Process for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions

Abstract

The present application relates to the technical field of plasma catalysis, and particularly relates to a method for catalytically converting methane and water into methanol and hydrogen under plasma conditions, a device used and a catalyst used. The bubbling-fluidized plasma reactor of the present application is formed by connecting a bubbling corona discharge plasma reactor at the lower part and a fluidized bed dielectric barrier discharge reactor at the upper part in series, and is filled with a catalyst in a discharge channel. Methane mixed with argon is preheated and then enters a gas bubbling column from a raw material inlet. A corona discharge is formed in the gas bubbles by a bubbling tip to generate plasma, so that the methane-water is preliminarily converted in cooperation. The gas after the preliminary conversion is introduced into the discharge channel to react under the action of the catalyst, and hydrogen and methanol are obtained by conversion.

Description

Technical Field

[0001] This invention relates to the field of plasma catalysis technology, specifically to a method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions, as well as the apparatus and catalyst used. Background Technology

[0002] Currently, with technological advancements, natural gas sources are becoming increasingly diverse, and the extraction costs of shale gas and combustible ice are decreasing, leading to a wider range of applications. Consequently, methane's role in the energy structure and chemical industry is rising. However, the CH bond in methane is highly stable, with a dissociation energy as high as 435 kJ / mol. This poses a challenge to the activation and conversion of methane, typically requiring harsh conditions such as high temperatures, strong acids, or free radicals. Therefore, the catalytic conversion of methane under mild conditions, especially with methanol as the target product, is considered the holy grail reaction. Due to the stringent conditions required for methane conversion and the need to protect methanol from excessive oxidation, this reaction currently employs a two-step process. The industrially adopted route is the syngas process, which involves first producing syngas from methane steam reforming, and then synthesizing methanol using the Fischer-Tropsch process. The steam reforming of methane presents thermodynamic obstacles and consumes a significant amount of energy.

[0003] Currently, the steam reforming reaction of methane using methane and water as raw materials involves two methods: high-temperature thermocatalysis and plasma catalysis. The products are mostly hydrogen and carbon monoxide. Summary of the Invention

[0004] The technical problem to be solved by the present invention is a method, apparatus and catalyst for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions.

[0005] To address the above problems, this invention provides a method for preparing a graphene-supported copper-silver-niobium nanoalloy catalyst, characterized by comprising the following steps:

[0006] 1) Disperse graphene oxide in deionized water (and sonicate it) to obtain a graphene oxide dispersion (a uniformly dispersed graphene oxide dispersion).

[0007] The metal precursor was dissolved in the graphene oxide dispersion, and urea (excess urea) was added and stirred (and ultrasonically treated) to form a mixed system.

[0008] The metal precursor is composed of copper precursor, silver precursor, and niobium precursor; the molar ratio of Cu:Ag:Nb is (1~2):(1~2):(1~2);

[0009] For every 3 mmol of metal atoms, 1.5-2.5 g of graphene oxide and 5-7 g of urea are used, wherein the metal atoms are composed of Cu, Ag and Nb;

[0010] 2) Transfer the mixture to an autoclave (an autoclave with a polytetrafluoroethylene liner) for aging reaction; the reaction temperature is 100~180℃ (160~180℃); the reaction time is 12~48h;

[0011] 3) Perform solid-liquid separation on the product obtained in step 2) (centrifugation or vacuum filtration), and wash and dry the resulting solid;

[0012] Note: Wash with deionized water and then transfer to an oven to dry;

[0013] 4) Place the product obtained in step 3) in a muffle furnace and calcine it in an air atmosphere; after calcination, allow it to cool naturally.

[0014] The calcination temperature is 300~800℃, and the calcination time is 1~12h;

[0015] 5) Place the material obtained in step 4) into a tube furnace and calcine it in a reducing gas atmosphere. After calcineation, allow it to cool naturally to obtain a graphene-supported nano-alloy catalyst.

[0016] The calcination temperature is 300~800℃, and the calcination time is 1~12h.

[0017] Note: The particle size of the graphene-supported nano-alloy catalyst is 10~100nm.

[0018] An improvement to the preparation method of the graphene-supported copper-silver-niobium nanoalloy catalyst of the present invention:

[0019] In step 1), the copper precursor is copper nitrate, the silver precursor is silver nitrate, and the niobium precursor is ammonium niobate oxalate.

[0020] As a further improvement to the preparation method of the graphene-supported copper-silver-niobium nanoalloy catalyst of the present invention:

[0021] In step 1), the stirring temperature is 10~60℃; the stirring time is 12~48h; and the ultrasonic treatment time is 1~8h.

[0022] In step 3), deionized water is used for washing (3 to 6 times); the drying temperature is 50 to 120°C; and the drying time is 12 to 48 hours.

[0023] The heating rate in step 2) is 3~10℃ / min, the heating rate in step 4) is 3~10℃ / min, and the heating rate in step 5) is 3~10℃ / min.

[0024] As a further improvement to the preparation method of the graphene-supported copper-silver-niobium nanoalloy catalyst of the present invention: in step 5), the reducing gas atmosphere is any of the following mixed gases:

[0025] The mixture of argon and hydrogen, nitrogen and hydrogen, and helium and hydrogen, wherein the volume percentage of hydrogen in the above three mixtures is 1% to 10% (preferably 5% to 10%).

[0026] The present invention also provides a bubbling-fluidized plasma reactor: which is composed of a bubbling corona discharge plasma reactor located below and a fluidized bed medium barrier discharge reactor located above, connected in series through a connecting channel;

[0027] The shell of the bubbling corona discharge plasma reactor consists of a cylindrical lower shell with a bottom surface, a conical upper bundle tube, and a conical lower bundle tube. The upper and lower ends of the cylindrical lower shell are respectively equipped with the upper and lower conical upper bundle tubes. A gas bubbling column is installed inside the cylindrical lower shell. The gas bubbling column is a hollow, cylindrical gas channel with a top but no bottom. A through-hole is provided on the wall of the gas channel, and a conical bubble tip shell is fitted at the through-hole. The conical bubble tip shell has no bottom surface, and a small through-hole is provided at its apex. The bottom of the gas bubbling column passes through the bottom surface of the cylindrical lower shell in a sealed manner and connects to the conical lower bundle tube. Water is contained inside the cylindrical lower shell.

[0028] The fluidized bed dielectric barrier discharge reactor consists of a cylindrical upper shell, an upper conical bundle tube, and a lower conical bundle tube. The upper and lower conical bundle tubes are respectively located at the upper and lower ends of the cylindrical upper shell. A stainless steel rod is fitted inside the cylindrical upper shell, with the axis of the upper shell coinciding with that of the stainless steel rod. A quartz tube is tightly fitted onto the outer wall of the stainless steel rod, and the inner wall of the cylindrical upper shell and the outer wall of the quartz tube form a discharge channel. A catalyst is placed within the discharge channel as packing material (the discharge area serves as both the catalyst filling area and the gas channel).

[0029] The upper conical upper bundle tube of the upper shell is connected to the product outlet; the lower conical bundle tube of the upper shell is connected to the upper conical bundle tube of the lower shell through a connecting channel; the lower conical lower bundle tube of the lower shell is connected to the raw material inlet.

[0030] The high-voltage conductor is electrically connected to the shell of the bubbling corona discharge plasma reactor, the shell of the fluidized bed medium barrier discharge reactor, or any connection channel.

[0031] The grounding wire is electrically connected to the stainless steel rod.

[0032] As an improvement to the bubbling-fluidized plasma reactor of the present invention:

[0033] The height of the cylindrical upper shell is the same as the length of the stainless steel rod;

[0034] The shells of the bubbling corona discharge plasma reactor, the fluidized bed dielectric barrier discharge reactor, and the connecting channels are all made of metal (e.g., stainless steel).

[0035] As a further improvement to the bubbling-fluidized plasma reactor of the present invention:

[0036] The gas enters the lower conical lower tube of the lower shell from the raw material inlet, and then enters the gas channel of the gas bubbling column from bottom to top and exits through the small through hole at the tip of the conical bubbling tip shell.

[0037] That is, the small through hole at the tip of the cone bubble is connected to the inner cavity (gas channel) of the gas bubble column through the cone-shaped inner cavity of the cone-shaped bubble tip shell and the corresponding through hole on the gas channel pipe wall of the gas bubble column.

[0038] As a further improvement to the bubbling-fluidized plasma reactor of the present invention:

[0039] On the wall of the gas channel of the gas bubbling column, four through holes are evenly provided on the same horizontal plane. Therefore, four rows of conical bubble tip shell assemblies are evenly and symmetrically arranged longitudinally on the surface of the gas bubbling column. Each row of conical bubble tip shell assemblies consists of conical bubble tip shells arranged from top to bottom.

[0040] The present invention also provides a method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions: a graphene-supported copper-silver-niobium nanoalloy catalyst prepared by any of the above methods, and the above-mentioned bubbling-fluidized plasma reactor.

[0041] The discharge channel is filled with catalyst, and the air in the reactor is discharged by introducing nitrogen gas from the raw material inlet; so that the cylindrical lower shell is filled with water, and the liquid level is basically level with the top of the cylindrical lower shell;

[0042] Methane and argon are mixed at a volume ratio of 1:9. After preheating (to 120~140℃), the mixture enters the gas bubble column through the lower conical bundle tube of the lower shell from the raw material inlet. The gas then exits from the small through hole at the tip of the conical bubble shell to generate bubbles. Corona discharge is generated in the bubbles at the tip of the bubble to form plasma, which enables the initial synergistic conversion of methane and water.

[0043] After preliminary co-conversion, the gas passes sequentially through the conical upper bundle tube of the lower shell, the connecting channel, and the conical lower bundle tube of the upper shell before entering the discharge channel inside the cylindrical upper shell. Under the action of the catalyst, it reacts and is converted into hydrogen and methanol.

[0044] The peak voltage is 12~18kV;

[0045] The residence time of the mixed gas of methane and argon in the gas bubbling column is approximately 0.05 to 0.1 minutes;

[0046] The gas after preliminary synergistic conversion resides in the discharge channel for approximately 2 to 4 minutes.

[0047] Reaction temperature 100~180℃;

[0048] The flow rate of the methane-argon mixture is 100~180mL / min, and the input frequency of the high-voltage power supply is 9kHz.

[0049] This invention provides a method for the direct production of methanol and hydrogen through the co-conversion of methane and water under plasma conditions, combined with a graphene-supported copper-silver-niobium nanoalloy catalyst. This method achieves comprehensive utilization of methane under mild conditions, namely, highly efficient catalytic co-conversion of methane and water to produce methanol and hydrogen with high selectivity. This invention enables the direct conversion of methane and water vapor into methanol and hydrogen under mild conditions, which not only shortens the process route but also reduces reaction conditions and saves energy, making it a feasible and ideal approach.

[0050] The present invention has the following beneficial effects:

[0051] 1. A method for directly synthesizing methanol and hydrogen using methane and water as raw materials has been developed, realizing the direct conversion of methane into high-value chemicals.

[0052] 2. The proposed catalyst exhibits high activity and selectivity for the target product, along with good lifetime and stability. The proposed plasma reactor can continuously carry out plasma catalytic reactions at a constant temperature.

[0053] 3. Plasma provides high-quality energy to the reaction, enabling methane to be converted under mild conditions, avoiding high-temperature conditions.

[0054] In summary, this invention develops a reaction system for the efficient catalytic conversion of methane and water to methanol and hydrogen under mild conditions, using a nano-alloy catalyst in the presence of plasma. Attached Figure Description

[0055] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0056] Figure 1 This is a schematic diagram of the plasma reactor device used in this invention.

[0057] Figure 2 for Figure 1 Enlarged schematic diagram of section AA in the middle. Detailed Implementation

[0058] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0059] Example of a device: A bubbling-fluidized plasma reactor, used as a reaction device for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions; the specific structure is as follows:

[0060] The bubbling-fluidized plasma reactor is composed of a bubbling corona discharge plasma reactor 12 located below and a fluidized bed medium barrier discharge reactor 11 located above, connected in series via a connecting channel 10.

[0061] The shell of the bubbling corona discharge plasma reactor 12 consists of a cylindrical lower shell 121 with a bottom surface, a conical upper tube 122, and a conical lower tube 123. That is, the cylindrical lower shell 121 has a bottom surface, and the conical upper tube 122 and the conical lower tube 123 are respectively provided at the upper and lower ends of the cylindrical lower shell 121. The cylindrical lower shell 121, the conical upper tube 122, and the conical lower tube 123 are all made of stainless steel.

[0062] A plurality of gas bubble columns 3 are evenly distributed within the cylindrical lower shell 121. These gas bubble columns 3 are in contact with the cylindrical lower shell 121 and connected to a high-voltage power supply. Each gas bubble column 3 is a cylindrical, hollow, top-less gas channel (i.e., a cylindrical gas channel). The bottom of the gas bubble column 3 passes through the bottom surface of the cylindrical lower shell 121 in a sealed manner and connects to the conical lower tube 123 of the lower shell. Water is contained within the cylindrical lower shell 121, and the liquid level inside the cylindrical lower shell 121 is approximately level with the top of the cylindrical lower shell 121. A corresponding water inlet switch can be installed at the top of the cylindrical lower shell 121 for adding water during the reaction process. For clarity of the diagram, this water inlet switch is located at... Figure 1 The text has been abbreviated.

[0063] Four through holes are evenly distributed on the same horizontal plane, with adjacent through holes forming a 90° angle. These through holes communicate with the inner cavity of the gas channel. A conical bubble tip shell 2 is fitted at each through hole. The conical bubble tip shell 2 has no bottom surface; a small through hole is located at its apex. This small through hole connects sequentially to the conical inner cavity of the conical bubble tip shell 2, the corresponding through hole on the gas channel wall, and the inner cavity (gas channel) of the gas bubble column 3. The bottom end of the conical bubble tip shell 2 is sealed and fixedly connected to the gas bubble column 3 via conventional welding. Therefore, four rows of conical bubble tip shell assemblies are evenly and symmetrically arranged longitudinally on the surface of the gas bubble column 3. Each row of conical bubble tip shell assemblies consists of conical bubble tip shells 2 arranged from top to bottom.

[0064] The fluidized bed medium barrier discharge reactor 11 has a shell composed of a cylindrical upper shell 111, an upper shell conical upper bundle tube 112, and an upper shell conical lower bundle tube 113. The upper shell conical upper bundle tube 112 and the upper shell conical lower bundle tube 113 are respectively installed at the upper and lower ends of the cylindrical upper shell 111. A stainless steel rod 5 is installed inside the cylindrical upper shell 111, with the axis of the cylindrical upper shell 111 coinciding with that of the stainless steel rod 5. The height of the cylindrical upper shell 111 is the same as the length of the stainless steel rod 5, i.e., they are horizontally aligned. The cylindrical upper shell 111, the upper shell conical upper bundle tube 112, and the upper shell conical lower bundle tube 113 are all made of stainless steel.

[0065] A quartz tube 6, prepared by tightly fitting a quartz medium onto the outer wall of a stainless steel rod 5, is formed. The inner wall of the quartz tube 6 is as close as possible to the outer surface of the stainless steel rod 5, i.e., the distance between the two is ≤0.05 mm.

[0066] The inner wall of the cylindrical upper shell 111 maintains a certain distance from the outer wall of the quartz tube 6, that is, the inner wall of the cylindrical upper shell 111 and the outer wall of the quartz tube 6 form a discharge channel 7, and a catalyst packing is placed in this discharge channel 7. The function of the catalyst packing is to improve the discharge effect and catalyze the reaction.

[0067] The upper conical upper tube 112 of the upper shell is connected to the product outlet 13; the upper conical lower tube 113 of the upper shell is connected to the lower conical upper tube 122 of the lower shell through the connecting channel 10. The lower conical lower tube 123 of the lower shell is connected to the raw material inlet 14.

[0068] Gas enters the lower shell conical lower bundle tube 123 from the raw material inlet 14, and then enters the gas bubble column 3 from bottom to top and generates bubbles through the small through hole at the tip of the conical bubble tip shell 2.

[0069] The high-voltage wire 8 is connected to the outer shell of the device. That is, the high-voltage wire 8 can be connected to any one of the shells of the bubble-type corona discharge plasma reactor 12, the shell of the fluidized bed medium barrier discharge reactor 11, or the connecting channel 10. The outer shell of the device is connected to a high-voltage power supply through the high-voltage wire 8. Since the gas bubble column 3 is in contact with the cylindrical lower shell 121, the high-voltage power supply is connected. Corona discharge is generated in the bubble through the tip at the bubble opening to form plasma, so that methane-water can be initially co-converted.

[0070] The grounding wire 9 is connected to the stainless steel rod 5.

[0071] Product outlet 13 is the gas outlet, and raw material inlet 14 is the gas inlet.

[0072] In actual use:

[0073] The stainless steel shell 1 serves as the high-voltage electrode, the stainless steel rod 5 serves as the grounding electrode, the conical bubble tip shell 2 serves as the corona discharge tip, and the quartz tube 6 serves as the dielectric material; a plasma high-voltage power supply provides high-voltage AC power with adjustable frequency and voltage peak value.

[0074] Specifically:

[0075] The cylindrical lower shell 121 is 100mm-1000mm long, with an inner diameter of 30mm-200mm, and is made of 022Cr17Ni12Mo2 stainless steel; the cylindrical upper shell 111 is 100mm-1000mm long, with an inner diameter of 30mm-200mm, and is also made of 022Cr17Ni12Mo2 stainless steel. The quartz tube 6 has a wall thickness of 1mm-3mm and an outer diameter of 20-100mm.

[0076] The length of the stainless steel rod 5 is equal to the length of the cylindrical lower shell 121; the stainless steel rod 5 is made of 022Cr17Ni12Mo2 stainless steel.

[0077] The length of the gas bubbling column 3 is equal to the length of the cylindrical lower shell 121, that is, the gas bubbling column 3 is 100mm-1000mm long, with an inner diameter of 1mm-3mm, and is made of 022Cr17Ni12Mo2 stainless steel.

[0078] The dimensions of the conical bubble tip shell 2 are 1-3 mm in bottom diameter and 2-10 mm in height.

[0079] The stainless steel casing of the device has a thickness of 1mm-3mm.

[0080] The plasma high-voltage power supply can generate stable alternating current with a peak voltage of 0-30kV and a frequency of 1kHz-50kHz. The width of discharge channel 7 is 5mm-50mm.

[0081] Example 1: A method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions:

[0082] I. A bubbling-fluidized plasma reactor as described in the device example: A cylindrical lower shell 121 is 300 mm long and has an inner diameter of 100 mm; a cylindrical upper shell 111 is 300 mm long and has an inner diameter of 100 mm. A quartz tube 6 has a wall thickness of 2 mm and an outer diameter of 90 mm. A stainless steel rod 5 is 300 mm long and has a diameter of 86 mm. The stainless steel outer shell 1 (cylindrical upper shell 111, upper shell conical upper bundle tube 112 and upper shell conical lower bundle tube 113, cylindrical lower shell 121, lower shell conical upper bundle tube 122 and lower shell conical lower bundle tube 123, and connecting channel 10) has a thickness of 2 mm. The discharge channel 7 has a width of 5 mm. The gas bubble column 3 is 300 mm long and has an inner diameter of 2 mm. The diameter of the through-hole in the gas channel wall of the gas bubble column 3 (the bottom diameter of the conical bubble tip shell 2) is approximately 1-2 mm. The diameter of the small through-hole at the tip of the conical bubble tip shell 2 is approximately 0.1-0.2 mm. The height of the conical bubble tip shell 2 is approximately 6 mm. In each row of conical bubble tip shell assemblies, the spacing between the conical bubble tip shells 2 is approximately 5-6 mm. On the horizontal plane, the small through-holes at the tips of adjacent conical bubble tip shells 2 maintain a spacing of approximately 5-6 mm.

[0083] II. Preparation of graphene-supported copper-silver-niobium nanoalloy catalyst: A Cu1Ag1Nb1 / graphene catalyst (x=1, y=1, z=1) was prepared by sequentially performing the following steps:

[0084] 1) Take 2g of graphene oxide and disperse it in 200mL of deionized water, and sonicate it for 1h to obtain a uniformly dispersed graphene oxide dispersion.

[0085] 0.13 g copper nitrate (1 mmol), 0.17 g silver nitrate (1 mmol), and 0.2 g ammonium niobate oxalate (1 mmol) were added to the above graphene oxide dispersion and dissolved; then 6 g urea was added, and the mixture was stirred thoroughly at 25 °C for 12 h and sonicated for 2 h to form a mixed system.

[0086] 2) Transfer the mixture to a high-pressure reactor with a polytetrafluoroethylene liner, increase the temperature to 160°C at a rate of 5°C / min, and allow it to age for 24 hours.

[0087] 3) After centrifugation and filtration, the obtained solid was washed three times with deionized water (until the pH of the eluent was neutral); then transferred to an oven and dried at 110°C for 24 hours.

[0088] Then it was placed in a muffle furnace and heated to 500°C at 5°C / min in an air atmosphere, held for 3 hours, and then cooled naturally to room temperature.

[0089] The catalyst was then placed in a tube furnace and heated to 500°C at a rate of 5°C / min under a mixed atmosphere of argon and hydrogen (5% hydrogen), held for 3 hours, and then allowed to cool naturally to room temperature. This yielded a graphene-supported copper-silver-niobium nanoalloy catalyst (hereinafter referred to as the catalyst). Scanning electron microscopy confirmed the particle size of the graphene-supported copper-silver-niobium nanoalloy catalyst. The particle size of the graphene-supported nanoalloy catalyst obtained in this invention is 10–100 nm.

[0090] III. During the reaction, assemble the reactor, fill the discharge channel 7 with catalyst, continuously introduce nitrogen gas through the raw material inlet 14 for 30 minutes, and expel the air from the reactor (the air exits the reactor through the product outlet 13); and add water into the cylindrical lower shell 121 through the water inlet switch, with the liquid level approximately level with the top of the cylindrical lower shell 121. Note: The water is located outside the gas bubbling column 3.

[0091] Methane and argon were mixed at a volume ratio of 1:9, with a total flow rate of 100 mL / min. The mixture was preheated to 130°C and introduced into the reaction apparatus through raw material inlet 14. The temperature within the entire reaction apparatus was controlled at 100°C. A high-voltage power supply with an input frequency of 9 kHz and a peak voltage of 12 kV AC was used to generate plasma and catalyze the reaction. The products were condensed and separated into gas and liquid phases, and then detected using gas chromatography-mass spectrometry.

[0092] The reaction process is as follows:

[0093] A mixture of methane and argon enters the gas bubble column 3 through the conical lower tube 123 in the lower shell from the raw material inlet 14, and then exits through the small through-hole at the tip of the conical bubble column 2, generating bubbles. Since the gas bubble column 3 is in contact with the cylindrical lower shell 121 and connected to a high-voltage power supply via the high-voltage wire 8, corona discharge occurs at the bubble tip, forming plasma and initiating the methane-water co-conversion. The mixed gas remains in the gas bubble column 3 for approximately 0.1 minutes. During the reaction, when the water level in the cylindrical lower shell 121 drops by more than 5%, water is added to the cylindrical lower shell 121 via a water supply switch until the liquid level is approximately level with the top of the cylindrical lower shell 121.

[0094] Subsequently, the gases after preliminary co-conversion (hydrogen, carbon monoxide, and unconverted methane and water, etc.) sequentially pass through the lower shell conical upper bundle tube 122, the connecting channel 10, and the upper shell conical lower bundle tube 113 before entering the discharge channel 7 inside the cylindrical upper shell 111. Under the action of a catalyst, they further react and are further converted to obtain hydrogen and methanol. Note: Methane and water undergo steam reforming to obtain syngas, which in turn yields methanol and hydrogen.

[0095] The gas after initial synergistic conversion stays in discharge channel 7 for approximately 4 minutes.

[0096] The products generated by the reaction are methanol, hydrogen, etc. (since the gas flow temperature is high, they are gases). They are then separated by condensation, and the resulting liquid is methanol. Hydrogen is then separated by pressure swing adsorption. This separation method is a conventional technology in this industry, so it will not be described in detail in this invention.

[0097] Example 2 series:

[0098] Compared to Example 1, the molar amount of copper nitrate was changed, thereby altering the proportion of copper in the alloy, i.e., changing x. All other operations remained the same as in Example 1, resulting in the Example 2 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 1.

[0099] Table 1

[0100]

[0101] Example 3 series:

[0102] Compared to Example 1, the molar amount of silver nitrate was changed, thereby altering the proportion of silver in the alloy, i.e., changing y. All other operations remained the same as in Example 1, resulting in the Example 3 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 2.

[0103] Table 2

[0104]

[0105] Example 4 series:

[0106] Compared to Example 1, the molar amount of ammonium niobate oxalate was changed, thereby altering the proportion of niobium in the alloy, i.e., changing z. All other operations remained the same as in Example 1, resulting in the Example 4 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 3.

[0107] Table 3

[0108]

[0109] Example 5 series:

[0110] Compared to Example 1, the reaction temperature in the autoclave was changed, while other operations remained the same as in Example 1, resulting in the Example 5 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 4.

[0111] Table 4

[0112]

[0113] Example 6 series:

[0114] Compared to Example 1, the calcination temperature of the muffle furnace was changed, while other operations remained the same as in Example 1, resulting in the Example 6 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 5.

[0115] Table 5

[0116]

[0117] Example 7 series:

[0118] Compared to Example 1, the calcination temperature of the tubular furnace was changed, while other operations remained the same as in Example 1, resulting in the Example 7 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 6.

[0119] Table 6

[0120]

[0121] Example 8 series:

[0122] Compared to Example 1, the proportion of hydrogen in the reducing gas was changed, while other operations remained the same as in Example 1, resulting in the Example 8 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 7.

[0123] Table 7

[0124]

[0125] Example 9 series:

[0126] Compared to Example 1, the peak-to-peak voltage was changed (twice the peak voltage), while other operations remained the same as in Example 1, resulting in the Example 9 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 8.

[0127] Table 8

[0128]

[0129] Example 10 series:

[0130] Compared to Example 1, the flow rate of the methane-argon gas mixture was changed, thereby altering the residence time; all other operations remained the same as in Example 1, resulting in the Example 10 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 9.

[0131] Table 9

[0132]

[0133] Example 11 series:

[0134] Compared to Example 1, the reactor temperature was changed, while other operations remained the same as in Example 1, resulting in the Example 11 series. A comparison of process parameters and reaction results with Example 1 is shown in Table 10.

[0135] Table 10

[0136]

[0137] Comparative Example 1-1: In Example 1, x is changed to 0, and the rest is the same as in Example 1.

[0138] The results are shown in Table 11 below.

[0139] Comparative Examples 1-2: Change y to 0 in Example 1, and the rest are the same as in Example 1.

[0140] The results are shown in Table 11 below.

[0141] Comparative Examples 1-3: z in Example 1 is changed to 0, and the rest is the same as in Example 1.

[0142] The results are shown in Table 11 below.

[0143] Comparative Example 2-1: The catalyst in Example 1 was replaced with quartz sand, and the rest was the same as in Example 1.

[0144] The results are shown in Table 11 below.

[0145] Comparative Example 2-2: The catalyst in Example 1 was replaced with none, and the rest was the same as in Example 1.

[0146] The results are shown in Table 11 below.

[0147] Comparative Example 3: The AC input in Example 1 was changed to none, while everything else remained the same as in Example 1. This case failed to produce a reaction.

[0148] Comparative Example 4: The "preliminary co-conversion of methane and water" was eliminated, specifically as follows: only the upper part of the reactor was retained, and a mixture of methane and water was directly introduced. The rest is the same as in Example 1.

[0149] Table 11

[0150]

[0151] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing graphene-supported copper-silver-niobium nanoalloy catalysts, characterized in that... Includes the following steps: 1) Graphene oxide is dispersed in deionized water to obtain a graphene oxide dispersion; The metal precursor was dissolved in the graphene oxide dispersion, and urea was added and stirred to form a mixed system. The metal precursor consists of copper precursor, silver precursor, and niobium precursor; Cu: The molar ratio of Ag:Nb is (1~2):(1~2):(1~2); For every 3 mmol of metal atoms, 1.5-2.5 g of graphene oxide and 5-7 g of urea are used, wherein the metal atoms are composed of Cu, Ag and Nb; 2) Transfer the mixture to an autoclave for aging reaction; the reaction temperature is 100~180℃; the reaction time is 12~48h; 3) Perform solid-liquid separation on the product obtained in step 2), and wash and dry the resulting solid; 4) Place the product obtained in step 3) in a muffle furnace and calcine it in an air atmosphere; after calcination, allow it to cool naturally. The calcination temperature is 300~800℃, and the calcination time is 1~12h; 5) Place the material obtained in step 4) into a tube furnace and calcine it in a reducing gas atmosphere. After calcineation, allow it to cool naturally to obtain a graphene-supported nano-alloy catalyst. The calcination temperature is 300~800℃, and the calcination time is 1~12h.

2. The method for preparing the graphene-supported copper-silver-niobium nanoalloy catalyst according to claim 1, characterized in that: In step 1), the copper precursor is copper nitrate, the silver precursor is silver nitrate, and the niobium precursor is ammonium niobate oxalate.

3. The method for preparing the graphene-supported copper-silver-niobium nanoalloy catalyst according to claim 2, characterized in that: In step 1), the stirring temperature is 10~60℃; the stirring time is 12~48h. In step 3), deionized water is used for washing; the drying temperature is 50~120℃; and the drying time is 12~48h. The heating rate in step 2) is 3~10℃ / min, the heating rate in step 4) is 3~10℃ / min, and the heating rate in step 5) is 3~10℃ / min.

4. The method for preparing the graphene-supported copper-silver-niobium nanoalloy catalyst according to any one of claims 1 to 3, characterized in that: In step 5), the reducing gas atmosphere is any of the following mixtures: The three gas mixtures are argon and hydrogen, nitrogen and hydrogen, and helium and hydrogen, in which the volume percentage of hydrogen is 1% to 10%.

5. A method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions, characterized in that: The graphene-supported copper-silver-niobium nanoalloy catalyst prepared by any of the methods described in claims 1 to 4 was used in a bubbling-fluidized plasma reactor. The bubbling-fluidized plasma reactor is composed of a bubbling corona discharge plasma reactor (12) located below and a fluidized bed medium barrier discharge reactor (11) located above, connected in series through a connecting channel (10). The shell of the bubble-type corona discharge plasma reactor (12) consists of a cylindrical lower shell (121) with a bottom surface, a conical upper tube (122) and a conical lower tube (123) of the lower shell. The conical upper tube (122) and the conical lower tube (123) of the lower shell are respectively provided at the upper and lower ends of the cylindrical lower shell (121). A gas bubble column (3) is provided inside the cylindrical lower shell (121). The gas bubble column (3) is a hollow, cylindrical gas channel with a top but no bottom. A through hole is provided on the tube wall of the gas channel. A conical bubble tip shell (2) is provided at the through hole. The conical bubble tip shell (2) has no bottom surface. A small through hole is provided at the top of the conical bubble tip shell (2). The bottom of the gas bubble column (3) passes through the bottom surface of the cylindrical lower shell (121) and is connected to the conical lower tube (123) of the lower shell. The shell of the fluidized bed medium barrier discharge reactor (11) is composed of a cylindrical upper shell (111), an upper shell conical upper bundle tube (112), and an upper shell conical lower bundle tube (113); the upper shell conical upper bundle tube (112) and the upper shell conical lower bundle tube (113) are respectively set at the upper and lower ends of the cylindrical upper shell (111); a stainless steel rod (5) is installed inside the cylindrical upper shell (111), and the axis of the cylindrical upper shell (111) coincides with that of the stainless steel rod (5); a quartz tube (6) is tightly fitted on the outer wall of the stainless steel rod (5), and the inner wall of the cylindrical upper shell (111) and the outer wall of the quartz tube (6) form a discharge channel (7), and a catalyst is set as packing material in the discharge channel (7); The upper conical upper bundle tube (112) of the upper shell is connected to the product outlet (13); the upper conical lower bundle tube (113) of the upper shell is connected to the lower conical upper bundle tube (122) of the lower shell through the connecting channel (10); the lower conical lower bundle tube (123) of the lower shell is connected to the raw material inlet (14); The high-voltage conductor (8) is electrically connected to any of the following: the shell of the bubbling corona discharge plasma reactor (12), the shell of the fluidized bed medium barrier discharge reactor (11), or the connecting channel (10); The grounding wire (9) is electrically connected to the stainless steel rod (5); The discharge channel (7) is filled with catalyst, and the air in the reactor is discharged by introducing nitrogen gas from the raw material inlet (14); so that the cylindrical lower shell (121) is filled with water and the liquid level is level with the top of the cylindrical lower shell (121); Methane and argon are mixed at a volume ratio of 1:

9. After being preheated to 120~140℃, they enter the gas bubble column (3) through the lower shell conical lower bundle tube (123) from the raw material inlet (14). Then, they are discharged from the small through hole at the tip of the conical bubble tip shell (2) to generate bubbles. The bubble tip generates corona discharge in the bubbles to form plasma, so that methane-water can be initially synergistically converted. After preliminary co-conversion, the gas passes through the conical upper bundle tube (122) of the lower shell, the connecting channel (10), and the conical lower bundle tube (113) of the upper shell in sequence, and then enters the discharge channel (7) in the cylindrical upper shell (111). Under the action of the catalyst, it reacts and is converted into hydrogen and methanol.

6. The method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions according to claim 5, characterized in that: The peak voltage is 12~18kV; The residence time of the mixed gas composed of methane and argon in the gas bubbling column (3) is 0.05~0.1 minutes; The gas after preliminary synergistic conversion stays in the discharge channel (7) for 2 to 4 minutes; The reaction temperature is 100~180℃.

7. The method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions according to claim 6, characterized in that: The height of the cylindrical upper shell (111) is the same as the length of the stainless steel rod (5); The shells of the bubbling corona discharge plasma reactor (12), the fluidized bed medium barrier discharge reactor (11), and the connecting channel (10) are all made of metal.

8. The method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions according to claim 7, characterized in that: Gas enters the lower shell conical lower tube (123) from the raw material inlet (14), and then enters the gas channel of the gas bubble column (3) from bottom to top and is discharged through the small through hole at the tip of the conical bubble tip shell (2).

9. The method for the catalytic co-conversion of methane and water to methanol and hydrogen under plasma conditions according to claim 8, characterized in that: On the wall of the gas channel of the gas bubble column (3), four through holes are uniformly provided on the same horizontal plane. Therefore, four rows of conical bubble tip shell assemblies are uniformly and symmetrically arranged longitudinally on the surface of the gas bubble column (3). Each row of conical bubble tip shell assemblies is composed of conical bubble tip shells (2) arranged from top to bottom.

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