role of Ge-pair structure for maintaining mild acid strength have been elucidated.In catalytic cracking of n-hexane and methanol-to-olefins reaction,the IWW-A germanosilicate exhibit high light olefins selectivity,good recyclability and low carbon deposition,outperforming the benchmark zeolite catalyst,ZSM-5 aluminosilicate.
