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
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.
