EP3083047A1

EP3083047A1 - Zeolite catalysts containing titanium for the oxidation of methane in exhaust gas streams

Info

Publication number: EP3083047A1
Application number: EP14809023.6A
Authority: EP
Inventors: Arno Tissler; Frank Klose; Roderik Althoff; Beate ARENDT; Sascha Podehl; Patrick Mueller
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2013-12-20
Filing date: 2014-12-08
Publication date: 2016-10-26
Also published as: DE102013021750A1; US20160310895A1; CN105828938A; WO2015091076A1; AU2014365306A1; CN105828938B; AU2014365306B2

Abstract

The present invention relates to a method for the oxidation of short-chain hydrocarbons, in particular methane. Said method uses a catalyst comprising a zeolite material which contains titanium and at least two noble metals. The invention also relates to the use of said catalyst for the oxidation of short-chain hydrocarbons, in particular methane, in exhaust gas streams.

Description

Titanium-containing zeolite catalysts for the oxidation of methane in exhaust gas streams

The present invention relates to a process for the oxidation of short-chain hydrocarbons, in particular methane, using a catalyst comprising a zeolite material containing titanium and at least two noble metals. Furthermore, the present invention relates to the use of this catalyst for the oxidation of short-chain hydrocarbons, in particular of methane in exhaust gas streams.

Methane, which is found in trace amounts (ie less than 2 ppm) in the atmosphere, is a greenhouse gas that is 25 times more effective than CO ₂ in this regard. Its emission by non-natural processes ("anthropogenic methane") should therefore be reduced or avoided as far as possible Anthropogenic methane is produced primarily in agriculture, in the extraction of natural gas, eg by leaks, and in the incomplete combustion of natural gas, eg by burners or Typical industrial applications that produce methane-containing exhaust gas streams are mobile or stationary gas engines or gas-fired power plants, such as those used to generate electricity, but also to heat greenhouses, etc. The methane content in the exhaust gas streams can be effectively reduced by catalytic oxidation with oxygen become.

In the prior art, noble metal-containing oxidation catalysts for exhaust gas purification are known both in stationary and in mobile applications. Some of these noble metal-containing oxidation catalysts are also suitable for the oxidation of short-chain hydrocarbons, such as methane. The use of noble metals dispersed on a carrier material is known, metal oxides or zeolites being used as carrier material. Usually, first a washcoat of the carrier material is produced, which is applied to a shaped body, usually ceramic or metal substrates (eg honeycomb bodies) or to bulk material. The coated shaped articles thus obtained are subsequently impregnated with a noble metal solution and after an optional drying nungsschritt and the final calcination of the molding, the finished catalyst is obtained.

Alternatively, the noble metal component can also be applied directly to the support material and fixed by a calcination after a drying step. The impregnated carrier material is then processed to a noble metal-containing washcoat, which is applied to a molding or forms a solid catalyst after molding. After an optional drying step and the final calcination of the shaped body or solid catalyst, the finished catalyst is obtained.

Precious metals that are used in oxidation catalysts are often the precious metals of the 8th subgroup, including in particular Pt. The noble metals in the final catalyst are usually metal clusters, i. in highly dispersed form.

DE 102008057134 A1 relates to novel metal-containing silicates, in particular redox-active and crystalline silicates, a process for the preparation of metal-containing crystalline silicates and their use as a high-temperature oxidation catalyst or Dieseloxi- dationskatalysator. The process for producing metal-containing crystalline silicates is characterized in that a metal is introduced into a gallo-silicate, gallo-titanium silicate, boron silicate or boron-titanium silicate and then the gallo-silicate, gallo-titanium silicate , Boron-silicate or boron-titanium-silicate is calcined. Also described are a catalytic composition and a catalyst form body containing the metal-containing crystalline silicates.

Mori et al. (Studies in Surface Science in Catalysis (2007), 170B, p. 1319-1324) describes nanoparticles of platinum and palladium effective on titanium under UV irradiation by a photo-assisted deposition ("PED") method The metals with a size in the nanometer range were deposited directly onto the irradiation-excited tetrahedrally coordinated titanium dioxide residues within the lattices Characterized by XAFS and TEM analysis showed that the size of the Metal particles depends on the manufacturing process and that, compared to conventionally by impregnation nation produced catalysts, metal particles of smaller size are formed on the catalysts prepared by the Fotoabscheideverfahren. These nanometallic catalysts are useful as effective catalysts in various reactions, such as the oxidation of carbon monoxide and the direct synthesis of H ₂ O ₂ from H ₂ and O ₂ under aqueous conditions.

WO 2007037026 A1 describes a process for producing a catalyst by the steps of suspending a porous silicate material containing titanium in a solution in which a metal salt is dissolved and irradiating with UV radiation to precipitate and deposit microdispersion grains on the surface to effect the porous silicate material contained in the titanium and to achieve a satisfactory improvement of the catalytic activity. Also described is a catalyst thus obtained having sufficiently improved catalytic activity.

WO 95/1 1726 A1 relates to a method and a catalyst composition for the destruction of volatile organic compounds ("volatile organic compounds", "VOCs"). The method includes the step of contacting the VOCs with an oxygen-containing gas in the presence of a catalyst that is a metal-exchanged, metal-impregnated aluminosilicate zeolite having at least one exchanged metal in the zeolite selected from the group consisting of Ti, V, Cr, Co, Ni, Cu, Fe, Mo, Mn, Pd and Pt and at least one impregnated metal in the zeolite selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Pd and Pt and wherein the difference between the exchanged metal and the impregnated metal has an effect on the temperature necessary to promote the oxidation of compounds during a contact time necessary to oxidize the compounds. The reaction temperature of the process may be between about 100 to about 650 and the contact time may be between about 0.01 to 20 seconds. Preferably, the reaction temperature is between about 150 to about 450 and the contact time is about 0.1 to 1.0 seconds. The CO / CO ₂ ratio and the CI ₂ / HCl ratio in the gaseous effluent can be determined by selecting at least two impregnated metals with at least one exchanged metal in the aluminosilicate Zeolite or by the use of at least one impregnated metal having at least two exchanged metals in the aluminosilicate zeolite.

DE 102012003032.0 A1 relates to a process for the preparation of a bimetallic catalyst comprising palladium and platinum on a zeolitic support material, a bimetallic catalyst obtainable by the process and the use of the catalyst in oxidation catalysis. The process for preparing the bimetallic catalyst comprises the steps of a) impregnating a zeolitic support material with sulfur-free Pt and Pd precursor compounds, b) drying the impregnated zeolitic support material in air, and c) calcining the impregnated and dried zeolitic support material under inert gas. The catalyst can be used as oxidation catalyst for the oxidation of alkanes.

The structures of some zeolites are thermally stable and therefore suitable for use as support materials in exhaust gas catalysis. However, the structures of the zeolites can be damaged or destroyed at high temperatures and the simultaneous action of gaseous water, one speaks of lack of hydrothermal stability. The destruction of the structure of the zeolite, for example by dealumination, leads to the reduction of the inner surface of the zeolite, which is accompanied by a deactivation of the catalyst. The collapse of the zeolite structure leads to sintering of the metal clusters, which lose their optimal size and form larger clusters with reduced active surface area. The lack of hydrothermal stability is a problem especially in the oxidative catalytic exhaust gas treatment, since in the exhaust gas streams of eg internal combustion engines or burners in addition to CO ₂ and carbon monoxide large amounts of water (often up to 20 vol .-%) is included, for example, by the previous fuel combustion or is caused by the catalytic oxidation of hydrocarbons. At the same time, the oxidation of the hydrocarbons requires an increased temperature and the oxidation of the hydrocarbons creates additional heat, so that peak temperatures of over 600 are reached.

The hydrothermal stability of the catalyst is therefore a decisive criterion in oxidative exhaust gas purification and the noble metal oxides known from the prior art. cationic catalysts with zeolitic carrier material have the disadvantage of lack of hydrothermal stability. The object of the invention is to provide a catalytic process with which hydrocarbons, including in particular methane, in water-containing exhaust gas streams can be effectively and stably reduced over a longer time.

This object is achieved by a method for the oxidation of short-chain hydrocarbons, in particular of methane, in which a catalyst is used which comprises a titanium-containing zeolite material containing at least two precious metals. Surprisingly, it has been found that catalysts containing a titanium-containing zeolite material containing at least two precious metals, have high activity and are extremely hydrothermally stable.

The zeolite material in this case corresponds to the zeolitic carrier material in which the active noble metals are contained. Zeolite materials in the context of the present invention consist of zeolites or zeotypes. According to the definition of the International Mineralical Association (DS Coombs et al., Canadian Mineralogist, 35, 1979, p. 1571), zeolites represent a crystalline substance from the group of aluminum silicates with a spatial network structure consisting of Si0 / Al0 tetrahedra common oxygen atoms are linked to a regular three-dimensional network. The zeolites are classified according to their topology in different structural types. The zeolites are distinguished mainly by the geometry of the cavities and channels formed by the rigid network of the Si0 / Al0 tetrahedra, ie the crystalline structure, which are characteristic of each type of structure. Certain zeolites show a uniform structure structure with linear or zigzag-shaped channels, z. For example, the ZSM-5 structure with MFI topology, in others close behind the pore openings larger cavities, z. As in the Y or A zeolites, with the topologies FAU and LTA. An overview of the different structures and their topologies can be found in "Atlas of Zeolite Framework Types" (Ch.Berercher, WM Meier, OH Olson, Elsevier, 5 ^th revised edition, 2001).

Zeotypes are crystalline substances whose structure corresponds to zeolites, in contrast to zeolites some or all Si0 / Al0 tetrahedra are replaced by foreign atoms in zeotypes, these can be eg P, N or Ti.

The zeolite material according to the invention may be, for example, a zeolite having the structure type MFI, BEA, MOR, MEL or CHA. Preference is given to zeolite materials of the structure type MFI or BEA. When a MFI-type zeolite material is used, the zeolite material is most preferably a zeolite material of the TS-1 type, also known as titanium silicalite. Titanium silicalite is a crystalline zeotype material with tetragonal [Ti0] and [Si0] units arranged in an MFI structure and whose pore openings are ring size 10. Due to this structure, TS-1 shows a three-dimensional pore system with pores of diameters between 5.1 and 5.6 angstroms, which are the micropores of the system. TS-1 is commercially available, e.g. by the manufacturer Polimeri Europa SpA.

If a zeolite material of the structural type MEL is used, the zeolite material is particularly preferably a zeolite material of the TS-2 type. TS-2 is a titanium-containing crystalline zeolite material structurally equivalent to ZSM-1 1. It has tetragonal [Ti0] and [Si0] units, which are arranged in a MEL structure and whose pore openings have the ring size 10. Due to this structure, TS-2 shows a three-dimensional pore system with pores that are 5.2 angstroms in diameter, which are the micropores of the system.

Preferably, the zeolite material is a zeolite material of the TS-1 or TS-2 type. The zeolite material of the TS-1 type is also known as titanium silicalite and has the structure type MFI. The TS-2 type zeolite material is a titanium-containing crystalline zeolite material which structurally corresponds to ZSM-1 1 and has the structural type MEL.

The zeolite material according to the invention is either aluminum-free zeolites or zeolites rich in silicon, ie the proportion of Al or other metals which are not noble metals is low. As silicon-rich zeolites in the context of this invention, zeolites are to be understood which have a Si / metal molar ratio of greater than 10: 1, preferably greater than 20: 1. The pore openings of the zeolites or zeotypes of the zeolite material according to the invention are formed by rings of the ring sizes 8, 10 or 12, wherein the indication refers to the number of SiO ₄ / AIO ₄ tetrahedra per ring of the opening. The expert speaks here of narrow, medium and large pore zeolites. According to the invention are medium and wide pore zeolites with pore openings of the ring size 10 or larger, more preferably with pore openings of the ring size 12 or greater.

The characteristic cavities and channels of the zeolite materials may be filled with water molecules and additional framework cations that can be exchanged. The catalytically active noble metals may be integrated atomically or in the form of clusters into the cavities and channels of the zeolite material or may be present on the outer surface of the zeolite material.

The titanium content in the zeolite material is preferably below 15% by weight, more preferably below 10% by weight, even more preferably below 3% by weight, particularly preferably below 2% by weight, most preferably below 1% by weight, in each case on the total weight of the titanium-containing zeolite material. In a particularly preferred manner, the titanium is embedded predominantly in the form of titanium tetrahedra in the crystalline structure of the zeolite material, so that no or only slightly crystalline titanium dioxide is present. This is realized with zeolite materials of the TS-1 or TS-2 type, which preferably have a Ti content of between 0.2 to 1% by weight.

The noble metal-containing zeolite material comprised by the catalyst must contain at least two precious metals, but may also contain more than two precious metals. The precious metal is preferably a noble metal selected from the group consisting of Pt, Pd, Rh, Ru, Cu, Ag and Au, preferably a bimetallic combination of the noble metals Pt and Pd. If the bimetallic precious metal combination of Pd and Pt is realized, the noble metals are typically present in an atomic ratio of Pd / Pt of 1:10 to 10: 1, preferably of 5: 2 to 7: 2 and more preferably of 3: 1. The noble metals used in the catalyst are preferably in the pores of the zeolite material. It can therefore choose a synthesis method which leads to the precious metals being present wholly or predominantly in the micropores of the zeolite and not or only to a small extent on the outer surface of the zeolite.

The catalyst according to the invention can be used as a powder, as a full catalyst or as a coating catalyst, i. applied to a shaped body, present.

The pulverulent catalyst according to the invention can consist of the zeolite material loaded with noble metals, but it can also be mixed with excipients such as binders prior to use.

An unsupported catalyst may be formed by forming the noble metal-loaded powdery zeolite material, for example, molding an extruded molded article or a monolith. Further preferred shaped bodies are, for example, spheres, rings, cylinders, perforated cylinders, trilobes or cones, with a monolith, such as, for example, a monolithic honeycomb body, being particularly preferred. For this purpose, either the pure powdered zeolite material loaded with noble metals is formed or adjuvants such as binders or porosity formers are added. Finally, the blank formed by the molding is dried and finally calcined.

Furthermore, the catalyst according to the invention can be present as a coating catalyst in which the catalyst is present as a layer on a shaped body. The noble metal-containing zeolite material can preferably be processed with a preferably silicate binder to a washcoat and applied as a washcoat coating on a shaped body. The mass ratio binder / catalytically noble metal-containing zeolite is in this case 0.01 to 0.5, preferably 0.02 to 0.3 and particularly preferably 0.04 to 0.25, based in each case on the solids content of binder and catalytically active composition. Finally, the crude still moist coating catalyst is dried and finally calcined.

The shaped body can be, for example, an open-pored foam structure, for example a metal foam, a metal alloy foam, a silicon carbide foam, an Al ₂ 0 ₃ foam, a mullite foam, an Al titanate foam or a monolithic support structure, for example, having parallel aligned channels, which may be conductively connected to each other or may contain certain internals for Gasverwirbelung.

Likewise preferred shaped bodies are formed, for example, from a metal sheet, from any metal or metal alloy, which have a metal foil or sintered metal foil or a metal mesh and are produced, for example, by extrusion, winding or stacking. In the same way, support bodies of ceramic material can be used. Often, the ceramic material is an inert, low surface material such as cordierite, mullite, alpha-alumina, silicon carbide or aluminum titanate. However, the support body used can also consist of hochoberflächigem material such as gamma-alumina or Ti0 ₂ .

The drying of the solid catalyst or the coated catalyst is carried out by a drying step at temperatures in the range between 50 to 150, preferably 80 to 120 for a period of more than 2 h, preferably about 16 hours. The calcination of the full catalyst or the coated catalyst is carried out by a calcining step preferably at temperatures of 300 to 600 s, more preferably at 400 to 550. The calcination time is in this case preferably 1 to 8 hours, more preferably 2 to 6 hours and especially about 3 to 5 hours.

The introduction of the at least two precious metals into the zeolite material may be e.g. by impregnation with one or more, preferably aqueous, solutions which contain the noble metals in the form of precursor compounds. The impregnation can be carried out by all methods known to the person skilled in the art. If the zeolite material is in the form of a powder, the impregnation of the zeolite material is preferably carried out according to the incipient wetness method known to the person skilled in the art.

If an unsupported catalyst or a coating catalyst is to be obtained, it can be prepared by molding the noble metal-containing zeolite material or by coating a shaped body with a noble metal-containing zeolite material. Al Alternatively, the production of the full catalyst or of a coating catalyst can also be effected by the impregnation of the shaped body or of the shaped body coated with the zeolite material with a noble metal-containing solution. The noble metal-containing solution is preferably an aqueous solution which contains one or more noble metal precursor compounds. As noble metal precursor compound, for example, nitrates, acetates, oxalates, tartrates, formates, amines, sulfides, carbonates, halides or hydroxides of the corresponding noble metals can be used, with nitrates being preferred. The precious metal precursor compounds should be substantially free of sulfur. It may also be preferred for the purposes of the invention that the noble metal precursor compounds have the same anion, for example nitrate. When a bimetallic precious metal combination of Pd and Pt is realized, the Pt and Pd precursor compounds are preferably platinum nitrate or palladium nitrate.

Optionally, after the impregnation, a drying step takes place. The drying step of the impregnated powdery zeolite material or of the impregnated shaped body or full catalyst is preferably carried out below the decomposition point of the noble metal precursor compound. The drying step preferably takes place in air. The drying temperatures are usually in the range from 50 to 150, preferably 80 to 120. The drying time is preferably more than 2 hours, more preferably about 16 hours.

Following the drying step, a calcining step of the powdered zeolite material or the impregnated molding takes place. The calcination step is preferably carried out at temperatures of 300 to 600, more preferably 400 to 550. The calcination time is preferably 1 to 8 hours, more preferably 2 to 6 hours and especially about 3 to 5 hours.

The total loading of noble metal based on the zeolite material is in the range of 0.1 to 10 wt .-%, preferably in the range of 1 to 5 wt .-%, based on the total weight of the calcined noble metal-containing zeolite material. The BET surface area of the noble metal-containing zeolite material is preferably in the range of 10 to 1000 m ² / g, more preferably 50 to 800 m ² / g, and most preferably 300 to 700 m ² / g. The BET surface is determined by adsorption of nitrogen in accordance with DIN 66131.

The catalyst of the invention is characterized by a high aging stability in the presence of water. Preferably, the exhaust gas stream contains at least 1% by volume of water in gaseous form, in particular the exhaust gas stream contains more than 5% by volume or more than 20% by volume of water in gaseous form.

Short-chain hydrocarbons are understood as meaning alkanes or alkenes which have not more than 5 carbon atoms, in particular methane, ethane, propane and also ethene and propene. Especially preferred are alkanes having not more than 5 carbon atoms, i. Pentane (e), butane (e), propane, ethane or especially methane. Particularly preferred are alkanes with less than three carbon atoms, including in particular methane.

The oxidation of the short-chain hydrocarbons takes place with the aid of an oxidizing agent, which is preferably a gaseous oxidizing agent. The gaseous oxidizing agent may in particular be molecular oxygen of the formula O ₂ or O ₃ , a nitrogen oxide of the formula N ₂ O, NO or NO ₂ , or mixtures of these gaseous oxidizing agents. If short-chain hydrocarbons are catalytically oxidized in an exhaust gas stream by the catalyst according to the invention, then the oxidizing agents are present in the untreated exhaust gas stream upstream of the catalyst.

characters

FIG. 1 shows the test results obtained in the testing of the catalyst Pt / Pd TS-1 No. 1 according to the invention and the comparative catalyst Pt / Pd BEA No. 1. The measurements were carried out at a water content of 0, 5, 10 and 20% by volume H ₂ O, an oxygen content of 10% by volume O ₂ and a methane content of 0.1% by volume in the educt. ktstrom. After the step of increasing the water content in the educt gas, a further test was carried out in each case.

FIG. 2 shows the test results which were obtained during the testing of the catalyst Pt / Pd TS-1 No. 1 according to the invention as a function of different water contents in the educt gas. The catalyst according to the invention was measured in each case twice at 0% by volume of H ₂ O and at 10% by volume of H ₂ O in a feedstock gas stream which otherwise contains 0.1% by volume of methane and 10% by volume. % 0 ₂ contained. Subsequently, under otherwise unchanged conditions, a measurement was carried out at a reduced oxygen content of 0.2% by volume O ₂ (the volume was equalized by the corresponding addition of nitrogen). This was followed by two hydrothermal aging steps, each followed by a test of the sample at 10 vol .-% H ₂ 0 and 10 vol .-% 0 ₂ in Eduktgasstrom and otherwise unchanged conditions.

FIG. 3 shows the test results obtained in the test of the comparative catalyst Pt / Pd Al ₂ O ₃ No. 1 as a function of the water content in the educt gas. The catalyst was measured successively at 0% by volume of H ₂ O and 10% by volume of H ₂ O in a feed gas stream which otherwise contained 10% by volume of O ₂ and 0.1% by volume of methane. This was followed by two hydrothermal aging steps, each followed by a test of the sample at 10 vol .-% H ₂ 0 and 10 vol .-% 0 ₂ in Eduktgasstrom and otherwise unchanged conditions.

FIG. 4 shows the test results which were obtained in the test of the comparative catalyst Pt / Pd BEA No. 1 as a function of different water contents in the educt gas. The catalyst was in each case tested twice at 0% by volume of H ₂ O and in each case once at 5, 10, 15 and 20% by volume of H ₂ O in a feed gas stream which was otherwise 0.1% by volume. Methane and 10 vol .-% 0 ₂ contained. This was followed by a hydrothermal aging step and the testing of the sample at 10 vol .-% H ₂ 0 and 10 vol .-% 0 ₂ in Eduktgasstrom and otherwise unchanged conditions.

FIG. 5 shows the test results obtained in the testing of the catalysts according to the invention (Pt / Pd TS-1 No. 1) and the comparative catalysts (Pt / Pd Al ₂ O ₃ No. 1 and No. 2 as well as Pt / Pd BEA No. 1 and No. 2). The catalysts were dissolved in a starting material tested gas stream containing 0.1 vol .-% of methane, 0 vol .-% H ₂ 0 and 10 vol .-% 0 ₂ . Subsequently, some of the catalysts were tested a second time under the same conditions (2nd measurement).

FIG. 6 shows the test results obtained in the testing of the catalysts according to the invention (Pt / Pd TS-1 No. 1) and the comparative catalysts (Pt / Pd BEA No. 1 and No. 2 as well as Pt / Pd Al ₂ O ₃ No. 1 and 2). The catalysts were tested in a reactant gas stream containing 0.1% by volume of methane, 10% by volume of H ₂ O and 10% by volume of O ₂ . Subsequently, some of the catalysts were tested a second time under the same conditions (2nd measurement).

FIG. 7 shows the test results obtained in the testing of the catalyst according to the invention (Pt / Pd TS-1 No. 1) and the comparative catalysts (Pt / Pd BEA No. 1 and 2 and Pt / Pd Al ₂ O ₃ No. 1 and 2 ) were carried out after a hydrothermal aging step. The measurement was carried out in each case in a reactant stream which contained 0.1% by volume of methane, 10% by volume of H ₂ O and 10% by volume of O ₂ .

FIG. 8 shows the test results which were carried out during the testing of the catalyst according to the invention (Pt / Pd TS-1 No. 1) and the comparative catalysts (Pt / Pd Al ₂ O ₃ Nos. 1 and 2) after a second hydrothermal aging step. The samples Pt / Pd BEA no. 1 and 2 showed no significant activity. The measurement was carried out in each case in a reactant stream which contained 0.1% by volume of methane, 10% by volume of H ₂ O and 10% by volume of O ₂ .

FIG. 9 shows the test results obtained in the testing of the catalyst according to the invention (Pt / Pd TS-1 No. 2) and the comparative catalysts (Pt / Pd SIL No. 1, Pt / Pd BEA No. 3 and 4 and Pt / Pd Al ₂ 0 ₃ Nos. 3 and 4) in a measurement with a reactant gas mixture, which simulates the exhaust gas of a gas engine. The educt gas mixture contained 3 vol .-% H ₂ 0, 10 vol .-% 0 ₂ , 0.08 vol .-% CO and 0.1 vol .-% methane (in addition to other hydrocarbons). Each sample was tested once more after a hydrothermal aging step. FIG. 10 shows the test results obtained in the time-dependent testing of the catalyst according to the invention (Pt / Pd TS-1 No. 2) and the comparative catalysts (Pt / Pd BEA No. 3 and 5 and Pt / Pd Al ₂ O ₃ No. 3). were obtained. The measurement was carried out at a temperature of 550, with a reactant gas mixture which simulates the exhaust gas of a gas engine. The educt gas mixture contained 3 vol .-% H ₂ 0, 10 vol .-% 0 _2, 0.08 vol .-% CO and 0.1 vol .-% methane (in addition to other hydrocarbons).

measurement methods

Elemental analysis with ICP:

The ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) for determining the elemental composition or the SiO ₂ / Al ₂ O ₃ ratio was carried out with the device ICP Spectro Modula / Arcos. The following chemicals were used: sulfuric acid 98% pA, hydrofluoric acid 37% pA, hydrochloric acid 37% pA The sample was finely ground.

To determine the Si and Al contents, 100 mg of sample were weighed into a 100 ml plastic beaker and admixed with 1 ml of sulfuric acid and 4 ml of hydrofluoric acid. The water bath was digested at 85 ° C. for 5 minutes, giving a clear solution. Now it was tempered, filled and shaken. All elements were measured at the ICP, as were corresponding standards. Si was measured with the following settings: Wavelength: 288.158 nm. Al was measured with the following settings: Wavelength: 396.152 nm.

For Pt and / or Pd, enough sample was weighed to contain about 3 mg of Pt or Pd therein. Subsequently, in each case 6 ml of hydrofluoric acid and hydrochloric acid were added. The mixture was then stirred for 30 minutes at 180 ° C with stirring to produce a clear solution. Now it was tempered, filled and shaken. All elements were measured at the ICP, as were corresponding standards. Pt was measured with the following settings: Wavelength: 214.423 nm. For Pd, the wavelengths are: 324.270 nm. All standards were adjusted with HF and HCl or H ₂ S0. The evaluation followed the following calculation:

w (E ^* in percent) = ß (E ^* value in mg / l) x V (volumetric flask in I) x 100 / m (weight in mg)

(E ^* = respective element). BET surface area:

The determination of the specific surface of the materials is carried out according to the BET method according to DIN 66131; a publication of the BET method can also be found in J. Am. Chem. Soc. 60, 309 (1938). The sample to be determined was dried in a quartz tube at 350 under vacuum (F = 50 ml (min) for 1.5 h). The reactor was then cooled to room temperature, evacuated, and dipped in a Dewar flask with liquid nitrogen. Nitrogen adsorption was performed at 77 K with an RXM 100 sorption system (Advanced Scientific Design, Inc.).

Example 1: Preparation of the catalyst based on TS-1 according to the invention

A zeolite of type TS-1 was impregnated with the Incipient Wetness method with a platinum nitrate and palladium nitrate solution. For this purpose, the water absorption of the zeolite was determined and added an appropriate amount of impregnating solution (228.5 ml) to 500 g of TS-1. During the impregnation, the batch was stirred continuously and ensured that a homogeneous impregnation takes place. Subsequently, the powder was transferred to a calcination dish.

The powder was dried at 90 for 16 h. Subsequently, the material was purged with argon in a special oven for about 5 minutes and heated from room temperature to 550 at a rate of 2 per minute. After 5 hours of calcination under argon at 550, the reaction was cooled to room temperature within 3 h.

The calcined Pd / Pt-TS-1 was mixed with 20 wt .-% in Bindzil 2034 Dl suspension (amorphous Silikaso Eka-Chemicals AB, Bohus Sweden) and water to a homogeneous suspension stirred up. The suspension was dispersed for 5 minutes with the Ultraturax, so that a washcoat with a D ₅₀ value of 3 to 4 μππ was obtained. The washcoat was then coated onto a cordierite honeycomb (200 cpsi) by immersing the backing in the washcoat. After draining and blowing the carrier with compressed air, a target loading of about 160 g / l was obtained. The coated honeycomb was air-dried at 120 overnight and then calcined at 550 in air for 3 hours.

Table 1: Synthesized catalysts based on TS-1 according to the invention

In each case based on the volume of the honeycomb.

2 Without precious metals

Comparative Example 1 Preparation of Comparative Catalyst Based on Zeolite BEA-150

Two comparative samples were prepared by the same method of preparation as described in Example 1, except that zeolite beta was used as the starting material and was calcined with air after impregnation. The approximate target loading was about 140-200 g / l each, based on the volume of the honeycomb. The honeycombs coated according to this example correspond to the comparative catalysts designated Pt / Pd BEA No. 1-5.

Table 2: Synthesized comparative catalysts based on zeolite beta

Pt / Pd BEA No. 2 BEA 0.766 2.163 0.9: 99.1 138.5

Pt / Pd BEA No. 3 BEA 0.96 2.78 0.7: 99.3 199.4

Pt / Pd BEA No. 4 BEA 0.80 2.64 1, 1: 98.9 199.4

Pt / Pd BEA # 5 BEA 0.82 2.31 1, 1: 98.9 148.0

In each case based on the volume of the honeycomb.

2 Without precious metals

Comparative Example 2, Preparation of honeycomb coated with noble metal-containing alumina

A comparative sample was prepared using the same preparation procedure as described in Example 1, except that the starting material used was a gamma-alumina doped with rare-earth elements for stabilization (referred to as Al ₂ O ₃ ). The approximate target loading was 50 g / l or 100 g / l, based on the volume of the honeycomb. The honeycombs coated according to this example correspond to the catalysts used for comparison with the designations Pt / Pd Al ₂ O ₃ Nos. 1 to 4.

Table 3: Synthesized comparative catalysts based on alumina

In each case based on the volume of the honeycomb.

2 Without precious metals Comparative Example 3 Preparation of the Comparative Catalyst Based on Zeolite Silicalite

A comparative sample was prepared by the same production method as described in Example 1, except that a silicalite type zeolite was used as the starting material. The approximate target loading was 165 g / l, based on the volume of the honeycomb. The honeycomb coated according to this example corresponds to a comparative catalyst and is referred to as Pt / Pd SIL No. 1.

Table 4: Synthesized comparative catalysts based on silicalite

¹ In each case based on the volume of the honeycomb.

² without precious metals

Hydrothermal aging

In order to simulate the aging of the catalysts, a hydrothermal aging process step has been carried out, in which the aging effects which occur during operation are accelerated. For this purpose, the sample was heated to 700 and treated for 24 h with a 10 vol .-% water and 10 vol .-% oxygen-containing gas. The hydrothermal aging process has sometimes been carried out several times.

testing

The samples were tested by testing for catalytic activity in the oxidation of methane. For this purpose, a reactant stream was used which contained 0.1% by volume of methane (1000 ppmV), 10% by volume of O ₂ and 0 to 20% by volume of H ₂ O and the rest of the nitrogen as the carrier gas. In some experiments, this resulted in a reduced oxygen concentration of 0.2 Vol .-% used. To simulate the exhaust flow of a gas engine, a special gas mixture was used, the 3 vol .-% H ₂ 0, 10 vol .-% 0 ₂ , 0.08 vol .-%, CO, 0.1 vol .-% Methane, 0.02 vol.% Ethane 0.02 vol.%, Ethene, 0.018 vol.% Propane.

The gas hourly space velocity was 40,000 h ^-1 in all experiments, and the carrier gas addition was set so that the flow rate remained constant despite different gas concentrations. The sample was heated to 550 at a rate of 50 / min and in the temperature range between about 550 and 350 with falling temperature ramps The analysis of the gas composition before and after the catalyst was carried out with the aid of an FTIR spectrometer.

Claims

claims:

A process for the oxidation of short chain hydrocarbons which uses a catalyst comprising a zeolite material containing titanium and at least two precious metals, characterized in that the zeolite material is a zeolite material of the TS-1 or TS-2 type.

2. The method according to any one of the preceding claims, characterized in that the crystalline structure of the zeolite material contains Ti atoms.

3. The method according to claim 2, characterized in that the Ti atoms are tetrahedrally coordinated.

4. The method according to any one of the preceding claims, characterized in that the zeolite material contains at least two precious metals selected from the group consisting of Pt, Pd, Rh, Ru, Cu, Ag and Au.

5. The method according to any one of the preceding claims, characterized in that the zeolite material contains the precious metals Pt and Pd.

6. The method according to claim 5, characterized in that the noble metals Pd and Pt in an atomic ratio of 1:10 to 10: 1, preferably from 5: 2 to 7: 2, are present.

7. The method according to any one of the preceding claims, characterized in that the noble metals are in the pores of the zeolite material.

8. The method according to any one of the preceding claims, characterized in that the catalyst is applied to a shaped body made of metal or ceramic.

9. The method according to any one of the preceding claims, characterized in that the method, an exhaust gas stream is treated.

10. The method according to claim 9, characterized in that the exhaust gas stream at least 1 vol .-% water, preferably more than 5 vol .-% water.

1 1. A method according to claim 9, characterized in that the exhaust gas stream contains more than 20 vol .-% water.

12. The method according to any one of the preceding claims, characterized in that the oxidation of the short-chain hydrocarbons by a gaseous oxidizing agent takes place.

13. The method according to claim 12, characterized in that the gaseous Oxidati- onsmittel molecular oxygen or a nitrogen oxide.

14. Use of a catalyst which comprises a zeolite material of the type TS-1 or TS-2 and which contains at least two noble metals for the oxidation of short-chain hydrocarbons in exhaust gas streams.