3 research outputs found
The Si-Ge substitutional series in the chiral STW Zeolite Structure Type
The whole compositional range (Ge = Ge/(Ge+Si)= 0 to 1) of zeolite STW
has been synthesized and studied by a comprehensive combined
experimental--theoretical approach. The yield of zeolite goes through a maximum
and then drops at the GeO side of the series, following the inverse of the
calculated free energy curve. The unit cell generally expands, roughly
linearly, as the Ge increases, but a notable resilience to expansion is
observed at the high silica side. This can be attributed to the more rigid
character of SiO and the ability of Ge units to deform. Density functional
theory calculations provide a new assignment of the previously controversial
F MAS NMR resonances for occluded fluoride, which is based not only in
the number of Ge atoms in the double-4-ring units but also on the way they are
associated (namely, no Ge, isolated Ge, Ge pairs or closed Ge clusters). While
we found an overall good agreement between the experimental and theoretical
trends in preferential occupation by Ge of different crystallographic sites,
the theoretical models show more sharp and abrupt tendencies, likely due both
to limitations of the approach and to kinetic factors that allow metastable
configurations to actually exist.Comment: 26 page
A new procedure for a zeolite synthesis from natural clays
This work proposes the synthesis of zeolite A by IZA standard proceedures starting from a natural clay. The clay was used in its natural form and after calcination at 900oC. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and porosity analysis by nitrogen adsorption. Results showed low surface area for Na-A zeolite in sodium form, but a higher one in CaA based on the nitrogen accessibility. The presence of cubic crystals for the A phase was observed in the SEM micrographies. The new procedure starting from natural clay favors the formation of sodalite while that using the calcinated clay gives A
A new procedure for a zeolite synthesis from natural clays
This work proposes the synthesis of zeolite A by IZA standard proceedures starting from a natural clay. The clay was used in its natural form and after calcination at 900oC. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and porosity analysis by nitrogen adsorption. Results showed low surface area for Na-A zeolite in sodium form, but a higher one in CaA based on the nitrogen accessibility. The presence of cubic crystals for the A phase was observed in the SEM micrographies. The new procedure starting from natural clay favors the formation of sodalite while that using the calcinated clay gives A