Crystallographic sites of Brönsted acids(Si-OH-Al)in zeolites,which are closely associated with the Al sites,play a significant and unique role in the catalytic application,especially when they are distributed in...Crystallographic sites of Brönsted acids(Si-OH-Al)in zeolites,which are closely associated with the Al sites,play a significant and unique role in the catalytic application,especially when they are distributed in open channel systems or confined in cavities with small pore openings.In this article,we unraveled constrained Al crystallographic sites in FER-type zeolites containing the distinct local environments(10-ring channels and ferrierite cavities)by Rietveld refinement against the powder X-ray diffraction data.Final refinement demonstrates that regardless of the types of structure-directing agents and synthetic medium utilized,T1 and/or T3 are Al-rich positions,which are further confirmed by theoretical calculations.This new finding of constrained Al sites in the FER-type zeolite can well explain its limited catalytic activity in the DME carbonylation reaction.展开更多
Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materi...Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.展开更多
文摘Crystallographic sites of Brönsted acids(Si-OH-Al)in zeolites,which are closely associated with the Al sites,play a significant and unique role in the catalytic application,especially when they are distributed in open channel systems or confined in cavities with small pore openings.In this article,we unraveled constrained Al crystallographic sites in FER-type zeolites containing the distinct local environments(10-ring channels and ferrierite cavities)by Rietveld refinement against the powder X-ray diffraction data.Final refinement demonstrates that regardless of the types of structure-directing agents and synthetic medium utilized,T1 and/or T3 are Al-rich positions,which are further confirmed by theoretical calculations.This new finding of constrained Al sites in the FER-type zeolite can well explain its limited catalytic activity in the DME carbonylation reaction.
文摘Cellulose nanofiber (CNF) and CNF micro-fibrils (CNF-MFs) are computationally modeled by molecular dynamics with united atom (UA) methodology of polymers. Structural stability and mechanical properties of these materials are focused on. Diffusion coefficient decreases with increase of the number of shells in CNF-MF. The structure of CNF-MFs with crystalline alignment is totally stabilized with twist which is an accumulation of torsion angles at Glycosidic bonds between monomers inside CNFs. Unique fiber drawing simulation, where a single CNF fiber is taken out of CNF-MF structure, is first conducted. The CNF fiber which is drawn out stretches up to relatively large strain, with linear increase of tensile stress. The computation results show that, the larger the number of shell structure of CNF-MF is, the larger the stretch and the stress of drawn fibers are.
