A methane selective oxidation catalyst, a method for preparing the same, and a method for preparing an oxygen-containing hydrocarbon

Abstract

The application discloses a kind of methane selective oxidation catalyst, its preparation method and the method for preparing oxygen-containing hydrocarbon compound.The copper molecular sieve catalyst of the application includes carrier ZSM-5 molecular sieve and active metal component copper supported on the carrier, and the mass percentage content of the active metal component copper is 0.25% to 2.5%.The metal oxide doped modified copper molecular sieve catalyst of the application includes copper molecular sieve catalyst and the metal oxide of doped modified copper molecular sieve catalyst;The metal oxide is any one of zinc oxide, molybdenum oxide, titanium dioxide, zirconium oxide and cerium oxide;The mass percentage content of the metal oxide is 1% to 20%.The catalyst of the application has excellent catalytic performance, under mild reaction system, copper molecular sieve catalyst can obtain good methanol yield and selectivity without metal oxide doping modification, and after doping modification, methane conversion rate, and oxygen-containing hydrocarbon compound yield and selectivity are doubled, and the method is simple, low in cost.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis, and particularly relates to a methane selective oxidation catalyst, its preparation method, and a method for preparing oxygen-containing hydrocarbons. Background Technology

[0002] Methane is an abundant and inexpensive gas, a major component of natural gas, shale gas, biogas, and methane hydrate. With increasingly sophisticated natural gas extraction technologies, and against the backdrop of climate change and the pursuit of net-zero carbon emissions, the efficient utilization of methane is particularly important. Because methane is flammable and explosive, and its storage locations are often remote, converting it at the extraction site into high-value-added oxygenated hydrocarbons such as methanol, formic acid, and acetic acid will facilitate long-distance transportation and storage, thus promoting the efficient utilization of methane resources.

[0003] Methane molecules exist in a tetrahedral form, exhibiting high symmetry and extreme stability, resulting in low polarizability of the CH bond and extremely high bond dissociation energy (439.3 kJ·mol⁻¹). -1 Therefore, the activation process of methane generally requires a high reaction temperature over a wide range of methane conversion rates. However, the target product is easily and deeply oxidized to carbon dioxide and water under harsh reaction conditions. The current low yield and selectivity make the direct oxidation of methane to oxygen-containing hydrocarbons uncompetitive with traditional petrochemical processes, hindering its large-scale development.

[0004] Currently, in conventional industrialized processes, methane is first reformed with steam to produce syngas, which is then converted into liquid hydrocarbons on a large scale via Fischer-Tropsch synthesis. This is an indirect route based on syngas, and because the reforming step is a strongly endothermic reaction, it requires a large amount of energy. Therefore, the direct oxidation of methane into high-value-added compounds under mild conditions has been a key research focus.

[0005] Research on the direct oxidation of methane can be traced back to the early 20th century, when French scientists Lance and Elworthy published a patent (publication number: GB190607297A) disclosing a method for synthesizing methanol from methane by oxidizing it with hydrogen peroxide in the presence of ferrous sulfate. This invention allowed people to foresee the possibility of converting methane into methanol. Inspired by the methane monooxygenase (MMO) in nature, which can selectively convert methane into methanol by reacting with molecular oxygen at ambient temperature, people have developed iron- or copper-containing zeolite catalysts. The stable dinuclear iron (J. Catal. 2000, 192(1), 236-247) or copper center (J. Am. Chem. Soc. 2003, 125, 25, 7629-7640) in the zeolite framework is similar to that of the MMO enzyme.

[0006] Meanwhile, using hydrogen peroxide as an oxidant can reduce the required temperature of the reaction system to some extent. Professor Guo Yun's team at East China University of Science and Technology (Appl. Catal. B 2021, 285, 119827) used a Cu / ZSM-5 single-atom catalyst under mild conditions to directly oxidize methane with hydrogen peroxide as the oxidant, achieving a total yield of 4800 μmol·g of hydrocarbons. cat. -1 With a selectivity as high as 99%, methanol selectivity accounted for 74% of the total product, effectively avoiding the problem of deep oxidation of the target product. The research group of Wang Xiaodong at the Dalian Institute of Chemical Physics (J. Am. Chem. Soc. 2023, 145, 24, 13169-13180) developed a metal-organic framework-supported single-atom Ru catalyst (Ru1 / UiO-66). The Ru1-modified Zr-oxo node can convert excess hydrogen peroxide into less reactive oxygen, thus similarly inhibiting the over-oxidation of the target product. Under similar reaction conditions, the yield of hydrocarbon oxygen-containing compounds was approximately 3700 μmol·g. cat. -1 ·h -1 The selectivity is almost 100%, and the turnover rate reaches 185.4 hours. -1 Supported oxides are widely used in many important catalytic reactions, and their surfaces and interfaces are often the active sites for these reactions. Professor Zhu Minghui's team (Nat. Catal. 2022, 5, 99-108) used hydrogen reduction of a commercial Cu / ZnO / Al2O3 catalyst, adding a mixture of water and methanol in a certain proportion to induce the migration of zinc oxide species from the support to the surface of metallic copper particles. Compared to traditional hydrogen-activated reactions, Cu-ZnO… x The construction of this key active site at the interface increased the catalyst's catalytic activity by two times and its stability by three times. Academician Bao Xinhe and Researcher Fu Qiang et al. (J. Am. Chem. Soc. 2023, 145, 31, 17056-17065) proposed a strategy to control the oxide-support interaction by forming different interfaces through mechanical mixing (Co3O4-ZnO) and chemical deposition (Co3O4 / ZnO), respectively. In the CO2 hydrogenation reaction, they measured 92% CH4 selectivity and 93% CO selectivity, respectively. This work clearly demonstrates that different oxide-oxide interactions lead to many different interfacial phenomena in the oxide-oxide catalytic system, providing new insights for the rational design of highly efficient catalysts for the direct oxidation of methane to methanol.

[0007] Therefore, modifying copper zeolite catalysts with oxides to provide a catalyst with superior performance that can catalyze the oxidation of methane to methanol in a milder system has become a pressing technical problem to be solved in this field. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a methane selective oxidation catalyst, its preparation method, and a method for preparing oxygen-containing hydrocarbons. This transition metal / oxide / molecular sieve catalyst first uses copper as the supported active component and ZSM-5 as the support to synthesize a copper molecular sieve catalyst. After modification with oxide doping, the yield and selectivity of oxygen-containing hydrocarbons will be further improved. It has the characteristics of simple method and low cost.

[0009] In a first aspect, the present invention provides a copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons, comprising a ZSM-5 molecular sieve support and an active metal component copper supported on the support, wherein the active component copper has a mass percentage content of 0.25% to 2.5% in the copper molecular sieve catalyst.

[0010] In the above-mentioned catalyst, the mass percentage of the active component copper in the copper molecular sieve catalyst can specifically be 0.25%, 0.5%, 1.0%, 1.5%, 2.0%, or 2.5%. Preferably, the mass percentage of the active component copper in the copper molecular sieve catalyst is 1.0% to 2.0%, more preferably 1.5%. In this invention, the active component copper is mainly supported on the ZSM-5 molecular sieve support in the form of clusters.

[0011] Secondly, the present invention provides a method for preparing a copper molecular sieve catalyst for the selective oxidation of methane to oxygen-containing hydrocarbons, comprising the following steps:

[0012] ZSM-5 molecular sieves were added to a copper salt solution and stirred to allow ion exchange between them. Then, the solution was washed, dried, and calcined to obtain the copper molecular sieve catalyst.

[0013] In the above preparation method, the copper salt can be any one of copper acetate, copper nitrate, and copper chloride;

[0014] The concentration of the aqueous solution of the copper salt can be 0.0007 to 0.007 mol / L, specifically 0.0007 mol / L;

[0015] The mass-volume ratio of the ZSM-5 molecular sieve to the copper salt solution is 1g:60mL, which can be adjusted according to the mass percentage of copper in the catalyst.

[0016] The ZSM-5 molecular sieve may specifically be H-ZSM-5;

[0017] The stirring time can be 12 to 24 hours, such as 24 hours, and the stirring speed can be 1000 to 1200 rpm, such as 1100 rpm;

[0018] The drying temperature can be 80-110℃, specifically 110℃, and the time can be 8-12 hours, specifically 10 hours;

[0019] The roasting is carried out in an air atmosphere at a temperature of 300–600°C, specifically 550°C, for a time of 2–4 hours, specifically 3 hours.

[0020] Thirdly, the present invention provides a metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons, comprising a copper molecular sieve catalyst and a metal oxide in the doped modified copper molecular sieve catalyst.

[0021] The copper molecular sieve catalyst comprises a ZSM-5 molecular sieve support and an active metal component copper supported on the support, wherein the active component copper in the copper molecular sieve catalyst has a mass percentage content of 0.25% to 2.5%.

[0022] The metal oxide is any one of zinc oxide, molybdenum oxide, titanium dioxide, zirconium oxide, and cerium oxide;

[0023] The metal oxide in the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons has a mass percentage of 1% to 20%.

[0024] In the above-mentioned catalyst, the mass percentage of the metal oxide in the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons can specifically be 2% to 20%, 1%, 2%, 4%, 8%, 12%, 16%, or 20%.

[0025] In a specific embodiment of the present invention, when the mass percentage of zinc oxide in the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons is 4%, the methanol selectivity is the highest.

[0026] In a specific embodiment of the present invention, the yield of oxygenated hydrocarbons is highest when the mass percentage of zinc oxide in the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygenated hydrocarbons is 16%.

[0027] Fourthly, the present invention provides a method for preparing the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to oxygen-containing hydrocarbons, comprising the following steps:

[0028] ZSM-5 molecular sieve was added to a copper salt solution and stirred to allow ion exchange between the molecules. Then, the solution was washed, dried, and calcined for the first time to obtain the copper molecular sieve catalyst.

[0029] The metal oxide and the copper molecular sieve catalyst are mixed in a certain proportion, ground evenly, and then calcined a second time to obtain the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons.

[0030] In the above preparation method, the copper salt is any one of copper acetate, copper nitrate, and copper chloride;

[0031] The concentration of the aqueous solution of the copper salt is 0.0007–0.007 mol / L, such as 0.0007 mol / L;

[0032] The mass-to-volume ratio of the ZSM-5 molecular sieve to the aqueous solution of the copper salt is 1 g: 60 mL, which can be adjusted according to the mass percentage of copper in the catalyst.

[0033] The ZSM-5 molecular sieve may specifically be H-ZSM-5;

[0034] The stirring time is 12 to 24 hours, such as 24 hours, and the stirring speed is 1000 to 1200 rpm, such as 1100 rpm;

[0035] The drying temperature can be 80-110℃, specifically 110℃, and the time can be 8-12 hours, specifically 10 hours;

[0036] The first roasting is carried out in an air atmosphere at a temperature of 300–600°C, specifically 550°C, for a time of 2–4 hours, specifically 3 hours.

[0037] The second calcination is carried out in an air atmosphere at a temperature of 200–600°C, specifically 200°C, 300°C, 400°C, 500°C, or 600°C; the time is 2–4 hours, specifically 3 hours. The preferred temperature for the second calcination varies depending on the different metal oxides in the doped and modified copper molecular sieve catalyst. For example, if the metal oxide is zinc oxide, the preferred temperature for the second calcination is 200–500°C, more preferably 200–400°C, and even more preferably 300°C.

[0038] Fifthly, the present invention provides a method for the selective oxidation of methane to prepare oxygen-containing hydrocarbons, comprising the following steps:

[0039] Under the catalytic action of the copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons or the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons, methane undergoes a selective oxidation reaction in the presence of an oxidant to obtain the oxygen-containing hydrocarbons.

[0040] The oxygen-containing hydrocarbons include at least one of methanol and formic acid.

[0041] In the above method, the oxidant is a hydrogen peroxide solution.

[0042] Furthermore, the concentration of the hydrogen peroxide solution can be 0.05–0.5 mol / L, specifically 0.5 mol / L;

[0043] Add 30 mg of the catalyst to 20 mL of the hydrogen peroxide solution.

[0044] In the above method, the total pressure of the selective oxidation reaction can be 0.35 to 3.5 MPa, specifically 0.4 MPa;

[0045] The temperature of the selective oxidation reaction can be 50–100°C, specifically 50°C;

[0046] The selected oxidation reaction time is 30 to 90 minutes, specifically 60 minutes.

[0047] In the above method, the oxygen-containing hydrocarbon mainly includes at least one of methanol and formic acid. The composition of the oxygen-containing hydrocarbon is related to whether the catalyst is doped with a modified metal oxide, the type of modified metal oxide, and its content, and can be adjusted according to the desired target product. For example, doping with the metal oxide may increase methanol production or generate formic acid without affecting methanol production. As another example, the oxygen-containing hydrocarbon may also be accompanied by small amounts of methyl hydroperoxide and / or acetic acid.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] First, the preparation method is simple and the synthesis cycle is short. The material can be synthesized by stirring, grinding and calcining. The synthesis efficiency is extremely high, avoiding tedious and delicate synthesis steps.

[0050] Secondly, it exhibits excellent catalytic performance. Under mild reaction conditions, the copper molecular sieve catalyst (Cu / ZSM-5) works without the presence of metal oxides (MO). x With doping modification, a good methanol yield can be obtained, and the selectivity of the target product exceeds 80%. (MO doping) xThe modification doubled the conversion rate of methane, while maintaining a high methanol yield and generating a large amount of formic acid. The selectivity of oxygen-containing hydrocarbons, mainly methanol and formic acid, was higher than 95%.

[0051] Third, under milder reaction conditions, using a certain proportion of zinc oxide-doped modified copper molecular sieve catalyst to selectively oxidize methane, the yield of oxygen-containing hydrocarbons, mainly methanol and formic acid, was 4103.42 μmol·g. cat. -1 Compared with the performance of other catalysts in similar reaction systems, this catalyst is quite competitive and achieves the goal of high yield and high selectivity of selective oxidation of methane to methanol and other oxygen-containing hydrocarbons.

[0052] In summary, this material is inexpensive, simple to synthesize, and produces excellent yields and stability of oxygen-containing hydrocarbons, mainly methanol and formic acid, and has broad application prospects. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0054] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0055] In the following embodiments, the conversion rate and selectivity are calculated as follows:

[0056] Product yield = (moles of product after reaction - moles of product before reaction) / mass of catalyst used;

[0057] Selectivity of oxygenated hydrocarbon products (%) = [(methanol production + formic acid production + methyl hydrogen peroxide production + acetic acid production) / (methanol production + formic acid production + methyl hydrogen peroxide production + acetic acid production + carbon dioxide production + carbon monoxide production)] × 100%;

[0058] Methanol selectivity (%) = [Methanol production / (Methanol production + Formic acid production + Methyl hydrogen peroxide production + Acetic acid production + Carbon dioxide production + Carbon monoxide production)] × 100%.

[0059] Unless otherwise specified, the roasting in the following examples is carried out in air.

[0060] Gas phase products were quantitatively analyzed using a Shimadzu gas chromatograph (GC-2014) equipped with a TCD detector, PQ, and MS-13X column. The test conditions were as follows: TCD detector temperature 208℃, current 150mA, hydrogen flow rate 40mL / min, air flow rate 400mL / min, column temperature 60℃ for 14min. The inlet gas flow rate was controlled at 40mL / min.

[0061] To accurately determine the amount of methanol generated, an internal standard method was employed, using n-propanol solution as the internal standard. Quantitative analysis was performed using a Shimadzu gas chromatograph (GC-2014) equipped with an FID detector and a WAX-DA capillary column. The test conditions were as follows: FID detector temperature 250℃, hydrogen flow rate 40 mL / min, air flow rate 400 mL / min, column temperature 80℃ for 5 min, then increased to 200℃ at a rate of 25℃ / min and held for 10 min.

[0062] For other liquid phase products such as formic acid, methyl hydroperoxide, and acetic acid, liquid NMR (JNM-ECZ400S) is required for determination. Quantitative analysis using liquid NMR also employs the internal standard method, using a solution of dimethyl sulfoxide and heavy water as the internal standard. The test conditions are as follows: rotation speed 12 kHz, 64 scans, chemical shifts expressed in ppm, and a water peak suppression program must be selected during the test.

[0063] All load values ​​in the following examples are theoretical load values.

[0064] Example 1

[0065] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0066] Weigh 7.8 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0067] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 0.25 wt%, denoted as Cu. 0.25 / ZSM-5.

[0068] The copper acetate and H-ZSM-5 used in the catalyst preparation process in this example are both commercially available.

[0069] Take 30 mg of catalyst Cu 0.25 / ZSM-5 was added to 20 mL of 0.5 mol / L hydrogen peroxide aqueous solution. Then, pure methane gas was introduced into the reactor and purged 3-5 times. After the pressure inside the reactor stabilized at 0.4 MPa, heating and stirring were started, and the reaction was carried out at 50℃ for 1 hour. After the reaction was completed, an ice bath was immediately applied. After the temperature of the solution inside the reactor dropped below 10℃, the product was collected and analyzed. The activity evaluation results are shown in Table 1.

[0070] Example 2

[0071] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0072] Weigh 15.9 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0073] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 0.5 wt%, denoted as Cu. 0.5 / ZSM-5.

[0074] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 1.

[0075] Example 3

[0076] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0077] Weigh 31.7 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0078] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 1.0 wt%, denoted as Cu. 1.0 / ZSM-5.

[0079] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 1.

[0080] Example 4

[0081] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0082] Weigh 47.9 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0083] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 1.5 wt%, denoted as Cu. 1.5 / ZSM-5.

[0084] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 1.

[0085] Example 5

[0086] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0087] Weigh 64.1 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0088] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 2.0 wt%, denoted as Cu. 2.0 / ZSM-5.

[0089] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 1.

[0090] Example 6

[0091] The preparation process of the catalyst Cu / ZSM-5 in this embodiment is as follows:

[0092] Weigh 80.6 mg of copper acetate, add 60 mL of water to make a suspension, add 1 g of H-ZSM-5, stir at room temperature for 24 hours (1100 rpm), wash clean, dry at 110℃ for 10 hours, and calcine in a muffle furnace at 550℃ for 3 hours.

[0093] The catalyst Cu / ZSM-5 prepared in this example has a copper mass fraction of 2.5 wt%, denoted as Cu. 2.5 / ZSM-5.

[0094] Comparative Example 1

[0095] This comparative example uses H-ZSM-5 to compare the performance of the catalyst of this invention in the selective oxidation of methane to methanol and other oxygen-containing hydrocarbon reactions.

[0096] During the performance testing process, except that the catalyst was replaced with commercial H-ZSM-5, the other steps were the same as in Example 1, and the activity evaluation results are shown in Table 1.

[0097] Table 1. Activity evaluation results of Examples 1-6 and Comparative Example 1

[0098]

[0099] As can be seen from the comparison between Example 1 and Comparative Example 1, when a small amount of copper is loaded onto ZSM-5, the methanol yield can be significantly increased, which verifies that copper can be used as an active component of the catalyst.

[0100] As can be seen from Examples 1 to 6, under mild reaction conditions, the catalyst prepared by the method provided by this invention exhibits the best catalytic activity when the mass fraction of active copper in the Cu / ZSM-5 catalyst is 1.5 wt%, and the resulting main product is relatively simple, with high yield and good selectivity.

[0101] Example 7

[0102] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0103] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0104] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 200°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0105] The calcination activation temperature of the catalyst Cu / ZnO / ZSM-5 prepared in this example is 200℃, denoted as Cu / ZnO / ZSM-5-200.

[0106] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 2.

[0107] Example 8

[0108] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0109] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0110] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0111] The calcination activation temperature of the catalyst Cu / ZnO / ZSM-5 prepared in this example is 300℃, denoted as Cu / ZnO / ZSM-5-300.

[0112] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 2.

[0113] Example 9

[0114] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0115] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0116] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 400°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0117] The calcination activation temperature of the catalyst Cu / ZnO / ZSM-5 prepared in this example is 400℃, denoted as Cu / ZnO / ZSM-5-400.

[0118] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 2.

[0119] Example 10

[0120] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0121] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0122] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 500°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0123] The calcination activation temperature of the catalyst Cu / ZnO / ZSM-5 prepared in this example is 500℃, denoted as Cu / ZnO / ZSM-5-500.

[0124] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 2.

[0125] Example 11

[0126] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0127] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0128] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 600°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0129] The calcination activation temperature of the catalyst Cu / ZnO / ZSM-5 prepared in this example is 600℃, denoted as Cu / ZnO / ZSM-5-600.

[0130] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 2.

[0131] Table 2. Activity evaluation results of Examples 7-11

[0132]

[0133] As can be seen from Table 2, under mild reaction conditions, the catalyst preparation method provided by this invention exhibits the best catalytic activity when the activation temperature of the Cu / ZnO / ZSM-5 catalyst is 300℃. The resulting oxygen-containing hydrocarbons have high yield and selectivity, and the main liquid phase products are methanol and formic acid.

[0134] Example 12

[0135] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0136] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0137] (2) Mix 52.4 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0138] The catalyst Cu / ZnO / ZSM-5 prepared in this example has a zinc oxide mass fraction of 4 wt%, denoted as Cu / 4ZnO / ZSM-5.

[0139] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0140] Example 13

[0141] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0142] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0143] (2) Mix 110.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0144] The catalyst Cu / ZnO / ZSM-5 prepared in this example has a zinc oxide mass fraction of 8 wt%, denoted as Cu / 8ZnO / ZSM-5.

[0145] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0146] Example 14

[0147] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0148] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0149] (2) Mix 175.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0150] The catalyst Cu / ZnO / ZSM-5 prepared in this example has a zinc oxide mass fraction of 12 wt%, denoted as Cu / 12ZnO / ZSM-5.

[0151] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0152] Example 15

[0153] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0154] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0155] (2) Mix 248.8 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0156] The catalyst Cu / ZnO / ZSM-5 prepared in this example has a zinc oxide mass fraction of 16 wt%, denoted as Cu / 16ZnO / ZSM-5.

[0157] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0158] Example 16

[0159] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0160] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0161] (2) Mix 331.6 mg of ZnO with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0162] The catalyst Cu / ZnO / ZSM-5 prepared in this example has a zinc oxide mass fraction of 20 wt%, denoted as Cu / 20ZnO / ZSM-5.

[0163] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0164] Comparative Example 2

[0165] This comparative example uses ZnO-doped H-ZSM-5 to compare the performance of the catalyst of this invention in the selective oxidation of methane to methanol and other oxygen-containing hydrocarbon reactions.

[0166] The preparation process of the catalyst ZnO-ZSM-5 in this embodiment is as follows:

[0167] 52.4 mg of ZnO and 1.0 g of ZSM-5 were mixed in an agate mortar and ground, and then calcined in a muffle furnace at 300 °C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0168] The catalyst ZnO-ZSM-5 prepared in this example has a zinc oxide mass fraction of 4 wt%, denoted as 4ZnO-ZSM-5.

[0169] Both ZnO and H-ZSM-5 used in the catalyst preparation process in this example are commercially available.

[0170] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0171] Comparative Example 3

[0172] This comparative example uses ZnO-doped H-ZSM-5 to compare the performance of the catalyst of this invention in the selective oxidation of methane to methanol and other oxygen-containing hydrocarbon reactions.

[0173] The preparation process of the catalyst ZnO-ZSM-5 in this embodiment is as follows:

[0174] 248.8 mg of ZnO and 1.0 g of ZSM-5 were mixed in an agate mortar and ground, and then calcined in a muffle furnace at 300 °C for 3 hours to obtain a zinc oxide-doped modified copper-supported ZSM-5 catalyst.

[0175] The catalyst ZnO-ZSM-5 prepared in this example has a zinc oxide mass fraction of 16 wt%, denoted as 16ZnO-ZSM-5.

[0176] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 3.

[0177] Table 3 shows the activity evaluation results of Examples 12-16 and Comparative Examples 2-3.

[0178]

[0179]

[0180] As can be seen from Table 3, under mild reaction conditions, using the catalyst preparation method provided by this invention, the Cu / ZnO / ZSM-5 series catalysts obtained by different proportions of zinc oxide doping stably maintain a selectivity of more than 93% for oxygen-containing hydrocarbons.

[0181] Comparing Comparative Example 2 with Comparative Example 1, it can be seen that when ZSM-5 is doped with a small amount of zinc oxide, the formic acid yield can be significantly increased, verifying that zinc oxide can also be used as an active component of this series of catalysts; comparing Comparative Example 3 with Comparative Example 2, it can be seen that when too much zinc oxide is doped into ZSM-5, its catalytic activity is reduced.

[0182] As can be seen from the comparison between Example 12 and Comparative Example 2, when the zinc oxide doping ratio in Cu / ZnO / ZSM-5 catalyst is too low, no formic acid is generated, showing a high methanol selectivity. This indicates that the copper active component inhibits the selective oxidation of methane to formic acid, and that the different copper-zinc ratios significantly affect the total yield of liquid phase products and the final distribution of the main products, methanol and formic acid.

[0183] As demonstrated in Example 15, under mild reaction conditions, the catalyst preparation method provided by this invention yields high production of oxygen-containing hydrocarbons catalyzed by Cu / 16ZnO / ZSM-5. From the perspective of carbon conversion, the catalytic process significantly improves the conversion rate of methane, indicating that the Cu-ZnO active component in this catalyst has a superior synergistic catalytic effect.

[0184] Example 17

[0185] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0186] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0187] (2) Mix 31.0 mg of MoO3 with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 200°C for 3 hours to obtain a molybdenum oxide-doped modified copper-supported ZSM-5 catalyst.

[0188] The catalyst Cu / MoO3 / ZSM-5 prepared in this example has a molybdenum oxide mass fraction of 2wt%, denoted as Cu / 2MoO3 / ZSM-5.

[0189] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 4.

[0190] Example 18

[0191] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0192] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0193] (2) Mix 71.6 mg of TiO2 with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 300°C for 3 hours to obtain a titanium dioxide-doped modified copper-supported ZSM-5 catalyst.

[0194] The catalyst Cu / TiO2 / ZSM-5 prepared in this example has a titanium dioxide mass fraction of 4 wt%, denoted as Cu / 4TiO2 / ZSM-5.

[0195] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 4.

[0196] Example 19

[0197] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0198] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0199] (2) Mix 121.2 mg of ZrO2 with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 400°C for 3 hours to obtain a zirconium oxide-doped modified copper-supported ZSM-5 catalyst.

[0200] The catalyst Cu / ZrO2 / ZSM-5 prepared in this example has a zirconium oxide mass fraction of 8 wt%, denoted as Cu / 8ZrO2 / ZSM-5.

[0201] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 4.

[0202] Example 20

[0203] This embodiment uses Cu / ZSM-5 and MO x The preparation process of the mixed catalytic system is as follows:

[0204] (1) As described in Example 4, Cu was prepared. 1.5 / ZSM-5.

[0205] (2) Mix 51.6 mg of CeO2 with 1.0 g of Cu 1.5 / ZSM-5 was mixed and ground in an agate mortar, and then calcined in a muffle furnace at 400°C for 3 hours to obtain a cerium oxide-doped modified copper-supported ZSM-5 catalyst.

[0206] The catalyst Cu / CeO2 / ZSM-5 prepared in this example has a cerium oxide mass fraction of 4wt%, denoted as Cu / 4CeO2 / ZSM-5.

[0207] The test results for the material's catalytic selective oxidation of methane to methanol and other oxygen-containing hydrocarbons were consistent with those in Example 1, and the activity evaluation results are shown in Table 4.

[0208] Table 4. Activity evaluation results of Examples 17-20

[0209]

[0210] As can be seen from Table 4, using the catalyst preparation method provided by the present invention, the suitable doping amount and the optimal activation temperature of Cu / ZSM-5 catalysts modified with different oxides are different, which are reflected in the differences in catalytic performance of each example.

[0211] As can be seen from the comparison between Examples 17 and 18 and Example 4, when Cu / ZSM-5 is doped with a small amount of molybdenum oxide or titanium dioxide and activated at a suitable temperature, methanol production can be increased, and high methanol selectivity is maintained while suppressing product peroxidation.

[0212] As can be seen from the comparison between Examples 19 and 20 and Example 4, when Cu / ZSM-5 is doped with a small amount of zirconium oxide or cerium oxide and activated at a suitable temperature, it can not only increase methanol production, but also promote the formation of formic acid, greatly improve the conversion rate of methane, and the selectivity of its oxygen-containing hydrocarbon production is close to 100%.

[0213] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for the selective oxidation of methane to prepare oxygen-containing hydrocarbons, comprising the following steps: In the selective oxidation of methane to prepare oxygen-containing hydrocarbons, under the catalytic action of a metal oxide-doped modified copper molecular sieve catalyst, methane undergoes a selective oxidation reaction in the presence of an oxidant to obtain the oxygen-containing hydrocarbons. The oxygen-containing hydrocarbons include at least one of methanol and formic acid; The oxidant is a hydrogen peroxide solution; The metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons includes a copper molecular sieve catalyst and metal oxides in the doped modified copper molecular sieve catalyst. The copper molecular sieve catalyst comprises a ZSM-5 molecular sieve support and an active metal component, copper, supported on the support. The active metal component copper has a mass percentage content of 0.25% to 2.5% in the copper molecular sieve catalyst; The metal oxide is any one of zinc oxide, molybdenum oxide, titanium dioxide, zirconium oxide, and cerium oxide; The metal oxide in the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons has a mass percentage of 1% to 20%. The method for preparing the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to oxygen-containing hydrocarbons includes the following steps: ZSM-5 molecular sieve was added to a copper salt solution and stirred to allow ion exchange between the molecules. Then, the solution was washed, dried, and calcined for the first time to obtain the copper molecular sieve catalyst. The metal oxide and the copper molecular sieve catalyst are mixed in a certain proportion, ground evenly, and then calcined a second time to obtain the metal oxide-doped modified copper molecular sieve catalyst for the selective oxidation of methane to prepare oxygen-containing hydrocarbons.

2. The method according to claim 1, characterized in that: The copper salt is any one of copper acetate, copper nitrate, and copper chloride; The concentration of the aqueous solution of the copper salt is 0.0007–0.007 mol / L; The stirring time is 12 to 24 hours, and the stirring speed is 1000 to 1200 rpm; The drying temperature is 80–110°C, and the time is 8–12 hours; The first calcination is carried out in an air atmosphere at a temperature of 300–600°C for 2–4 hours. The second calcination is carried out in an air atmosphere at a temperature of 200–600°C for 2–4 hours.

3. The method according to claim 1, characterized in that: The concentration of the hydrogen peroxide solution is 0.05–0.5 mol / L; 30 mg of the catalyst is added to 20 mL of the hydrogen peroxide solution.

4. The method according to any one of claims 1-3, characterized in that: The total pressure of the selective oxidation reaction is 0.35–3.5 MPa; The temperature for the selective oxidation reaction is 50–100°C; The selected oxidation reaction time is 30 to 90 minutes.

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