JPS5941775B2 - Platinum group metal catalyst composition - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing a noble metal catalyst for high temperature oxidation.

The catalyst obtained according to the invention is capable of converting carbonaceous substances such as carbon monoxide, hydrocarbons, oxygen-containing organic compounds into intermediate oxidation products, carbon dioxide and water (the latter two substances being relatively harmless from the point of view of air pollution). can be used to increase oxidation to products with higher weight percentages of oxygen in molecular formulations such as

Advantageously, essentially complete oxidation of gaseous wastes containing unburned or partially burned carbonaceous fuel components such as carbon monoxide, hydrocarbons and intermediate oxidation products consisting primarily of carbon, hydrogen and oxygen is advantageously carried out. can be used to do

The catalyst obtained according to the invention has a catalytically active calcined mixture of rare earth metal oxides and alumina to which a platinum group metal component is added.

This firing is carried out at a temperature of about 900 to 1200 DEG C. or higher, but not so high or so long as to unduly sinter the material so that it no longer has sufficient catalytic activity.

The force fired material generally has a surface area of at least about 75 square meters per duram.

Surface areas referred to herein are defined by BET or similar methods.

Power calcining is performed prior to addition of the platinum group metal component to the mixture containing the rare earth metal oxide and alumina.

This catalyst retains platinum group metals, alumina and rare earth metal oxides.

It has a solid support that is relatively catalytically inert.

This catalyst is made by the following method.

The rare earth metal oxide-alumina mixture is calcined and coated as an aqueous slurry on an inert support, then platinum group metal 9
is added and the composite is then dried.

Alternatively, the platinum group metal component can be added to the calcined mixture of rare earth metal and aluminum oxide, and the composite can be deposited on a relatively inert support at the desired time.

When carbonaceous fuels are combusted to produce power, such as in reciprocating piston engines, rotary engines, etc., combustion is generally incomplete, and products of incomplete combustion are often exhausted to the atmosphere.

The exhaust gas contains a mixture of pollutants including carbon monoxide, hydrocarbons (saturated and unsaturated), and oxygenated organic compounds such as aldehydes, organic acids, and the like.

Air pollution from these and other exhaust emissions is particularly undesirable in urban areas where heavy automobiles and other motorized vehicles are present.

The importance of reducing the release of these oxidizing substances into the atmosphere is due to the fact that they are a significant factor in the problem of air pollution and smog formation, and that humans, animals and plants are often exposed to these concentrated pollutants. It cannot be ignored as it has a negative impact.

One means of reducing the content of oxidizing substances in the exhaust gas is to oxidize it in contact with molecular oxygen in the presence of a catalyst.

Catalysts are typically placed in the exhaust line leading from the combustion zone and are used to catalyze the reaction between free oxygen, either from low-fuel operation of the combustion zone or from external air or other oxygen sources, and unburned and partially burned fuel components. It works to protect.

A common drawback of this catalyst is that its activity decreases considerably when they are used at elevated temperatures for extended periods of time.

This is due in part to the unstable structure, which has a tendency to sinter at high temperatures, causing shrinkage and reducing the available surface area of the catalyst.

Still, in internal combustion engines and turbine exhaust systems, generally about 5
40℃ (approximately 1000'F) or 650℃ (1200”F)
Thermal degradation and loss of strength of the catalyst caused by prolonged exposure to high temperatures in excess of ) can lead to attrition of the catalyst body, particularly when used in mobile vehicles where the catalyst is subject to significant vibrations.

The resulting micronization or structural deterioration reduces the effectiveness of the catalyst.

Furthermore, many catalysts for treating exhaust gases provide satisfactory results for carbon monoxide conversion but only relatively poor conversion of hydrocarbons.

Another problem that must be overcome is, for example, when driving distances of at least approximately 80,000 kilometers (approximately 50,000 miles)
The object of the present invention is to provide an oxidation catalyst which maintains its effectiveness over a relatively long period of time and is suitable for treating exhaust gas.

The potential and cost of this system to reduce pollution caused by the presence of unburned and partially oxidized components in the exhaust gas, if frequent removal and regeneration of the catalyst is required to maintain the desired activity. would be an impediment to the adoption of this system and, in any case, would be a burdensome expense.

When the combustion zone is cold or at a relatively low temperature, for example in internal combustion engines, a high proportion of hydrocarbons in the exhaust gas,
Carbon monoxide and some other combustible substances are produced in the first moments of combustion initiation.

Thus, a satisfactory catalyst for the oxidation of exhaust gases will work effectively at this temperature, as well as at the elevated temperatures at which catalysts are used to promote oxidation.

The catalyst composition obtained according to the invention is a partially combusted fuel exhaust stream containing carbonaceous materials, especially carbon monoxide, hydrocarbons, and oxygenated organic acids, such as aldehydes, organic acids, and other combustion intermediates. It is effective at relatively low or high temperatures in catalytically oxidizing carbon dioxide, water, or other substances containing a large proportion of bound oxygen per average particle.

This reaction takes place in the presence of free oxygen, which supports oxidation.

The catalyst composition is capable of being exposed to high temperatures, e.g., up to about 900° C. or higher, depending on the support used, as may be experienced when processing flue gas streams or other oxidizing systems. It is resistant.

Thermal degradation, shrinkage, and loss of strength and catalytic activity in the catalyst during use is minimal.

The treatment of exhaust gases using the catalyst composition obtained according to the invention is effective and avoids frequent regeneration or replacement of the catalyst composition, thereby reducing the production of hydrocarbons, intermediate oxidation products and monoxide. Converting carbon to, for example, carbon dioxide and water provides a practical and relatively hassle-free means of reducing the release of oxidizing pollutants to the atmosphere.

In the catalyst obtained according to the invention, the platinum group metal is a promoter of oxidation reactions and is present in an amount sufficient to provide a composition with significant activity for catalyzing these reactions.

Platinum group elements include, for example, platinum, ruthenium, palladium and rhodium, and mixtures of these metals serve as platinum group metal catalysts.

The amount of platinum group metal is a minor portion of the catalyst and generally does not exceed about 2% by weight from an economic standpoint.

For example, this amount may be about 0.0601 to 2%, preferably about 0.02 to 1%.

When the platinum group metal i of these catalysts contains one or more of these metals, this component consists of a major amount of platinum and a small amount of one or more other platinum group metals, such as palladium.

For example, the catalyst component may have about 65 to 95 weight percent platinum and about 5 to 45 weight percent palladium.

It is preferred that the platinum and palladium when used in making the catalysts of this invention are in the amine hydroxide form and that they are present as chloroplatinic acid and palladium nitrate.

The platinum group metals may be present in the catalyst in elemental or combined form, such as oxides, sulfides, etc., and the amounts of these metals are considered based on the metals present regardless of their form.

The catalyst of the present invention comprises a catalytically active form of alumina and a rare earth metal oxide.

These aluminas are members of the γ family, e.g. γ- and η-
The catalyst includes alumina, and as distinct from the relatively inert alpha-alumina and sigma-alumina, and the catalyst may also contain small amounts of other refractory oxides, such as silica.

The respective amounts of alumina and rare earth metal oxide in the catalyst are sufficient to provide a catalytic effect.

Often, the amount of alumina, based on its total weight, is about 5
0 to 99% by weight, preferably about 75 to 95% by weight, while the amount of rare earth metal oxide is about 1 to 50% by weight.
, preferably 5 to 25% by weight.

Among the rare earth metal oxides that can be used in the catalyst are oxides of lanthanum, samarium, praseodymium, etc., and this component is preferably cerium oxide.

It is also possible to use mixtures of these oxides, for example mixtures in which cerium oxide is the main component.

The catalyst may also contain small amounts of other non-noble metal components, such as manganese, vanadium, copper, iron, cobalt, nickel, etc., which may serve as promoters of the oxidation reaction.

This component includes various metal oxides and other compounds of metals.

During calcining of rare earth metal oxides and alumina at temperatures of at least about 750°C, these oxides are completely associated and no undue sintering of the alumina occurs, but rather a catalytically active product is obtained. It will be done.

A power calcining mixture of finely ground alumina and rare earth metal oxide can be made, for example, by calcining a mixture of oxygen-containing compounds of rare earth metal and aluminum that decomposes into their oxides as calcining proceeds.

These oxygen-containing compounds are precursors of oxides and are inorganic in nature, for example oxygen-containing metal salts that are soluble in water.

Preferably, an aqueous solution of the rare earth metal salt is mixed in hydrated or catalytically active form with finely divided alumina and the joint is calcined to provide a mixed oxide.

Preferred power firing conditions are temperatures of about 900 to 1200°C.

Power firing conditions are such as to provide a catalytically active solid having a relatively high surface area, eg, at least about 75 square meters per duram.

This force calcining is preferably carried out while the alumina and rare earth metal oxide are unsupported and in a free flowing state.

In any event, this roasting is performed prior to the addition of the essential platinum group metal components.

In one method of making the catalyst of the present invention, an aqueous slurry of a calcined mixture of alumina and rare earth metal oxide is contacted with a relatively catalytically inert support.

The rare earth metal and aluminum components of the slurry are oxides or other essentially water-insoluble forms that convert to oxides under conditions of subsequent calcining.

The solids of the slurry are deposited onto a support and the resulting composition is dried or dried at a temperature that provides a catalytically active product that is an improved catalyst of the type described in U.S. Pat. No. 3,565,830. Being roasted by force.

The temperature of heating is not so high that the rare earth metal and aluminum oxide mixture unduly sinters, but rather has a coverage of at least 75 rrL2/y after power firing.

These surface areas contrast with the relatively low surface areas of relatively inert catalyst supports, which have 1
It has a small surface area, such as less than about 10 m 2 per gram, and in some cases less than 1 m 2 .

The surface area referred to herein is measured by BET or similar methods.

The method of making the catalyst of the present invention involves adding a platinum group metal component to the calcined mixture containing the rare earth metal and aluminum oxide before the mixture is deposited onto a relatively inert support. Including.

For example, when making a catalyst with a relatively inert support,
An aqueous slurry of the oxide power-calcined mixture is prepared, and the water-soluble form of the platinum group metal component is added to and thoroughly mixed with the slurry.

The platinum group metal component may be in acid form, such as chloroplatinic acid or other ionic form as described above, and may be precipitated onto the preheated oxide by, for example, addition of hydrogen sulfide.

The mixture containing the platinum group metal is dried or calcined to form the material containing the platinum group metal, rare earth metal, and aluminum oxide into a form more suitable for depositing onto a relatively inert catalyst support. Give with.

Power firing is carried out at a temperature of about 400 to 600°C.

The power firing is not so severe that the catalytic activity of the composite is undesirably reduced, and the power firing material is at least about 75 rIL2.
/y.

The relatively inert supports that can be used in preparing catalysts according to the present invention can be made of a variety of materials, but are preferably composed primarily of refractory metal oxides.

The catalyst supports, and thus these catalysts of the invention, are preferably single, relatively large-sized skeletal structures, for example honeycomb-shaped.

These catalysts are preferably monomorphic and have a unitary or unitary solid refractory framework structure.

The skeletal structure is cylindrical, but not necessarily annular in cross-section, and can have internal and surface pores and/or pores communicating with gas flow channels extending through the skeletal structure.

The channels have various shapes in cross section.

An activated material carried by a support whose material is a mixture of rare earth metal oxide and gamma group or activated alumina can be formed on the surface of the gas flow channel and also on the surface of the pores in the surface communicating with the channel.

The platinum group metal component is supported by an activated rare earth metal oxide-alumina material and includes one platinum group metal or a combination thereof.

The single, skeletal support of the honeycomb shaped catalyst is characterized by having a number of flow channels or passageways extending therethrough in the general direction of the gas flow.

In use, the catalyst is usually arranged in a vessel in such a way that its single skeletal configuration occupies a major portion of the cross-sectional area of the reaction zone.

Conveniently, the single skeletal structure is shaped to fit into the reaction zone in which it is placed and the single supported catalyst directs the gas flow with respect to its cellular gas flow channels, i.e. between the inlet and the outlet. It is arranged vertically in the interior with respect to channels extending in the general direction of flow, so that gas flows through the channels during its passage through the container.

The flow channels need not pass straight through the catalyst structure and may include flow transducers or spoilers.

The relatively inert support for the catalyst obtained in accordance with the present invention is preferably a substantially chemical and relatively inert support for the catalyst that is capable of retaining its shape and strength at elevated temperatures, e.g. Manufactured from a hard, solid material that is physically inert.

This support has a low coefficient of thermal expansion, good thermal shock resistance and low thermal conductivity.

Often, the support is porous, but its surface is relatively non-porous, and especially if the support is relatively non-porous, the support is such that it retains the catalyst well. It is desirable to roughen the surface.

This support may be metallic or ceramic in nature or a combination thereof.

A suitable support, either in skeletal form or in other forms, is cordierite.
Consists of α-alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica-magnesia and zirconium silicate.

Examples of other refractory ceramic materials that can be used in place of the suitable material as support or carrier are siliconite, magnesium silicate, zircon, feldspar, alpha-alumina and aluminosilicates.

The support may be a glass-ceramic, preferably unglazed and essentially completely crystalline in shape and containing no significant amount of glassy or amorphous substrates, such as those found in porcelain materials. characterized by the absence of a substrate.

Additionally, this structure is characterized by a relatively non-applicable porosity, unlike the substantially non-porous porcelain utilized in electrical applications such as spark plugs, which is characterized by a relatively non-applicable porosity. have

The structure has a water pore volume of at least about 10%.

The channel walls of a single skeletal support structure can contain numerous surface macropores communicating with the channels, significantly increasing the accessible catalyst surface, and substantially increasing the number of micropores for high temperature stability and strength. Provide non-existence.

This support is described in US Pat. No. 3,565,830, incorporated herein by reference.

The geometrical, superficial or apparent surface area of the skeletal support, including the walls of the gas flow channels, is often about 0.5 to 6, preferably 1 to 5 square meters per liter of support.

Channels through the unitary body or framework structure may be of any shape and size to match the desired surface and must be large enough to permit relatively free passage of the gaseous mixture undergoing the reaction.

The channels are parallel or approximately parallel and extend through the support from the -M section to the opposite side, and the channels are preferably separated from each other by thin walls.

This channel may also be multidirectional and communicate with one or more adjacent channels.

The channel inlet openings may be distributed throughout the entire surface or cross-section of the support which undergoes initial contact with the gas to be reacted.

The gas flow channels of single skeleton supported catalysts are thin-walled channels that provide a relatively large amount of surface area.

The channels may be of one or more of a variety of cross-sectional shapes and dimensions.

Channels may be e.g. trapezoidal, rectangular to square, sinusoidal (si
nusoid) or circular cross-sectional shapes, so that the cross-section of the support exhibits a repeating pattern that can be described as a honeycomb, wavy, or lattice structure.

The walls of the cellular channels are generally strong and thick enough to provide a single pod, and this thickness is often about 50 to
It falls within the range of 250 microns (approximately 2-10 mils).

With this wall thickness, the structure has approximately 15 to 3
85 (approximately 100 to 2,500) or more gas inlet openings and a corresponding number of gas flow channels per square inch; Contains flow channels.

The open area of the cross section may be 60% or more of the total area.

The dimensions and nature of the single refractory skeletal support of the present invention can vary, and the length of the flow channels is at least about 2.5 mm.
5 rum (about 0.1 inch) or at least about 25.
4mmC approximately 1 inch).

The catalysts obtained according to the invention can be used to promote the oxidation of various chemical feedstocks through contact with molecular oxygen.

Although some oxidation reactions occur at relatively low temperatures, these are often carried out at elevated temperatures, such as at least about 150° C., preferably from about 200 to 900° C., generally in the vapor phase with the feedstock.

A feed is a material that undergoes oxidation, contains carbon, and is therefore referred to as carbonaceous, whether it is organic or inorganic in nature.

The catalyst is thus useful for promoting the oxidation of hydrocarbons, oxygen-containing organic components, carbon oxides, and the like.

These types of materials are present in the exhaust gas from the combustion of carbonaceous fuels, and thus the catalyst of the present invention is useful in promoting the oxidation of this exhaust.

Exhaust from internal combustion engines operating on hydrocarbon fuels, as well as other waste gases, are present in the gas stream as part of the catalyst and exhaust, or as air or other desired form with a greater or lesser oxygen concentration. Oxidized by contact with added molecular oxygen.

The product from oxidation contains a greater weight ratio of oxygen to carbon than in the feed material undergoing oxidation.

Many such reaction systems are known to those skilled in the art.

The invention will be further illustrated by the following examples.

All parts and percentages are by weight unless otherwise specified.

Reference example ■ H2O1 for the final volume of solution of approximately 13907111
188m1KCe(NOa)l ・6H203
CeO2-A stabilized by dissolving 369
Produce a l2O5 slip.

Activated Al2O8 powder 12σ02 is stirred into this solution, which is dried with constant stirring, transferred to a drying oven at 110° C. and dried for 17 hours.

Grind the dried solids to less than 40 mesh and dry for 1 hour.
Power bake at 100℃.

This force-baked powder 1000. @H2O10001'n
1. and 320,1 rnl of concentrated HNO and 170 ml of concentrated HNO in a 1 gallon mill jar at 68 RPM.
Time to crush the ball.

1000 parts of the resulting slip was mixed with 83.3 parts of concentrated HNO and H
Dilute with a solution of 33 parts of 2O.

Cross-sectional area square meter (square inch) approximately 38 (
A 49 cubic centimeter (3 cubic inch) cordierite honeycomb with approximately 250 parallel gas passages is immersed in this dilution slip, blown with air, dried at 110° C. for 2 hours and power calcined at 500° C. for 2 hours.

Approximately 13-14% by weight of total cerium dioxide and alumina are deposited on the honeycomb.

Platinum is added to the catalyst by the following steps.

K2PtCl4 aqueous solution (containing pt3.5s#) 1
3.05 fl- of NaHCOs were added to 245 ml.

21.5 kg of NaCHO was added to this solution at 95°C.

The cerium dioxide and alumina-coated honeycombs are immersed in this solution, cleaned free of CI, dried at 110 DEG C. for 2 hours and calcined at 500 DEG C. for 2 hours.

The honeycomb produced as described contains 0.40% pt by weight.

Example 1 A cerium dioxide-alumina composite was produced as follows.

Ce(NO3)3.6 H2O3 to 970ml of H2O
419 to a final volume of 3460ml and activated alumina powder 3000ml. Add @ to this solution.

Dry this slurry while stirring constantly at 110°C.
Transfer to a drying oven and then dry for 16 hours.

Grind the dried solid to 40 mesh or less for 2 hours.
Power bake at 100°C.

A solution of platinum tetramine hydroxide and platinum palladium hydroxide is added to 108 g of this powder.

The total solution volume is 1517711 te, and this is Pt2
．． 75. Contains @ and PdO, 60p.

The wet powder is thoroughly mixed and dried at 110° C. for 2.5 hours.

181, @pTotal sample of powder to be weighed 1 qt was transferred to a ball mill jar and added to a 188 g ball with H2O18.
0 cc and 3.6 cc of concentrated HNO3 were added.

They were ball milled at 6ORPM for 16 hours.

The slurry was poured out and then used to coat the same honeycombs and in the same process as in Reference Example (1).

After calcining at 500°C, the catalyst thus prepared has a temperature of 0.18
It contained % PT and 0.04% Pd by weight.

Example ■ A force-calcined cerium dioxide-alimina composite is prepared as in Example ■ and then force-calcined at 1100°C.

The powder is ball-milled with a solution of (NH4)2Pt(SCN)a and then used to soak a honeycomb as in Reference Example ①.

The soaked honeycombs are dried and then calcined at 500°C'.

The force-calcined catalyst contains 0.28% pt by weight.

EXAMPLE ■ Catalysts made essentially according to the methods of Reference Example ■ and Example ■ were tested to illustrate that the catalyst of the present invention has improved properties for promoting exhaust gas oxidation.

In this test process, the gas was heated to 40,000 at various temperatures.
It was passed through contact with the catalyst at a volumetric space velocity.

This gas is 3.0% oxygen, 1.0% carbon monoxide, 300%
ppm ethylene, 10.0% carbon dioxide, 500p
pm, nitric oxide and residual nitrogen.

The gas was preheated above the catalyst to raise the catalyst temperature to a constant level and the gaseous emissions were analyzed for carbon monoxide and ethylene content at each temperature tested.

Measurements were taken approximately 1/4'' upstream of the catalyst and this value was plotted versus oxidation temperature.

From a plot of oxidation temperature against the amount of carbon monoxide and ethylene in the effluent, the temperature for 50% conversion of carbon monoxide to carbon dioxide and the 50% conversion of ethylene to carbon dioxide and water.
Temperature versus % conversion was measured.

These numbers are shown in Table 1 below, along with test results obtained using similar catalysts that do not contain cerium dioxide.

These data demonstrate that the catalyst of the present invention (Test 3) compares favorably with a similar catalyst having only alumina as a coating on the support (Test 1).
and a catalyst containing CeO2.Al2O3 (Test 2).

Example ■ 5000 activated alumina spheres with a diameter of 0.10”
, @Ce(NO3)3 in H2O50507rLl
6H201401,? Soak in a solution of

After drying at 110°C for 16 hours, the spheres were heated to 100°C in air.
It was calcined at 0°C for 2 hours.

After cooling, pt3. o33# (as tetramine hydroxide) and P, dl, 517. ? 1400 ml of a solution containing (as tetramine hydroxide) were sprayed.

For spraying, the treated spheres were dried at 110°C for 16 hours.
It was then calcined in air at 500'C for 2 hours.

The final catalyst was 0.087 wt% pt+o on alumina,
o43wt, %P d + 10 NV t N%Ce
Contained 02.

The performance of the catalyst was evaluated in the US Government CVS 1975'' Cold Start 11 Vehicle Emission Test.

The result is 0.075 hydrocarbons per kilometer (mile) driven. (o, 129) and COO, 81 per kilometer (mile) traveled? Show the emission of (1, 3,?).

Example ■ Alumina spheres impregnated with cerous nitrate solution, dried and force calcined and cooled as in Example ■35
00. A solution of platinum tetramine hydroxide (Pt4.s5
o, @-total solution volume--1400 ml) and then dried and calcined as in Example ①.

The final catalyst was 0.13 wt%%Pt+1 on alumina.
Contained 0 wt, % CeO2.

The performance of the catalyst was evaluated in the US Government CVS 1975'' Cold Start 11 Vehicle Emission Test.

The result is 0.14 hydrocarbons per vehicle mile. @ and COo per vehicle mile, 7. It shows the emission of @.

The following is an example of the implementation of the present invention.

Catalyst compositions according to claims, wherein the platinum group metal comprises 50 to 95% by weight platinum.

Claims (1)

[Claims] 11) Coating at least a portion of the inert carrier with a film of a liquid slurry containing pre-calcined active ingredient particles and a platinum group metal component dispersed therein, and then evaporating the slurry liquid phase. a) 1 to 50% by weight of ceria, 0 to 1% by weight of a non-precious metal promoter for oxidation reactions, and a sufficient amount in the range of 50 to 99% by weight; b) the mixture of ceria, promoter and catalytically active alumina at 900-1200°C; temperature for a sufficient time to reduce the surface area to 75
m2/i or more, C) Preheat baking of the above-mentioned activity 51, and before coating the active ingredient on the inert carrier, the platinum group metal or its compound is heated to the above reserve force. 2) The inert carrier, the coated pre-calcining active component and the platinum group metal are then calcined at a temperature of 400-600°C to obtain the desired A method for producing a noble metal catalyst for high-temperature oxidation, the method comprising obtaining a catalyst.