Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1995-07-21
1998-12-01
Lewis, Michael
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
502 74, 502 77, B01J 800
Patent
active
058433929
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst system of the structured type, to a reactor provided with a structured reactor packing and to a method for the selective reduction of nitrogen oxides, utilizing a compound comprising a NH group in the presence of such catalyst system.
2. Description of the Prior Art
Dutch Patent Application 9000454 discloses a method of producing a reactor packing, in which solids particles are connected with each other by connecting means, and in which the individual solids particles locally surround the connecting means completely. A reactor packing of this type possesses a low pressure drop, a relatively small volume and a relatively large active surface. The external surface of all solids particles comes into direct contact with a fluid to be treated.
The solids particles can be attached to the connecting means in many ways. For instance, solids beads can be strung on a threadlike connecting means. Preferably, however, the solids particles are applied to the connecting means by extrusion or precipitation.
The solids particles can be catalytically active themselves, but it is also possible to use support material particles which, after being interconnected, are provided with catalytically active material. Incidentally, none of these possible methods is specifically elucidated in the patent application referred to.
SUMMARY OF THE INVENTION
It has now been found that when molecular sieve crystals are grown in particular orientations on a suitable structured support, catalyst systems with very favorable properties are obtained. More particularly, according to the invention, catalyst systems are obtained which are very suitable for carrying out selective chemical reactions, for instance the reduction of nitrogen oxides.
The catalyst system of the structured type is characterized, according to the invention, in that a structured support is covered with a layer of molecular sieve crystals and/or modifications thereof, which posses substantially the same orientation relative to the support surface.
The catalyst system according to the invention is covered with substantially one layer of molecular sieve crystals and/or modifications thereof which are directly chemically bound to the structured support. It is essential to the invention that the sieve crystals be grown directly on the support surface. Accordingly, the sieve crystals are not fixedly bonded or glued to the support surface by means of other joints.
The layer of sieve crystals is not continuous. The point is that it is necessary that the main faces of these molecular sieve crystals be accessible to substances which are to be converted under the influence of the catalyst system according to the invention.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawing wherein:
FIG. 1. is an electron microscope photograph of a coated gauze prepared in accordance with the invention;
FIG. 2a is an electron microscope photograph of gauze coated with ZSM-5 crystals in accordance with the procedure described in example 4; and
FIG. 2b is another electron microscope photograph of gauze coated with ZSM-5 crystals in accordance with the procedure described in example 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although preferably all molecular sieve crystals are chemically bound to the surface, it is also possible that one or more layers of sieve crystals are deposited on the chemically bound layer of sieve crystals. In that case, however, it is necessary that sufficient open pore space is available in the direction of the support, so that the compounds to be converted can come into contact with the active sieve crystal surfaces to a sufficient degree.
By the expression "substantially the same orientation" is meant that anisotropically formed sieve molecule crystals are, for an important part, arranged in a particular direction relative to the support surface. Sin
REFERENCES:
patent: 5266542 (1993-11-01), Hashimoto et al
patent: 5310714 (1994-05-01), Grasseli et al.
Galis Hans Peter Alexander
Gerritsen Albert Willem
Jansen Jacobus Cornelis
Legein Colette Henriette
Van Bekkum Henk
Dunn Jr. Thomas G.
Fink Edward M.
Lewis Michael
Michaelson Peter L.
Technische Universiteit Delft
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