Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Boron or compound containing same
Reexamination Certificate
1996-05-14
2003-10-28
Hendrickson, Stuart L. (Department: 1751)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Boron or compound containing same
C423S628000, C502S208000, C502S211000, C502S248000, C502S263000
Reexamination Certificate
active
06638888
ABSTRACT:
The present invention relates to a mesoporous gel comprising an alumina matrix in which one or more oxides selected from silica, boron oxide, phosphorus oxide, oxides of metals from groups VIII and VIB, may be uniformly dispersed. The present invention also relates to a process for the preparation of this gel and its uses as carrier, as catalyst for acid-catalyzed reactions and as hydrotreating catalyst.
The possibility of synthesizing an amorphous alumino-silicate with a high silica content (molar ratio SiO
2
/Al
2
O
3
=70-100) and with a high surface area, characterized by a limited distribution of mesoporosity (with pore dimensions within the range of 37 Å and 150 Å), is known in literature (M. R. Manton and J. C. Davidtz, Journal of Catalysis (1979), Vol. 60, pages 156-166). These materials have not however found practical applications. More recently, European patent 463.673 and U.S. Pat. Nos. 4.992.608 and 5.049.536 describe the possibility of obtaining amorphous alumino-silicates with a high silica content (SiO
2
/Al
2
O
3
=30-500) with a rather limited distribution of the pore dimensions (average diameter about 10 Å or less, basic absence of pores with a diameter of more than 30 Å) and excellent catalytic properties in acid-catalyzed reactions.
Even more recently, Italian patent application MI 93 A 002696 describes amorphous alumino-silicates with a high silica content characterized by a dimensionally very limited distribution of the micro-mesoporosity, obtained by a process in which the gelification is carried out at the boiling point (or a little higher) of the alcohols produced by the hydrolysis of the reagents, without eliminating the alcohols themselves from the reagent mixture.
Patent application WO 91/11390 discloses the possibility of obtaining a new group of mesoporous alumino-silicates with a high silica content, called M41S, having an average pore diameter of between 20 Å and 100 Å and regularly organized in the material according to a hexagonal (MCM-41) or cubic (MCM-48) structure.
The product obtained is characterized by an X-ray diffraction spectrum from powders (XRD) leading to a hexagonal structure with a bidimensional order or to a structure with cubic symmetry. Analyses carried out via high resolution transmission electron microscopy (HREM) show, in the case of mesoporous silico-aluminates with a hexagonal symmetry (called MCM-41), the presence of monodimensional mesoporosity regularly organized according to a honeycomb hexagonal structure.
In Italian patent application Mi 94 A 01399 it has been found that it is possible to produce micro-mesoporous metal-silicates, with a ratio SiO
2
/Al
2
O
3
of more than 20, characterized by a narrow distribution of the pore dimensions and with a partial order of these. In fact, whereas the alumino-silicates obtained with the process described in the above Italian patent application Mi 93A002696 are completely amorphous, these new materials called ERS-8, are characterized by an X-ray diffraction spectrum (XRD) from powders which has a diffuse reflection at low angles, indicating a short-range order of the mesoporous structure. The existence of a short-range structural order allows this group of materials to be identified as intermediates among analogous orderly materials (M41S) and completely disorderly materials (amorphous alumino-silicates).
The necessity of having materials with a high surface area, a high pore volume with controlled dimensions is not however only limited to silicas.
At present for example there is a particular interest in hydrotreating catalysts which mostly consist of metals belonging to groups VIB and VIII, supported on alumina (A. B. Stiles, “Catalysts manufacture, laboratory and commercial preparation”, Dekker, N.Y., 1983; B. Delmon, “Studies in surface science and catalysis”, vol. 53, 1989, page 1-40). For these hydrotreating catalysts of heavy charges it now seems evident, on the basis of information obtained in this field, that the following characteristics are desirable:
a limited microporous fraction (d<20 Å) to minimize shape-selectivity phenomena;
a pore distribution not centered in the macroporous region (d<500 Å), as the consequent low surface area would be incompatible with a good dispersion of the active phase.
At present these catalysts are prepared for impregnating the carrier with the above metals, in excess or deficiency of the solvent. Gamma-alumina, characterized by a surface area of 200-250 m
2
/g and an enlarged distribution of the pore diameter centered on 100 Å, is the most widely-used carrier at the moment. Its surface area is further reduced by occlusion during the impregnation processes.
The Applicant has now surprisingly found a new group of materials which have improved characteristics compared to the catalysts of the prior art. These materials are mesoporous gels which comprise an alumina matrix in which one or more oxides selected from silica, boron oxide, phosphorus oxide, oxides of metals of groups VIII and VIB, may be uniformly dispersed, characterized by a controlled distribution of the porosity, a high surface area and a high dispersion of the above oxides, when present.
These materials, depending on their chemical composition, can be well used in various applications. For example, they can be used as mesoporous carriers with a controlled porosity for catalysts, as catalysts for acid-catalyzed reactions and as hydrotreating catalysts. In particular for example gels consisting of alumina alone or gels comprising alumina and one or more oxides selected from silica, boron oxide and phosphorus oxide, preferably silica, can be very suitably used as a carrier for catalysts. In the latter case the presence of these oxides makes the materials with this composition also appropriate as catalysts for acid-catalyzed reactions.
The gels of the present invention which comprise alumina, metal oxides of group VIB and/or VIII, and possibly one or more oxides selected from silica, boron oxide and phosphorus oxide, preferably silica, have a high stability as hydrotreating catalyst.
A first object of the present invention therefore relates to a mesoporous gel comprising an alumina matrix in which one or more oxides selected from silica, boron oxide, phosphorus oxide, the oxide of a metal of group VIII and/or VIB having general formula MO
x
, may be uniformly dispersed, with the following molar ratios between said oxides and the alumina:
SiO
2
/Al
2
O
3
=0-3.0
B
2
O
3
/Al
2
O
3
=0-4.0
P
2
O
5
/Al
2
O
3
=0-0.2
MO
x
/Al
2
O
3
=0-0.2
with a surface area of between 260 and 700 m
2
/g, with a pore volume of between 0.2 and 1.0 cm
3
/g and with an average pore diameter of between 20 and 70 Å.
The surface area is preferably between 400 and 700 m
2
/g and the pore diameter between 20 and 60 Å. According to a preferred aspect of the present invention, the gel consists of alumina alone or comprises alumina and one or more oxides selected from silica, boron oxide and/or phosphorus oxide, preferably silica. According to another preferred aspect of the present invention, the gel comprises alumina, oxides of metals of group VIB and/or VIII, and possibly one or more oxides selected from silica, boron oxide and/or phosphorus oxide, preferably silica. The metal of group VIB is preferably Mo, that of group VIII is preferably Ni.
The X-ray diffraction spectrum from powders (XRD) of these mesoporous gels (called TEG), recorded by means of a Philips vertical diffractometer, equipped with a proportional pulse counter, divergent and receiving sleds of 1/6° and with CuK&agr; radiation (&lgr;=1.54178 Å), may have an enlarged diffraction line, or however a diffuse scattering, at angular values of not more than 2&thgr;=5°, which can be interpreted with the presence of a short-range order of the mesoporous structure, with a limited structural correlation basically only at the first neighbours, whereas weak and enlarged reflections can always be observed in the high angular r
Bellussi Giuseppe
Calemma Vicenzo
Millini Roberto
Peratello Stefano
Eniricerche S.p.A.
Hendrickson Stuart L.
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