DE102007001129A1 - Oxidation catalyst for hydrocarbons, carbon monoxide and carbon particles, comprises metallic substrate, metal migration preventing layer, e.g. of silicate, and catalytically active layer - Google Patents

Abstract

A new catalyst (I) comprises: (i) a metallic substrate with an internal surface; (ii) a first layer, located on at least part of the external and/or internal surface of (i), containing a silicate, a phosphate or an early transition metal oxide; and (iii) a second, catalytically active layer, covering at least part of the first layer.

Description

The The present invention relates to a catalyst, in particular a Catalyst for use in the oxidation of hydrocarbons and for the oxidation of carbon monoxide and deposited organic Particles (soot), as well as a method for producing the catalyst according to the invention.

The Application of filters in the exhaust system of internal combustion engines is known. Particle filters, for example, are capable of soot particles from the exhaust of internal combustion engines, especially diesel engines, filter out and so reduce their emissions to the atmosphere.

there find different filter concepts use, such. B. so-called "wall-flow filter" or filters made of ceramic or metallic foams. The real difficulty does not exist in the filtration of Soot particles, but in the regeneration of the used Filter.

Carbon soot burns depending on the operational composition of the particles spontaneously at Temperatures between 500 ° C and 700 ° C. These temperatures but are z. B. of modern diesel engines in general only reached at full load.

Therefore are additional supportive measures, For example, for the oxidation of the separated from the exhaust soot particles, necessary. This can be done by adding additives or by catalytic Coating the filter or catalysts happen. From the state The technology is exhaust gas purification catalysts with a high oxidation efficiency known so that the particles burned at a low temperature can be. The surface of the filter chamber therefore often has a catalytically active coating for acceleration the combustion of soot particles collected on the filter on. The catalytically active coating oxidizes the gas contained in the exhaust gas Nitric oxide to nitrogen dioxide. The resulting nitrogen dioxide improves then the oxidation of the deposited particles.

Out The prior art are further a variety of catalytic with active materials coated carriers for Exhaust filter or catalytic converter known. Typically based the catalytically active layers of such supported Catalysts on aluminum, cerium, tungsten, titanium and zirconium oxide, the additionally catalytically active precious metals for Oxidation of hydrocarbons, oxidation of CO and of deposited organic particles such. As soot and the like contain.

catalytic active metal oxides or their hydroxides, including those specifically for the purpose of the present Used in the invention are essentially water-insoluble. Common it is therefore in the prior art z. B. aluminum oxides as aqueous Slurry with water-soluble salts of the oxides, in particular nitrates, chlorides, hydroxides, sulfites, acetates or Complex compounds of the catalytically active metals on substrates apply or impregnate them with it and this Salts then decompose at high temperatures, wherein their oxides are formed.

The aim will be a continuous regeneration of the particulate filter, without that z. B. a periodic post-injection of fuel to Increasing the exhaust gas temperature is required. To the efficiency Therefore, to increase the catalyst, it must be a large Surface be provided so that the catalytic active centers with the soot particles in contact can come. The necessary large surface is produced, for example, by a layer of a catalyst carrier, such as high surface area gamma-alumina or titanium oxide is deposited on a filter material and a Metal, in particular a platinum group metal, which is active Species known for the oxidation of particulate material is by means of a metal salt solution or metal complex compound is integrated into the filter.

For the catalytic coating of such substrates, in particular with inner surface, d. H. so porous substrates or metal monoliths with essentially continuous channels, be different as already stated above Coating methods and coating materials using of so-called "washcoats" (under which usually mostly aqueous slurries of solids understood) are used.

This is what the U.S. Patents 3,894,965 . 4,900,712 and 4,003,976 various "washcoats" containing a plurality of oxides that are catalytically active, such as La ₂ O ₃ , Co ₂ O ₃ , Nd ₂ O ₃ , TiO ₂ , ZrO ₂ , CeO _2, etc., alone or in combination.

The US 2004/0192546 A1 discloses a catalyst for the low temperature oxidation of hydrocarbons in the presence of oxygen and water vapor. This catalyst comprises a high surface area alumina, further tin oxide, and at least one noble metal selected from the group consisting of palladium, platinum, rhodium or a combination thereof, which is applied to a monolithic carrier by means of a washcoat.

The US 6,887,815 further discloses a porous material for the catalytic conversion of exhaust gases comprising a catalyst containing as active species iron and silver.

Further simple procedures, such as dipping the catalyst support into a washcoat and removing excess Washcoat by blowing out with air, are also out of the state the technique known, as well as coating method using of centrifuges. As well as the possibility of spraying porous molded body proposed with a washcoat Service. As a coating are usually usually on alumina based washcoats used by their large surface area are characterized.

there are in the example based on alumina washcoat Metals such as platinum group metals, e.g. By solution, Total absorption or by impregnation with precious metal-containing Solutions or by incorporating in the washcoat before Coating, integrated.

The available for particle oxidation Surface has a significant influence on the catalytic Sales and in particular the long - term stability of the Catalyst. It is known that to increase stability the alumina surface of washcoats often stabilizing elements, such as As cerium or lanthanum, can be added.

The However, catalysts known from the prior art have the problem on that after a period of aging of the Catalyst during operation a significant decrease catalytic activity was observed. Especially This applies to long-term use at elevated temperatures to, as they occur for example in internal combustion engines. A Such aging can also be prolonged, for example Laboratory-scale heating to study the properties of new ones Catalysts are simulated.

It It is believed that the loss of catalytic activity by sintering the resulting (noble) metal clusters and He niedigung the BET surface of the washcoat is caused.

Especially with metal substrates deactivation or loss of catalytic occurs Activity also by migration of metals from the substrate in the washcoat layer. This is especially true for transition metals to, for example, on the surface of the on alumina based washcoats can form catalytically inactive spinels, the the catalytic activity of this layer considerably decrease. Likewise, these metals, which originally come from the metal substrate, with the catalytically active metals interact and thus their catalytic activity decrease.

task Therefore, it was the object of the present invention to provide a metal substrate to provide a catalyst based on the migration of metals and in particular prevents the formation of catalytically inactive phases and thus increases the long-term stability of the catalyst.

• i) ein metallisches Substrat, das eine innere Oberfläche aufweist;
• ii) eine erste Schicht, die zumindest bereichsweise sowohl auf der äußeren und/oder der inneren Oberfläche des Substrats angeordnet ist, enthaltend ein Silikat, ein Phosphat oder ein Oxid der frühen Übergangsmetalle;
• iii) eine zweite Schicht, die katalytisch aktiv ist, und die zumindest bereichsweise die erste Schicht bedeckt.

According to the invention, this object is achieved by providing a catalyst comprising:

• i) a metallic substrate having an inner surface;
• ii) a first layer at least partially disposed on both the outer and / or inner surface of the substrate, comprising a silicate, a phosphate, or an early transition metal oxide;
• iii) a second layer, which is catalytically active, and at least partially covering the first layer.

By the at least partially applying a first layer the outer and / or the inner surface the preferably porous metallic catalyst substrate, the silicates, phosphates or an early transition metal oxide or mixtures thereof, preferably aluminum silicates, titanium and Contains zirconium oxide, the migration of metals, in particular of catalytically active transition metals, such as nickel, chromium, iron, etc., from the metallic substrate prevented in the washcoat.

Of the The term "metallic" includes both pure metals as well as metal alloys.

One Inventive catalyst surprisingly even at an aging in the laboratory experiment at 800 ° C over 48 h only a drop in catalytic activity of less as 5%, measured as the oxidation effect of hydrocarbons and carbon monoxide.

Of the Term "inner surface" means presently, that the substrate molding in the interior openings or has recesses whose surface is coated can be. Including z. As pores, channels, etc. in Inside the molding understood.

The Metallic substrate is preferably porous or channels at least partially completely traversed, not restrictive Examples are, for example, so-called metal foams and metal monoliths as z. From the companies Inco and Emitec are commercially available.

The For example, oxide of the early transition metals Titanium dioxide, zirconia, yttria, hafnia, lanthanum dioxide, Scandium dioxide or tantalum dioxide or mixtures thereof. All most preferred are titanium dioxide and zirconia zirconia is preferred.

In further particularly preferred embodiments of the invention can be the oxide of the early transition metals, here in particular titanium and / or zirconium oxide, by a divalent Metal cation, such as magnesium, calcium, barium or strontium, doped be what has the beneficial effect that possibly migrating transition metals from the metallic substrate particularly preferred alkaline earth transition metal compounds form, which are particularly stable and the further migration of the Metal cations from the metallic substrate into the catalytically active Stop shift. The doping can not only by a single divalent metal cation, but also by several of the aforementioned metals or metal cations.

When Silicate can almost all naturally occurring or artificially produced silicates, For example, so-called island or neosilicates such as phenakite, Forsterite, grenade, for example Grossular, and zircon (zirconium silicate). Other silicates for the purposes of the present invention are so-called group or sorosilicates with disilicate assemblies, such as hemimorphite.

Further Examples according to the invention are natural Ring silicates (cyclosilicates) with cyclotri- and -hexasilikatbaugruppen like alpha wollastonite, bentoite, beryll etc.

Yet further examples can be used according to the invention Silicates are so-called chain and ribbon silicates (inosilicates) with chain-shaped polysilicate units, such as Beta wollastonite and the group of pyroxenes, such as enstatite or spodumene. Other preferred silicates are amphiboles, such as Tremolite and mold panels.

Furthermore can phyllosilicates (layered silicates), the layered Having polysilicate units, used according to the invention become. Typical examples which are suitable according to the invention are, for example, serpentine and kaolinite. Further examples from this group are the so-called fibrous serpentine (chrysotile) as well as leafy serpentine (antigorite) as well as kaolinite and same formula, but Dikkit or Nakrit as well as different from the layer structure Halloysite. In addition, pyrophyllite can also be used.

In further preferred embodiments also be used so-called aluminosilicates in which Silicon is partially replaced by aluminum. Examples include the group of mica, such as sillimanite, mollit, phlogopite, paragonite, vermiculite and morillonite. As phosphates according to the invention, for example Phosphorite, polyphosphates, cyclic metaphosphates, ultraphosphates can be used.

The thickness of the first layer (also called "protective layer") is <500 μm, preferably <100 μm, particularly preferably <20 μm This protective layer is only slightly porous and has a low BET surface area (DIN 66131) of <1 m ² / g, preferably <0.5 m ² / g.

In particularly advantageous embodiments of the invention, the catalytically active layer contains metal oxides which are selected from Al ₂ O ₃ , CeO ₂ , La ₂ O ₃ , ZnO, ZrO ₂ , SnO ₂ , Y ₂ O ₃ , WO ₃ , TiO ₂ and mixtures from that.

The In addition, catalytically active layer preferably contains a Another catalytically active metal selected from the Group consisting of tungsten, iron, vanadium, platinum, silver, gold, Palladium, ruthenium, rhodium or mixtures thereof.

The Layer thickness of the catalytically active layer is <500 μm, preferably <100 μm, especially preferably <20 microns.

• i) des Bereitstellens eines metallischen Substrats, das eine innere Oberfläche aufweist;
• ii) des zumindest bereichsweisen Aufbringens einer ein Silikat, Phosphat oder ein Oxid der frühen Übergangsmetalle enthaltenden ersten Schicht auf die innere und/oder äußere Oberfläche des Substrats;
• iii) des anschließenden Aufbringens einer Washcoat-Zusammensetzung enthaltend katalytisch aktive Substanzen.

A typical process for preparing a catalyst according to the invention comprises the steps:

• i) providing a metallic substrate having an inner surface;
• ii) at least partially applying a first layer containing a silicate, phosphate or an early transition metal oxide to the inner and / or outer surface of the substrate;
• iii) subsequently applying a washcoat composition containing catalytically active substances.

As already stated is the metallic substrate porous or has at least partially through channels on.

Of the Step of at least partially applying a first layer takes place in a simple manner preferably by soaking containing the substrate in a suspension, in a sol-gel or in a solution a silicate, phosphate or early transition metal oxide.

Between Steps b) and c) are followed by a drying and / or calcining step.

The Catalytically active layer is preferably in the form of a washcoat applied by soaking, spraying or soaking, the preferred catalytically active substances metal compounds of contains catalytically active metals described above. Such metal compounds are, for example, nitrates, chlorides, Sulfates, sulfites, acetates, etc. or complex compounds of these metals. Naturally are also the corresponding oxides in the form of slurries usable.

To the application of the washcoat is typically carried out by a drying or calcination step, whereupon in addition a metal or precious metal doping of the washcoat surface with other catalytically active metals or their compounds, such as Nitrates, chlorides, sulfates, sulfites, acetates or complex compounds, can be done.

use finds the catalyst according to the invention in the Oxidation of hydrocarbons or in the oxidation of CO and of deposited organic particles, especially soot in internal combustion engines. However, the particular preferred use depends in particular on the type of metals and metal oxides.

The Invention will be described below with reference to the figures and the examples however, the following examples are described in detail not as limiting to the scope of the invention to be understood.

characters

1 Figure 3 shows the EDX spectrum of a porous substrate coated with a prior art washcoat.

2 shows the EDX spectrum of the washcoated substrate after aging.

3 shows the EDX spectrum of a catalyst according to the invention based on a porous substrate having an intermediate layer of CaO stabilized zirconia between the substrate and the catalytically active layer.

4 shows the EDX spectrum of a catalyst according to the invention based on a porous substrate having an intermediate layer of aluminum silicate between the substrate and catalytically active layer.

One nickel-containing, porous metal foam body following Alloy composition was for all following embodiments as a catalyst support used: 55.90 wt.% Ni, 0.23 wt.%, Co, 4.84 wt.% Fe, 22.49 Wt% Cr, 10.79 wt% Mo, 3.83 wt% Nb, 0.20 wt% Al, 1.71 Wt.% Si.

The washcoat used in the present embodiments is in Example 3 of US 4,900,712 described in detail. The washcoat had a density of 1.45 kg / l and a solids content of 45.26%.

Embodiment 1

A nickel- and chromium-containing strip-shaped Inconel625 metal foam body was first dipped in a suspension containing aluminum silicate (ceramic coating grade HE, Office for Applied Mineralogy, Dr. S. Rudolph in Tönisvorst) and then dried at 120 ° C. and cured at 400 ° C coated with a thin layer (intermediate layer or protective layer). The ceramic coating HE contains 70% Al ₂ O ₃ .SiO ₂ and, as binder, 30% alkali silicate. This layer is characterized by a low porosity combined with a low BET surface area (DIN 66131) of <1 m ² / g, preferably <0.5 m ² / g. Subsequently, the support was coated with an alumina-based washcoat, dried at 120 ° C and calcined at 550 ° C for three hours. The coated body was aged by thermal treatment at 750 ° C for 24 hours in air atmosphere, simulating the interaction of metal substrate and catalytic coating in regenerating a particulate filter.

The coating was examined for the presence of nickel and chromium by SEM and EDX analyzes. The results are in 3 and show that neither nickel nor chromium was found in the washcoat layer, ie the catalytically active layer. The thin layer based on aluminum silicate therefore suppressed the migration of nickel and chromium from the metal substrate into the catalytically active washcoat layer.

In 2 In comparison, it can be seen that a strip-shaped Inconel625 metal foam body without such an intermediate layer between the metal substrate and the alumina-based washcoat after aging shows clear signals for nickel (signal at about 7.5 keV) and chromium (signal at about 5.45 keV). in the EDX spectrum.

1 shows the EDX spectrum of the previously described Inconel625 metal foam body without intermediate layer before aging. No chromium and nickel signals were observed.

Embodiment 2

embodiment 2 was obtained as Embodiment 1 except that instead of the ceramic coating grade HE based on aluminum silicate a ceramic coating grade LE based on CaO stabilized Zirconia was used. Calcination and aging of the coated metal foam body was carried out as in the embodiment 1. The ceramic coating grade LE, also from the office for Applied Mineralogy, Dr. Ing. S. Rudolph in Tönisvorst 72% CaO stabilized zirconia and 28% alkali silicate as a binder.

The EDX analysis according to 4 revealed that neither nickel nor chromium could be detected in the aged washcoat layer.

Summarized showed in contrast to the provided with the protective layer metal foam bodies the untreated metal foam body after aging a clear Signal from chrome and some nickel in the washcoat layer. The The protective layer according to the invention is thus able to migrate of metal cations from the metallic catalyst carrier to prevent.

The in the embodiments 1 and 2 obtained foams were after their metallization at 800 ° C for Aged 48 hours and then became a catalytic Reaction and the implementation of CO and hydrocarbons and NO followed to the oxidation products.

One Decrease in the catalytic activity of the coated Substrate of more than 5% based on the activity before Aging was unlike catalysts that do not have a first "protective layer" show, not observed.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 3894965 [0010]
• US 4900712 [0010, 0050]
• US Pat. No. 4003976 [0010]
• US 2004/0192546 A1 [0011]
• US 6887815 [0012]

Claims (12)

Catalyst comprising i) a metallic one Substrate having an inner surface; ii) a first layer, at least partially, both on the outer and / or the inner surface of the substrate containing a silicate, phosphate or an early transition metal oxide; iii) a second layer that is catalytically active, and that at least partially covered the first layer. Catalyst according to claim 1, characterized in that the oxide of the early transition metals is TiO ₂ or ZrO ₂ . Catalyst according to claim 2, characterized in that the TiO ₂ and / or ZrO _{2 are} additionally doped with divalent metal cations. Catalyst according to claim 1, characterized in that that the silicate and / or phosphate is a silicate and / or phosphate of aluminum and / or magnesium. Catalyst according to claim 4, characterized in that that the silicate and / or phosphate anion at least partially by other anions is replaced. Catalyst according to one of the preceding claims, characterized in that the substrate is porous or of channels at least partially completely is traversed. Catalyst according to claim 6, characterized in that the thickness of the first layer is <500 μm is. Catalyst according to one of the preceding claims, characterized in that the catalytically active layer contains metal oxides which are selected from Al ₂ O ₃ , CeO ₂ , La ₂ O ₃ , ZnO, ZrO ₂ , SnO ₂ , Y ₂ O ₃ , WO ₃ , TiO ₂ . Catalyst according to claim 8, characterized in that that the catalytically active layer at least one further catalytic contains active metal selected from the group consisting of tungsten, iron, vanadium, platinum, silver, gold, palladium, Ruthenium and rhodium. Catalyst according to claim 9, characterized in that the layer thickness of the catalytically active layer is <500 μm is. Use of a catalyst according to one of the claims 1 to 10, for the oxidation of hydrocarbons. Use of a catalyst according to one of the claims 1 to 10 for the oxidation of carbon monoxide and carbonaceous Particles.