Catalysis
Today, Available online 10 June 2013, In Press, Corrected Proof
“Ideal”
bifunctional catalysis over Pt-acid zeolites
Michel Guisnet (a,b)
a Technical University of Lisbon, Portugal
b University of Poitiers, France
Abstract
The conditions of “ideal” bifunctional catalysis
were specified on the example of two reactions involved in major refining and
petrochemical processes: the hydroisomerisation of n-alkanes (n-Cx); and of
ethylbenzene (EB) over PtHzeolites. In both cases, researchers observe that the
balance between the hydrogenating and acid functions (CPt/CH+)
positively affected the activity, the stability and the selectivity of the
bifunctional catalysts.
They achieved optimal
catalytic characteristics for CPt/CH+ values which were
high enough that the acid catalysed steps were rate-limiting, as long as an
additional condition is satisfied. That condition is that there is a low number
of acid sites between two Pt sites so that only one skeletal transformation of
n-Cx= intermediates can occur or distance between zeolite protonic
sites sufficient for limiting the demanding reaction of ethylbenzene
disproportionation. The analysis can be generalized to other reactions, which
can facilitate the design of the “ideal” bifunctional catalysts, opening the route to
cleaner commercial processes.
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