Process for the preparation of a catalyst or catalyst precursor

Details Process for the preparation of a catalyst or catalyst precursor Process for the preparation of a catalyst or catalyst precursor

1996-11-26

2003-05-13

Bell, Mark L. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Zeolite or clay, including gallium analogs

And additional al or si containing component

C502S074000, C502S201000, C502S217000, C502S218000, C502S221000, C502S223000, C502S224000, C502S229000, C502S230000, C502S325000, C502S326000, C502S327000, C502S344000, C502S347000, C502S349000, C502S350000, C502S353000, C502S354000

Reexamination Certificate

active

06562749

ABSTRACT:

The present invention relates to a process for the preparation of ceramic foams supporting one or more catalytically active components and/or precursors thereof, and catalytic applications thereof, in particular the preparation of ceramic foams supporting catalytically active components, or precursors thereof for use in gas treating and as catalysts in catalytic conversion reactions, particularly in the preparation of carbon monoxide and hydrogen by the partial oxidation of a hydrocarbon feed, in nitric oxides reduction processes, in ethylene oxidation, and the like.
Ceramic foams are known for various applications, in particular more recently as supports for catalytically active materials fulfilling several requirements simultaneously, as described in “Preparation and properties of ceramic foam catalyst supports” by M V Twigg and J T Richardson published in the “Scientific Bases for the preparation of heterogeneous catalysts” 6th International Symposium Sep. 5-8, 1994 Louvain-la-Neuve, Belgium. Open pore ceramic foams and the more traditional extrudates may be made from materials with high temperature resistance, and promote surface-catalyzed reaction by means of tortuous flow patterns, in foams by virtue of connecting adjacent pores or “cells” providing non-linear channels, and in extrudate beds by virtue of random particle packing. Ceramic foams enable the passage of gases at high space velocities and acceptable pressure drop, are readily shaped and provide good conductivity.
EP 0 260 826 discloses ceramic foam supports suited for use in steam reforming of methane, comprising a network of irregular passages extending therethrough, comprising supported catalytically active material and an inorganic oxide stabilizer to prevent sintering of the active material. The stabilizer and the active material are introduced by impregnation of the foam by means of immersion of the foam in an aqueous solution of a salt of the stabilizer and the active component, draining to remove excess solution and firing at 450° C. This process is repeated to build up sufficient impregnant layer on the foam. The foams described are to be used at relatively low temperatures, of the order of 760° C.
FR 2 590 887 discloses zirconium oxides having stable surface area at elevated temperatures, the oxide comprising as additive an oxide of silicon, the rare earths, yttrium, cerium and/or aluminum. The additive may be introduced by various means including coprecipitation, mixing of salt with sol hydrate and impregnation of the zirconium oxide with a salt precursor of the additive. Impregnation is preferably performed “dry” whereby the total volume of the impregnating solution is approximately equal to the total pore volume of the (oxide) support. It is taught by means of example to impregnate extruded support granules with the aqueous impregnating solution, to dry at 160° C. for 16 hours and calcine at 400° C. There is no reference to supports in the form of foam structures, which comprise pores of one or more orders of magnitude greater than the mesoporous, and for which a different mechanism of supporting of the additive is involved.
The provision of ceramic foams having significant loadings of inorganic oxides remains a problem, even more so in applications employing extreme conditions typical of some processes, for which improved surface area retention is needed compared with known foam supports. It has now surprisingly been found that the limitation on inorganic oxide loading and on surface area lies not with the concept of providing an additional layer, as is known from the referred publications, but in the manner of its provision, whereby full advantage is not obtained. European Patent Application No. 94 203453.9 is directed to the surprising finding that in a particular process for the preparation of ceramic foams supporting inorganic oxide(s) a significant increase in inorganic oxide loading and in surface area can be attained, which increase is still favorable at temperatures at or above 800° C. The process disclosed in European Patent Application No. 94 203453.9 comprises impregnating the foam with an impregnating phase comprising the inorganic oxide(s) in an impregnating phase and drying wherein the impregnating phase has a viscosity greater than 1 cps, i.e. greater than water, and drying is performed without substantial prior draining of impregnating phase from the ceramic foam.
Surprisingly, it has now been found that the process described in European Patent Application No. 94 203453.9 for preparing ceramic foams supporting one or more inorganic oxides may also be applied in the preparation of ceramic foams supporting one or more catalytically active components which are wholly or partly active in forms other than an inorganic oxide.
Accordingly, the present invention provides a process for the preparation of a ceramic foam supporting one or more catalytically active components or precursors thereof, which component is active in a form other than an inorganic oxide, the process comprising impregnation of the foam with an impregnating phase comprising the catalytically active component or a precursor thereof and drying, wherein the impregnating phase has a viscosity greater than 1 cps at 20° C., wherein drying is performed without substantial prior draining of impregnating phase from the ceramic foam, and wherein the catalytically active component or precursor thereof is present throughout the process in one or more forms other than the inorganic oxide thereof.
It is a particular feature of the invention that the use of an impregnating phase more viscous than water allows significant retention of the impregnating phase in the foam pores prior to and during drying. This is a problem not encountered in the impregnation of other materials having pore sizes orders of magnitude less than typically found in ceramic foams.
Suitably the impregnating phase has a viscosity of greater than 1 cps, preferably 1 cps at 20° C., preferably of from 5 to 80 cps, more preferably from 7 to 50 cps. A suitable viscosity may be selected according to the properties of the ceramic foam, in particular the pore size thereof, whereby a smaller pore size would require a less viscous impregnating phase. The impregnation is suitably carried out at a temperature between 0 and 90° C., especially 10 to 50° C., more especially at 20° C.
Suitably the drying is performed without substantial prior draining of impregnating phase from the ceramic foam. Reference herein to “substantial prior draining” is to draining practices common in the art of washcoating and impregnation, and which may involve subjecting the foam to vacuum, centrifuging or blowing air through the foam for example. It is intended that substantially none of the impregnating phase introduced into the foam pores should be deliberately removed but rather should be allowed to be-retained, aided by the viscosity thereof. Suitably, therefore, any drainage of impregnating phase from the pores prior to drying is less than 60%, preferably less than 50%, more preferably from 0% to 40%, still more preferably 0% to 20% of that introduced. Preferably the pores of the foam are substantially filled with impregnating phase prior to drying. Preferably the foam pores are filled by at least 60% with impregnating phase, more preferably by at least 85%. Suitably the ceramic foam is immersed slowly or incrementally into the impregnating phase whereby formation of air pockets is prevented, this enabling filling of the pores. The rate of immersion or extent of initial immersion may be determined appropriately according to the pore size (ppi) of the foam, and the viscosity of the impregnating phase. The impregnation may be carried out at or below atmospheric pressure. With use of foams of small pore diameters it may be particularly advantageous to impregnate at reduced pressure of between 0.5 and 1 atmosphere. The pore volume may be calculated for example on the basis of the density, weight and dimensions of the foam, whereby the amount of impregnating phase required may be determined.
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