Hydrocarbon oxidation catalyst, method for producing the same, and hydrocarbon treatment method

Abstract

A hydrocarbon oxidation catalyst according to the present invention comprises: a catalyst carrier that contains zirconia; and an active metal that is supported by the catalyst carrier. The zirconia comprises a monoclinic zirconia phase and a tetragonal zirconia phase. With respect to the zirconia, the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase is not less than 0.005 but less than 0.8 as determined by X-ray diffractometry, and the crystallite diameter of the monoclinic zirconia phase is 35 Å to 115 Å.

Description

[Technical Field]

[0001] The present invention relates to a hydrocarbon oxidation catalyst, a method for producing the same, and a hydrocarbon treatment method. [Background technology]

[0002] Internal combustion engines that operate using natural gas (which mainly contains hydrocarbons such as methane) as fuel are known. Such internal combustion engines are operated under conditions where some of the hydrocarbons in the fuel gas (for example, about 3-7% of the fuel methane in a two-stroke low-pressure gas engine, and about 6-13% in a four-stroke low-pressure gas engine) do not burn, for example, from the standpoint of energy efficiency. In other words, the exhaust gas from such internal combustion engines contains unburned hydrocarbons. Unburned hydrocarbons include gases with a higher greenhouse effect than carbon dioxide. For example, methane has 25 times the greenhouse effect of carbon dioxide. When such exhaust gas is released into the atmosphere, it is desirable to remove unburned hydrocarbons such as methane from the exhaust gas.

[0003] One known method for removing unburned hydrocarbons from exhaust gas is to use a catalyst to oxidize the unburned hydrocarbons and decompose them into carbon dioxide and water. Regarding technologies related to methane oxidation catalysts, for example, see Patent Document 1 below. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2018-510767 [Overview of the project] [Problems that the invention aims to solve]

[0005] Patent Document 1 describes a methane oxidation catalyst comprising a catalyst support and palladium as an active metal supported on the catalyst support, with a palladium load of 4% by mass. In this catalyst, the amount of expensive palladium (active metal) is relatively large. However, from the viewpoint of cost reduction, there is a need to oxidize and decompose hydrocarbons in exhaust gas using a catalyst with a smaller amount of active metal.

[0006] The present invention provides a hydrocarbon oxidation catalyst, a hydrocarbon treatment method, and a method for producing a hydrocarbon oxidation catalyst that are suitable for achieving good catalytic activity while suppressing the amount of active metal supported. [Means for solving the problem]

[0007] The present invention [1] provides a hydrocarbon oxidation catalyst comprising a catalyst support containing zirconia and an active metal supported on the catalyst support, wherein the zirconia comprises a monoclinic zirconia phase and a tetragonal zirconia phase, the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase in X-ray diffraction measurements being 0.005 or more and less than 0.8, and the crystallite size of the monoclinic zirconia phase being 35 Å or more and 115 Å or less.

[0008] The present invention [2] includes the hydrocarbon oxidation catalyst described in [1] above, wherein the catalyst support is zirconia oxoxide.

[0009] The present invention [3] includes the hydrocarbon oxidation catalyst described in [1] or [2] above, wherein the oxo-zirconia oxide comprises at least one selected from the group consisting of sulfated zirconia and tungsten-zirconia oxide.

[0010] The present invention [4] includes a hydrocarbon oxidation catalyst according to any one of [1] to [3] above, wherein the active metal comprises at least one selected from the group consisting of palladium, platinum, and ruthenium.

[0011] The present invention [5] includes a hydrocarbon oxidation catalyst according to any one of [1] to [4] above, wherein the active metal contains palladium, and the amount of palladium supported is 0.1% by mass or more and less than 4% by mass.

[0012] The present invention [6] includes a hydrocarbon treatment method comprising the step of contacting a hydrocarbon with a hydrocarbon oxidation catalyst described in any one of [1] to [5] above.

[0013] The present invention [7] includes a method for producing a hydrocarbon oxidation catalyst, comprising: a first step of preparing a slurry containing a catalyst support material containing zirconia and an active metal; a second step of drying the slurry to obtain a powder; and a third step of calcining the powder at 400°C to 600°C to obtain a hydrocarbon oxidation catalyst according to any one of [1] to [5] above, wherein the zirconia in the first step comprises a monoclinic zirconia phase and a tetragonal zirconia phase, the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase in X-ray diffraction measurement is 0.005 to 0.85, and the crystallite size of the monoclinic zirconia phase is 35 Å to 115 Å. [Effects of the Invention]

[0014] In the hydrocarbon oxidation catalyst of the present invention, as described above, the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase measured by X-ray diffraction in the zirconia supporting the active metal is 0.005 or more and less than 0.8, and the crystallite size of the monoclinic zirconia phase is 35 Å or more and 115 Å or less. Therefore, this hydrocarbon oxidation catalyst is suitable for achieving good catalytic activity while suppressing the amount of active metal supported. A hydrocarbon treatment method including a step of contacting such a hydrocarbon oxidation catalyst with hydrocarbons is suitable for efficiently decomposing hydrocarbons. Furthermore, in the method for producing the hydrocarbon oxidation catalyst of the present invention, the above ratio measured by X-ray diffraction in the zirconia used in the first step is 0.005 or more and 0.85 or less, the crystallite size of the monoclinic zirconia phase is 35 Å or more and 115 Å or less, and the calcination temperature in the third step is 400°C or more and 600°C or less. Therefore, the above hydrocarbon oxidation catalyst can be produced efficiently. [Brief explanation of the drawing]

[0015] [Figure 1] The XRD patterns obtained for the hydrocarbon oxidation catalysts of Examples 1-10 and Comparative Examples 1-5 are shown. [Figure 2] The XRD patterns obtained for the various zirconia used as catalyst support raw materials in Examples 1-10 and Comparative Examples 1-5 are shown. [Figure 3] This graph shows the correlation between the methane oxidation activity ratio and the ratio of the peak intensity P2 of the tetragonal zirconia phase to the peak intensity P1 of the monoclinic zirconia phase (P2 / P1) in XRD measurements for the hydrocarbon oxidation catalysts of Examples 1-10 and Comparative Examples 1-5. [Figure 4] This graph shows the correlation between the methane oxidation activity ratio and the crystallite size R1 of the monoclinic zirconia phase for the hydrocarbon oxidation catalysts of Examples 1-10 and Comparative Examples 1-5. [Figure 5] This graph shows the correlation between the methane oxidation activity ratio and temperature T50(CH4) and the sulfuric acid content in the catalyst support for the hydrocarbon oxidation catalysts of Examples 1-3 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0016] A hydrocarbon oxidation catalyst as one embodiment of the present invention is a catalyst for oxidatively decomposing hydrocarbons, and includes a catalyst carrier and an active metal supported on the catalyst carrier. The hydrocarbon oxidation catalyst can be used to remove unburned hydrocarbons such as methane from the exhaust gas when the exhaust gas is discharged into the atmosphere. Examples of the hydrocarbons in the exhaust gas include aliphatic hydrocarbons and alicyclic hydrocarbons. Examples of the aliphatic hydrocarbons include aliphatic saturated hydrocarbons and aliphatic unsaturated hydrocarbons. Examples of the aliphatic saturated hydrocarbons include methane, ethane, propane, butane, and pentane.

[0017] The catalyst support contains zirconia. This zirconia contains both a monoclinic zirconia (m-ZrO2) phase and a tetragonal zirconia (t-ZrO2) phase. This zirconia contains a relatively large amount of the monoclinic zirconia phase. Specifically, in the hydrocarbon oxidation catalyst, the ratio of the peak intensity P2 of the tetragonal zirconia phase to the peak intensity P1 of the monoclinic zirconia phase in X-ray diffraction (XRD) measurements (P2 / P1) is 0.005 or higher and less than 0.8. The ratio (P2 / P1) is an indicator of the acidity of the surface of the hydrocarbon oxidation catalyst. A ratio (P2 / P1) of 0.005 or higher is suitable for ensuring the surface acidity necessary for oxidation reactions such as methane oxidation, and therefore suitable for achieving good catalytic performance (a ratio of less than 0.005 is not suitable for ensuring surface acidity). From this viewpoint, the ratio (P2 / P1) is preferably 0.01 or higher, more preferably 0.1 or higher, even more preferably 0.2 or higher, and particularly preferably 0.3 or higher. The ratio (P2 / P1) also serves as an indicator of the degree of difference between the monoclinic zirconia phase and the more stable tetragonal zirconia phase. A ratio (P2 / P1) of less than 0.8 is suitable for securing a monoclinic zirconia phase in which the active metal-supporting sites are more easily activated than in the tetragonal zirconia phase, and therefore suitable for achieving good catalytic activity (a ratio of 0.8 or higher is not suitable for securing a monoclinic zirconia phase). From this viewpoint, the ratio (P2 / P1) is preferably 0.7 or lower, more preferably 0.6 or lower, and even more preferably 0.5 or lower. In XRD measurement, the peak intensity P1 of the monoclinic zirconia phase is the integral value of the intensity (cps) of the X-ray diffraction signal having a diffraction peak at 2θ = 28.1° (θ is the Bragg angle). The peak intensity P2 of the tetragonal zirconia phase is the integral of the intensity (cps) of the X-ray diffraction signal having a diffraction peak at 2θ = 30.2°. Specifically, XRD measurements can be performed by the method described later with respect to the examples.

[0018] The catalyst support is preferably zirconia oxooxide. Such a configuration is preferable for stabilizing the tetragonal zirconia phase that is unstable at room temperature (the bulk pure zirconia crystal is monoclinic at room temperature). Examples of zirconia oxooxide include sulfated zirconia, tungsten zirconia oxide, titanium zirconia oxide, and phosphorylated zirconia. The zirconia oxooxide preferably contains at least one selected from the group consisting of sulfated zirconia and tungsten zirconia oxide. Also, the proportion of the oxoacid in the catalyst support is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and is preferably 4% by mass or less, more preferably 3.5% by mass or less, still more preferably 3% by mass or less. These configurations are for the oxoacid transformation It is preferable for stabilizing the tetragonal zirconia phase to exist in zirconia at the above ratio (P2 / P1). Also, the configuration in which the catalyst support is zirconia oxooxide is also preferable for acidifying the surface of the hydrocarbon oxidation catalyst. The acidification of the hydrocarbon oxidation catalyst surface helps to ensure catalytic activity.

[0019] The crystallite size R1 of the monoclinic zirconia phase is 35 Å or more and 115 Å or less. From the viewpoint of ensuring the area where the active metal can be highly dispersed per crystallite of the monoclinic zirconia phase, the crystallite size R1 is 35 Å or more, preferably 40 Å or more, more preferably 50 Å or more, still more preferably 60 Å or more. From the viewpoint of ensuring the crystallite surface area per crystallite volume in the monoclinic zirconia phase (where the active metal is supported), the crystallite size R1 is 115 Å or less, preferably 110 Å or less, more preferably 105 Å or less.

[0020] The crystallite size R2 of the tetragonal zirconia phase is preferably 40 Å or more, more preferably 45 Å or more, from the viewpoint of ensuring an area where the active metal can be supported with high dispersion per crystallite of the tetragonal zirconia phase. The crystallite size R2 is preferably 115 Å or less, more preferably 110 Å or less, and even more preferably 105 Å or less, from the viewpoint of ensuring a crystallite surface area (where the active metal is supported) per crystallite volume in the tetragonal zirconia phase. Such miniaturization of the tetragonal zirconia phase to the nanoparticle level also helps in stabilizing the tetragonal zirconia.

[0021] The crystallite sizes R1 and R2 can be determined based on XRD measurements. Specifically, the crystallite size R1 of the monoclinic zirconia phase can be determined based on the peak full width at half maximum (FWHM) as the diffraction line width at 2θ = 28.1° (θ is the Bragg angle) in the XRD measurement, and Scherrer's formula (D = Kλ / Bcosθ). The crystallite size R2 of the tetragonal zirconia phase can be determined based on the peak full width at half maximum as the diffraction line width at 2θ = 30.2° in the XRD measurement, and Scherrer's formula. In Scherrer's formula, D is the crystallite size (nm), λ is the wavelength of the X-ray (Cu-Kα line) in the XRD measurement (nm), B is the broadening of the diffraction line width (rad), and θ is the Bragg angle (rad). Also, K is Scherrer's constant, and 0.89 is adopted. The XRD measurement can be performed by the method described later with respect to the examples.

[0022] Examples of active metals include platinum group metals. Examples of platinum group metals include palladium (Pd), platinum (Pt), iridium (Ir), and ruthenium (Ru). From the viewpoint of ensuring catalytic activity, the active metal preferably includes at least one selected from the group consisting of Pd, Pt, and Ru, more preferably two selected from the group consisting of Pd, Pt, and Ru, and even more preferably Pd and Ru or Pt (Pd-Pt composite support, Pd-Ru composite support).

[0023] When the active metal contains Pd, the amount of Pd supported in the hydrocarbon oxidation catalyst is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.7% by mass or more, from the viewpoint of catalytic activity for high-ignition-point hydrocarbons such as methane. From the viewpoint of cost reduction, the amount of Pd supported is preferably less than 4% by mass, more preferably 3.5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2.5% by mass or less. The amount of Pd supported may be 4% by mass or more as needed, for example, 8% by mass or less. The amount of Pd supported in the hydrocarbon oxidation catalyst is expressed as the mass ratio of the amount of Pd to the total amount of the catalyst support and the total amount of active metal supported thereon (the same applies to the active metal elements described later).

[0024] When the active metal includes Pt, the amount of Pt supported in the hydrocarbon oxidation catalyst is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, even more preferably 0.9% by mass or more, and particularly preferably 1% by mass or more, from the viewpoint of ensuring catalytic activity. From the viewpoint of cost reduction, the amount of Pt supported is preferably 3% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less.

[0025] When the active metal contains Ru, the amount of Ru supported in the hydrocarbon oxidation catalyst is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of ensuring catalytic activity. From the viewpoint of cost reduction, the amount of Ru supported is preferably 7% by mass or less, more preferably 6% by mass or less, and even more preferably 5.5% by mass or less.

[0026] In the case of Pd-Pt composite support, the total amount of Pd and Pt supported in the hydrocarbon oxidation catalyst is preferably 0.2% by mass or more, more preferably 0.8% by mass or more, and even more preferably 1% by mass or more, from the viewpoint of ensuring catalytic activity. From the viewpoint of cost reduction, the total amount of Pd and Pt supported is preferably less than 7% by mass, more preferably 6% by mass or less, and even more preferably 5% by mass or less.

[0027] In the case of Pd-Ru composite support, the total amount of Pd and Ru supported in the hydrocarbon oxidation catalyst is preferably 1.1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of ensuring catalytic activity. From the viewpoint of cost reduction, the total amount of Pd and Ru supported is preferably less than 11% by mass, more preferably 9% by mass or less, and even more preferably 7.5% by mass or less.

[0028] A method for producing a hydrocarbon oxidation catalyst as one embodiment of the present invention includes the following steps.

[0029] First, a slurry containing a catalyst support material including zirconia and an active metal is prepared (step 1). For example, powdered catalyst support material containing zirconia is suspended in a solution containing the active metal (active metal-containing solution), and the suspension is continuously stirred. The stirring temperature is, for example, 5°C to 35°C. The stirring time is, for example, 15 to 21 hours, depending on the amount being prepared.

[0030] Examples of active metals include platinum group metals. Examples of platinum group metals include Pd, Pt, Ru, Os, Rh, and Ir. From the viewpoint of ensuring catalytic activity, the active metal preferably includes at least one selected from the group consisting of Pd, Pt, and Ru, and more preferably P t Or Ru and P d This includes the active metal-containing solution, for example, an aqueous solution of the nitrate, chloride, or acetate of these active metals.

[0031] The zirconia in the catalyst support material contains a monoclinic zirconia phase and a tetragonal zirconia phase, and the ratio of the peak intensity P2 of the tetragonal zirconia phase to the peak intensity P1 of the monoclinic zirconia phase in XRD measurement (P2 / P1) is 0.005 or more and 0.85 or less, and the crystallite size of the monoclinic zirconia phase is 35 Å or more and 115 Å or less. The ratio (P2 / P1) in this step is preferably 0.01 or more, more preferably 0.02 or more, and also preferably 0.82 or less, and more preferably less than 0.8. The crystallite size R1 in this step is preferably 40 Å or more, more preferably 45 Å or more, and also preferably 100 Å or less, and more preferably 90 Å or less. The crystallite size R2 in this step is preferably 35 Å or more, more preferably 40 Å or more, and also preferably 115 Å or less, and more preferably 80 Å or less.

[0032] In the first step, oxo-zirconia oxide is preferably used as the catalyst support material, and more preferably at least one selected from the group consisting of sulfated zirconia and tungsten oxide zirconia. Alternatively, commercially available catalyst support materials may be used, or calcined precursors of catalyst support materials may be used. Examples of catalyst support material precursors include amorphous zirconia, zirconium hydroxide sol, zirconium hydroxide gel, zirconium lactate, and zirconium alkoxide. When oxo-zirconia oxide is used as the catalyst support material, examples of catalyst support material precursors include amorphous zirconia, zirconium hydroxide sol, zirconium hydroxide gel, zirconium lactate, or a mixture of zirconium alkoxide and an oxoacid. Examples of oxoacids include sulfuric acid, tungstic acid, titanic acid, and phosphoric acid.

[0033] Next, the slurry obtained in the first step is dried to obtain a powder (second step). The drying temperature is, for example, 80°C or higher, preferably 100°C or higher, and also, for example, 150°C or lower, preferably 130°C or lower. The drying time is, for example, 1 hour or more, preferably 3 hours or more, and also, for example, 9 hours or less, preferably 7 hours or less.

[0034] Next, the powder obtained in the second step is calcined at a temperature of 400°C to 600°C (third step). The calcination temperature in this step is preferably 450°C or higher, more preferably 480°C or higher, and also preferably 550°C or lower, more preferably 520°C or lower. The calcination time is preferably 3 hours or more, more preferably 5 hours or more, and also preferably 20 hours or less, more preferably 15 hours or less. These calcination conditions are suitable for suppressing changes in the above-mentioned ratio (P2 / P1) and crystallite sizes R1,R2 related to zirconia in the catalyst support raw material, and are therefore suitable for obtaining the above-mentioned hydrocarbon oxidation catalyst.

[0035] The obtained hydrocarbon oxidation catalyst may be pulverized. One pulverization method is compression pulverization. Alternatively, the pulverized hydrocarbon oxidation catalyst may be sieved to separate hydrocarbon oxidation catalysts of a desired size. The hydrocarbon oxidation catalyst before or after pulverization may be compressed and molded into a predetermined shape. Examples of shapes for the hydrocarbon oxidation catalyst include spherical, tablet-shaped, and honeycomb-shaped (monolithic) forms.

[0036] For example, hydrocarbon oxidation catalysts can be manufactured in the manner described above.

[0037] One embodiment of the hydrocarbon treatment method includes a step of contacting a hydrocarbon with the hydrocarbon oxidation catalyst (contact treatment step). In the contact treatment step, for example, a gas containing hydrocarbons, such as exhaust gas (hydrocarbon-containing gas), is brought into contact with the hydrocarbon oxidation catalyst. The hydrocarbon-containing gas may be brought into contact with the hydrocarbon oxidation catalyst as a fixed bed arranged in a predetermined container, or it may be brought into contact with the hydrocarbon oxidation catalyst as a fluidized bed arranged in a predetermined container. The treatment temperature in the contact treatment step is, for example, 190°C to 550°C. The flow rate of the hydrocarbon-containing gas in the contact treatment step is, for example, 100 Nm³. 3 It is greater than / h, and also, for example, 480,000 Nm 3 It is less than or equal to / h.

[0038] In the hydrocarbon oxidation catalyst of the present invention, as described above, the ratio of the peak intensity P2 of the tetragonal zirconia phase to the peak intensity P1 of the monoclinic zirconia phase measured by XRD (P2 / P1) in the zirconia supporting the active metal is 0.005 or more and less than 0.8, and the crystallite size R1 of the monoclinic zirconia phase is 35 Å or more and 115 Å or less. Such a hydrocarbon oxidation catalyst is suitable for achieving good catalytic activity while suppressing the amount of active metal supported. Specifically, this is shown in the examples and comparative examples described below. Furthermore, the hydrocarbon treatment method described above, which includes the step of contacting such a hydrocarbon oxidation catalyst with a hydrocarbon, is suitable for efficiently decomposing hydrocarbons. [Examples]

[0039] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Specific numerical values ​​such as blending ratios (contents), physical properties, and parameters used in the following description can be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the blending ratios (contents), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0040] [Example 1] First, a palladium(II) nitrate solution (product name "Low Chlorine Nitrate Pd Solution", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), a tetraammineplatinum(II) nitrate solution (product name "TetraamminePt Nitrate Solution", manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), and deionized water were mixed to obtain an aqueous solution (metal solution preparation step). The mass ratio of palladium (Pd) to platinum (Pt) in this aqueous solution was 1:1. Next, powdered first sulfated zirconia (product name "Z-3300", sulfated zirconia with a sulfuric acid content of 1% by mass (1 wt% SO4 / ZrO2), manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) was added to the aqueous solution and mixed to prepare a slurry (slurry preparation step). The amount of sulfated zirconia in this slurry was 98 parts by mass per 2 parts by mass of total Pd and Pt. Next, this slurry was stirred at room temperature for about 16 hours. Next, the slurry was dried at 110°C to obtain a powder. Next, this powder was calcined at 500°C for 9 hours. This yielded a hydrocarbon oxidation catalyst. Next, this catalyst was compressed and pulverized, and then sieved to separate the powder (hydrocarbon oxidation catalyst) with a particle size of 16 to 31 mesh (0.5 to 1.00 mm). In this manner, the powdered hydrocarbon oxidation catalyst of Example 1 (catalyst support: 1 wt% SO4 / ZrO2, active metal: 1.0 wt% Pd + 1.0 wt% Pt) was prepared.

[0041] [Examples 2, 3] Powdered hydrocarbon oxidation catalyst for Example 2 (catalyst support: 2wt%SO4 / ZrO2, active metal: 1.0wt%Pd+1.0wt%Pt) and powdered hydrocarbon oxidation catalyst for Example 3 (catalyst support: 3wt%SO4 / ZrO2, active metal: 1.0wt%Pd+1.0wt%Pt) were prepared in the same manner as the catalyst for Example 1, except as follows. In the slurry preparation step in Example 2, powdered second sulfated zirconia (product name "Z-3301", sulfated zirconia with a sulfuric acid content of 2% by mass (2wt%SO4 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia. In the slurry preparation step of Example 3, a third type of sulfated zirconia in powder form (product name "Z-2964", sulfated zirconia with a sulfuric acid content of 3% by mass (3wt%SO4 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia.

[0042] [Example 4] A powdered hydrocarbon oxidation catalyst for Example 4 (catalyst support: 3 wt% SO4 / ZrO2, active metal: 2.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the metal solution preparation step, the mass ratio of Pd to Pt in the aqueous solution was set to 2:1. In the slurry preparation step, a powdered third sulfated zirconia (product name "Z-2964") was used instead of the first sulfated zirconia, and the amount of sulfated zirconia added was 97 parts by mass per 3 parts by mass of the total of Pd and Pt.

[0043] [Example 5] A powdered hydrocarbon oxidation catalyst for Example 5 (catalyst support: 3 wt% SO4 / ZrO2, active metal: 2.0 wt% Pd + 2.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the slurry preparation step, a powdered third sulfated zirconia (product name "Z-2964") was used instead of the first sulfated zirconia, and the amount of sulfated zirconia was set to 96 parts by mass per 4 parts by mass of Pd and Pt combined.

[0044] [Example 6] A powdered hydrocarbon oxidation catalyst for Example 6 (catalyst support: 10 wt% WO3 / ZrO2, active metal: 1.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the slurry preparation step, powdered tungsten zirconia oxide (product name "Z-2233", tungsten zirconia oxide with a tungstic acid content of 10% by mass (10 wt% WO3 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia, and the amount of tungsten zirconia oxide blended was 98 parts by mass per 2 parts by mass of total Pd and Pt.

[0045] [Example 7] A powdered hydrocarbon oxidation catalyst for Example 7 (catalyst support: 10 wt% WO3 / ZrO2, active metal: 2.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the metal solution preparation step, the mass ratio of Pd to Pt in the aqueous solution was set to 2:1. In the slurry preparation step, powdered tungsten oxide zirconia (product name "Z-2233", manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia, and the amount of tungsten oxide zirconia added was 97 parts by mass per 3 parts by mass of the total of Pd and Pt.

[0046] [Example 8] A powdered hydrocarbon oxidation catalyst for Example 8 (catalyst support: 1 wt% SO4 / ZrO2, active metal: 1.0 wt% Pd + 2.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the metal solution preparation step, the mass ratio of Pd to Pt in the aqueous solution was set to 1:2. In the slurry preparation step, the amount of first sulfated zirconia added was 97 parts by mass per 3 parts by mass of the total of Pd and Pt.

[0047] [Example 9] A powdered hydrocarbon oxidation catalyst for Example 9 (catalyst support: 1 wt% SO4 / ZrO2, active metal: 2.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the metal solution preparation step, the mass ratio of Pd to Pt in the aqueous solution was set to 2:1. In the slurry preparation step, the amount of first sulfated zirconia added was 97 parts by mass per 3 parts by mass of the total of Pd and Pt.

[0048] [Example 10] A powdered hydrocarbon oxidation catalyst for Example 10 (catalyst support: 1 wt% SO4 / ZrO2, active metal: 2.0 wt% Pd + 5.0 wt% Ru) was prepared in the same manner as the catalyst for Example 1, except as follows: In the metal solution preparation step, ruthenium nitrate solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of tetraammineplatinum nitrate solution. The mass ratio of Pd to Ru in the aqueous solution obtained in the same step was 2:5. In the slurry preparation step, the amount of first sulfated zirconia added was 93 parts by mass per 7 parts by mass of the total of Pd and Ru.

[0049] [Comparative Example 1] A powdered hydrocarbon oxidation catalyst for Comparative Example 1 (catalyst support: m-ZrO2, active metal: 1.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the slurry preparation step, powdered zirconia (product name "RC-100", monoclinic zirconia (m-ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia, and the amount of zirconia added was 98 parts by mass per 2 parts by mass of the total of Pd and Pt.

[0050] [Comparative Examples 2, 3, 4] The hydrocarbon oxidation catalysts for Comparative Example 2 (catalyst support: 5wt%SO4 / ZrO2, active metal: 1.0wt%Pd+1.0wt%Pt), Comparative Example 3 (catalyst support: 6wt%SO4 / ZrO2, active metal: 1.0wt%Pd+1.0wt%Pt), and Comparative Example 4 (catalyst support: 10wt%SO4 / ZrO2, active metal: 1.0wt%Pd+1.0wt%Pt) were prepared in the same manner as the catalyst for Example 1, except as follows. In the slurry preparation step in Comparative Example 2, a fourth sulfated zirconia in powder form (product name "Z-3314", sulfated zirconia with a sulfuric acid content of 5% by mass (5wt%SO4 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia. In the slurry preparation step of Comparative Example 3, a fifth type of sulfated zirconia in powder form (product name "Z-3294", sulfated zirconia with a sulfuric acid content of 6% by mass (6wt%SO4 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first type of sulfated zirconia. In the slurry preparation step of Comparative Example 4, a sixth type of sulfated zirconia in powder form (product name "Z-3295", sulfated zirconia with a sulfuric acid content of 10% by mass (10wt%SO4 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first type of sulfated zirconia.

[0051] [Comparative Example 5] A powdered hydrocarbon oxidation catalyst for Comparative Example 5 (catalyst support: 30 wt% TiO2 / ZrO2, active metal: 1.0 wt% Pd + 1.0 wt% Pt) was prepared in the same manner as the catalyst for Example 1, except as follows: In the slurry preparation step, powdered titanium zirconia oxide (product name "30 wt% TiO2 / ZrO2", titanium zirconia oxide with a titanic acid content of 30% by mass (30 wt% TiO2 / ZrO2), manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd.) was used instead of the first sulfated zirconia, and the amount of titanium zirconia oxide added was 98 parts by mass per 2 parts by mass of Pd and Pt combined.

[0052] <X-ray diffraction measurement> Powder samples of hydrocarbon oxidation catalysts from Examples 1-10 and Comparative Examples 1-5 were subjected to X-ray diffraction (XRD) analysis to measure the peak intensity P1 of the monoclinic zirconia (m-ZrO2) phase, the peak intensity P2 of the tetragonal zirconia (t-ZrO2) phase, the crystallite size R1 of the m-ZrO2 phase, and the crystallite size R2 of the t-ZrO2 phase. In this analysis, an X-ray diffractometer "Ultima IV" and an X-ray detector "D / teX Ultra" (both manufactured by Rigaku) ​​were used, and the crystal structure was analyzed by the Bragg-Brentano method. Furthermore, a CuKα X-ray source (λ=1.54815Å, Ni filter, applied power: 40kV, 40mA) was used, the scanning range was set to 2θ from 5° to 90°, the scanning speed was set to 5.0° / min, the sampling width was set to 0.01°, the divergence slit was set to 0.20mm, the divergence longitudinal limiting slit was set to 2mm, the scattering slit was set to 2°, the photodetecting slit was set to 0.15mm, and the offset angle was set to 0°.

[0053] The analysis was performed using Rigaku's analysis software "PDXL 2 (Version 2.7.2.0)". The peak intensity P1 of the m-ZrO2 phase is the integrated intensity (cps·deg) of the X-ray diffraction signal with a diffraction peak at 2θ = 28.1° (θ is the Bragg angle), and is the value obtained by integrating the intensity (cps) within the range of the integration width (deg) calculated by the analysis software for that diffraction peak. The peak intensity P2 of the t-ZrO2 phase is the integrated intensity (cps·deg) of the X-ray diffraction signal with a diffraction peak at 2θ = 30.2°, and is the value obtained by integrating the intensity (cps) within the range of the integration width (deg) calculated by the analysis software for that diffraction peak. The crystallite size R1 of the m-ZrO2 phase was determined based on the peak full width at half maximum (FWHM) as the diffraction line width at 2θ = 28.1° and Scherrer's equation shown below. The crystallite size R2 of the t-ZrO2 phase was determined based on the peak full width at half maximum (FWHM) as the diffraction line width at 2θ = 30.2° and Scherrer's equation shown below. In Scherrer's equation, D is the crystallite size (nm), λ is the wavelength of the X-ray (Cu-Kα line) (nm), B is the broadening of the diffraction line width (rad), and θ is the Bragg angle (rad). Also, K is Scherrer's constant, and 0.89 was adopted.

[0054] Scherrer's formula: D = Kλ / Bcosθ

[0055] The measurement results are shown in Tables 1 and 2. The ratio of the peak intensity P2 of the t-ZrO2 phase to the peak intensity P1 of the m-ZrO2 phase (P2 / P1) is also shown in Tables 1 and 2. Figure 1 shows the XRD patterns obtained for the hydrocarbon oxidation catalysts of Examples 1 to 10 and Comparative Examples 1 to 5. In the graph in Figure 1, the horizontal axis represents 2θ (deg) in the XRD measurement, and the vertical axis represents the XRD signal intensity.

[0056] Meanwhile, XRD measurements were similarly performed on the powder samples of the first to sixth sulfated zirconia, monoclinic zirconia, tungsten oxide zirconia, and titanium oxide zirconia used as catalyst support raw materials. The peak intensity P1 of the monoclinic zirconia (m-ZrO2) phase, the peak intensity P2 of the tetragonal zirconia (t-ZrO2) phase, the crystallite size R1 of the m-ZrO2 phase, and the crystallite size R2 of the t-ZrO2 phase were determined. The results are shown in Table 3. Figure 2 shows the XRD patterns obtained for the various zirconias used as catalyst support raw materials. In the graph in Figure 2, the horizontal axis represents 2θ (deg) in the XRD measurement, and the vertical axis represents the XRD signal intensity.

[0057] <Catalytic performance> For each hydrocarbon oxidation catalyst in Examples 1-10 and Comparative Examples 1-5, a methane oxidation test was conducted to determine the methane oxidation rate at 400°C as a catalytic performance indicator.

[0058] Specifically, methane oxidation tests were conducted at six temperature points (in 30°C to 40°C increments) selected from the range of 290°C to 460°C, and the methane oxidation rate was measured. In the methane oxidation tests, a catalyst was first packed into a fixed-bed reactor, and the reactor was then placed in the middle of the flow path of the test gas. Next, the test gas was heated to a predetermined temperature and then introduced into the reactor. In the test gas used, the CH4 concentration was 1000 ppmv-dry (inlet concentration D1), the O2 concentration was 12 vol%-wet, the NO concentration was 200 ppmv-dry, the SO2 concentration was 0.2 ppmv-dry, the H2O concentration was 10 vol%, and the remainder was N2. In this test, the temperature inside the reactor was 400°C, the pressure inside the reactor was 0.2 MPa, the flow rate of the test gas was 1.0 NL / min, and the gas space velocity (GHSV) of the test gas was 55000 h -1 The gas space velocity is the flow rate (Nm³) of the test gas. 3 ( / h) catalyst volume (m³ 3 It is calculated by dividing by ). The methane concentration (outlet methane concentration D2) of the test gas that passed through the fixed-bed reactor under these conditions was measured. A gas chromatography system "GC-8A" (manufactured by Shimadzu Corporation) with a thermal conductivity detector (TCD) was used to quantify the methane concentration. In the measurement using this system, a dual-packed column "Shincarbon-ST 50 / 80 mesh" (manufactured by Shinwa Chemical Co., Ltd.) 2.0m x 3 was used as the column, He gas (flow rate 50 NmL / min) was used as the carrier gas, the column temperature was set to 180°C, and the detector temperature was set to 140°C. The methane oxidation rate, expressed by the following formula, was then determined from the inlet concentration D1 and outlet concentration D2 of methane.

[0059] Methane oxidation rate (%) = [(Inlet concentration D1 - Outlet concentration D2) / Inlet concentration D1] × 100

[0060] Next, by substituting the methane oxidation rate into equation (1) below, the reaction rate constant k(h) in the methane oxidation reaction at a given temperature can be obtained. -1 The reaction rate constant k at the above six temperatures was determined. In equation (1), GHSV is the gas space velocity as described above.

[0061] k = - GHSV × ln(1 - methane oxidation rate ÷ 100) ···(1)

[0062] Next, based on the reaction rate constant k at the above six temperatures, the Arrhenius equation for the methane oxidation reaction using the specified catalyst was identified by the Arrhenius plot method, and the reaction rate constant k(h) at 400°C was determined in the same equation. -1 The following was determined: Then, using this value and the above formula (1), the methane (CH4) oxidation rate at 400°C was calculated. The values ​​are shown in Tables 1 and 2.

[0063] Furthermore, the methane oxidation activity ratio, expressed by the following equation (2), was determined. In equation (2), k0 is the value of the reaction rate constant k(400°C) of the hydrocarbon oxidation catalyst of Comparative Example 1. That is, the methane oxidation activity ratio is the ratio of the reaction rate constant k(400°C) of each hydrocarbon oxidation catalyst to the reaction rate constant k(400°C) of the hydrocarbon oxidation catalyst of Comparative Example 1. The values ​​are shown in Tables 1 and 2.

[0064] Methane oxidation activity ratio = k / k0···(2)

[0065] Figure 3 is a graph showing the correlation between the methane oxidation activity ratio and the ratio of the peak intensity P2 of the tetragonal zirconia phase to the peak intensity P1 of the monoclinic zirconia phase (P2 / P1) in XRD measurements for the hydrocarbon oxidation catalysts of Examples 1-10 and Comparative Examples 1-5. In the graph of Figure 3, the horizontal axis represents the ratio (P2 / P1), and the vertical axis represents the methane oxidation activity ratio. Figure 4 is a graph showing the correlation between the methane oxidation activity ratio and the crystallite size R1 of the monoclinic zirconia phase for the hydrocarbon oxidation catalysts of Examples 1-10 and Comparative Examples 1-5. In the graph of Figure 4, the horizontal axis represents the crystallite size R1 (Å) of the monoclinic zirconia phase, and the vertical axis represents the methane oxidation activity ratio. As shown in Figures 3 and 4, the hydrocarbon oxidation catalysts of Examples 1 to 10, which had a ratio (P2 / P1) of 0.005 or more and less than 0.8, and a crystallite size R1 of the monoclinic zirconia phase of 35 Å or more and 115 Å or less, showed higher methane oxidation activity than the hydrocarbon oxidation catalysts of Comparative Examples 1 to 5, which did not meet these criteria.

[0066] For each of the hydrocarbon oxidation catalysts of Examples 1 to 10 and Comparative Examples 1 to 5, the reaction temperature T 50 (CH4) at which the methane oxidation rate becomes 50% was determined. Specifically, from the above formula (1), the reaction rate constant k at which the methane oxidation rate becomes 50% was determined, and the k was substituted into the above Arrhenius formula identified as described above to obtain the reaction temperature T 50 (CH4) at which the methane oxidation rate becomes 50%. The values are shown in Tables 1 and 2.

[0067] FIG. 5 shows the methane oxidation activity ratio and the temperature T 50 (CH4) with respect to the sulfuric acid ratio in the catalyst carrier for the hydrocarbon oxidation catalysts of Examples 1 to 3 and Comparative Examples 1 to 4. In the plots of the graph of FIG. 5, the sulfuric acid ratio is 0% by mass (Comparative Example 1), 1% by mass (Example 1), 2% by mass (Example 2), 3% by mass (Example 3), 5% by mass (Comparative Example 2), 6% by mass (Comparative Example 3), or 10% by mass (Comparative Example 4). As shown in FIG. 5, the hydrocarbon oxidation catalysts of Examples 1 to 3 containing sulfated zirconia containing 3% by mass or less of sulfuric acid as the catalyst carrier showed higher methane oxidation activity than the hydrocarbon oxidation catalysts of Comparative Examples 1 to 4 that did not.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3] <着0000283

Industrial Applicability

[0071] The hydrocarbon oxidation catalyst of the present invention can be used, for example, to remove unburned hydrocarbons from the exhaust gas of an internal combustion engine operating with natural gas as a fuel gas.

Claims

1. A hydrocarbon oxidation catalyst for oxidizing hydrocarbons, A catalyst support containing zirconia, The catalyst carrier comprises an active metal supported on the catalyst carrier, The active metal includes a platinum group metal, The zirconia is oxo-zirconia oxide, The zirconia comprises a monoclinic zirconia phase and a tetragonal zirconia phase. A hydrocarbon oxidation catalyst wherein the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase in X-ray diffraction measurements of the hydrocarbon oxidation catalyst is 0.005 or more and less than 0.8, and the crystallite size of the monoclinic zirconia phase is 35 Å or more and 115 Å or less.

2. The hydrocarbon oxidation catalyst according to claim 1, wherein the oxo-zirconia oxide comprises at least one selected from the group consisting of sulfated zirconia and tungsten-zirconia oxide.

3. The hydrocarbon oxidation catalyst according to claim 1, wherein the active metal comprises at least one selected from the group consisting of palladium, platinum, and ruthenium.

4. The hydrocarbon oxidation catalyst according to claim 1, wherein the active metal contains palladium, and the amount of palladium supported is 0.1% by mass or more and less than 4% by mass.

5. A hydrocarbon treatment method comprising the step of contacting a hydrocarbon with a hydrocarbon oxidation catalyst according to any one of claims 1 to 4.

6. The first step involves preparing a slurry containing a catalyst support material including zirconia and an active metal including a platinum group metal, A second step involves drying the slurry to obtain a powder, The process includes a third step of calcining the powder at a temperature of 400°C or higher and 600°C or lower to obtain the hydrocarbon oxidation catalyst described in any one of claims 1 to 4. A method for producing a hydrocarbon oxidation catalyst, wherein the zirconia in the first step is oxo-zirconia oxide, the zirconia comprises a monoclinic zirconia phase and a tetragonal zirconia phase, the ratio of the peak intensity of the tetragonal zirconia phase to the peak intensity of the monoclinic zirconia phase in X-ray diffraction measurement of the hydrocarbon oxidation catalyst is 0.005 or more and 0.85 or less, and the crystallite size of the monoclinic zirconia phase is 35 Å or more and 115 Å or less.

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