Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-03-13
2003-12-02
Dunn, Tom (Department: 1725)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S344000, C502S348000, C502S300000, C502S325000, C502S302000, C502S216000, C502S208000, C502S202000, C502S224000
Reexamination Certificate
active
06656874
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the preparation of catalysts with improved catalytic properties, particularly improved initial activity, initial selectivity and/or activity and/or selectivity performance over time.
BACKGROUND OF THE INVENTION
Numerous methods are known for the deposition of catalytically reactive metals on a carrier in order to manufacture catalysts. For example, U.S. Pat. No. 3,972,829, issued Aug. 3, 1976, discloses a method for distributing catalytically reactive metallic components on carriers using an impregnating solution of catalyst precursor compound and an organic thioacid or a mercaptocarboxylic acid. U.S. Pat. No. 4,005,049, issued Jan. 25, 1977, teaches the preparation of a silver/transition metal catalyst useful in oxidation reactions. International publication WO 96/23585, published Aug. 8, 1996, teaches that boosting the amount of alkali metal promoter in a silver solution results in improved properties.
Literature also warns against certain methods. U.S. Pat. No. 4,908,343, issued Mar. 13, 1990, warns against having a silver solution which has a strong acidity or basicity as the strongly acid or base solution would leach any leachable impurities from the carrier, becoming part of the silver catalyst in amounts which adversely affects the performance of the catalyst in an oxidation reaction.
It has surprisingly been found that the metal deposition and catalytic properties of a catalyst may be greatly improved by lowering the hydrogen ion activity of the impregnation solution.
SUMMARY OF THE INVENTION
According to one embodiment of the invention, there is provided a process for depositing one or more catalytically reactive metals on a carrier, said process comprising:
selecting a carrier; and
depositing a catalytically effective amount of one or more catalytically reactive metals on said carrier, said deposition effected by an impregnating solution wherein a hydrogen ion activity of said impregnation solution is lowered.
There is further provided a process for preparing a catalyst suitable for the vapor phase production of epoxides, said process comprising:
selecting a carrier; and
depositing a catalytically effective amount of silver on the carrier, wherein said deposition is effected by an impregnation solution wherein a hydrogen ion activity of said impregnation solution is lowered.
There is still further provided catalysts made by the processes of the embodiments herein described.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been found that lowering the hydrogen ion activity of the impregnation solution used to deposit catalytically reactive metals on a carrier provides catalysts which have improved catalytic properties, such as activity, selectivity and the activity and/or selectivity performance over time. The process is believed to work to improve the properties of most catalysts wherein metal is deposited on a carrier by use of an impregnation solution.
Catalysts are commonly made by depositing a catalytically effective amount of one or more catalytically reactive metals on a carrier to make a catalyst precursor. Typically, the carrier is impregnated with metal or compound(s), complex(es) and/or salt(s) sufficient to deposit or impregnate the catalytically reactive material. As used herein, “catalytically effective amount” means an amount of metal that provides a measurable catalytic effect.
The impregnated carrier, or catalyst precursor, is dried in the presence of an atmosphere which also reduces the catalytic metal. Drying methods known in the art include steam drying, drying in an atmosphere with a controlled oxygen concentration, drying in reducing atmospheres, air drying, and staged drying using a suitable ramped or staged temperature curve.
In the process of the invention, improvement in the catalytic properties are seen when the metal deposition is effected by use of an impregnation solution whose hydrogen ion activity has been lowered. “Hydrogen ion activity” as used herein is the hydrogen ion activity as measured by the potential of a hydrogen ion selective electrode. As used herein, a solution with “lowered” hydrogen ion activity refers to a solution whose hydrogen activity has been altered by the addition of a base, such that the hydrogen ion activity of the altered solution is lowered compare to the hydrogen ion activity of the same solution in an unaltered state. The base selected to alter the solution may be chosen from any base or compound with a pKb lower an the original impregnation solution. It is particularly desirable to choose a base which does not alter the formulation of the impregnation solution; i.e., which does not alter the desired metals concentration in the impregnation solution and deposited on the carrier. Organic bases will not alter the impregnation solution metals concentrations, examples of which are tetraalkylammonium hydroxides and 1,8-bis-(dimethylamino)-naphthalen. If changing the metals concentration of the impregnation solution is not a concern, metal hydroxides may be used.
When the impregnation solution is at least partially aqueous, an indication of the change in the hydrogen activity may be measured with a pH meter, with the understanding that the measurement obtained is not pH by a true, aqueous definition. ‘“Measured pH’” as used herein shall mean such a non-aqueous system pH measurement using a standard pH probe. Even small changes in the “measured pH” from the initial impregnation solution to that with added base are effective and improvements in catalytic properties continue as the “measured pH” change increases with base addition. High base additions do not seem to adversely affect catalyst performance; however, high additions of hydroxides have been seen to cause sludging of the impregnation solution, creating manufacturing difficulties. When the base addition is too low, the hydrogen ion activity will not be affected.
As described, the process is effective in improving at least one of the catalytic properties of catalyst wherein an impregnating solution is used to deposit or impregnate a catalytically reactive metal upon a carrier. “Improvement in catalytic properties” as used herein means the properties of the catalyst are improved as compared to a catalyst made from the same impregnation solution which has not had the hydrogen ion activity lowered. Catalytic properties include catalyst activity, selectivity, activity and/or selectivity performance over time, operability (resistance to runaway), conversion and work rate.
Further improvement in properties may be achieved by lowering the concentration of ionizable species present on the surface of the carrier prior to the deposition step. Carriers are commonly inorganic materials such as refractory inorganic materials, for example alumina-, silica-, or titania-based compounds, or combinations thereof, such as alumina-silica carriers. Carriers may also be made from carbon-based materials such as, for example, charcoal, activated carbon, or fullerenes. Ionizable species typically present on the inorganic type carriers include sodium, potassium, aluminates, soluble silicate, calcium, magnesium, aluminosilicate, cesium, lithium, and combinations thereof. Lowering the undesirable ionizable species concentration may be accomplished by any means (i) which is effective in rendering the ionizable species ionic and removing that species, or (ii) which renders the ionizable species insoluble, or (iii) which renders the ionizable species immobile; however, use of aggressive medias, such as acids or bases, is discouraged as these media tend to dissolve the carrier, extract too much material from the bulk, and generate acidic or basic sites in the pores. Effective means of lowering concentration include washing the carrier; ion exchange; volatilizing, precipitating, or sequestering the impurities; causing a reaction to make the ionizable species on the surface insoluble; and combinations thereof. Examples of wash and ion exchange solutions include aqueous and/or organic solvent-based solutions which may also contain
Dunn Tom
Ildebrando Christina
Shell Oil Company
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