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
We report a computational study of the distribution of germanium ions among the double four-membered rings(D4Rs)in SCM-14 germanosilicate and the influence of a structure-directing agent(SDA)on the stability of the as...We report a computational study of the distribution of germanium ions among the double four-membered rings(D4Rs)in SCM-14 germanosilicate and the influence of a structure-directing agent(SDA)on the stability of the as-synthesized material.For the pure zeolite structure,the calculations suggested clustering of Ge ions and the formation of D4Rs populated entirely by Ge heteroatoms,while part of the D4Rs contain only Si as T-atoms.As a general trend,structures with more Ge–O–Ge bridges are more stable.展开更多
The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process o...The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process on germanosilicate zeolites. In situ synchrotron X-ray diffraction technique was applied to study the mechanism of these two steps in HCl vapour,which it is often unfeasible to capture using conventional ex situ characterisation. Three germanosilicate zeolites with different pore systems,i.e. UTL,UOV and IWR,were selected as models to compare the reaction behaviours. Three key steps,including fast hydrolysis of d4r units (ca. 1 min),further disassembly (ca. 3–5 min),and self-organisation after disassembly (ca. 2–3 min),were observed in the HCl acid vapour. An unusual lattice expansion of the intralayer was observed at the very beginning of the hydrolysis process in IWR,while the UTL and UOV showed continuous shrinkage. Owing to the diffusion differences related to the structural features,extra-large-pore UTL zeolite showed faster kinetics than the other two large-pore zeolites,although UTL zeolite has much larger crystals. These findings potentially guide further modification of the treatment parameters in the ADOR process to prepare new zeolites.展开更多
Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials w...Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.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.
文摘We report a computational study of the distribution of germanium ions among the double four-membered rings(D4Rs)in SCM-14 germanosilicate and the influence of a structure-directing agent(SDA)on the stability of the as-synthesized material.For the pure zeolite structure,the calculations suggested clustering of Ge ions and the formation of D4Rs populated entirely by Ge heteroatoms,while part of the D4Rs contain only Si as T-atoms.As a general trend,structures with more Ge–O–Ge bridges are more stable.
基金support from the BL14B station of the Shanghai Synchrotron Radiation Facility is sincerely acknowledged.This work was supported by the National Natural Science Foundation of China(no.12175235)supported by Charles University.M.O.acknowledges the Czech Science Foundation for supporting this work through project 20-12099S.
文摘The assembly–disassembly–organisation–reassembly (ADOR) approach extends the synthesis of new zeolites. Understanding the disassembly and organisation mechanism is important to optimise the post-treatment process on germanosilicate zeolites. In situ synchrotron X-ray diffraction technique was applied to study the mechanism of these two steps in HCl vapour,which it is often unfeasible to capture using conventional ex situ characterisation. Three germanosilicate zeolites with different pore systems,i.e. UTL,UOV and IWR,were selected as models to compare the reaction behaviours. Three key steps,including fast hydrolysis of d4r units (ca. 1 min),further disassembly (ca. 3–5 min),and self-organisation after disassembly (ca. 2–3 min),were observed in the HCl acid vapour. An unusual lattice expansion of the intralayer was observed at the very beginning of the hydrolysis process in IWR,while the UTL and UOV showed continuous shrinkage. Owing to the diffusion differences related to the structural features,extra-large-pore UTL zeolite showed faster kinetics than the other two large-pore zeolites,although UTL zeolite has much larger crystals. These findings potentially guide further modification of the treatment parameters in the ADOR process to prepare new zeolites.
基金support provided by the Shandong Energy Institute(SEI S202107)Nature Science Foundation of Shandong Province(ZR2022MB053 and ZR2022QB216).
文摘Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.
