JPS5823138B2 - supported catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst and its structure consisting of a substrate, an intermediate oxide layer and a catalyst layer that can be used in a wide range of catalytic reactions.

The above catalytic reactions include, for example, the catalytic oxidation of ammonia in the production of nitric acid, the catalytic oxidation of organic compounds (such as methane, ethane, and propylene) for heating purposes, the catalytic oxidation of carbon-containing compounds such as carbon monoxide, and the reduction of fuels. Examples include catalytic reduction of nitrogen oxides and catalytic reduction of □ for automobile exhaust control units.

The catalyst of the present invention can also be used in a NOX removal device suitable for attachment to a nitric acid production plant.

Many nitric acid plants employ a high-pressure method in which the oxidation of ammonia is carried out in the presence of a solid rhodium-platinum wire woven into a wire mesh.

It would also be of great benefit to recover energy from the tail gas plant that could be used to power the system.

The system can recover enough energy to maintain its own processes, and can also provide surplus power.

This is usually carried out as a catalytic process in which nitrogen oxides are reacted with a gaseous reducing fuel.

It is important that the catalyst used is highly active, exhibits minimal resistance to gas flow and catalyzes the reaction at low initial reaction or ignition temperatures.

However, the catalyst itself is at a fairly high temperature (e.g. 750
-800°C) stability.

It is an object of the present invention to provide improved catalysts and catalyst structures for said process, replacing those currently in use.

Air pollution control through catalytic combustion imposes many restrictions on the type of catalyst used.

Furthermore, it is also required that the catalyst be active at low temperatures and stable under both oxidizing and reducing conditions.

In addition, when the catalyst is packed in a reactor, the pressure drop in the catalyst bed must be extremely small, and it must have excellent wear resistance, heat resistance,
It must be resistant to mechanical impact and soil damage from dust particles.

According to the present invention, (a) Excluding impurities, chromium is 3 to 40% by weight, aluminum is 1 to 10% by weight, cobalt is O to 5.0% by weight,
a metal substrate made of an extended-shaped heat-resistant and oxidation-resistant alloy consisting of nickel O~72% by weight, carbon O~0.5% by weight and substantially the remainder iron; (b) the surface of the extended metal substrate; (c) at least an oxide of alumina, titania and zirconia deposited on the aluminum oxide film and fixed onto the substrate through the film; and (d) selected from the group of metals ruthenium, rhodium, palladium, iridium, platinum, silver and gold and alloys containing at least one of these metals retained by said coating. A supported catalyst is provided comprising at least one catalyst layer.

Preferably 10% by weight or less, and more preferably 3
or silicon, manganese, zirconium, copper, tungsten, vanadium, molybdenum, cerium, with a weight ratio of 5 or less,
Iron alloys comprising - or more of the additional elements niobium, tantalum and titanium are used.

Base metals that can be included in the catalyst layer include aluminum, magnesium, chromium, molybdenum, tungsten,
It can be manganese, iron, rhenium, cobalt, titanium, vanadium, copper, zinc, cadmium, iridium, thorium, bismuth, tin, lead, antimony, lanthanides or actinides.

The metal substrate constituting the catalyst of the present invention, apart from impurities, includes chromium of 3 to 40% by weight, aluminum of 1 to 10% by weight, cobalt of 5.0% by weight of tracel, nickel of 2% by weight of tracel, and 0% of tracel by weight. Extended configurations made of heat and oxidation resistant iron alloys containing .5% carbon are preferred.

When an alloy is used as the catalyst layer, it is preferable to use an alloy containing at least 10 parts by weight of the above-mentioned metals.

Furthermore, the inventors have found that under different reaction environments, for example in automotive exhaust gas purification, a metal substrate allows the catalyst to reach operating temperature faster, and therefore compared to conventional catalysts with, for example, ceramic substrates. It was found to be extremely efficient.

As used herein, the term "extended metal substrate" refers to a metal substrate that has been mechanically deformed to provide a greatly increased surface area compared to a flat, undeformed metal.

This increased surface area is typically first made into a corrugated shape and
or by folding and rolling up this corrugated foil together with a flat foil into a tube with a helical cross section.

In a preferred embodiment of the invention, the metal substrates used in the construction of the catalysts of the invention are first creased, corrugated, folded, scored, and/or perforated to provide a greatly increased surface area.

The surface areas obtained in this way are usually much larger than those obtained with the same volume of ceramic honeycomb structures or special catalyst supports.

An example of a metal carrier made in accordance with the present invention, consisting of a roll of non-corrugated sheets of heat-resistant alloy with corrugated sheets of heat-resistant alloy inserted therein, is shown in FIG.

Alternatively, two corrugated plates may be used with the liquid portions of each plate being parallel to each other or at an angle.

A coated substrate is then provided with a firmly adhered oxide coating.

This oxide coating is a porous absorber with a high surface area and acts as a support for the second catalytically active layer containing one or more platinum group metals as defined herein.

Preferably, the heat resistant alloys comprising an extended metal substrate have a combined nickel and chromium content of 20 wt%.

Therefore, typical alloys that can be used as extended metal substrates are high nickel and chromium stainless steels, such as "Inconel® J600
and products such as Inconel 601.

We recommend preparing the first firmly adherent oxide layer in essentially a two-step process.

The first step is to thermally oxidize the metal substrate to provide a first thin oxide layer that acts as a key.

It is recommended that this thermal oxidation be carried out by holding the shaped metal substrate in air or in moist decomposed ammonia vapor at 1000 DEG -1200 DEG C. for 1 hour.

Higher temperatures are required for highly oxidation resistant alloys of the type such as Kanthal, and a moist hydrogen atmosphere is preferred for alloys with high nickel content.

The deposited oxygen-containing or oxide coating can be produced by any of a number of known methods, including chemical treatment.

The coating must be thick enough to provide adequate absorption capacity to retain the catalytically active alloy of platinum group metals or more.

Preferably, the thickness of this coating is between 0.5004 and 0.001 inches.

This oxide coating can be prepared by treating the aluminum-containing surface with an alkaline carbonate solution, usually a sodium chromate carbonate solution.

Coatings can be produced by anodizing the metal surface, where the metal becomes an anode in an electrolytic solution.

When anodizing surfaces containing aluminum, a 15% sulfuric acid solution is usually used as the electrolyte, but other acid electrolytes such as chromic acid, oxalic acid, phosphoric acid and sometimes boric acid can also be used. You can also do it.

The oxide coatings involved in this invention are intentionally deposited and do not include the relatively thin native oxides that occur on metal surfaces exposed to air.

A preferred deposited oxide coating on an extended metal substrate is alumina.

The method for attaching water-use alumina is described in US Patent No. 24.
It is proposed in No. 06420.

Common aluminum compounds such as alkali metal aluminates and aluminum salts can be used as starting materials.

Either acidic or basic precipitants can be used depending on the characteristics of the starting materials.

Suitable acidic precipitants include ammonium chloride, ammonium sulfate, ammonium nitrate, hydrochloric acid, nitric acid, and the like; suitable basic precipitants include ammonium hydroxide, sodium hydroxide, hexamethylenetetramine, and the like.

One method is to precipitate hydrated alumina directly from an alkali metal aluminate solution containing excess aluminum and alkali metal hydroxide onto the extended metal substrate that forms part of this invention.

If the aluminate solution is kept at a temperature of 60 DEG to 85 DEG C., a film or coating of trihydrate alpha-alumina (gibbsite) is deposited.

Subsequent heating to 150-180°C converts the trihydrate to monohydrate, and further heating to 540°C converts the monohydrate to γ-alumina.

During this time there is no loss of the very high surface area coating obtained according to the invention.

This high surface area is a result of the formation of hexagonal crystal aggregates of approximately 8X8X20 microns in size, in which micropores with a diameter of 40 mm are present, but are not important for the catalytic activity in the catalyst structure. It doesn't seem to play any role.

This high surface area is evidenced in Example 12 by resistance to phosphorus and lead deposition after catalytic metal deposition.

The heat-resistant antioxidant alloy comprising the extended metal substrate of the present invention comprises an alloy of iron, chromium and aluminum, in which the elements cobalt, nickel and carbon are also preferably present.

The range of each element present in the alloy, excluding trace elements and impurities, is as follows.

The preferred ranges of the above elements are as follows.

Typical amounts of trace elements that can be present in the alloy to improve strength, antioxidant properties and heat resistance are as follows.

Specific heat resistant and oxidation resistant alloys suitable for use in practicing the present invention are illustrated in the Examples below.

Example 1 - Kanthal D®: Product supplied by Kanthal, Sweden Example 2 Megapyr® Telcon Metals Ltd.
More commercially available.

Example 3 Stainless steel 316 (one of the austenitic standard composition stainless steels) - Example 4 An alloy with the following composition is commercially available from Kanthal of Sweden.

In the above composition, Ta can be partially replaced with Ti, and Ce can be partially replaced with Ca.

Optionally, the following constituents may be present to improve the mechanical strength and antioxidant properties of the alloy.

(Note that P and S may exist as impurities.

) Examples of this range are:

Example 5 Immacnlate 5 (registered trademark): Firth Vick Co., Ltd.
ersLid, ) commercial product example 6 Inconel 600 (registered trademark) Henry Wiggin Co. (
Example of a commercial product from Henry Wiggin Ltd. Inconley 800 (registered trademark) = 9 Example of a commercial product from Henry Wiggin Ltd. 8 Brightray S (registered trademark) Commercial product from Henry Wiggin Ltd. w/w Example 9 Stainless Steel Ita 309 Example 10 Stainless Steel A, 310 (7') commercially available from Teish Steel Corporation) Example 11 Stainless Steel 4321 Example 12 Armco 18 S R (commercially available from Armco Corporation) ) Generally speaking, in the Fe-Cr-A I system, it is sufficient to have a small amount of ferritic steel with a Cr content of 12-12.5 wt% or less, and an aluminum content of 1-6 wt% of the alloy. If it works satisfactorily outside the range, it's a no-no.

The metal substrate according to the invention is modified to provide a large surface area for the vapor phase reactants of the catalyzed reaction.

For example, a thin sheet alloy is first produced by rolling, then passed through fluted forming rolls to form a corrugated sheet, and this corrugated sheet is then formed into a round sieve-like body (the holes of which correspond to the depth of the grooves in the corrugated sheet). This can be done by winding it in a spiral to form a

This corrugated plate, a flat fJ plate, and a corrugated plate having a corrugated structure different from that of the corrugated plate and arranged at an angle with the first corrugated plate. ,2
Roll up two boards at the same time.

When using elongated plates, flat and corrugated, their drawer edges are spot welded together, and the strips of appropriate length are rolled between three spring-loaded rollers. It is fed through a winding device to form a spirally wound collar-like or annular shaped module as shown in the accompanying figures.

The extended metal substrate of the present invention has a surface area 1.5 to 3 times larger by volume than that obtained with a ceramic honeycomb substrate.

Typical ceramic substrates have 600 to 7
00ft2.

An example is EX20 (with a surface area of 576 ft2/ft3).
Corning) and Gra with a surface area of 780 ft2/ft3
There is a ce 400.

This is the largest ever obtained, with 1100 mm of 0.003" thick Kanthal D sheet.
ft2/ft3 and 2000f t2/ft3 of 0.002" thick Kanthal D sheet.

We recommend using foils between 0.0015 and 0.0045 inches thick, and approximately 400 per square inch when considering cross-sections with 0.002 inch thick corrugations.
More preferred are those assembled to form a structure with cells.

The preferred range of cell size is 200 to 800 cells/in².

Suitable surface area to volume ratios are 1200 ft2/ft3 for 400 cells/in² and 2000 ft''/ft3 for 800 cells/in².

Another method of forming the module consists of spot welding two strip-like bases to, for example, 1 inch outside diameter stainless steel tubing to aid in the winding and module forming operations.

Yet another method involves spot welding two simultaneously wound strips of foil together along their leading edges, then first wrapping them into a hollow cone-shaped model, and then using friction rollers and slides on the cone. The strip is then rolled up and pushed into a retaining collar or shell in one operation.

If a retaining collar or shell is not used, it is preferred to weld each connecting turn of the module by constructing one or more radially extending weld runs on each end of the module.

Stitching or tacking is used to prevent spirally wound modules from unraveling.
Other methods of fixing each successive turn or at least the outermost turn by folding can also be used.

After the module has been formed into the finished form and preferably before the formation of the attached oxygen-containing film or coating, the module is cleaned;
This cleaning is accomplished using vapor degreasing techniques using halogen-containing solvents such as trichlorethylene.
Preferably, this is carried out by a washing technique, followed by washing in acetone and drying.

Example 13 In this example, the thermally oxidized kanthal D shown in FIG.
Gibbsite was attached onto the module.

After combustion, this washcoat was found to be almost pure gamma alumina.

This wash coat was applied to 7.5% Rh using a known technique.
/Metalized with Pt alloy and 30g/f per total catalyst structure volume
t” metal loading
g) was given.

It has been found that such structures have better poisoning resistance than washcoated ceramics or non-washcoated metal substrates.

Below are the results obtained by conducting simulated lead and phosphoric acid poisoning tests on catalyst structures with metal and ceramic substrates.

(a) Mock test before lead coating Test exhaust gas composition Hydrocarbon 1000 ppm Co 2.5 NOX 1001000 pp 0.5 gm/hrN2
Residual Washcoat: γ-Alumina Metallization Treatment 7.5% Rh/Pt Instead of pb, the exhaust gas in this test had a space velocity of 100
11,000 pp of P in the form of monovalent tributyl phosphate/toluene in 000 hr-'' of air.

The inventors have developed a metal monolith
) A washcoat loading within the range of 5-30 wt% based on substrate weight is preferred.

A suitable loading of A1□03 on 400 cells/inch square Kanthal D is 10 wt%.

The surface area of alumina is 50 to 500 m per alumina gr.
It is.

Alumina deposition by the aluminate method described above provides a surface area of 120 to 160 g/g of alumina.

Another suitable method for the deposition of adherent alumina washcoats on metal substrates is preactivated gibbsite (
Solid-liquid ratio of trihydrated alumina) and -hydrated alumina: 25
This is a method in which a slurry with a pH of less than 7 is prepared at ~50% and is used to impregnate a molded substrate by complete immersion.

The exact strength of the slug IJ- used (which can be determined by trial and error) must be sufficient to produce an alumina washcoat of the desired thickness.

The substrate is then dried in hot air and finally fired at 450 DEG C. for 2 hours to form a deposited coating of X- and .gamma.-alumina to a thickness of 0.002' inch on the metal substrate.

Crystal aggregates having micropores of approximately the same size, ie, a diameter of 40λ, are produced.

Yet another method of depositing a deposited alumina washcoat on a metal substrate is to use a monohydrate alpha-alumina slurry.

After combustion at 450 DEG C., .gamma.-alumina is obtained with a surface area of 180-300 rrl/g.

Gamma-alumina is added to monohydrate alpha-alumina in a pre-combustion slurry step to produce a chicken-tropic mixture.

Microcrystals or crystal aggregates with a diameter of 20-100λ are produced.

The diameter of the micropore remains at 40.

A suitable commercially available trihydrate alumina (gibbsite) is available from British Aluminum Chemicals Limited.
FRF8'OJ and Aluminum Company of America's 1-C333J.

A suitable monohydrate alumina (boehmite) is United Kingtom Atomic Energy Authority's [Sol-Gel Al
There is umina)j.

Also, Di5pal MJ is commercially available from Conoco, and Condea FJ is commercially available from Conde Ageloop.

Sol-gel alumina (microcrystalline boehmite) is added during the slurry stage to produce the chicken tropic mixture.

- or more of the oxides consisting of titania, zirconia, hafnia and thoria, as described in the applicant's UK Patent Application Nos. 28283/71 and 28314771 (both filed 16 June 1971). It can be optionally present in the alumina to provide additional stability to the intermediate oxide (washcoat) layer.

If desired, red earth metal oxides, alkali metal oxides and alkali metal oxides can also be used.

Many of the aluminum-containing metal substrates of the present invention have an internal oxidizing property Φ, that is, the success factor of the present invention is that the extended metal substrate itself, which constitutes a part of the catalyst structure of the present invention, is exposed to very strong oxidizing conditions. This is due to the fact that the first layer of oxide coating deposited in believe

Impregnating or depositing alloys of platinum group metals, silver and gold, and in some cases base metals, onto high surface area oxide coatings of alumina, titania, and zirconia deposits catalytically active metals onto washcoats or other substrates. This can be done by a known method.

Such methods include, for example, when a high surface area refractory metal oxide is deposited as an oxygen-containing coating, the support is placed in a solution of water-soluble inorganic salts or salts of platinum group metals, such as platinum, rhodium, and nickel. Can be immersed.

In this case, chloroplatinic acid, rhodium trichloride and nickel chloride can be used.

We prefer that the composition of the outermost layer of catalytic metals consist of platinum group metals or alloys of platinum group metals with each other or with platinum group metals and base metals.

Particularly preferred combinations include 7.5% Rh/Pt for automobile exhaust oxidation catalysts, 10% Rh/Pt for ammonia oxidation, and gas reduction of nitrogen compounds for NOX removal, that is, purification of nitric acid tail gas. For reduction with fuel, it is 20-50% Rh/Pt.

A particularly preferred alloy of platinum, rhodium and base metal suitable for the outermost catalytic metal alloy layer of the catalytic structure in the present invention has the following composition.

Here, base metals include At, Mg, Cr, Mo,
W.

Mn, Fe, Co, Ni, Ti, V, Th, U, C
uAg, Zn, Cd, Hg, In, TI, Bi, S
n.

This combination, selected from the group of Pb, lanthanides and actinides, is useful for oxidation and reduction reactions, and is also useful in scheme reforming of naphtha and naphtha cuts.

However, the base metals described above are also useful with other combinations of platinum group metal alloys, as well as with the catalyst structures of the present invention in which the outermost catalytic metal layer includes silver or gold.

Ruthenium is useful for NOx decomposition in automobile exhaust purification.

[Brief explanation of the drawing]

FIG. 1 is a four-dimensional diagram showing an example of a metal carrier constituting the improved catalyst according to the present invention.

Claims (1)

[Claims] 1(a) Excluding impurities, chromium 3-40% by weight, aluminum 1-10% by weight, cobalt O-5.0% by weight, nickel 0-72% by weight, carbon 0-0. a metal substrate consisting of a heat-resistant and oxidation-resistant iron alloy in an extended form, comprising 5% by weight and substantially the balance iron; (b) formed on the surface of said extended metal substrate by oxidizing the metal substrate surface; (c) a high surface area coating of at least one of alumina, titania, and zirconia oxides deposited on the aluminum oxide coating and fixed through the coating onto the substrate; d) a catalyst layer □ consisting of at least one member selected from the group of metals ruthenium, rhodium, palladium, iridium, platinum, silver and gold and alloys containing at least one of these metals retained by said coating; A supported catalyst comprising: