Catalyst for p-xylene production, method for producing catalyst for p-xylene production, and method for producing p-xylene

Abstract

Provided are: a catalyst for p-xylene production, the catalyst including a first catalyst that includes a binary composite oxide of zinc and zirconium, and a second catalyst that includes an H-ZSM-5 zeolite coated with an oxide including amorphous silicon, wherein the molar ratio (Zn / Zr) of zinc to zirconium in the binary composite oxide is 1 / 15 or less; a method for producing the same; and a method for producing p-xylene using the same.

Description

Catalyst for the production of paraxylene, method for producing a catalyst for the production of paraxylene, and method for producing paraxylene

[0001] This disclosure relates to a catalyst for the production of paraxylene, a method for producing the catalyst for the production of paraxylene, and a method for producing paraxylene.

[0002] In recent years, concern about global warming has been growing. At the Conference of the Parties (COP), which discusses international frameworks for reducing greenhouse gas emissions, the long-term global goal is to keep the increase in average temperature since the pre-industrial era well below 2°C, aiming to suppress peak emissions as early as possible and reduce them rapidly in accordance with the latest scientific findings. The COP21 Paris Agreement stipulates that all countries should strive to formulate and submit long-term low-emission greenhouse gas development strategies, and Japan has formulated a long-term goal of reducing greenhouse gas emissions by 80% by 2050. Among anthropogenically emitted greenhouse gases, carbon dioxide is estimated to have the greatest impact, and the development of countermeasures technologies to reduce carbon dioxide is being actively pursued in various places. As one countermeasure technology, several attempts have been proposed to convert emitted carbon dioxide into useful substances, but a large amount of energy is required to convert carbon dioxide into another substance, and the development of effective catalysts to promote the reaction is desired.

[0003] Furthermore, in order for this technology to contribute to carbon dioxide reduction, it is necessary to produce useful substances that are in high demand. Paraxylene is a useful compound as a raw material for polyethylene terephthalate (PET), a general-purpose resin. If it is possible to efficiently produce such compounds from carbon dioxide and hydrogen, it could be a useful measure for reducing carbon dioxide emissions.

[0004] Conventionally, para-xylene has been produced by reforming crude oil and naphtha. Additionally, a technology for producing para-xylene using a mixed gas of carbon monoxide and hydrogen, so-called synthesis gas, as a raw material has been proposed. On the other hand, a method for producing para-xylene from carbon dioxide and hydrogen has also been disclosed. For example, Patent Document 1 discloses a catalyst for para-xylene production, which comprises a first catalyst containing chromium oxide for synthesizing para-xylene from carbon dioxide and hydrogen in one step, and a second catalyst comprising H-ZSM-5 zeolite coated with silicalite-1. Patent Document 2 discloses a catalyst for para-xylene production, which comprises a first catalyst containing a ternary composite oxide of chromium, zinc, and zirconium, and a second catalyst comprising H-ZSM-5 zeolite coated with an oxide containing amorphous silicon. Patent Document 3 discloses a catalyst for para-xylene production comprising a composite oxide and H-ZSM-5 zeolite coated with silica.

[0005] Also, a catalyst for para-xylene production using a binary composite oxide of zinc and zirconium has been disclosed (see Non-Patent Documents 1 to 7).

[0006] Patent Document 1: Japanese Unexamined Patent Publication No. 2019-205969 Patent Document 2: International Publication No. WO 2024 / 203963 Patent Document 3: International Publication No. WO 2019 / 062815

[0007] Non-Patent Document 1: App. Cat. B, 286 (2021) 119929 Non-Patent Document 2: Chem. Comm., 59 (2023) 7607 Non-Patent Document 3: ACS Sus. Chem. Eng., 11(2023) 12967 Non-Patent Document 4: ACS Catal., 10 (2020) 302 Non-Patent Document 5: Joule, 3 (2019) 570 Non-Patent Document 6: J. Environ. Chem. Eng., 10 (2022) 108032 Non-Patent Document 7: Catal. Sci. Technol., 12 (2022) 799

[0008] The Cr-containing catalysts (Cr-based catalysts) disclosed in Patent Documents 1 and 2 are effective in that they can efficiently produce paraxylene from carbon dioxide and hydrogen. However, Cr-based catalysts may partially convert to hexavalent chromium, and catalysts with lower toxicity are desirable. The binary composite oxides of Zn and Zr (ZnZr-based catalysts) disclosed in Patent Document 3 and Non-Patent Documents 1 to 7 do not contain Cr, but it is desirable that they can produce paraxylene with higher selectivity.

[0009] Therefore, the object of this disclosure is to provide a catalyst for the production of paraxylene, a method for producing the catalyst for the production of paraxylene, and a method for producing paraxylene, which can improve the selectivity of paraxylene when producing paraxylene using carbon dioxide and hydrogen as raw materials with a Cr-free catalyst.

[0010] The gist of the present disclosure is as described below. <1> A catalyst for producing para-xylene, comprising: a first catalyst containing a binary composite oxide of zinc and zirconium; and a second catalyst containing H-ZSM-5 zeolite coated with an oxide containing amorphous silicon, wherein the molar ratio of zinc to zirconium (Zn / Zr) in the binary composite oxide is 1 / 15 or less. <2> The catalyst for producing para-xylene according to <1>, wherein the molar ratio of zinc to zirconium (Zn / Zr) in the binary composite oxide is 1 / 16 or less. <3> The catalyst for producing para-xylene according to <1> or <2>, wherein the molar ratio of zinc to zirconium (Zn / Zr) in the binary composite oxide is 1 / 50 or more. <4> The catalyst for producing para-xylene according to <3>, wherein the molar ratio of zinc to zirconium (Zn / Zr) in the binary composite oxide is 1 / 36 or more. <5> The catalyst for producing para-xylene according to any one of <1> to <4>, wherein the content of the second catalyst relative to the first catalyst is 10 mass% or more and 1000 mass% or less. <6> A method for producing para-xylene, comprising bringing a raw material gas containing carbon dioxide and hydrogen into contact with the catalyst for producing para-xylene according to any one of <1> to <4> to synthesize para-xylene. <7> A method for producing the catalyst for producing para-xylene according to any one of <1> to <5>, comprising: obtaining a coprecipitate containing zinc and zirconium at a molar ratio of Zn / Zr of 1 / 15 or less by a coprecipitation method, and performing one or both of drying and calcination of the coprecipitate to obtain the first catalyst; performing hydrothermal synthesis or heating in the presence of a silicon compound and H-ZSM-5 zeolite to obtain the second catalyst containing H-ZSM-5 zeolite coated with the oxide containing amorphous silicon; and mixing the first catalyst and the second catalyst.

[0011] According to the present disclosure, there can be provided a catalyst for producing para-xylene, a method for producing the catalyst for producing para-xylene, and a method for producing para-xylene, which can improve the selectivity of para-xylene when para-xylene is produced from carbon dioxide and hydrogen as raw materials by using a chromium-free catalyst.

[0012] This figure shows an example of a TEM-EDS image of the first catalyst (a binary composite oxide of Zn and Zr).

[0013] An embodiment, which is an example of this disclosure, will be described. In this disclosure, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. Regarding the element content contained in the catalyst, "%" means "mass %" unless otherwise specified. In numerical ranges described in stages in this disclosure, the upper limit of one stage of numerical range may be replaced with the upper limit of another stage of numerical range, or with the value shown in the example. Also, in numerical ranges described in stages in this disclosure, the lower limit of one stage of numerical range may be replaced with the lower limit of another stage of numerical range, or with the value shown in the example. The term "process" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0014] The inventors of this disclosure, in their diligent efforts to develop a Cr-free catalyst while maintaining the productivity of paraxylene produced from carbon dioxide and hydrogen, have developed a conventional ZnZrO ｘ In the catalyst, the molar ratio of Zn to Zr (Zn / Zr) is 1 / 15 or less. ｘ By using a catalyst, the known ZnZrO ｘ We found that it improves the selectivity of paraxylene compared to a catalyst.

[0015] Preferred embodiments of this disclosure will be described in detail below.

[0016] <1. Catalyst for Paraxylene Production> First, preferred embodiments of the paraxylene production catalyst of the present disclosure will be described. The paraxylene production catalyst according to the present disclosure catalyzes the synthesis reaction of hydrocarbon compounds, particularly paraxylene, using carbon dioxide and hydrogen as raw materials. The paraxylene production catalyst according to the present disclosure includes a first catalyst comprising a binary complex oxide containing zinc (Zn) and zirconium (Zr), with a Zn / Zr molar ratio of 1 / 15 or less, and a second catalyst comprising H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide.

[0017] A first catalyst containing a composite oxide comprising zinc and zirconium catalyzes the conversion of carbon dioxide and hydrogen to methanol. On the other hand, a second catalyst containing H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide catalyzes the conversion of methanol to paraxylene. In other words, the paraxylene production catalyst according to this disclosure is a catalyst composition (composite catalyst) comprising a first catalyst and a second catalyst having different functions. Furthermore, by having a Zn / Zr molar ratio of 1 / 15 or less in the zinc and zirconium-containing composite oxide of the first catalyst, high paraxylene selectivity can be achieved.

[0018] (1.1. First Catalyst) As described above, the first catalyst is a binary composite oxide of zinc and zirconium (in this disclosure, it may be referred to as a "specific ratio binary composite oxide of zinc and zirconium") having a Zn / Zr molar ratio (hereinafter sometimes simply referred to as "Zn / Zr") of 1 / 15 or less. The specific ratio binary composite oxide of zinc and zirconium catalyzes the conversion of carbon dioxide and hydrogen to methanol. Since the specific ratio binary composite oxide of zinc and zirconium has oxygen vacancies, carbon dioxide is easily adsorbed on the surface of the specific ratio composite oxide of zinc and zirconium, and the reaction between carbon dioxide adsorbed on the specific ratio composite oxide of zinc and zirconium and hydrogen occurs efficiently, resulting in the efficient production of methanol. Furthermore, the first catalyst in this disclosure can efficiently produce methanol even if carbon monoxide gas is present in the raw material gas, by recycling a portion of the reaction gas (including unreacted carbon dioxide gas and by-product carbon monoxide gas). As a result, the selectivity of paraxylene can be improved.

[0019] The molar ratio of zinc to zirconium in the first catalyst, Zn / Zr, is 1 / 15 or less. From the viewpoint of efficiently producing methanol, it is 1 / 16 or less, 1 / 18 or less, or 1 / 20 or less. On the other hand, if the molar ratio of zinc to zirconium in the first catalyst, Zn / Zr, is too small, the effect of the zinc-zirconium composite oxide is difficult to obtain. Therefore, it is preferable that the molar ratio of zinc to zirconium in the first catalyst, Zn / Zr, is 1 / 50 or more, 1 / 45 or more, 1 / 40 or more, 1 / 36 or more, or 1 / 32 or more.

[0020] The first catalyst can be identified as a binary composite oxide of Zn and Zr in specific ratios from SEM-EDS and TEM images. Figure 1 shows an example of a TEM-EDS image of the first catalyst (a binary composite oxide of Zn and Zr). The TEM image in Figure 1 shows a single particle, and EDS analysis of the circular area indicated by "a" confirmed the presence of Zr and Zn. The presence of both Zn and Zr elements in a single particle indicates that it is a binary composite oxide.

[0021] The catalyst in this disclosure may contain impurities introduced during the catalyst manufacturing process. However, from the viewpoint of improving catalytic activity, the less impurities there are, the better, and it is preferable to avoid introducing impurities as much as possible (for example, 1% by mass or less relative to the total mass of the first catalyst). Examples of impurities that may be introduced during the manufacturing process include N, Cl, C, etc.

[0022] Furthermore, the metal mass concentration in the first catalyst can be quantified by scanning radio frequency inductively coupled plasma (ICP-AES) spectroscopy. Specifically, after grinding the sample, an alkaline fusion agent (e.g., sodium carbonate, sodium borate) is added and heated and melted in a platinum crucible. After cooling, the entire volume is dissolved in a hydrochloric acid solution under heating. When this solution is injected into an ICP analyzer, the sample solution is atomized and thermally excited in the high-temperature plasma state within the analyzer. As it returns to its ground state, it produces an emission spectrum at wavelengths specific to each element. From the emission wavelength and intensity, the types and amounts of elements contained can be qualitatively and quantitatively determined. The concentration of each metal element is defined by taking the total concentration of all metals calculated by the ICP-AES method as 100 mol%, and then determining the molar concentration of each metal element within that total. The molar ratio of Zn / Zr can be determined by converting the molar concentration of each metal element to a molar ratio.

[0023] The form of the first catalyst is not particularly limited and, for example, it may be granular. The first catalyst is usually porous and therefore has pores for the reaction to take place, and has a relatively large specific surface area. The specific surface area and other properties when the first catalyst is porous will be described below.

[0024] The specific surface area of ​​the first catalyst is not particularly limited, but for example, 3 m² ２ / g or more 500m ２ / g or less, preferably 10m ２ / g or more 100m ２The specific surface area is less than or equal to / g. This ensures a sufficient supply of active sites for the reaction between hydrogen and carbon dioxide. Furthermore, by keeping the specific surface area below the upper limit mentioned above, the pore diameter becomes excessively small, preventing a difference in the gas diffusion rates of carbon dioxide and hydrogen within the pores, and thus preventing a difference in the partial pressure of carbon dioxide and hydrogen within the first catalyst. As a result, the conversion of hydrogen and carbon dioxide to methanol is carried out efficiently. The specific surface area can be measured by the BET method.

[0025] Furthermore, the average pore size of the first catalyst is not particularly limited, but is, for example, 0.5 nm to 100 nm, preferably 2 nm to 30 nm. This prevents a difference in gas diffusion rates between carbon dioxide and hydrogen within the pores, and also increases the specific surface area of ​​the first catalyst, allowing for a sufficient supply of active sites. As a result, the conversion of hydrogen and carbon dioxide to methanol is carried out efficiently.

[0026] The pore size can be determined by analyzing data obtained from the gas adsorption method (BET specific surface area measurement) using the BJH (Barrett-Joyner-Halenda) method. The adsorbent gas used for measurement is, for example, N ２ This method can utilize molecules, allowing for the measurement of specific surface area from the amount of adsorbed gas molecules and the weight of the sample. Furthermore, by performing this measurement at the temperature at which the adsorbed molecules liquefy, the pore volume and pore diameter can be determined by measuring the liquid adsorbed molecules filling the pores.

[0027] The pore capacity of the first catalyst is not particularly limited, and is, for example, 0.1 cc / g or more and 5 cc / g or less, preferably 0.5 cc / g or more and 2 cc / g or less.

[0028] Pore ​​volume can be determined by the mercury intrusion method. If the mercury intrusion method is not available, it can be measured by water titration. Average pore diameter can be measured by the mercury intrusion method using a mercury porosimeter. If the mercury intrusion method is not available, it can be determined by the gas adsorption method described above.

[0029] Further, when the first catalyst is in granular form, the average particle diameter of the first catalyst is, for example, 1 µm or more and 800 µm or less, preferably 10 µm or more and 200 µm or less. This accelerates mass transfer between the first catalyst and the second catalyst, and also reduces flow resistance of the raw material gas (pressure loss reduction). In the present specification, the "average particle diameter" refers to the volume-based 50% particle diameter (D50) measured by a wet laser diffraction / scattering method.

[0030] (1.2. Second Catalyst) As described above, the second catalyst comprises H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide. The second catalyst catalyzes the conversion of methanol produced via the first catalyst into para-xylene. Here, in the second catalyst, H-ZSM-5 zeolite mainly catalyzes the selective conversion of methanol into para-xylene, while the amorphous silicon-containing oxide coating the surface of H-ZSM-5 zeolite prevents isomerization of para-xylene.

[0031] The second catalyst is mainly composed of H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide. Meanwhile, the amorphous silicon-containing oxide in the second catalyst may contain trace amounts of other elements derived from production, or elements derived from a carrier used for supporting the second catalyst. Examples of such other elements include aluminum, magnesium and the like.

[0032] The amorphous nature of the silicon-containing oxide is determined by observing a broad X-ray diffraction pattern. In the case of a crystalline silicon-containing oxide, SiO ２ exhibits a high-intensity peak, whereas if it is amorphous, it appears as a low-intensity peak, enabling discrimination. Furthermore, crystallinity and amorphousness can also be determined based on an electron diffraction pattern obtained by transmission electron microscopy. In the case of crystallinity, since the structure has periodicity, strong diffraction is obtained and a clear electron diffraction pattern is obtained. In contrast, in the case of amorphousness, since the structure has no periodicity, diffraction is weak and a halo (halo-shaped) image is obtained. Hereinafter, amorphous SiO ２ is simply referred to as "SiO ２ " in some cases.

[0033] Specifically, within the 10-membered ring pores of H-ZSM-5 zeolite, numerous acid sites are present. These acid sites act as active sites, and an aromatic ring (benzene ring) is formed from methanol via dimethyl ether and light olefins. Furthermore, within the pores of H-ZSM-5 zeolite, the benzene ring is methylated at its 1 and 4 positions via a Friedel-Crafts reaction by further methanol. Here, the pore size of the 10-membered ring pores of H-ZSM-5 zeolite is such that paraxylene can pass through, but orthoxylene and metaxylene cannot. Therefore, paraxylene is preferentially formed due to the so-called spatial localization effect. The spatial localization effect refers to the phenomenon or effect in which, when a reaction proceeds within a certain space, the reaction is controlled or localized (restricted) according to the shape and size of the space, and a specific reaction or reaction at a specific site proceeds preferentially.

[0034] On the other hand, on the outer surface of the H-ZSM-5 zeolite, excluding the pores, there are no spatial limitations, and therefore the spatial localization effect does not occur. Consequently, there is a risk of orthoxylene, metaxylene, and trimethylbenzene being generated at acid sites on the outer surface. In contrast, in this disclosure, the surface (outer surface) of the H-ZSM-5 zeolite is coated with an amorphous silicon-containing oxide.

[0035] Amorphous silicon-containing oxides are oxides mainly composed of silica, and more preferably SiO ２ It is SiO ２ SiO has low acidity and basically does not have the function of catalyzing reactions with methanol or methanol-derived compounds. ２ By coating the outer surface of H-ZSM-5 zeolite with SiO2, the acid sites, which are active sites on the outer surface of H-ZSM-5 zeolite, are eliminated, and the isomerization of paraxylene to metaxylene and orthoxylene, and the methylation reaction to trimethylbenzene can be prevented. On the other hand, paraxylene generated in the pores of H-ZSM-5 zeolite is SiO2 ２ It is released to the outside of the second catalyst through its pores.

[0036] In the second catalyst, the amorphous silicon-containing oxide and the H-ZSM-5 zeolite can be in any positional relationship, as long as the amorphous silicon-containing oxide coats the surface of the H-ZSM-5 zeolite. For example, the second catalyst may have a so-called core-shell structure in which H-ZSM-5 zeolite particles form a core, and amorphous silicon-containing oxide coats the core as a shell.

[0037] Furthermore, in the second catalyst, the thickness of the amorphous silicon-containing oxide coating the surface of the H-ZSM-5 zeolite is not particularly limited, but is, for example, 0.01 μm or more and 200 μm or less, preferably 0.02 μm or more and 20 μm or less. This makes it possible to more reliably prevent the isomerization of paraxylene to metaxylene and orthoxylene, and also prevents a decrease in reaction efficiency due to insufficient methanol supply to the H-ZSM-5 zeolite caused by a thickness of amorphous silicon-containing oxide that is too large.

[0038] The thickness of the amorphous silicon-containing oxide film formed on the outer surface of H-ZSM-5 zeolite can be measured by observing the cross-section of the catalyst using a scanning electron microscope (SEM). One method for preparing a sample for observing the catalyst cross-section is to embed catalyst particles in resin and then polish it. The above thickness is an average value. When measuring by observing the catalyst cross-section with an SEM, if the thickness is uniform, only a few measurement points are needed. If it is not uniform, set up enough measurement points (for example, 16 points at approximately equal intervals in the circumferential direction) to calculate the average value. If the thickness differs for each particle, observe multiple particles (for example, 10 particles) as representatives and average the results. When selecting multiple representative particles, observe more particles than the representative particle, and then select particles with an average thickness after removing particles with extremely different thicknesses. If catalysts of different particle sizes are mixed, when observing as a representative as described above, select particles with a particle size approximately equal to the average particle size. To measure the average particle size, a laser diffraction particle size analyzer is used, which irradiates dispersed catalyst particles with laser light and measures the angular dependence of the scattered light intensity from the particles to determine the particle size distribution. In some cases, there may be defective areas where an amorphous silicon oxide film is not formed; however, in such cases, the defective areas are not included in the measurement, and the average value is taken from the areas where the amorphous silicon oxide is formed.

[0039] Furthermore, in the second catalyst, the mass ratio of the amorphous silicon-containing oxide is not particularly limited, but for example, it is 5% by mass or more and 100% by mass or less, preferably 10% by mass or more and 40% by mass or less, relative to the mass of H-ZSM-5 zeolite. This makes it possible to more reliably prevent the isomerization of paraxylene to metaxylene and orthoxylene, and also prevents a decrease in reaction efficiency due to insufficient methanol supply to the H-ZSM-5 zeolite because the film thickness of the amorphous silicon-containing oxide is too large.

[0040] The mass percentage of amorphous silicon-containing oxides in the second catalyst is determined by the following method. First, the silica (SiO₂) of the second catalyst is determined by scanning radio frequency inductively coupled plasma (ICP-AES) spectroscopy. ２The silica / alumina ratio of H-ZSM-5 (+H-ZSM-5) and alumina is quantitatively analyzed. Next, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) is used to obtain the silica / alumina ratio of H-ZSM-5 obtained from cross-sectional analysis. Then, considering the silica / alumina ratio of H-ZSM-5, the total silica quantified by ICP-AES is separated into amorphous silicon-containing oxide and H-ZSM-5, thereby calculating the mass percentage of amorphous silicon-containing oxide.

[0041] The average pore size of the second catalyst is not particularly limited, but is, for example, 0.1 nm to 2.5 nm, preferably 0.4 nm to 0.6 nm. This makes it possible to more reliably obtain the spatial localization effect within the pores described above, and the pore size becomes large enough for the paraxylene synthesized by H-ZSM-5 inside the second catalyst to pass through.

[0042] The specific surface area of ​​the second catalyst is not particularly limited, but for example, 20 m² ２ / g or more 1000m ２ / g or less, preferably 100m ２ / g or more 400m ２ The value is less than or equal to / g. This ensures a sufficient supply of active sites for the methanol reaction and the synthesis of paraxylene, and also allows the pore size of the second catalyst to be easily set to the aforementioned range.

[0043] The pore capacity of the second catalyst is not particularly limited, and is, for example, 0.1 cc / g or more and 5 cc / g or less, preferably 0.5 cc / g or more and 2 cc / g or less.

[0044] Furthermore, if the second catalyst is granular, the average particle size of the second catalyst can be, for example, 0.1 μm or more and 50 μm or less, preferably 0.5 μm or more and 5 μm or less. This accelerates mass transfer between the first catalyst and the second catalyst, and also reduces the flow resistance of the raw material gas (reduction of pressure loss).

[0045] (1.3. Positional relationship between the first catalyst and the second catalyst) As described above, in this disclosure, the catalyst for the production of paraxylene includes a first catalyst and a second catalyst. In this disclosure, the statement that the catalyst for the production of paraxylene includes a first catalyst and a second catalyst means that the first catalyst and the second catalyst are not physically separated by other elements such as glass wool. The positional relationship between the first catalyst and the second catalyst in the catalyst for the production of paraxylene is not particularly limited. For example, if the first catalyst and the second catalyst are granular, they may be physically mixed. Alternatively, if the first catalyst and the second catalyst each constitute layers, the layers of the first catalyst and the layers of the second catalyst may be stacked. In this case, the amorphous silicon-containing oxide of the second catalyst is arranged on the outer surface side of the catalyst for the production of paraxylene. Specifically, one example is a configuration in which the second catalyst is arranged around the first catalyst.

[0046] Furthermore, it is preferable that the first and second catalysts are in close proximity. Proximity can be achieved by granulation after physical mixing. This is because proximity suppresses other side reactions from the intermediate methanol, thereby improving the selectivity of paraxylene.

[0047] In the catalyst for paraxylene production, the second catalyst is present in an amount of, for example, 10% to 1000% by mass relative to the first catalyst (i.e., 10 to 1000 parts by mass of the second catalyst per 100 parts by mass of the first catalyst), preferably 50% to 200% by mass, from the viewpoint of improving the space-time yield. This makes it possible to make the methanol synthesis rate in the first catalyst and the methanol consumption rate in the second catalyst relatively similar, and prevents unintended side reactions from occurring due to excess compounds. However, depending on the desired selectivity, space-time yield, etc., a smaller amount (e.g., 5% by mass) or a larger amount (e.g., 1500% by mass) may be used.

[0048] During the production of the paraxylene catalyst according to this disclosure, the ratio of the second catalyst to the first catalyst can be optimized by adjusting the respective masses (blending amounts) of the first and second catalysts when they are mixed. In the catalyst after the first and second catalysts have been mixed (including when they have been molded or granulated thereafter), this ratio can be determined, for example, using scanning radio frequency inductively coupled plasma (ICP-AES) spectroscopy. Specifically, after grinding the sample, an alkaline fusion agent (e.g., sodium carbonate, sodium borate, etc.) is added and heated and melted in a platinum crucible, and after cooling, the entire amount is dissolved in a hydrochloric acid solution under heating. When this solution is injected into an ICP analyzer, the sample solution is atomized and thermally excited in the high-temperature plasma state inside the analyzer, and when it returns to the ground state, it produces an emission spectrum of wavelengths specific to the elements. From the emission wavelength and intensity, the types and amounts of elements contained can be qualitatively and quantitatively determined. Then, considering the ratio of the quantified types of elements contained, the ratio of the first catalyst to the second catalyst can be calculated.

[0049] The catalyst for paraxylene production according to this disclosure has been described above. According to this disclosure, paraxylene can be produced with high selectivity using carbon dioxide and hydrogen as raw materials. Specifically, by using a binary composite oxide of zinc and zirconium as the first catalyst, in which the molar ratio of zinc to zirconium (Zn / Zr) is 1 / 15 or less, carbon dioxide is easily adsorbed and the reaction between carbon dioxide and hydrogen proceeds efficiently. By using H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide as the second catalyst, a spatial limiting effect is achieved, enabling the selective and efficient synthesis of paraxylene, resulting in the synthesis of paraxylene with high selectivity. It should be noted that carbon monoxide may be included in part of the raw material gas.

[0050] <2. Method for Producing a Catalyst for Paraxylene Production> Next, a method for producing a catalyst for paraxylene production according to this disclosure will be described. The method for producing a catalyst for paraxylene production according to this disclosure is not particularly limited, but for example, it includes a step (third step) of obtaining a second catalyst by performing hydrothermal synthesis or heating in the presence of at least a silicon compound and H-ZSM-5 zeolite to coat the surface of the H-ZSM-5 zeolite with an amorphous silicon-containing oxide, and a step (fourth step) of mixing a first catalyst containing a binary complex oxide of zinc and zirconium in a molar ratio of Zn / Zr of 1 / 15 or less with the second catalyst. The method for producing a catalyst for paraxylene production according to this disclosure may optionally include a step (second step) of synthesizing H-ZSM-5 zeolite from a silicon compound and an aluminum compound by hydrothermal synthesis prior to the third step. Furthermore, the method for producing a paraxylene catalyst according to this disclosure may optionally include, separately from the second and third steps described above, a step (first step) of obtaining a first catalyst containing a binary complex oxide of zinc and zirconium by a coprecipitation method, wherein the coprecipitation contains a coprecipitation (precipitate containing a complex hydroxide) containing zinc and zirconium in a molar ratio of Zn / Zr of 1 / 15 or less, and the coprecipitation is dried and / or calcined.

[0051] (2.1. First step) First, in the first step, although not particularly limited, a coprecipitation (precipitate containing a complex hydroxide) containing a binary metal system of zinc and zirconium in a molar ratio of Zn / Zr of 1 / 15 or less is obtained by a coprecipitation method, and the coprecipitation is dried and / or calcined to obtain the first catalyst.

[0052] In the coprecipitation method, specifically, a zinc compound and a zirconium compound are first dissolved in an aqueous solution so that the molar ratio of Zn / Zr is 1 / 15 or less, and then a precipitating agent is added to precipitate the zinc and zirconium complex hydroxide. The zinc compound (zinc source) is not particularly limited as long as it is soluble in aqueous solution, and for example, zinc nitrate, zinc acetate, zinc chloride, zinc bromide, etc. can be used. The zirconium compound (zirconium source) is not particularly limited as long as it is soluble in aqueous solution, and for example, zirconium nitrate, zirconium acetate, zirconium chloride, zirconium bromide, etc. can be used.

[0053] Furthermore, the precipitating agent is not particularly limited as long as it can precipitate (release) the zinc and zirconium complex hydroxide, and for example, ammonium carbonate, sodium carbonate, sodium bicarbonate, urea, potassium carbonate, aqueous ammonia, etc. can be used.

[0054] Furthermore, in order to control the particle size and shape of the zinc-zirconium composite hydroxide, a maturation treatment may be performed after the zinc-zirconium composite hydroxide has settled. The maturation treatment can be carried out, for example, by letting it stand for 30 minutes to 12 hours.

[0055] In the aging process described above, the temperature of the aqueous solution is not particularly limited, but can be, for example, above room temperature and below 100°C.

[0056] Next, the obtained zinc-zirconium composite hydroxide is subjected to either drying or calcination, or both, to obtain a first catalyst containing the zinc-zirconium composite hydroxide. It is preferable to perform calcination after drying, but drying or calcination alone may also be performed. Prior to drying and calcination, the zinc-zirconium composite hydroxide may be washed as appropriate.

[0057] Drying can be carried out, for example, in an atmospheric atmosphere at 100°C to 200°C for 30 minutes to 12 hours. Alternatively, it can be carried out using supercritical carbon dioxide at 50°C to 200°C for 20 minutes to 24 hours. Furthermore, calcination can be carried out, for example, in an atmospheric atmosphere at 400°C to 600°C for 30 minutes to 10 hours. In this way, a first catalyst containing a zinc and zirconium composite oxide having a Zn / Zr molar ratio of 1 / 15 or less is obtained.

[0058] (2.2. Second Step) In this step, H-ZSM-5 zeolite is synthesized from a silicon compound and an aluminum compound by hydrothermal synthesis. The formation of H-ZSM-5 zeolite is carried out, for example, by heating an aqueous solution (precursor solution) containing a silicon compound (silica source) and an aluminum compound (alumina source).

[0059] Examples of silicon compounds that can be used include tetramethyl orthosilicate and tetraethyl orthosilicate, and examples of aluminum compounds that can be used include aluminum nitrate and aluminum acetate, but the invention is not limited to these.

[0060] Furthermore, the precursor solution may contain amine compounds, such as tetrapropylammonium hydroxide or tetraethylammonium hydroxide, as a template agent (organic structure-determining agent). In addition, while the solvent of the precursor solution is mainly water, it may also contain alcohol-based solvents such as ethanol or methanol to control the hydrolysis rate of the silicon compound.

[0061] The temperature in hydrothermal synthesis is not particularly limited, but can be, for example, 150 to 200°C, preferably 170 to 190°C.

[0062] As the time of hydrothermal synthesis increases, the particle size of H-ZSM-5 zeolite increases. The time of hydrothermal synthesis is, for example, 1 hour to 168 hours, preferably 24 hours to 72 hours.

[0063] In addition, the reaction mixture may be stirred as needed during hydrothermal synthesis. The stirring conditions can be set as appropriate. Furthermore, the physical properties of H-ZSM-5 zeolite, such as particle size, pore size, and specific surface area, can be controlled by the hydrothermal synthesis conditions, such as time.

[0064] The H-ZSM-5 zeolite produced by hydrothermal synthesis is subjected to washing and drying as appropriate after the completion of hydrothermal synthesis. The drying time is not particularly limited, but can be, for example, 0.5 to 20 hours. The drying temperature is not particularly limited, but can be, for example, 50 to 150°C.

[0065] Next, the dried catalyst is subjected to calcination to remove organic matter present in the pores of the zeolite. This yields H-ZSM-5 zeolite. The calcination time is not particularly limited, but can be, for example, 0.5 to 15 hours. The calcination temperature is not particularly limited, but can be, for example, 400 to 600°C.

[0066] If H-ZSM-5 zeolite is available separately, this step may be omitted. Furthermore, notwithstanding the above explanation, H-ZSM-5 zeolite does not necessarily have to be manufactured by hydrothermal synthesis.

[0067] (2.3. Third Step) In this step, hydrothermal synthesis is performed in the presence of a compound containing at least silicon and H-ZSM-5 zeolite, or heating is performed in the presence of a compound containing silicon and H-ZSM-5 zeolite to form an amorphous silicon-containing oxide (preferably SiO₂) on the surface of the H-ZSM-5 zeolite. ２ A second catalyst is obtained by coating it with SiO. ２ The formation is carried out, for example, by adding tetraethoxysilane (TEOS) dropwise to an organic solvent in which H-ZSM-5 zeolite is dispersed, and then heating the mixture.

[0068] Also, SiO ２ When coating, hexane or the like is used as the organic solvent to disperse H-ZSM-5. Other organic solvents, alcohols, etc., may also be included.

[0069] Furthermore, stirring is performed to disperse H-ZSM-5 in the organic solvent, but the stirring speed is not particularly limited. For example, it can be 200 to 1000 rpm / min, preferably 300 to 800 rpm / min.

[0070] The heating temperature after adding TEOS dropwise to the H-ZSM-5 dispersed organic solvent is not particularly limited. For example, it can be 50 to 150°C, preferably 50 to 80°C.

[0071] TEOS is added dropwise to the H-ZSM-5 dispersed organic solvent, and then the organic solvent is removed while heating. The heating temperature at this time is not particularly limited, but for example, it can be 50 to 150°C, preferably 50 to 80°C.

[0072] As described above, SiO ２ The H-ZSM-5 zeolite coated with the coating is subjected to drying and calcination after heating, if necessary. The drying time is not particularly limited, but can be, for example, 0.5 to 20 hours. The drying temperature is not particularly limited, but can be, for example, 50 to 150°C.

[0073] Next, the dried catalyst is subjected to a calcination treatment to remove organic matter present in the pores of the zeolite. This results in SiO ２ A coated H-ZSM-5 zeolite is obtained. The firing time is not particularly limited, but can be, for example, 0.5 to 15 hours. The firing temperature is not particularly limited, but can be, for example, 400 to 600°C.

[0074] (2.4. Fourth step) A first catalyst containing a binary composite oxide of zinc and zirconium having a Zn / Zr molar ratio of 1 / 15 or less is physically mixed with a second catalyst containing H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide. This yields the paraxylene production catalyst according to the present disclosure. The mixing can be carried out, for example, using a mortar and pestle, a ball mill, an automatic kneader, etc.

[0075] Furthermore, after mixing, in order to improve the adhesion between the first catalyst and the second catalyst, pellets of the catalyst for paraxylene production may be formed and these pellets may be crushed.

[0076] <3. Method for Producing Paraxylene> Next, a method for producing paraxylene using the above-described paraxylene production catalyst will be explained based on a preferred embodiment.

[0077] Paraxylene can be produced by contacting a source gas containing carbon dioxide and hydrogen with a paraxylene production catalyst according to this disclosure. Carbon dioxide and hydrogen may be supplied separately, but are usually supplied as a mixed gas.

[0078] For the carbon dioxide and hydrogen mixture used in the method described herein, a gas in which the total amount of carbon dioxide and hydrogen is 50% or more of the total is preferable from the standpoint of productivity, and in particular, a molar ratio of hydrogen to carbon dioxide (hydrogen / carbon dioxide) in the range of 0.5 to 4.0 is desirable. This is because if the molar ratio of hydrogen to carbon dioxide is less than 0.5, the amount of hydrogen present in the raw material gas is too small, making it difficult for the hydrogenation reaction of carbon dioxide to proceed and resulting in low productivity. On the other hand, if the molar ratio of hydrogen to carbon dioxide exceeds 4.0, the amount of carbon dioxide present in the raw material gas is too small, resulting in low productivity of liquid hydrocarbons regardless of catalytic activity.

[0079] Furthermore, the reactor used for contact between the mixed gas and the catalyst according to this disclosure is not particularly limited and includes, for example, general gas-phase synthesis reactors such as fixed-bed reactors, jet-bed reactors, and fluidized-bed reactors, liquid-phase synthesis reactors such as slurry-bed reactors, and microchannel reactors.

[0080] When carrying out the reaction to produce paraxylene, the binary complex oxide (first catalyst) of zinc and zirconium in a specific ratio must be in a reduced state. Therefore, before supplying the mixed gas to produce paraxylene, a reducing gas such as hydrogen gas is passed through to reduce the catalyst for paraxylene production. Such a reduction treatment is not particularly limited, but can be carried out, for example, at a temperature of 300 to 500°C for 1 to 40 hours.

[0081] Furthermore, the catalyst for paraxylene production may be reduced after loading the reactor, or it may be reduced before loading. For example, it is possible to perform the reduction treatment before charging the reactor with the paraxylene production catalyst, and then load the reactor.

[0082] The conditions for the production of paraxylene are not particularly limited and can be set according to the type of reactor.

[0083] For example, the reaction temperature during the reaction to produce paraxylene is not particularly limited, but is 200 to 500°C, preferably 300 to 400°C. Also, the pressure in the system during the reaction is not particularly limited, but is, for example, 4.0 to 10.0 MPa, preferably 5.0 to 8.0 MPa.

[0084] If the activity decreases due to factors such as an extremely high conversion rate or a long reaction time, the catalyst for paraxylene production can be regenerated by supplying a gas containing air (regeneration gas) instead of the mixed gas. The air content of the regeneration gas is preferably 0.01% or more. However, the air content in the regeneration gas may be 100%. Furthermore, the regeneration gas may contain inert gases such as nitrogen or argon in addition to air.

[0085] The conditions for regeneration of the paraxylene production catalyst are not particularly limited, as long as catalyst regeneration progresses. It is presumed that this is achieved by contacting the paraxylene production catalyst with a regeneration gas containing air, thereby removing precipitated carbon by the air.

[0086] The following describes in more detail the paraxylene production catalyst and the like related to this disclosure with reference to examples and comparative examples, but this disclosure is not limited to these examples and comparative examples.

[0087] [Example 1] (Production of a catalyst for paraxylene production) 6 g of zinc nitrate and 86.5 g of zirconium nitrate were accurately weighed and dissolved in 550 mL of ultrapure water to make solution A. Then, 45 g of aqueous ammonia (concentration 28%) was added to solution A under stirring. After that, the mixture was stirred overnight at room temperature. After that, the precipitate was filtered and washed with ultrapure water. The obtained filtrate was dried overnight at 120°C. The obtained solid was coarsely ground and then calcined in air at 500°C for 3 hours. This yielded a zinc and zirconium composite oxide powder (Zn / Zr = 1 / 16) as the first catalyst. The obtained zinc and zirconium composite oxide powder is N ２ The BET specific surface area due to adsorption and desorption is 59 m². ２ The average pore size was 7.2 nm per g.

[0088] Meanwhile, to produce H-ZSM-5 zeolite, tetramethyl orthosilicate, aluminum nitrate, water, tetrapropylammonium hydroxide, and ethanol were accurately weighed and dissolved in a molar ratio of 1:0.025:50:0.24:4. This solution was introduced into a Teflon® sealed autoclave, stirred with a magnetic stirrer for 4 hours, and then reacted at 180°C for 24 hours. The resulting product was washed with distilled water, dried overnight at 120°C, and then calcined in air at 550°C for 5 hours to decompose and remove organic matter present in the zeolite pores, thereby obtaining H-ZSM-5 zeolite powder. The obtained H-ZSM-5 zeolite powder is N ２ The BET specific surface area due to adsorption and desorption is 367.6 m². ２ The average pore size was 2.0 nm per g.

[0089] The 5 g of zeolite (H-ZSM-5) obtained in this way was added to 50 g of n-hexane and dispersed for 10 min using ultrasound. Next, 12 g of TEOS was added dropwise to this solvent. After adding TEOS, stirring was continued at a stirring speed of 300 rpm for 4 hours. Then, the solution was heated to 80°C while stirring to remove the n-hexane. The obtained sample was dried at 120°C for 16 hours and then calcined at 550°C for 6 hours to obtain amorphous SiO as a second catalyst. ２ H-ZSM-5 zeolite coated with (hereinafter referred to as "SiO２ It is sometimes called a "coated zeolite." ) was obtained. The obtained SiO ２ Coated zeolite powder is N ２ The BET specific surface area due to adsorption and desorption is 263.7 m². ２ The average pore size was 2.4 nm per g. In Tables 1 and 2 described later, the second catalyst is referred to as "H-ZSM-5 + SiO ２ It is abbreviated as "".

[0090] The binary composite oxide of zinc and zirconium obtained in this way (first catalyst) and SiO ２ The coated zeolite (second catalyst) was accurately weighed in a mass ratio of 1:10 and physically mixed in a mortar for 10 minutes to obtain a mixed powder. Then, the mixed powder was pressed into 3 mmφ tablets using a compression molder, and SiO ２ After obtaining a tablet molded body containing 25% by mass of the total, it was crushed and granulated to a size of 20-40 mesh to obtain a catalyst for the production of paraxylene.

[0091] (Production of paraxylene) Using 0.5 g of the obtained paraxylene production catalyst, it was fixed with quartz wool so that it was located in the center of a SUS reaction tube with an inner diameter of 6 mm, a thermocouple was inserted in the center of the catalyst layer, and these fixed-bed reaction tubes were set in the predetermined position.

[0092] Before starting the synthesis reaction, the reactor was first heated under a nitrogen atmosphere at room temperature, with a hydrogen gas flow rate of 60 N mL / min, to 400°C, and then reduced for 2 hours. After that, it was cooled to room temperature and then treated with 18% CO2. ２ +12%CO+4%Ar+H ２ The remaining mixed gas was circulated at 200 N mL / min, pressurized to 5 MPa, and then heated to 360°C to initiate the reaction. Data was collected at 4 hours. After removing water from the reaction product, it was injected into two gas chromatographs (Shimadzu Corporation: GC-8A) and analyzed using a thermal conductivity detector (TCD) and a flame ionization detector (FID).

[0093] The degree of reaction in the synthesis reaction (the rate of paraxylene production) is CO ２ Conversion rate, CO selectivity, methane selectivity, C2-C4(O) selectivity from ethane, propane, and butane, C2-C4(=) selectivity from ethylene, propylene, and butylene, CH4 from methanol and dimethyl ether ３ The selectivity for OH+DME, pentane, long-chain aliphatic hydrocarbons (C5+) and aromatics (Aromatics) from pentane onward, as well as the selectivity for benzene (B), toluene (T), ethylbenzene (E), orthoxylene (o-X), metaxylene (m-X), paraxylene (p-X), C9 aromatic hydrocarbons (cumene) (A(C9)), tetralin, aromatic hydrocarbons with 10 or more carbon atoms (A(C10+)), and p-X / X as the proportion of paraxylene in total xylene (orthoxylene, metaxylene, and paraxylene) were calculated from the concentrations of each component using the following formula. Of these, the aromatic selectivity, PX selectivity, and space-time yield are shown in Example 1 of Table 1.

[0094] CO ２ Conversion rate (%) = {1 - (CO after reaction) ２ (Amount of carbon molars derived) / (Supplied CO ２ (Molar amount of carbon derived from CO) × 100 CO selectivity (%) = (Molar amount of carbon derived from CO) / (Supplied CO ２ (Amount of carbon molars derived) - (CO after reaction) ２ (Amount of carbon molars derived) × 100 CO + CO ２ Conversion rate (%) = {1 - (CO after reaction) ２ (Molar amount of carbon derived from CO + Molar amount of carbon derived from CO after reaction) / (Supplied CO) ２ Hydrocarbon selectivity (%) = (Molar amount of carbon derived from hydrocarbons + Molar amount of carbon derived from supplied CO) × 100 ２ (Amount of carbon molars derived) - (CO after reaction) ２ (Molar amount of carbon derived) × 100 CH ４ Selection rate (%) = (CH ４Ethane selectivity (%) = (moles of carbon derived from hydrocarbons) / (moles of carbon derived from hydrocarbons) × 100 Propane selectivity (%) = (moles of carbon derived from propane) / (moles of carbon derived from hydrocarbons) × 100 Butane selectivity (%) = (moles of carbon derived from butane) / (moles of carbon derived from hydrocarbons) × 100 C2-C4(O) selectivity (%) = (ethane selectivity) + (propane selectivity) + (butane selectivity)

[0095] Ethylene selectivity (%) = (moles of carbon derived from ethylene) / (moles of carbon derived from hydrocarbons) × 100 Propylene selectivity (%) = (moles of carbon derived from propylene) / (moles of carbon derived from hydrocarbons) × 100 Butylene selectivity (%) = (moles of carbon derived from butylene) / (moles of carbon derived from hydrocarbons) × 100 C2-C4 selectivity (%) = (ethylene selectivity) + (propylene selectivity) + (butylene selectivity)

[0096] CH ３ OH selectivity (%) = (CH ３ (Molar amount of carbon derived from OH) / (Molar amount of carbon derived from hydrocarbons) × 100 DME selectivity (%) = (Molar amount of carbon derived from DME) / (Molar amount of carbon derived from hydrocarbons) × 100 CH ３ OH + DME selectivity (%) = (CH ３ Pentane selectivity (%) = (moles of carbon derived from pentane) / (moles of carbon derived from hydrocarbons) × 100 Long-chain aliphatic hydrocarbon (C5+) selectivity (%) = (pentane selectivity) + (long-chain aliphatic hydrocarbon selectivity of C6 or higher)

[0097] Selectivity for B (%) = (moles of carbon derived from benzene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for T (%) = (moles of carbon derived from toluene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for E (%) = (moles of carbon derived from ethylbenzene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for o-X (%) = (moles of carbon derived from orthoxylene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for m-X (%) = (moles of carbon derived from metaxylene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for p-X (%) = (moles of carbon derived from paraxylene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for A (C9) (%) = (moles of carbon derived from cumene) / (moles of carbon derived from hydrocarbons) × 100 Selectivity for tetralin (%) = (moles of carbon derived from tetralin) / (moles of carbon derived from hydrocarbons) × 100 A(C10+) selectivity (%) = (tetraline selectivity) + (C11 or higher aromatic hydrocarbon selectivity) Aromatic selectivity (%) = (B selectivity) + (T selectivity) + (o-X selectivity) + (m-X selectivity) + (p-X selectivity) + (A(C9) selectivity) + (A(C10+) selectivity) Percentage of paraxylene in total xylene (%) = (p-X selectivity) / ((o-X selectivity) + (m-X selectivity) + (p-X selectivity)) × 100 Space-time yield of paraxylene (amount of paraxylene produced per unit catalyst and unit time) (g / kg / h) = (CO + CO ２ (Conversion rate) × ((CO flow rate supplied (mol / h / g)) cat ) + supplied CO ２ Flow rate (mol / h / g cat ))) × p-X selectivity × 10⁶ / 8 (g / mol) × 1000 Note that the space-time yield of paraxylene (PX) is (CO + CO ２ This value is obtained by converting the amount of carbon consumed by the conversion to the amount of PX molars using the number of carbon atoms in PX (8), converting it to mass using the molecular weight of PX (106 g / mol), and further converting it to g / kg / h based on the catalyst mass.

[0098] [Example 2] 0.13 g of zinc nitrate and 2.5 g of zirconium nitrate were accurately weighed and dissolved in 200 mL of ultrapure water to make solution A. Furthermore, 2.2 g of ammonium carbonate was dissolved in 300 mL of ultrapure water to make solution B. 500 mL of ultrapure water was heated to 80°C and stirred to make solution C. Solution A was titrated against solution C, and immediately afterwards, solution B was also titrated, adjusting the titration rate of solution B so that the pH was 7-8. The precipitate obtained from the reaction of solution A and solution B was allowed to stand for 3 hours at 80°C. The precipitate was then filtered and washed five times with 80°C warm water. The resulting filtrate was dried overnight at 120°C. The resulting solid was coarsely ground and then calcined in air at 500°C for 3 hours. This allowed for the preparation of a zinc and zirconium composite oxide powder (Zn / Zr = 1 / 20) as the first catalyst, thereby obtaining a catalyst for paraxylene production. Paraxylene was synthesized using the obtained catalyst in the same manner as in Example 1. The results are shown in Example 2 in Table 1.

[0099] [Examples 3 and 4] Except for varying the amounts of zinc nitrate and zirconium nitrate so that the molar ratio of metal oxides contained in the resulting composite oxide was Zn / Zr = 1 / 32 (Example 3) and 1 / 40 (Example 4), the catalysts for paraxylene production were prepared in the same manner as in Example 1. Paraxylene was synthesized using the obtained paraxylene production catalysts in the same manner as in Example 1. The results are shown in Examples 3 and 4 in Table 1.

[0100] [Examples 5-7] The binary composite oxide of zinc and zirconium in Examples 1-3 (first catalyst) and SiO ２ Catalysts for the production of paraxylene were obtained in the same manner as in Examples 1 to 3, except that the coated zeolite (second catalyst) was accurately weighed and mixed in a mass ratio of 1:1. Paraxylene was synthesized using each of the obtained paraxylene-producing catalysts in the same manner as in Example 1. The results are shown in Examples 5 to 7 in Table 1.

[0101] [Examples 8-10] The binary composite oxide of zinc and zirconium in Examples 1-3 (first catalyst) and SiO ２Catalysts for the production of paraxylene were obtained in the same manner as in Examples 1 to 3, except that the coated zeolite (second catalyst) was accurately weighed and mixed in a mass ratio of 1:0.25. Paraxylene was synthesized using each of the obtained catalysts for the production of paraxylene in the same manner as in Example 1. The results are shown in Examples 8 to 10 in Table 1.

[0102] [Example 11] The binary composite oxide of zinc and zirconium in Example 3 (first catalyst) and SiO ２ A catalyst for the production of paraxylene was obtained in the same manner as in Example 3, except that the coated zeolite (second catalyst) was accurately weighed and mixed in a mass ratio of 1:15. Paraxylene was synthesized using the obtained catalyst for the production of paraxylene in the same manner as in Example 1. The results are shown in Example 11 in Table 1.

[0103] [Comparative Example 1] 6.4 g of zinc nitrate, 8.6 g of chromium nitrate, and 5.7 g of zirconium nitrate were accurately weighed and dissolved in 100 mL of pure water. This aqueous solution was heated to 70°C, and an aqueous solution of ammonium carbonate was added to precipitate a ternary complex hydroxide of zinc, chromium, and zirconium, which was then thoroughly stirred with a stirrer. After that, stirring was continued for 3 hours while maintaining the temperature at 70°C for maturation, followed by filtration and thorough washing with pure water at 80°C. The obtained solid was coarsely ground and then calcined in air at 500°C for 3 hours. This yielded a complex oxide powder of chromium, zinc, and zirconium (Cr / Zn / Zr = 1 / 1 / 1) as the first catalyst. The obtained complex oxide powder of chromium, zinc, and zirconium was N ２ The BET specific surface area due to adsorption and desorption is 115 m². ２ The average pore size was 3.0 nm per g.

[0104] Meanwhile, to produce H-ZSM-5 zeolite, tetramethyl orthosilicate, aluminum nitrate, water, tetrapropylammonium hydroxide, and ethanol were accurately weighed and dissolved in a molar ratio of 1:0.025:50:0.24:4. This solution was introduced into a Teflon® sealed autoclave, stirred with a magnetic stirrer for 4 hours, and then reacted at 180°C for 24 hours. The resulting product was washed with distilled water, dried overnight at 120°C, and then calcined in air at 550°C for 5 hours to decompose and remove organic matter present in the zeolite pores, thereby obtaining H-ZSM-5 zeolite powder. The obtained H-ZSM-5 zeolite powder is N ２ The BET specific surface area due to adsorption and desorption is 367.6 m². ２ The average pore size was 2.0 nm per g.

[0105] The 5 g of zeolite (H-ZSM-5) obtained in this way was added to 50 g of n-hexane and dispersed for 10 min using ultrasound. Next, 12 g of TEOS was added dropwise to this solvent. After adding TEOS, stirring was continued at a stirring speed of 300 rpm for 4 hours. Then, the solution was heated to 80°C while stirring to remove the n-hexane. The obtained sample was dried at 120°C for 16 hours and then calcined at 550°C for 6 hours to obtain amorphous SiO as a second catalyst. ２ H-ZSM-5 zeolite coated with (hereinafter referred to as "SiO ２ It is sometimes called a "coated zeolite." ) was obtained. The obtained SiO ２ Coated zeolite powder is N ２ The BET specific surface area due to adsorption and desorption is 263.7 m². ２ The average pore size was 2.4 nm per g. In Tables 1 and 2 described later, the second catalyst is referred to as "H-ZSM-5 + SiO ２ It is abbreviated as "".

[0106] The ternary composite oxide of zinc, chromium, and zirconium obtained in this way (first catalyst) and SiO ２Coated zeolite (second catalyst) was accurately weighed in a mass ratio of 1:2 and physically mixed in a mortar for 10 minutes to obtain a mixed powder. The mixed powder was then pressed into 3 mmφ tablets using a compression molder to obtain the tablet bodies, which were then crushed to a size of 20-40 mesh to obtain a catalyst for paraxylene production. Paraxylene was synthesized using the obtained catalyst for paraxylene production in the same manner as in Example 1. The results are shown in Comparative Example 1 in Table 1.

[0107] [Comparative Example 2] A catalyst for paraxylene production was obtained in the same manner as in Example 1, except that the amounts of zinc nitrate and zirconium nitrate were changed so that the molar ratio of metal in the metal oxide contained in the resulting composite oxide was Zn / Zr = 1 / 12. Paraxylene was synthesized using the obtained paraxylene production catalyst in the same manner as in Example 1. The results are shown in Comparative Example 2 in Table 1.

[0108] [Comparative Example 3] A catalyst for paraxylene production was obtained in the same manner as in Example 1, except that the amounts of zinc nitrate and zirconium nitrate were changed so that the molar ratio of metal in the metal oxide contained in the resulting composite oxide was Zn / Zr = 1 / 14. Paraxylene was synthesized using the obtained paraxylene production catalyst in the same manner as in Example 1. The results are shown in Comparative Example 3 in Table 1.

[0109]

[0110] In Examples 1-8, 10, and 11, which used a binary composite oxide of zinc and zirconium with a Zn / Zr (metal molar ratio) of 1 / 15 or less as the first catalyst, the catalyst did not contain Cr and showed a paraxylene selectivity of over 20%. In particular, in Examples 1-3, 5-8, and 10, where the Zn / Zr (molar ratio) was 1 / 36 or more, the productivity (space-time yield) of paraxylene was also high. In Example 9, the catalyst did not contain Cr and the paraxylene selectivity was below 20%, but it was higher than that of Comparative Example 1 which contained Cr, and Example 9 also showed high paraxylene productivity (space-time yield).

[0111] As shown in Table 1, when comparing Examples 3, 7, 10, and 11, in which the Zn / Zr (molar ratio) in the first catalyst is 1 / 32, the space-time yield was higher when the weight of the second catalyst was 25% by mass (Example 10), 100% by mass (Example 7), or 1000% by mass (Example 3) compared to when the weight of the second catalyst was 1500% by mass (Example 11) relative to the first catalyst (100% by mass). Thus, it can be seen that the catalysts shown in the examples exhibit performance at or above the level of conventional Cr-based catalysts and conventional Cr-free catalysts (at least in terms of paraxylene selectivity), and in the preferred composition range, they exhibit performance superior to conventional Cr-based catalysts and conventional Cr-free catalysts.

[0112] While preferred embodiments and examples of the present disclosure have been described in detail above, the present disclosure is not limited to such embodiments. It is clear to any person with ordinary skill in the art to which the present disclosure pertains that various modifications or alterations may be conceived within the scope of the technical idea set forth in the claims, and these will naturally also be understood to fall within the technical scope of the present disclosure.

[0113] The disclosure of Japanese Patent Application No. 2025-057254, filed on 28 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were described specifically and individually.

Claims

1. A catalyst for the production of paraxylene, comprising: a first catalyst containing a binary composite oxide of zinc and zirconium; and a second catalyst containing H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide, wherein the binary composite oxide has a molar ratio of zinc to zirconium (Zn / Zr) of 1 / 15 or less.

2. The catalyst for producing paraxylene according to claim 1, wherein the binary composite oxide has a molar ratio of zinc to zirconium (Zn / Zr) of 1 / 16 or less.

3. The catalyst for producing paraxylene according to claim 1 or claim 2, wherein the binary composite oxide has a molar ratio of zinc to zirconium (Zn / Zr) of 1 / 50 or more.

4. The catalyst for producing paraxylene according to claim 3, wherein the binary composite oxide has a molar ratio of zinc to zirconium (Zn / Zr) of 1 / 36 or more.

5. A catalyst for producing paraxylene according to any one of claims 1 to 4, wherein the second catalyst is contained in an amount of 10% by mass or more and 1000% by mass or less relative to the first catalyst.

6. A method for producing paraxylene, comprising contacting a raw material gas containing carbon dioxide and hydrogen with a paraxylene production catalyst according to any one of claims 1 to 5 to synthesize paraxylene.

7. A method for producing a paraxylene production catalyst according to any one of claims 1 to 5, comprising: obtaining a coprecipitation by coprecipitation method to obtain a coprecipitation containing zinc and zirconium in a molar ratio of Zn / Zr of 1 / 15 or less; drying and / or calcining the coprecipitation to obtain the first catalyst; performing hydrothermal synthesis or heating in the presence of a silicon compound and H-ZSM-5 zeolite to obtain the second catalyst containing H-ZSM-5 zeolite coated with an amorphous silicon-containing oxide; and mixing the first catalyst and the second catalyst.

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