Preparation method of molecular sieve catalyst for selective oxidation of methane to methanol and application thereof

Abstract

The present application relates to the technical field of catalyst preparation, and particularly discloses a preparation method of a molecular sieve catalyst for selective oxidation of methane to methanol and application thereof. The AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol at low temperature is prepared by a two-step calcination method. Through the synergistic effect of Au-Cu bimetal, the activation process of the C-H bond of methane is optimized, the reaction efficiency is improved, the product selectivity is accurately controlled, and a new strategy is provided for the development of methane directional conversion catalysts. The Au-Cu / ZSM-5 catalyst prepared by the present application has excellent catalytic activity in the reaction of selective oxidation of methane to methanol, high methane conversion rate and good methanol selectivity, and effectively inhibits the methanol peroxidation to generate by-products such as CO2.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a method for preparing an Au-Cu / ZSM-5 catalyst for the low-temperature selective oxidation of methane to methanol and its application, which is particularly suitable for natural gas conversion and high-value-added chemical synthesis processes. Background Technology

[0002] Methane, a major component of natural gas, is an abundant and economically viable carbon resource. Developing technologies to efficiently convert methane into high-value-added liquid chemicals is of great value in solving energy storage and transportation challenges. Among these, methanol, possessing both energy carrier and platform molecule properties, can be further converted into bulk chemicals such as olefins and aromatics, and is considered one of the most promising products for industrialization.

[0003] Currently, the industrial process for producing methanol from methane mainly employs an energy-intensive two-step method: first, methane is converted into syngas (a mixture of CO and H2) through high-temperature reforming, followed by catalytic synthesis of methanol under high-pressure conditions. In contrast, the direct catalytic oxidation of methane to methanol is widely recognized as the "holy grail" reaction in catalytic chemistry due to its significant advantage of simplified process flow. The main scientific challenges facing this technology are: 1. The C(sp) content in the methane molecule... 3 1. The -H bond has extremely high chemical inertness and usually requires harsh conditions to activate; 2. The reactivity of the target product methanol is usually higher than that of methane itself, and it is very easy to undergo excessive oxidation, making it difficult to control the product selectivity.

[0004] Currently reported methane partial oxidation catalysts can be classified into four categories based on their active components: non-noble metal-based catalysts (Fe, Cu, etc.); noble metal-based catalysts (Au, Pd, Rh, etc.); composite metal catalysts (Fe-Cu, Au-Pd, Ni-Ru, etc.); and metal oxide catalysts (LaCoO3, LaNiO3, etc.). However, existing catalyst systems generally suffer from excessively high reaction temperatures (typically >400 °C) and insufficient methanol selectivity (generally <70%), which not only increases energy consumption costs but also accelerates catalyst deactivation. Therefore, developing novel catalysts that combine high activity and high selectivity at low temperatures (150-200 °C) and promoting industrial applications has become an important research direction in the field of methane catalytic partial oxidation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, thereby solving the problems of low activity and poor selectivity in existing catalysts for the selective oxidation of methane to methanol. Simultaneously, it addresses the issues of high operating temperatures and cumbersome synthesis processes associated with existing ZSM-5-based catalysts for the selective oxidation of methane to methanol.

[0006] The present invention provides a method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, comprising the following steps: (1) Preparation of Cu / ZSM complex: Add soluble copper salt (preferably CuCl2•2H2O) to the molecular sieve ZSM-5 suspension, sonicate to completely dissolve it, transfer it to an oil bath, heat it in the oil bath until the liquid evaporates, dry it, grind it thoroughly, and then calcine it to obtain Cu / ZSM-5 complex. (2) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension; (3) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (2), and ultrasonication was continued to dissolve it completely. The solution was then transferred to an oil bath, heated in the oil bath until the liquid evaporated, dried, ground thoroughly, and calcined to obtain AuCu / ZSM-5 catalyst. In step (3), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5 is 1:100 ~ 1:500 (preferably 1:100).

[0007] Furthermore, in step (1), the molecular sieve ZSM-5 suspension is obtained by dispersing molecular sieve ZSM-5 in deionized water, with a solid content of 5 ~ 20 mg / mL. During the dispersion process, ultrasound is used to make it uniform, preferably with an ultrasound frequency of 60 kHz and a time of 10 ~ 20 min. Furthermore, in step (1), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200~1:100 (preferably 1:200), the preferred stirring speed of the oil bath is 200-300 r / min, the temperature is 60~80 ℃, and the heating time is 1~2 h.

[0008] Furthermore, in step (2), the solid content of the Cu / ZSM-5 suspension is controlled to be 5 ~ 20 mg / mL, and the ultrasonic treatment frequency is preferably 60 kHz and the time is 10 ~ 20 min. Furthermore, in step (3), the stirring speed of the oil bath is 200-300 r / min, and the temperature is 60-80 ℃.

[0009] Furthermore, in step (1), the calcination temperature is 400 ~ 600 ℃ and the time is 4 ~ 5 h, preferably calcination at 500 ℃ for 4 h; in step (3), the calcination temperature is 300 ~ 350 ℃ and the time is 2 ~ 3 h, and the heating rate is 5 ℃ / min.

[0010] This invention also provides the application of the molecular sieve catalyst obtained by the above preparation method in the low-temperature catalytic selective oxidation of methane to methanol.

[0011] Furthermore, the low temperature is 150-180 °C.

[0012] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. High efficiency catalytic performance: The Au-Cu / ZSM-5 catalyst prepared in this invention exhibits excellent catalytic activity in the selective oxidation of methane to methanol, with high methane conversion rate and good methanol selectivity, while effectively inhibiting the peroxidation of methanol to generate byproducts such as CO2.

[0013] 2. Simple and environmentally friendly process: The preparation method uses readily available and inexpensive raw materials, mild reaction conditions, simple process flow, and no pollution emissions, making it a promising candidate for industrial application.

[0014] 3. Innovative methane catalytic reaction mechanism: Through the synergistic effect of Au-Cu bimetallic compounds, the activation process of methane CH bonds was optimized, which improved reaction efficiency while precisely controlling product selectivity, providing a new strategy for the development of methane-directed conversion catalysts. Attached Figure Description

[0015] Figure 1 Preparation of Au for this invention x XRD pattern of Cu / ZSM-5 catalyst; Figure 2 Preparation of Au for this invention x UV-Vis spectrum of Cu / ZSM-5 catalyst; Figure 3 Preparation of Au for this invention 1.0 TEM images of Cu / ZSM-5 and Cu / ZSM-5 catalyst; Figure 4 The 1H NMR spectrum of the product; Figure 5 Preparation of Au for this invention x Comparison chart of the performance of Cu / ZSM-5 catalyst in the conversion of methane to methanol; Figure 6 Au prepared by different methods 1.0 Comparison chart of the performance of Cu / ZSM-5 catalyst in the conversion of methane to methanol; Figure 7 Comparison of the catalytic performance of methane to methanol conversion by changing the loading order of Au and Cu; Figure 8Comparison of the performance of Au-supported Cu / ZSM-5 catalysts calcined at different temperatures in the catalytic conversion of methane to methanol; Figure 9 For Au under different temperature conditions 1.0 Performance diagram of Cu / ZSM-5 catalyst for the conversion of methane to methanol. Detailed Implementation

[0016] To better understand the present invention, the technical solution of the present invention will be described below through specific implementation schemes.

[0017] Example 1: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: The molecular sieve ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0018] (2) Preparation of Cu / ZSM-5 composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and evenly and calcined in a muffle furnace to obtain the Cu / ZSM-5 composite.

[0019] (3) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0020] (4) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min until completely dissolved. The solution was then transferred to an oil bath and heated until the liquid evaporated. Afterward, it was dried in an oven at 80 ℃ for 6 h. The resulting solid was thoroughly and uniformly ground and calcined in a muffle furnace to obtain Au. 0.2 Cu / ZSM-5 catalyst.

[0021] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0022] In step (3), the mass of Cu / ZSM-5 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5 is 1:500, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0023] Example 2: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: The molecular sieve ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0024] (2) Preparation of Cu / ZSM-5 composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and evenly and calcined in a muffle furnace to obtain the Cu / ZSM-5 composite.

[0025] (3) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0026] (4) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min until completely dissolved. The solution was then transferred to an oil bath and heated until the liquid evaporated. Afterward, it was dried in an oven at 80 ℃ for 6 h. The resulting solid was thoroughly and uniformly ground and calcined in a muffle furnace to obtain Au. 0.4 Cu / ZSM-5 catalyst.

[0027] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0028] In step (3), the mass of Cu / ZSM-5 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5 is 1:250, the stirring speed of the oil bath is 200 r / min, the temperature is 60 ~ 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0029] Example 3: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: The molecular sieve ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0030] (2) Preparation of Cu / ZSM-5 composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and evenly and calcined in a muffle furnace to obtain the Cu / ZSM-5 composite.

[0031] (3) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0032] (4) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min until completely dissolved. The solution was then transferred to an oil bath and heated until the liquid evaporated. Afterward, it was dried in an oven at 80 ℃ for 6 h. The resulting solid was thoroughly and uniformly ground and calcined in a muffle furnace to obtain Au. 0.8 Cu / ZSM-5 catalyst.

[0033] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0034] In step (3), the mass of Cu / ZSM-5 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5 is 1:125, the stirring speed of the oil bath is 200 r / min, the temperature is 60 ~ 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0035] Example 4: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0036] (2) Preparation of Cu / ZSM composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and evenly and calcined in a muffle furnace to obtain the Cu / ZSM-5 composite.

[0037] (3) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0038] (4) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min until completely dissolved. The solution was then transferred to an oil bath and heated until the liquid evaporated. Afterward, it was dried in an oven at 80 ℃ for 6 h. The resulting solid was thoroughly and uniformly ground and calcined in a muffle furnace to obtain Au. 1.0 Cu / ZSM-5 catalyst, namely AuCu / ZSM-5-500.

[0039] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0040] In step (3), the mass of Cu / ZSM-5 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5 is 1:100, the stirring speed of the oil bath is 200 r / min, the temperature is 60 ~ 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0041] Example 5: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0042] (2) Preparation of AuCu / ZSM-5 catalyst by one-step calcination: CuCl2•2H2O and HAuCl4•4H2O were added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and calcined in a muffle furnace to obtain the AuCu / ZSM-5 catalyst.

[0043] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, and the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to ZSM-5 is 1:100. The stirring speed of the oil bath is 200 r / min, the temperature is 80ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0044] Example 6: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0045] (2) Preparation of AuCu / ZSM-5 catalyst by one-step liquid phase reduction method: CuCl2•2H2O and HAuCl4•4H2O were added to the suspension obtained in step (1), and the suspension was sonicated for 5 min until it was completely dissolved. Then, NaBH4 solution was added, and the mixture was transferred to an oil bath for oil bath reaction. After washing and drying, AuCu / ZSM-5 catalyst was obtained.

[0046] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, where the mass ratio of Cu to ZSM-5 is 1:200, and the mass of HAuCl4•4H2O is also controlled, where the mass ratio of Au to ZSM-5 is 1:100. Excess NaBH4 (>2 mg) is added to ensure complete metal reduction. The oil bath is stirred at 200 r / min, at 80 ºC, for 2 h. The mixture is washed three times with pure water and dried in an oven at 80 ℃ for 6 h.

[0047] Example 7: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: The molecular sieve ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0048] (2) Preparation of Au / ZSM-5 complex: Add HAuCl4•4H2O to the suspension obtained in step (1), continue sonicating for 5 min to completely dissolve it, transfer it to an oil bath, heat the oil bath until the liquid evaporates, and then place it in an oven at 80 ℃ for 6 h to dry. After the obtained solid is thoroughly ground, it is placed in a muffle furnace for calcination to obtain Au / ZSM-5 complex.

[0049] (3) Preparation of Au / ZSM-5 suspension: Au / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0050] (4) Preparation of CuAu for selective oxidation of methane to methanol 0.8 / ZSM-5 catalyst: Add CuCl2•2H2O to the suspension obtained in step (3), continue sonicating for 5 min to completely dissolve it, transfer it to an oil bath, heat the oil bath until the liquid evaporates to dryness, and then place it in an oven at 80 ℃ for 6 h to dry. Grind the obtained solid and calcine it in a muffle furnace to obtain CuAu. 0.8 / ZSM-5 catalyst.

[0051] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to ZSM-5 is 1:125, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0052] In step (3), the mass of Au / ZSM-5 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to Au / ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 500 ℃, and the calcination time is 4 h.

[0053] Example 8: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0054] (2) Preparation of Cu / ZSM-400 composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and calcined in a muffle furnace to obtain the Cu / ZSM-5 composite.

[0055] (3) Preparation of Cu / ZSM-5-400 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0056] (4) Preparation of AuCu / ZSM-5-400 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After drying, the solution was placed in an oven at 80 °C for 6 h. The resulting solid was ground and calcined in a muffle furnace to obtain the AuCu / ZSM-5-400 catalyst.

[0057] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 400 ℃, and the calcination time is 4 h.

[0058] In step (3), the mass of Cu / ZSM-5-400 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5-400 is 1:100, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0059] Example 9: A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, specifically comprising the following steps: (1) Preparation of ZSM-5 suspension: ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0060] (2) Preparation of Cu / ZSM-600 composite: CuCl2•2H2O was added to the suspension obtained in step (1), and the mixture was sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After that, it was dried in an oven at 80 °C for 6 h. The resulting solid was then ground thoroughly and calcined in a muffle furnace to obtain the Cu / ZSM-5-600 composite.

[0061] (3) Preparation of Cu / ZSM-5-600 suspension: Cu / ZSM-5-600 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension.

[0062] (4) Preparation of AuCu / ZSM-5-600 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (3), and sonicated for 5 min to completely dissolve it. The solution was then transferred to an oil bath and heated until the liquid evaporated. After drying, the solution was placed in an oven at 80 °C for 6 h. The resulting solid was ground and calcined in a muffle furnace to obtain the AuCu / ZSM-5-600 catalyst.

[0063] In step (1), the mass of molecular sieve ZSM-5 is controlled to be 100 mg, the volume of deionized water is 10 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (2), the mass of CuCl2•2H2O is controlled, wherein the mass ratio of Cu to ZSM-5 is 1:200, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ºC, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 600 ℃, and the calcination time is 4 h.

[0064] In step (3), the mass of Cu / ZSM-5-600 is controlled to be 100 mg, the volume of deionized water is 15 mL, the ultrasonic frequency is 60 kHz, and the time is 10 min. In step (4), the mass of HAuCl4•4H2O is controlled, wherein the mass ratio of Au to Cu / ZSM-5-600 is 1:100, the stirring speed of the oil bath is 200 r / min, the temperature is 80 ℃, the grinding time is 0.5 h, the heating rate of the muffle furnace is 5 ℃ / min, the temperature is 300 ℃, and the calcination time is 2 h.

[0065] Au prepared in Examples 1-4 x The phase structure of the Cu / ZSM-5 catalyst (where x is the mass percentage of Au in Cu / ZSM-5 in step (4)) was determined using the data from Panaco X'pert in the Netherlands. 3 The measurements were performed using a diffractometer (operating voltage 40 kV, current 40 mA), and the results are as follows: Figure 1 As shown in the XRD pattern, although the characteristic diffraction peaks of Au (111) crystal plane and ZSM-5 support can be observed, this indicates that the loading of Au nanoparticles on ZSM-5 does not change the phase structure of ZSM-5. In addition, due to the low loading of Cu, no Cu diffraction peaks were detected.

[0066] Au prepared in Examples 1-4 x The optical properties of the Cu / ZSM-5 catalyst were measured using a Cary 4000 UV-Vis spectrometer with BaSO4 as a reference. The results are as follows: Figure 2 As shown, strong absorption signals are observed at 360 nm and 520 nm, originating from Cu. 2+ The local surface plasmon resonance effect of gold nanoparticles also proves the presence of gold nanoparticles and Cu.

[0067] Prepared Au 1.0 The Cu / ZSM-5 catalyst was analyzed using a JEOL-JEM-2010 transmission electron microscope (TEM). The electron beam accelerating voltage used in the sample analysis was 200 kV. The results are as follows: Figure 3 As shown, Cu is highly dispersed on ZSM-5 without agglomeration, and Au is anchored on the ZSM-5 support in the form of nanoparticles.

[0068] Au x Performance evaluation of Cu / ZSM-5 catalyst for methane to methanol conversion Au was tested using a 50 ml high-pressure reactor. x The Cu / ZSM-5 catalyst was used to selectively oxidize methane. 10 mg of catalyst was ultrasonically dispersed in 20 ml of deionized water, placed in a sealed reactor, and purged three times with O2 to remove air. Then, 5 bar O2, 3 bar CO, 2 bar N2, and 20 bar CH4 gases were introduced before sealing. The reactor was reacted at 1000 r / min and a relatively low temperature of 150 °C for 1 h (the reaction time for all subsequent activity experiments was 1 h). After the reaction, the high-pressure reactor was cooled to below 10 °C using an ice-water bath. The liquid product was filtered and then... 1 H liquid nuclear magnetic resonance spectrometer ( 1 The product was analyzed by ¹H NMR. 1 The H NMR spectra are similar, and one of the results is as follows: Figure 4 As shown (the product after catalysis in Example 4).

[0069] Figure 5 Au for different Au / Cu ratios x A comparison of the activity of Cu / ZSM-5 catalysts in the selective oxidation of methane. As shown in the figure, the Cu / ZSM-5 catalyst without Au exhibits lower activity, with a methanol production rate of only 35.7 μmol g. cat. - 1 h -1 The selectivity was 87.7%. Under the condition of fixed Cu loading, the catalyst performance was significantly improved with the increase of Au introduction: the methanol production rate reached a maximum of 4288 μmol g. cat. -1 h -1 Furthermore, the selectivity is close to 100%. Compared with a single Cu catalyst, its activity is increased by approximately 120 times. These results indicate that under low-temperature reaction conditions, the synergistic effect of Au and Cu effectively promotes the activation of the CH bond in methane, significantly improving reaction efficiency while achieving precise control over product selectivity.

[0070] Figure 6 A comparison of the activity performance of AuCu / ZSM-5 catalysts prepared by different synthetic methods for the selective oxidation of methane; from Figure 6It can be seen that the AuCu / ZSM-5 catalyst prepared by the one-step calcination method (Example 5) has low activity, with a product formation rate of only 20.5 μmol g. cat. -1 h -1 The methanol selectivity was 76.3%. The AuCu / ZSM-5 catalyst prepared via a one-step liquid-phase reduction method (Example 6) showed improved activity, with the product formation rate increasing to 62.2 μmol g. cat. - 1 h -1 The methanol selectivity reached 80.5%. This is mainly due to the different phase structures of Au and Cu. However, the catalytic activity of both methods is far lower than that of the AuCu / ZSM-5 catalyst prepared by the two-step impregnation-calcination method developed in this invention (Example 4). Further, as Figure 7 As shown, when the loading order of Au and Cu was changed, although the characteristic diffraction peaks of the Au(111) crystal plane could be observed in the XRD pattern, indicating successful loading of Au nanoparticles, its methane conversion activity was significantly reduced compared with the catalyst in Example 3, and the product formation rate was only 353.4 μmol g. cat. -1 h -1 Additionally, such as Figure 8 As shown in Figure a, after loading Au onto Cu / ZSM-5 supports prepared at different calcination temperatures, the XRD patterns of all showed characteristic diffraction peaks of the Au(111) crystal plane, confirming the successful loading of Au nanoparticles. However, the methane conversion activity test results ( Figure 8 b) shows that the catalytic activity decreases regardless of whether the calcination temperature of Cu / ZSM-5 is decreased or increased. These results further confirm the unique advantages of the synthesis method described in this invention in constructing highly efficient active sites.

[0071] Figure 9 Au was shown at different temperatures 1.0 The activity change of Cu / ZSM-5 catalyst in the selective oxidation of methane is shown in the figure. As can be seen from the figure, within the temperature range of 60-180℃, the Au catalyst prepared by the two-step impregnation-calcination method described in this invention exhibits [activity variation]. 1.0 The Cu / ZSM-5 catalyst exhibits excellent methanol selectivity, consistently approaching 100%. The reaction activity reaches its peak at 150℃; further increases in temperature lead to a decrease in catalytic performance. Notably, the catalyst retains methane conversion activity at lower temperatures (e.g., 60℃), demonstrating good low-temperature reaction performance.

Claims

1. A method for preparing a molecular sieve catalyst for the selective oxidation of methane to methanol, comprising the following steps: (1) Preparation of Cu / ZSM complex: Add soluble copper salt to molecular sieve ZSM-5 suspension, sonicate to completely dissolve it, transfer to oil bath, heat in oil bath until the liquid evaporates, dry, grind thoroughly, and calcine to obtain Cu / ZSM-5 complex. (2) Preparation of Cu / ZSM-5 suspension: Cu / ZSM-5 was dispersed in deionized water and subjected to ultrasonic treatment to make it uniformly dispersed to form a suspension; (3) Preparation of AuCu / ZSM-5 catalyst for selective oxidation of methane to methanol: HAuCl4•4H2O was added to the suspension obtained in step (2), and ultrasonication was continued to completely dissolve it. The solution was then transferred to an oil bath, heated in the oil bath until the liquid evaporated, dried, ground thoroughly, and calcined to obtain AuCu / ZSM-5 catalyst; wherein the mass ratio of Au to Cu / ZSM-5 was 1:100 ~ 1:

500.

2. The preparation method according to claim 1, characterized in that, In step (1), the molecular sieve ZSM-5 suspension is obtained by dispersing molecular sieve ZSM-5 in deionized water, with a solid content of 5 ~ 20 mg / mL. Ultrasonication is used to make it uniform during the dispersion process.

3. The preparation method according to claim 1, characterized in that, The soluble copper salt in step (1) is CuCl2•2H2O, and the mass ratio of Cu to ZSM-5 in CuCl2•2H2O is controlled to be 1:200 ~ 1:

100.

4. The preparation method according to claim 1, characterized in that, Step (2) control the solid content of Cu / ZSM-5 suspension to be 5 ~ 20 mg / mL.

5. The preparation method according to claim 1, characterized in that, In step (1), the calcination temperature is 400 ~ 500℃ and the time is 4 ~ 5 h; in step (3), the calcination temperature is 300 ~ 350℃ and the time is 2 ~ 3 h.

6. The application of the molecular sieve catalyst obtained by the preparation method according to any one of claims 1-5 in the selective oxidation of methane to methanol at low temperature.

7. The application according to claim 6, characterized in that, The low temperature is 150-180℃.

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