Abstract
The layered MFI zeolite allows a straightforward hierarchization of the pore system which accelerates mass transfer and increases its lifetime as a catalyst. Here, we present a theoretical study of the structural features of the pure-silica and aluminium-substituted MFI nanosheets. We have analysed the effects of aluminium substitution on the vibrational properties of silanols as well as the features of protons as counter-ions. The formation of the two-dimensional system did not lead to appreciable distortions within the framework. Moreover, the effects on the structure due to the aluminium dopants were the same in both the bulk and the slab. The principal differences were related to the silanol groups that form hydrogen-bonds with neighbouring aluminium-substituted silanols, whereas intra-framework hydrogen-bonds increase the stability of aluminium-substituted silanols toward dehydration. Thus, we have complemented previous experimental and theoretical studies, showing the lamellar MFI zeolite to be a very stable material of high crystallinity regardless of its very thin structure.
Highlights
Zeolites are microporous aluminosilicate crystals widely recognised for their extraordinary characteristics as solid acids [1,2,3], size-selective molecular sieves [4,5], and ion-exchange matrices [6,7]
Bulk structure The pure-silica MFI zeolite has a monoclinic structure (P21/n) which undergoes a phase transition toward an orthorhombic symmetry (Pnma) at temperatures above the range 317–325 K; these temperatures decrease with Al content [62]
The starting atomic positions and cell parameters were extracted from the structural database of the International Zeolite Association (IZA) [63] and further optimised whilst keeping the orthorhombic symmetry; Fig. 2 shows the MFI unit cell
Summary
Zeolites are microporous aluminosilicate crystals widely recognised for their extraordinary characteristics as solid acids [1,2,3], size-selective molecular sieves [4,5], and ion-exchange matrices [6,7]. The practical applications of these materials are numerous, ranging from water treatment [8] and membranes for gas permeation [9] to fuel and solar cell materials [10,11]. Zeolites find their largest relevance as acid–base catalysts, accounting for more than 40% of the catalysed industrial processes [12], with the environmental and petrochemical sectors among the main users [13].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
