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Modifications of MCM-22 zeolite through sequential post-synthesis treatments. Implications on the acidic and catalytic behaviour

2012-11-28Journal article Restricted access
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dc.contributor.authorMachado, V.
dc.contributor.authorRocha, J.
dc.contributor.authorCarvalho, A. P.
dc.contributor.authorMartins, A.
dc.date.accessioned2015-09-08T14:53:14Z
dc.date.available2015-09-08T14:53:14Z
dc.date.issued2012-11-28
dc.description.abstractDesilication and a combination of alkaline followed by acid treatment were applied to MCM-22 zeolite using two different base concentrations. The samples were characterised by powder X-ray diffraction, Al-27 and Si-29 MAS-NMR spectroscopy, SEM, TEM and low temperature N-2 adsorption. The acidity of the samples was study through pyridine adsorption followed by FTIR spectroscopy and by the analyses of the hydroxyl region. The catalytic behaviour, anticipated by the effect of post-synthesis treatments on the acidity and space available inside the two internal pore systems was evaluated by using the model reaction of m-xylene transformation. The generation of mesoporosity was achieved upon alkaline treatment with 0.05 M NaOH solution and practically no additional gain was obtained when the more concentrate solution, 0.1 M, was used. Instead, Al extraction takes place along with Si, as shown by Si-29 and Al-27 MAS-NMR data, followed by Al deposition as extraframework species. Samples submitted to alkaline plus acid treatments present distinct behaviour. When the lowest NaOH solution was used no relevant effect was observed on the textural characteristics. Additionally, when the acid treatment was performed on an already fragilized MCM-22 structure, due to previous desilication with 0.1 M NaOH solution, the extraction of Al from both internal pore systems promotes their interconnection, evolving from a 2-D to a 3-D porous structure. This transformation has a marked effect in the catalytic behaviour, allowing an increase of m-xylene conversion as a consequence of an easier and faster molecular traffic in the 3-D structure. On the other hand, the continuous deposition of extraframework Al species inside the pores leads to a shape selective effect that privileges the formation of the more valuable isomer p-xylene.por
dc.identifier.citationMACHADO, V.; [et al] – Modifications of MCM-22 zeolite through sequential post-synthesis treatments. Implications on the acidic and catalytic behaviour. Applied Catalysis A-General. ISSN: 0926-860X. Vol. 445 (2012), pp. 328-338por
dc.identifier.doi10.1016/j.apcata.2012.09.001
dc.identifier.issn0926-860X
dc.identifier.urihttp://hdl.handle.net/10400.21/5111
dc.language.isoengpor
dc.peerreviewedyespor
dc.publisherElsevier Science BVpor
dc.relationFCT (Portugal) - PEst-OE/QUI/UI0612/2011
dc.relationFCT (Portugal) - PEst-OE/EQB/UI0702/2011
dc.relationFCT - PEst- OE/QUI/UI0612/2011
dc.relationFCT - PEst-OE/EQB/UI0702/2011
dc.subjectMCM-22por
dc.subjectDesilicationpor
dc.subjectAcid Treatmentpor
dc.subjectAciditypor
dc.subjectM-Xylene Transformationpor
dc.subjectH-MCM-22 Zeolite
dc.subjectPore Systems
dc.subjectDealumination
dc.subjectIsomerization
dc.subjectMechanisms
dc.subjectDiffusion
dc.subjectZSM-5
dc.titleModifications of MCM-22 zeolite through sequential post-synthesis treatments. Implications on the acidic and catalytic behaviourpor
dc.typejournal article
dspace.entity.typePublication
oaire.citation.conferencePlaceAmsterdam
oaire.citation.endPage338por
oaire.citation.startPage328por
oaire.citation.titleApplied Catalysis A-Generalpor
oaire.citation.volume445por
rcaap.rightsclosedAccesspor
rcaap.typearticlepor

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