Hydrocarbon oxidation catalyst and method for producing the same

Abstract

To provide a hydrocarbon oxidation catalyst that can oxidize hydrocarbons such as methane contained in exhaust, with high efficiency, even under low temperature conditions.SOLUTION: A hydrocarbon oxidation catalyst includes a carrier and a catalytic active component supported on the carrier, where the catalytic active component includes a catalyst metal and a carbide of the catalyst metal.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a hydrocarbon oxidation catalyst, and more particularly to a hydrocarbon oxidation catalyst suitable for use in purifying exhaust gas from an internal combustion engine, and a method for producing the same. [Background technology]

[0002] Exhaust gas discharged from internal combustion engines such as boilers, gas turbines, gasoline engines, and diesel engines contains many harmful substances derived from the fuel and combustion air. These harmful substances include hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). Regulations on the emission of these harmful substances are becoming stricter every year, and various catalysts are being investigated to effectively purify exhaust gas containing these harmful substances.

[0003] The environmental temperature required for a catalyst to purify the above-mentioned harmful components is generally 200°C or higher, and the heat of the exhaust gas is usually used. However, when the temperature of the exhaust gas purification catalyst has not yet reached the temperature required for purification, such as immediately after a cold start of the engine, the activity of the exhaust gas purification catalyst is insufficient, and there is a risk that unpurified harmful components (also known as cold emissions) will be discharged into the environment.

[0004] In recent years, carbon dioxide (CO 2 ) emissions regulations are being strengthened. 2 Since the amount of CO2 emissions is proportional to the amount of fuel used to run the engine, it is desirable for internal combustion engines to use less fuel and have good fuel economy. Therefore, research into various efficient combustion conditions with less heat loss and exhaust loss is underway, but this means a decrease in combustion temperature, and the exhaust gas temperature required for catalytic activity tends to become lower. As a result, the time that conventional catalysts are maintained at their active temperature is becoming shorter, giving rise to a new problem in that they are no longer able to sufficiently remove harmful substances.

[0005] Furthermore, when internal combustion engines use fuels that consist of methane, such as compressed natural gas (CNG) or liquefied natural gas (LNG), CO 2 However, methane, which has a high global warming potential, is emitted as an unburned component, and when combined with the fuel efficiency improvement measures mentioned above, there was a problem that the greenhouse gas reduction effect of conventional catalysts became even more insufficient.

[0006] In response to the above problems, for example, Patent Document 1 proposes a catalyst that supports platinum, ruthenium, and chlorine on a zirconium support having a specific specific surface area as a catalyst that can efficiently remove methane from exhaust gas. Patent Document 2 also proposes that a decrease in the hydrocarbon oxidation performance of the catalyst can be suppressed by supporting platinum and palladium on an alumina support under specific conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-169480 A [Patent Document 2] JP 2001-129400 A Summary of the Invention [Problem to be solved by the invention]

[0008] Currently, the main fuel for internal combustion engines is petroleum and other fossil fuels, but in the future, it is expected that this will be changed to fuels with lower environmental impact (for example, natural gas, shale gas, methane and ammonia mixed gas), and it is expected that unburned methane and other hydrocarbons will be emitted in greater quantities than at present. Therefore, it is believed that there will be an increasing demand in the future for exhaust gas purification catalysts with excellent purification performance for hydrocarbons such as methane.

[0009] Therefore, an object of the present invention is to provide a hydrocarbon oxidation catalyst capable of oxidizing hydrocarbons such as methane contained in exhaust gas with high efficiency even under low temperature conditions. Another object of the present invention is to provide a method for producing the above-mentioned hydrocarbon oxidation catalyst. [Means for solving the problem]

[0010] As a result of intensive research conducted by the inventors to achieve the above object, they have found that a catalyst carrying a catalytic metal and a carbide of the catalytic metal can oxidize hydrocarbons such as methane contained in exhaust gas with high efficiency even at relatively low temperatures. They have also found that the catalyst can be produced by subjecting catalytic particles carrying a catalytic metal to a predetermined temperature environment in the presence of hydrocarbons, so that a carbide of the catalytic metal precipitates on the carrier. The present invention is based on such findings. That is, the gist of the present invention is as follows.

[0011] [1] A hydrocarbon oxidation catalyst comprising a support and a catalytically active component supported on the support, A hydrocarbon oxidation catalyst, wherein the catalytically active component comprises a catalytic metal and a carbide of the catalytic metal. [2] The hydrocarbon oxidation catalyst according to [1], wherein the catalytic metal comprises at least one metal selected from the platinum group elements. [3] The hydrocarbon oxidation catalyst according to [2], wherein the platinum group metal is at least one selected from the group consisting of rhodium, palladium, platinum and ruthenium. [4] The hydrocarbon oxidation catalyst according to [3], wherein the catalytic metal further contains at least one transition metal selected from the group consisting of nickel, iron and copper. [5] The hydrocarbon oxidation catalyst according to any one of [1] to [4], wherein the support contains at least one inorganic oxide selected from the group consisting of alumina, silica, zirconia and ceria. [6] The hydrocarbon oxidation catalyst according to any one of [1] to [5], which is used for purifying exhaust gas from an internal combustion engine. [7] A method for producing the hydrocarbon oxidation catalyst according to any one of [1] to [6], comprising the steps of: preparing catalyst particles including a support and a catalytic metal supported on the support; contacting the catalyst particles with a feed gas containing a hydrocarbon having 1 to 10 carbon atoms in an environment of 600°C or less; A carbide of the catalytic metal is supported on a support of the catalytic particle. A method for producing a hydrocarbon oxidation catalyst, comprising: [8] The method according to [7], wherein the raw material gas is brought into contact with the catalyst particles in an environment of 300°C or lower. [9] The manufacturing method according to [7] or [8], wherein the hydrocarbon concentration in the raw material gas is higher than the oxygen gas concentration.

[10] The method according to any one of [7] to [9], wherein the hydrocarbon comprises methane. Effect of the Invention

[0012] According to the hydrocarbon oxidation catalyst of the present invention, by using a catalyst supported on a catalytic metal and a carbide of the catalytic metal, hydrocarbons such as methane contained in exhaust gas can be oxidized with high efficiency even under low temperature conditions. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a photoelectron spectrum of the Pd3d inner shell of the catalyst particles of Example 1 measured by the XPS method. [Diagram 2] FIG. 2 is a photoelectron spectrum of the Pd3d inner shell of the catalyst particles of Example 2 measured by the XPS method. [Diagram 3] FIG. 3 is a photoelectron spectrum of the Pd 3d inner shell of the catalyst particles of Comparative Example 1 measured by the XPS method. [Figure 4] FIG. 4 shows the results of a CH4 conversion test using the catalyst particles of Example 1, Example 2, and Comparative Example 1. [Diagram 5] FIG. 5 shows a comparison of the temperatures (T50) at which a purification rate of 50% is shown, calculated from CH4 conversion tests using the catalyst particles of Example 1, Example 2, and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The hydrocarbon oxidation catalyst according to the present invention comprises a carrier and a catalytically active component supported on the carrier, and is characterized in that a catalytic metal and a carbide of the catalytic metal are used in combination as the catalytically active component. In the present invention, the term "supporting the catalytically active component" refers to a state in which the catalytically active component is physically or chemically adsorbed or held on the outer surface or inner pore surfaces of the carrier. Each of the components of the hydrocarbon oxidation catalyst according to the present invention will now be described.

[0015] <Carrier> As the carrier for supporting the catalytically active component, any carrier known in the art for use in exhaust gas purification catalysts can be used without any restrictions, and in particular, inorganic oxides can be used. As the inorganic oxide, alumina (Al 2 O 3 ), zirconia (ZrO 2 ), silica (SiO 2 ), Celia (CeO 2 ), titanium dioxide (TiO 2 ), lanthanum oxide (La 2 O 3 ) and other rare earth oxides (Re 2 O 3 ), zeolite (aluminosilicate), MgO, ZnO, SnO 2 Examples of oxide materials include oxide materials based on Al, Zr, Si, Ti, rare earth elements, phosphates and borates of Mg, Zn, etc., and poorly soluble sulfates of alkaline earth metals such as Ba and Sr.

[0016] Among the above inorganic oxides, alumina, silica, zirconia, and ceria can be preferably used. In particular, by using a carrier containing zirconia or ceria, the catalytic activity at low temperatures can be improved.

[0017] Examples of alumina include γ-alumina, δ-alumina, and θ-alumina. Silica includes amorphous, glassy, ​​and colloidal silica, as well as crystalline silica with various different phase transformations. Silica generally has a higher BET specific surface area than alumina, and platinum group elements are highly dispersed in silica. Silica-alumina is available in crystalline and non-crystalline forms. In silica-alumina, the Si / Al ratio varies and is appropriately set according to the application. Examples of titania include anatase-type titania. Examples of crystalline zeolites include ZSM-type zeolites and β-type zeolites. The base particles can be used alone or in appropriate combination of two or more types.

[0018] Examples of ceria include cerium (IV) oxide, cerium-rare earth element composite oxides other than cerium, cerium-transition element composite oxides, and cerium-rare earth element-transition element composite oxides other than cerium. Among these, cerium (IV) oxide or ceria-zirconia composite oxides are preferred. Note that the ceria-based (composite) oxide is one in which the mass ratio of Ce is greater than or equal to the oxide (CeO 2 ) is preferably used in an amount of 50% by mass or more and 95% by mass or less in total.

[0019] Examples of zirconia include zirconium (IV) oxide, zirconium-cerium and rare earth element composite oxides other than zirconium, zirconium-transition element composite oxides, zirconium-cerium and rare earth element-transition element composite oxides other than zirconium, and the like. Among these, zirconia-based composite oxides in which rare earth elements other than cerium and zirconium are dissolved in solid solution are more preferred. Note that, as for zirconia-based (composite) oxides, those in which the mass ratio of Zr is an oxide (ZrO 2 ) is preferably used.

[0020] The above-mentioned ceria-based (composite) oxide and zirconia-based (composite) oxide may contain rare earth elements other than cerium and zirconium, such as scandium, yttrium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these rare earth elements, yttrium, lanthanum, praseodymium, and neodymium are preferable. The rare earth elements can be used alone or in appropriate combination of two or more. When a rare earth element is contained, its content is not particularly limited, but is preferably 0.1 to 50 mass%, more preferably 3 to 50 mass%, and even more preferably 5 to 45 mass% or less in terms of the total amount of oxide of the rare earth element relative to the total amount of the carrier.

[0021] The support may contain a transition element such as chromium, cobalt, iron, nickel, titanium, manganese, and copper. The transition elements may be used alone or in appropriate combination of two or more. When the transition element is contained, the content is not particularly limited, but is preferably 0.01 to 10 mass%, more preferably 0.1 to 5 mass%, and even more preferably 0.5 to 3 mass% or less in terms of the total amount of the transition element oxide relative to the total amount of the support.

[0022] When the above-mentioned ceria-based oxide and zirconia-based oxide are contained as the support, a part of cerium or zirconium may be substituted with an alkali metal element such as lithium, sodium, or potassium, or an alkaline earth metal element such as beryllium, magnesium, calcium, strontium, or barium. Here, the alkali metal element and the alkaline earth metal element may be used alone or in any combination of two or more. In addition, the ceria-based oxide and the zirconia-based oxide may contain hafnium (Hf), which is usually contained in zirconia ore at about 1 to 2 mass%, as an inevitable impurity.

[0023] The support containing ceria or zirconia can be produced by a coprecipitation method or an alkoxide method, but commercially available products can also be used.

[0024] An example of the coprecipitation method is a method in which an alkaline substance is added to an aqueous solution in which a rare earth salt and various salts of other elements, such as zirconium salt, which are mixed as necessary, are mixed in a predetermined stoichiometric ratio, and hydrolyzed or a precursor is coprecipitated, and the hydrolysis product or coprecipitate is calcined. The types of various salts used here are not particularly limited. In general, hydrochloride, oxyhydrochloride, nitrate, oxynitrate, carbonate, phosphate, acetate, oxalate, citrate, etc. are preferred. The type of alkaline substance is also not particularly limited. In general, an aqueous ammonia solution is preferred.

[0025] As the alkoxide method, for example, a method of hydrolyzing a mixture of the above-mentioned rare earth alkoxide and the alkoxide of another element, such as zirconium alkoxide, which is mixed as necessary, in a predetermined stoichiometric ratio, and then calcining the mixture is preferable. The type of alkoxide used here is not particularly limited. In general, methoxide, ethoxide, propoxide, isopropoxide, butoxide, or ethylene oxide adducts thereof are preferable. In addition, the rare earth metal element may be mixed as a metal alkoxide or as the above-mentioned various salts.

[0026] The firing conditions of the subsequent firing treatment may be according to the usual method and are not particularly limited. The firing atmosphere may be any of an oxidizing atmosphere, a reducing atmosphere, and an air atmosphere. The firing temperature and treatment time vary depending on the desired composition and its stoichiometric ratio, but from the viewpoint of productivity, etc., they are generally 150°C to 1300°C for 30 minutes to 12 hours, and more preferably 350°C to 800°C for 30 minutes to 2 hours. Prior to the high-temperature firing, reduced pressure drying may be performed using a vacuum dryer or the like.

[0027] The carrier is preferably in a particulate form, and in this case, the average particle diameter (D50) can be appropriately set according to the desired performance and is not particularly limited, but from the viewpoint of maintaining a large specific surface area and increasing the number of its own catalytic active sites by improving heat resistance, it is preferably 0.5 μm to 30 μm, more preferably 1 μm to 20 μm, and even more preferably 3 μm to 15 μm. In this specification, the average particle diameter D50 means the median diameter measured using a laser diffraction type particle size distribution measuring device.

[0028] <Catalytic active component> The hydrocarbon oxidation catalyst according to the present invention contains a catalytic metal as a catalytically active component. As the catalytic metal, any conventionally known catalytic metal used in exhaust gas purification catalysts can be used without limitation, and platinum group elements can be used in particular. Examples of platinum group metal elements include ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), and among these, rhodium, palladium, platinum, and ruthenium can be preferably used. These elements may be used alone or in combination of two or more.

[0029] The catalytic metal supported on the carrier is preferably supported in the form of particles. From the viewpoint of catalytic activity, the particle size of the catalytic metal is preferably 1 nm to 100 nm, more preferably 2 nm to 50 nm. If the particle size is too small, the catalyst tends to be in an oxide state that does not exhibit catalytic activity, while if the particle size is too large, the amount of active sites is reduced, and the catalytic activity per unit amount of the catalytic metal tends to decrease.

[0030] In order to make the catalytic metal have a predetermined particle diameter as described above, for example, a method is used in which a support is immersed in a solution containing a source of the catalytic metal (e.g., the nitrate or acetate of the above-mentioned element) and a source of the promoter component (e.g., the nitrate or acetate of the above-mentioned element) to impregnate the support with a predetermined amount of the solution, and then the support is calcined to support the catalyst, and the particle diameter of the catalytic particles can be adjusted by controlling the solution concentration (concentration of the catalytically active species), the amount of the solution impregnated, and the calcination conditions (temperature and time).

[0031] The above-mentioned catalytically active species is supported on a carrier, but may contain other components in addition to the catalytically active species. However, the ratio of the above-mentioned catalytically active species to the catalyst excluding the carrier is preferably 70 mass% or more, more preferably 90 mass% or more, and particularly preferably 95 mass% or more (including 100 mass%).

[0032] The hydrocarbon oxidation catalyst according to the present invention is characterized in that, in addition to the above-mentioned catalytic metal, a carbide of the catalytic metal is supported on a carrier. When a carbide of a specific catalytic metal coexists with the catalytic metal and is exposed to a lean combustion exhaust gas atmosphere at 180°C or higher, the carbide of the catalytic metal is oxidized and decomposed to produce a catalytic metal (e.g., Pd, etc.) or an oxide of the catalytic metal (e.g., PdOx, etc.) that has been reported to be advantageous for the complete oxidation of methane, and this is thought to improve the catalytic activity of hydrocarbons such as methane under low temperature conditions.

[0033] To support the catalytic metal carbide on the support, for example, a method such as that described in JP 2013-163609 A or the like can be used, that is, a gas containing a hydrocarbon is introduced and deposited on the support by a plasma CVD method, but in the present invention, the catalytic metal carbide can be efficiently supported on the support together with the catalytic metal by adopting the following method. The method will be described below.

[0034] In the present invention, the catalyst particles having the catalyst metal supported on the carrier as described above are heated to an environment of 600°C or less, and a raw material gas containing a hydrocarbon having 1 to 10 carbon atoms is brought into contact with the heated catalyst particles, thereby carbonizing a part of the catalyst metal of the catalyst particles and converting it into a carbide of the catalyst metal. Normally, a high temperature such as plasma is required to use a hydrocarbon such as methane as a carbon source for carbonization, but in the present invention, the hydrocarbon and oxygen come into contact with the catalyst metal heated to a predetermined temperature, and the carbide of the catalyst metal is precipitated and generated on the carrier.

[0035] The upper limit of the heating temperature of the catalyst particles is preferably 400°C or lower, and more preferably 300°C or lower. If the heating temperature of the catalyst particles is too high, the thermal decomposition of the catalyst metal carbide proceeds. On the other hand, the lower limit of the heating temperature of the catalyst particles is preferably 100°C or higher, and more preferably 180°C or higher. If the heating temperature of the catalyst particles is too low, the reaction for generating the catalyst metal carbide becomes insufficient. In the present invention, in particular, by setting the heating temperature of the catalyst particles to 180°C or higher and 300°C or lower, the catalyst metal carbide can be sufficiently generated while suppressing the thermal decomposition of the catalyst metal carbide. As a result, the hydrocarbon oxidation catalyst can be further activated.

[0036] In order to effectively support the carbide of a specific catalytic metal on the catalyst particles, the concentration of hydrocarbons contained in the raw gas must be less than that of oxygen gas (O 2 It is preferable that the hydrocarbon concentration in the raw material gas is higher than that in the oxygen gas. By using a raw material gas having a higher hydrocarbon concentration than that of the oxygen gas, the carbide of the specified catalytic metal is more efficiently produced. A more preferable composition of the raw material gas is a ratio of the hydrocarbon gas and the oxygen gas of 1:1 to 100:1 on a volume basis.

[0037] The hydrocarbon gas contained in the raw material gas is preferably a hydrocarbon having a carbon number of 1 to 4, and more preferably methane (C=1). In addition to the hydrocarbon gas and oxygen gas, the raw material gas may contain an inert gas such as argon as a carrier gas. In addition, the raw gas contains CO and CO 2 Or H2 Other fuel combustion exhaust gas components such as O may coexist. In this case, a suitable composition ratio of hydrocarbon gas and oxygen gas can be achieved by, for example, injecting a large amount of fuel, reducing the amount of intake air, or increasing the EGR (Exhaust Gas Recirculation) rate.

[0038] When a raw material gas containing a hydrocarbon gas is brought into contact with heated catalyst particles, hydrocarbons are also generated in addition to carbides of the catalyst metal. That is, in the present invention, it is not necessary for all of the hydrocarbons to become carbides of the catalyst metal, and the carbides of the catalyst metal and the hydrocarbons may be mixed.

[0039] Whether or not catalytic metal carbides are supported on catalyst particles (particles in which catalytic metal is supported on a carrier) can be confirmed by XPS (X-ray Photoelectron Spectroscopy). XPS is an analytical method that can perform elemental analysis of a sample non-destructively using X-rays. The measurement conditions for evaluation by XPS can be adjusted appropriately depending on the sample to be measured.

[0040] The catalytically active component may contain a transition metal element or a carbide thereof in addition to the above-mentioned catalytic metal and the carbide thereof. Examples of the transition metal element include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), and copper (Cu). Among these, nickel, iron, and copper can be preferably used. These elements may be used alone or in combination of two or more. These transition metal elements function as promoter components, and by using them in combination with the catalytic metal made of the platinum group element as described above, the catalytic activity and poisoning resistance are improved.

[0041] [Catalyst structure] When the above-mentioned hydrocarbon oxidation catalyst is used as a catalyst for purifying exhaust gas from an internal combustion engine, for example, it is preferable to use the catalyst structure in which the hydrocarbon oxidation catalyst is supported as a catalyst layer on a substrate. The substrate is not particularly limited as long as it is made of a material that can support the catalyst layer described below and has a certain degree of fire resistance, and a conventionally known material can be used. For example, examples of the substrate material include ceramics such as alumina, silica, mullite (alumina-silica), cordierite, cordierite-alpha alumina, zircon mullite, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, aluminosilicates, aluminum titanate, silicon carbide, and silicon nitride, and metal materials such as corrosion-resistant alloys such as stainless steel or iron-based ferritic stainless steel. The above-mentioned inorganic or metal materials may be used alone or in combination of two or more. Among the above, alumina, silica, mullite, cordierite, stainless steel, and silicon carbide are preferred, and those containing cordierite, stainless steel, and silicon carbide are more preferred. In this case, it is preferable to use a substrate in which preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 99% by mass or more (including 100% by mass) of the entire substrate is made of the above materials.

[0042] The substrate may contain other components with the above-mentioned materials as the main components. For example, Fe, which is known to improve the heat resistance of the support, may be used. 2 O 3 , SiO 2 , Na 2 O etc. may be added to the above materials.

[0043] The shape of the substrate is not particularly limited, and may be various shapes such as spherical, cylindrical, bead, pellet, prism, tablet, needle, membrane, honeycomb monolith, etc., depending on the application. Among these, bead, pellet, and honeycomb monolith shapes are preferable. Therefore, the substrate according to the preferred embodiment of the present invention is made of alumina, silica, mullite, cordierite, or stainless steel as a material, and the shape is preferably bead, pellet, or honeycomb monolith, and more preferably a honeycomb monolith made of cordierite.

[0044] When the substrate is bead-shaped or pellet-shaped, the average diameter of the substrate is preferably 0.5 mm to 10 mm, more preferably 0.7 mm to 5 mm, and even more preferably 1 mm to 3 mm, from the viewpoint of handling and fluidity in the container. When the substrate is spherical, the average diameter of the substrate is preferably 1 mm to 10 mm, more preferably 1 mm to 5 mm, from the viewpoint of handling and fluidity in the container. The average diameter of the substrate can be determined by observing the substrate using an optical microscope or the like, measuring the major axis and minor axis of 100 arbitrarily selected substrates (catalyst particles), calculating the average of the major axis and minor axis as the particle diameter, and calculating the average value of the particle diameters of the 100 individual particles.

[0045] In one embodiment of the substrate having a honeycomb monolith shape, the length of the substrate is about 25.4 mm to 400 mm, depending on the outer diameter. The outer diameter of the substrate is about 25.4 mm to 400 mm. When the cross section of the flow passage 40 is square, the size of one flow passage 40 defined by the wall is about 1.0 mm to 2.15 mm on a side. Specifically, a honeycomb monolith substrate having 200 to 900 cells is preferred.

[0046] As an example of the catalyst structure, a slurry solution can be prepared by mixing a metal salt of a catalyst component, a metal salt of a promoter component, a carrier, and, if necessary, a binder, a dispersant, and a solvent, and then impregnating a substrate with the slurry solution by a washcoating method or the like, and firing the substrate impregnated with the slurry solution to obtain a honeycomb catalyst holding the fuel reforming catalyst.

[0047] The solvent of the slurry solution is not particularly limited, but examples thereof include water (preferably pure water such as ion-exchanged water and distilled water), etc. The concentration of such a metal salt solution is not particularly limited, but is preferably 0.001 mol / L or more and 0.5 mol / L or less in terms of metal salt ions.

[0048] The catalyst layer may contain other components as long as it contains the above-mentioned hydrocarbon oxidation catalyst. Examples of other components include, but are not limited to, various additives known in the art, such as binders such as boehmite and alumina sol, dispersion stabilizers such as nonionic surfactants and anionic surfactants, pH adjusters, and viscosity adjusters. In addition, the catalyst layer may contain catalysts, co-catalysts, etc. known in the art.

[0049] Examples of the binder include various sols such as boehmite, alumina sol, titania sol, silica sol, and zirconia sol. In addition, soluble salts such as aluminum nitrate, aluminum acetate, titanium nitrate, titanium acetate, zirconium nitrate, and zirconium acetate can also be used as the binder. In addition, acids such as acetic acid, nitric acid, hydrochloric acid, and sulfuric acid can also be used as the binder.

[0050] The amount of the binder used is not particularly limited, but is preferably 0.01% by mass to 15% by mass, and more preferably 0.05% by mass to 10% by mass, based on the total amount of the catalyst layer. In addition to the above-mentioned components, the catalyst layer may contain catalysts, co-catalysts, and various additives known in the art.

[0051] The content of the hydrocarbon oxidation catalyst in the catalyst layer can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 50 mass% to 100 mass%, more preferably 70 mass% to 95 mass%, and even more preferably 90 mass% to 95 mass%, relative to the total amount of the catalyst layer.

[0052] The catalyst layer provided on the surface of the substrate does not need to have the same composition throughout; the composition of the catalyst layer near the inlet end side of the substrate may be different from that near the outlet end side, or another catalyst layer may be laminated thereon.

[0053] The catalyst layer can be formed by adding the hydrocarbon oxidation catalyst and other components, such as a binder and a dispersion stabilizer, which are added as desired, to a liquid medium such as water and mixing them in a ball mill or the like to prepare a slurry, applying the slurry to the surface of the substrate, and then drying the slurry. As the application method, various known coating methods, wash coating methods, and zone coating methods can be applied. Note that a catalyst layer of the desired thickness can be formed by adjusting the amount of coating.

[0054] The drying temperature is not particularly limited, but is preferably 70°C to 200°C, more preferably 80°C to 150°C. The calcination temperature is not particularly limited, but is preferably 300°C to 650°C, more preferably 400°C to 600°C. The heating means used at this time can be, for example, a known heating means such as an electric furnace or a gas furnace. If the drying temperature is too low, the catalyst metal supply source does not sufficiently decompose thermally, and it is difficult to become a metal state that exhibits catalytic activity, so that the activity tends to be low. On the other hand, if the calcination temperature is too high, the supported catalyst metal tends to become coarse particles. The calcination time can also be adjusted as appropriate, but is usually preferably 0.1 hours or more and 100 hours or less. If the calcination time is too short, the catalyst metal element supply source is not sufficiently pyrolyzed, and it is difficult to reach a metallic state that exhibits catalytic activity, so activity tends to be low. On the other hand, if the calcination time is longer than necessary, no effect is obtained, and costs and production volume per unit time tend to decrease.

[0055] The amount of coating can be appropriately set according to the desired performance and is not particularly limited, but considering the influence of pressure loss, engine output, fuel consumption, etc., it is preferably 10g to 500g, more preferably 20g to 400g, and even more preferably 50g to 300g per unit volume (1L) of the substrate. In this specification, per unit volume (1L) of the substrate means the total bulk volume 1L including not only the net volume of the substrate but also the volume of voids formed inside the substrate. In addition, when cells are partitioned and formed inside the substrate, it means the total bulk volume 1L including the net volume of the substrate, the volume of voids, and the volume of the cells.

[0056] The amount of catalytic metal in the entire catalytic layer can be appropriately set depending on the desired performance and is not particularly limited, but is preferably 0.01 g to 20 g, more preferably 0.1 g to 15 g, and even more preferably 1.0 g to 10 g, calculated as the amount of metal per unit volume (1 L) of the substrate.

[0057] The hydrocarbon oxidation catalyst of the present invention can be used as a catalyst for purifying exhaust gas from, for example, diesel engines, gasoline engines, jet engines, boilers, gas turbines, etc. When used for exhaust gas purification, the hydrocarbon oxidation catalyst can be disposed in the exhaust system of various engines. The number of catalysts to be installed and the installation locations can be appropriately designed according to exhaust gas regulations. For example, when exhaust gas regulations are strict, the number of installation locations can be two or more, and the installation locations can be located under the floor behind the catalyst immediately below the exhaust system. Furthermore, according to the hydrocarbon oxidation catalyst of the present invention, hydrocarbons such as methane contained in exhaust gas can be oxidized with high efficiency even under low temperature conditions. EXAMPLES

[0058] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way as long as the gist of the invention is not exceeded. In other words, the materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention.

[0059] [Preparation of catalyst particles] First, pure water was added to the ceria particles, which were then immersed in a palladium (II) nitrate solution (containing 20% ​​by mass of Pd), dried at 100°C for 3 hours, and then fired at 550°C for 60 minutes to obtain a 3%Pd / CeO 2 The treated catalyst particles are hereinafter referred to as "AS-Pd / CeO 2 "It is called "

[0060] [Example 1] The AS-Pd / CeO obtained as above 2 50 mg of catalyst particles were packed in a reaction tube, and a raw material gas consisting of 0.5% methane, 0.2% oxygen, and the balance Ar was passed through the reaction tube at 300 cc / min. Next, while the pretreatment gas was still passing through, the reaction tube was heated from room temperature to 600°C at a temperature increase rate of 20°C / min, and then the reaction tube was naturally cooled under the flow of the raw material gas. Hereinafter, the treated catalyst particles are referred to as "ST-Pd / CeO 2 "It is called "

[0061] ST-Pd / CeO treated as above 2 The Pd3d core level of the catalyst particles was measured by the XPS method. The measurement results are shown in FIG. 1. As is clear from FIG. 1, Pd-C bonds can be confirmed in the catalyst particles of Example 1, and therefore it is recognized that palladium carbide is supported on the catalyst particles. In FIG. 1, the gray solid line is the measurement result, the long two-dot chain line is palladium oxide (PdOy), the dotted line is palladium carbide (PdCx), the long dashed line is a separated peak attributed to metal Pd, and the sum of the separated peaks is shown by a dashed line.

[0062] [Example 2] In addition, the AS-Pd / CeO 2300 mg of catalyst particles were packed into a reaction tube, and a raw material gas consisting of 9.0% methane, 0.9% oxygen, and the balance Ar was passed through the reaction tube at 111 cc / min. Next, while the pretreatment gas was still passing through, the reaction tube was heated from room temperature to 230°C at a temperature increase rate of 10°C / min, and then treated at 230°C for 100 hours, after which the reaction tube was naturally cooled under the flow of the raw material gas. Hereinafter, the treated catalyst particles will be referred to as "LT-Pd / CeO 2 "It is called "

[0063] LT-Pd / CeO treated as above 2 The Pd3d core level of the catalyst particles (hereinafter referred to as catalyst) was measured by XPS in the same manner as described above. The measurement results are shown in FIG. 2. As is clear from FIG. 2, Pd-C bonds can be confirmed in the catalyst particles of Example 2, and therefore it is recognized that palladium carbide is supported on the catalyst particles. The gray solid line is the measurement result, the long two-dot chain line is palladium oxide (PdOy), the dotted line is palladium carbide (PdCx), the long dashed line is a separated peak attributed to metallic Pd, and the sum of the separated peaks is shown by a dashed line.

[0064] [Comparative Example 1] AS-Pd / CeO treated as above 2 The Pd3d core level of the catalyst particles was measured by XPS in the same manner as described above. The measurement results are shown in Figure 3. As is clear from Figure 3, no Pd-C bond was observed in the catalyst particles of Comparative Example 1. The gray solid line is the measurement result, the long two-dot chain line is a separated peak attributable to palladium oxide (PdOy), the long dashed line is a separated peak attributable to metal Pd, and the sum of the separated peaks is shown by a dashed line.

[0065] [Evaluation of catalyst particles] A gas simulating an exhaust gas under lean conditions consisting of 0.1% methane, 8.0% oxygen, and the remainder He was passed through a reaction tube filled with 50 mg of the catalyst particles of Example 1 obtained as described above at 300 mL / min, and the reaction tube was heated to 600 ° C. at a temperature increase rate of 20 ° C. / min. The composition of the gas passing through the reaction tube was analyzed to evaluate how much methane was decomposed. In addition, the catalyst particles of Example 2 and Comparative Example 1 were also evaluated in the same manner as in Example 1. The methane conversion rate using each catalyst particle was as shown in FIG. 4. In addition, the temperature (T50) at which the methane decomposition rate reached 50% was as shown in FIG. 5. It can be said that the lower the T50 value, the better the catalyst is in terms of methane decomposition characteristics at low temperatures.

[0066] As is clear from Figures 4 and 5, the hydrocarbon oxidation catalyst (ST-Pd / CeO 2 Catalyst particles and LT-Pd / CeO 2 The catalyst particles are catalyst particles that do not support the catalytic metal carbide (PdCx) (AS-Pd / CeO 2 Compared to conventional catalytic converters (catalyst particles), it has superior methane oxidation properties even in low-temperature environments.

Claims

1. A hydrocarbon oxidation catalyst comprising a support and a catalytically active component supported on the support, A hydrocarbon oxidation catalyst, wherein the catalytically active component comprises a catalytic metal and a carbide of the catalytic metal.

2. 2. The hydrocarbon oxidation catalyst of claim 1, wherein the catalytic metal comprises at least one metal selected from the platinum group elements.

3. 3. The hydrocarbon oxidation catalyst according to claim 2, wherein the platinum group metal is at least one selected from the group consisting of rhodium, palladium, platinum and ruthenium.

4. 4. The hydrocarbon oxidation catalyst of claim 3, wherein the catalytic metal further comprises at least one transition metal selected from the group consisting of nickel, iron and copper.

5. 2. The hydrocarbon oxidation catalyst according to claim 1, wherein the support comprises at least one inorganic oxide selected from the group consisting of alumina, silica, zirconia and ceria.

6. The hydrocarbon oxidation catalyst according to claim 1, which is used for purifying exhaust gas from an internal combustion engine.

7. A method for producing the hydrocarbon oxidation catalyst according to claim 1, comprising the steps of: preparing catalyst particles including a support and a catalytic metal supported on the support; contacting the catalyst particles with a feed gas containing a hydrocarbon having 1 to 10 carbon atoms in an environment of 600° C. or less; A carbide of the catalytic metal is supported on a support of the catalytic particle. A method for producing a hydrocarbon oxidation catalyst, comprising:

8. The method according to claim 7 , wherein the raw material gas is brought into contact with the catalyst particles in an environment of 300° C. or less.

9. The method according to claim 7 , wherein the hydrocarbon concentration in the source gas is higher than the oxygen gas concentration.

10. The process of claim 7 , wherein the hydrocarbon comprises methane.

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