Influência do método de preparação de catalisadores bifuncionais, Pt-Ni/HUSY, na isomerização do n-hexano
Abstract
Gasoline containing high amount of linear chain compounds have low
octane number. However, this number can be increased when linear alkanes are
subjected to isomerization, able to change linear chain compounds to ramificationcontaining
alkanes. Such reactions require the use of bifunctional catalysts,
containing acid and metal sites, which show high efficiency in the isomerization of
linear chain paraffins. Most work in the literature involves the use of bifunctional
catalysts with constant mass of metal and with high activation time of the catalyst, the
so-called "Traditional Activation ".
Therefore, the goal of this work is to study the influence of the method
of preparation of bifunctional metallic catalysts through two methods of activation, in
order to obtain a catalyst with well dispersed metallic particles. These catalysts had
been reduced through the "Fast Activation" that consists in using high speed of
heating in the process of reduction of cations.
In this work, bifunctional and bimetallic catalysts supported in the FAU
zeolitic structure containing constant molar content of Pt-Ni were prepared. The
addition of these metals in the solid was accomplished through competitive ionic
exchange, using solutions of these metals cations. Three series of metallic catalyst
had been prepared, contaning 130, 230 and 280 µmol M/gcat. They have been
characterized by temperature programmed of reduction (TPR), hydrogen
chemisorption, transmission electronic microscopy (TEM), CO infrared spectroscopy
and submitted to catalytic evaluation in the isomerization of n-hexane.
From analysis of the results, it is possible to conclude that the fast
activation process is more advantageous than the traditional one, then it avoids the
migration of cations to small cavities of the zeolitic structure, minimizes the process
of sintering of metallic particles and requires a much less time of activation.
The insertion of a second metal (nickel) in the platinum bifunctional
catalyst leads to getting solids with different properties from those that contain only
platinum. Thus, it becomes possible to obtain bimetallic catalysts that are more active
than the ones containing only one metal, even if it is noble metal.