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B. Gil et al. / Catalysis Today 152 (2010) 24–32
conversion is carried out not at the external surfaces of the zeolitic
crystals but at the internal, acidic sites. To which extent given reac-
tion proceeds on the external surface, or in the pore system, or even
in a rim of the crystal is not known in details for most of the zeo-
lite systems studied so far. The only exception is when a very large
difference between the molecule diameter and the entrance to the
channel system exists, which is not a case here. Generally, discus-
sion on this problem was carried out by Gündüz et al. [18] and
Dimitrova et al. [33]. Authors show that if the reaction proceeds on
the internal strong Brønsted sites, the main products of ␣-pinene
conversion are the isomerisation products, and disproportionation
of terpinene and terpinolene. For that reason we can suppose that
the increased accessibility of the internal acidic centres on which
such reactions, leading to HRTP, are proceeding (despite increased
external surface area) is responsible for the better catalytic perfor-
mance of desilicated zeolites.
surface. Desilication process affected pore structure, acidity and
catalytic activity of the zeolites under study.
IR measurements were made in the frames of the grant from the
Ministry of Science and Higher Education, Warsaw, Poland (project
no. N N204 1987 33).
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Textural properties for both ZSM-5 and ZSM-12 zeolites change
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parallel with the changes in the eternal surface and the number
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