Vanadotungstate-based zeolite-like octahedral metal oxide catalysts, methods for their preparation and use

Abstract

The application discloses a vanadium tungstate-based zeolite-like octahedral metal oxide catalyst, and the molecular formula of the catalyst is X 0.5～2 H 0～1 [(VO)3W4O 16 ] with a cubic crystal system, a space group of PA-3 and a cell parameter of alpha=90°, wherein X is K, Co or Cs, [W4O 16 ] 8‑ is a building unit, VO 2+ is a connecting point, the number of the building units in the unit cell is 8, and the number of the connecting points is 8. The vanadium tungstate-based zeolite-like octahedral metal oxide catalyst disclosed by the application has high catalytic activity, controllable structure and low cost, can efficiently catalyze direct oxidation of methane to methanol by oxygen at a low temperature of 60-150 DEG C, solves the problems of high cost, high reaction temperature and low activity of a noble metal catalyst, and the preparation method of the catalyst is simple, the reaction process is controllable, and the preparation repeatability is good.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a zeolite-like octahedral metal oxide catalyst based on vanadium tungstate, its preparation method, and its application. Background Technology

[0002] Methane is the main component of natural gas and coalbed methane, and its efficient conversion and utilization is a major development direction for natural gas processing and utilization. Currently, methane utilization mainly involves two aspects: one is direct combustion as a fuel to provide energy; the other is using methane as a carbon source to synthesize methanol and other important chemicals, which is also the most widespread industrial application of methane. Methanol has a high heat of vaporization and air compressibility, making it an ideal fuel. Because it retains most of the energy of the raw material methane, it is considered the most ideal product of methane. Furthermore, it is an important chemical raw material that can be further converted into olefins, aromatics, and other important fuels and chemical raw materials. At the same time, methanol is a liquid at normal temperature and pressure, making it easy to store and transport. How to convert methane into high-value-added methanol is of great significance for the efficient utilization of natural gas resources.

[0003] The main methods for producing methanol from methane are divided into direct partial oxidation and indirect oxidation. Industrially, the indirect oxidation method is more mature, involving the high-temperature reforming of methane to obtain syngas (H2 and CO), which is then converted into methanol under the action of a catalyst. However, the indirect oxidation method requires high temperatures and harsh reaction conditions, thus necessitating the development of a clean, environmentally friendly, and energy-efficient green process for producing methanol from methane. Direct partial oxidation can overcome the shortcomings of the indirect oxidation method. The literature (Silver and Copper Dual Single Atoms Boosting Direct Oxidation of Methane to Methanol via Synergistic Catalysis) discloses the direct oxidation of methane to methanol using hydrogen peroxide (H2O2) as the oxidant and Ag1-Cu1 / ZSM-5 as the catalyst, with a selectivity of up to 81%. The literature (Oxidation of methane to methanol over Pd@Pt nanoparticles undermild conditions in water) also reports the direct oxidation of methane to methanol using H2O2 as the oxidant and Pd@Pt nanoparticles as the catalyst, with a selectivity of up to 92%. However, compared to oxygen as an oxidant, H2O2 has drawbacks such as higher cost and greater difficulty in transportation.

[0004] Oxygen is a more readily available and inexpensive oxidant than H2O2. Developing a direct methane oxidation process to methanol using O2 as the oxidant is therefore more advantageous. In this regard, noble metal catalysts have demonstrated excellent activity. For example, according to the literature (Au-ZSM-5 catalysts the selective oxidation of CH4 to CH3OH and CH3COOH using O2), Au-ZSM-5, as a catalyst, can directly catalyze the oxidation of methane to methanol at 200°C with oxygen as the oxidant, achieving a selectivity of 82.2%. The literature (Metal-Organic Framework-Derived IrO2 / CuO Catalyst for Selective Oxidation of Methane to Methanol) also discloses that IrO2 / CuO can oxidize methane to methanol at 150°C in an oxygen atmosphere, with a methanol yield of 1.9 mmol / g and a selectivity of 95%. The copper-iridium composite oxide catalyst synthesized by the published patent CN110038591A (patent number CN201910450316.3) is composed of iridium oxide, copper oxide and co-catalyst zinc, cobalt or iron oxide. The catalyst has the characteristics of simple preparation method, high methanol yield in the reaction of methane oxidation to methanol, and can be repeatedly recycled.

[0005] However, the catalysts and reaction systems reported above have shortcomings. First, the high cost of precious metals limits their industrial application; using more widely available and inexpensive metals as catalysts is preferable. Second, the reaction needs to be carried out under high pressure and a closed system; excessively high reaction temperatures increase the risk, making it essential to further reduce the reaction temperature. Third, the low activity of the catalyst results in a low methanol production rate. Therefore, it is necessary to develop a non-precious metal-based catalyst that can efficiently catalyze the direct oxidation of methane to methanol at low temperatures. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a zeolite-like octahedral metal oxide catalyst with high catalytic activity, controllable structure, and low cost, as well as its preparation method and its application in catalyzing the low-temperature hydroxylation of methane, in order to address the shortcomings of the prior art.

[0007] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a zeolite-like octahedral metal oxide catalyst based on vanadium tungstate, wherein the molecular formula of the catalyst is X. 0.5～2 H 0～1 [(VO)3W4O 16 The crystal system is cubic, the space group is PA-3, and the unit cell parameter is... α = 90° Where X is K, Co, or Cs, [W4O 16 ] 8- As a building block, VO 2+ As connection points, there are 8 building blocks in a single cell and 8 connection points.

[0008] In the first embodiment, X is K, and the molecular formula of the catalyst is K2[(VO)3W4O] 16 ].

[0009] In the second embodiment, X is Co, and the catalyst has the molecular formula Co. 0.4～1 H 0～1.2 [(VO)3W4O 16 ].

[0010] In the third embodiment, X is Cs, and the molecular formula of the catalyst is Cs. 0～1 H 0～1 [(VO)3W4O 16 ].

[0011] The preparation method of the catalyst in the first embodiment above includes the following steps: dissolving 3-4.2g of KOH and 3.5-5.5g of WO3 in 100-300mL of deionized water, stirring until clear, cooling to room temperature, adding 18-20g of 10%wt H2SO4 aqueous solution and 2.410-2.946g of VOSO4·xH2O, controlling the pH value at 3-5, stirring at room temperature for 5-15 minutes, then loading into a high-pressure reactor, and then heating in a high-temperature oven at 150-200℃ for 8-16 hours. After removal, centrifugation and drying are performed to obtain the hydrothermally synthesized K2[(VO)3W4O] 16 ]catalyst.

[0012] The catalyst preparation method in the second embodiment described above uses K2[(VO)3W4O] 16 Catalysts and Co 2+ Co was prepared from chloride as a raw material via ion exchange method. 0.4～1 H 0～1.2 [(VO)3W4O 16 The catalyst, specifically prepared as follows: Weigh 0.5–1 g of K₂[(VO₃W₄O₂]₂]. 16 The catalyst and 0.2–0.8 g of CoCl2·6H2O were dissolved in 30 mL of water. The resulting mixture was stirred at room temperature for 1–2 h, washed three times with water, and then centrifuged at 8000 rpm / min for 5 min.

[0013] The catalyst preparation method in the third embodiment described above uses K2[(VO)3W4O] 16 Catalysts and Cs+ Cs was prepared by ion exchange using chloride as a raw material. 0～1 H 0～1 [(VO)3W4O 16 The catalyst, specifically prepared as follows: Weigh 0.5–1 g of K₂[(VO₃W₄O₂]₂]. 16 The catalyst and 0.05–0.15 g of CsCl were dissolved in 30 mL of water. The resulting mixture was stirred at room temperature for 1–2 h, washed three times with water, and then centrifuged at 8000 rpm / min for 5 min.

[0014] As a preferred embodiment, in the above three implementation schemes, the drying temperature is 60-80℃, the drying atmosphere is an air atmosphere, and the drying time is 12-24h.

[0015] The above-mentioned application of vanadium tungstate-based zeolite-like octahedral metal oxide catalysts in the catalytic oxidation of methane to methanol.

[0016] Preferably, when the above-mentioned vanadium tungstate-based zeolite-like octahedral metal oxide catalyst is applied to the catalytic oxidation of methane to methanol, 0.1 to 0.001 g of the catalyst and 15 mL of water are added to a high-pressure reactor. Subsequently, oxygen and methane are introduced into the high-pressure reactor, wherein the pressure of oxygen is 0.1 to 0.35 MPa and the pressure of methane is 0.586 to 2.05 MPa, and the reaction is carried out at 60 to 150 °C for 1 to 120 min.

[0017] Compared with the prior art, the present invention has the following advantages: the vanadium tungstate-based zeolite-like octahedral metal oxide catalyst disclosed in the present invention has high catalytic activity, controllable structure, and low cost. It can efficiently catalyze the direct oxidation of methane to methanol with oxygen at low temperatures of 60-150℃, solving the problems of high cost, high reaction temperature, and low activity of precious metal catalysts. Moreover, the preparation method of the catalyst is simple, the reaction process is controllable, and the preparation has good reproducibility. Attached Figure Description

[0018] Figure 1 In Example 1, K2[(VO)3W4O 16 The crystal structure of ], in which Figure 1 (a) is [W4O 16 ] 8- Construction unit, Figure 1 (b) is [(VO)3W4O 16 ] 2- Crystal structure;

[0019] Figure 2 The XRD powder diffraction patterns of the catalysts in Examples 1-3 are shown below.

[0020] Figure 3The nitrogen adsorption-desorption isotherms of the catalysts in Examples 1-3 are shown.

[0021] Figure 4 The methane adsorption-desorption isotherm of the catalyst in Example 2;

[0022] Figure 5 The XPS spectrum of the catalyst in Example 2 is shown below. Figure 5 (a) Figure 5 (b) Figure 5 (c) Figure 5 (d) correspond to the signals W(4f), V(2p), Co(2p), and O(1s), respectively. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. All raw materials used in the following embodiments are commercially available.

[0024] The vanadium tungstate-based zeolite-like octahedral metal oxide catalyst used in Example 1 is K2[(VO)3W4O] 16 The vanadium tungstate-based zeolite-like octahedral metal oxide catalyst used in Example 3 is Cs. 0～1 H 0～1 [(VO)3W4O 16 The vanadium tungstate-based zeolite-like octahedral metal oxide catalysts used in Examples 2 and 4-12 are Co. 0.4～1 H 0～1.2 [(VO)3W4O 16 ].

[0025] The vanadium tungstate-based zeolite-like octahedral metal oxide catalyst K2[(VO)3W4O] used in Example 1 16 For example, its crystal system is cubic, its space group is PA-3, and its unit cell parameters are... α = 90° Where X is K, Co, or Cs, [W4O 16 ] 8- As a building block, VO 2+ As connection points, there are 8 building blocks in a single cell, and 8 connection points. K2[(VO)3W4O 16 The crystal structure of the catalyst is as follows: Figure 1 As shown, the crystallographic data is presented in Table 1, and some bond lengths are presented in Table 2.

[0026] A certain amount of catalyst (0.1 g for Examples 1-3 and 7-12, and 0.05 g, 0.01 g, and 0.001 g for Examples 4-6, respectively) was added to a high-pressure reactor. 15 mL of water was added to the reactor, and O2 at 0.35 MPa and CH4 at 2.05 MPa were introduced. The reaction was carried out in the high-pressure reactor. The reaction conditions for Examples 1-6 were 90°C for 2 hours; the reaction temperatures for Examples 7-9 were 60°C, 120°C, and 150°C, respectively, with reaction times of 2 hours; and the reaction temperatures for Examples 10-12 were 90°C, with reaction times of 1 min, 20 min, and 1 hour, respectively. After the reaction, the aqueous solutions obtained in Examples 1-12 were divided into three equal portions. Two portions were analyzed by headspace gas chromatography to obtain the methanol yield. The remaining portion was diluted tenfold and analyzed by ion chromatography to obtain the formic acid yield. The results are shown in Tables 3 and 4.

[0027] Figure 2 The images show the XRD powder diffraction patterns of the catalysts in Examples 1-3. The characteristic diffraction peaks of the catalysts in Examples 1-3 are all at 10.27°, 14.59°, 17.21°, 20.75°, 22.66°, 27.05°, 30.98°, 31.37°, 31.84°, 33.15°, 34.48°, 42.59°, 43.7°, 45.00°, 53.73°, and 57.73°.

[0028] Figure 3 The figures show the nitrogen adsorption-desorption isotherms of the catalysts in Examples 1-3. The catalysts in Examples 1 and 2 are microporous materials with specific surface areas of 249 m² and 21 m², respectively. 2 / g and 325m 2 / g; The catalyst in Example 3 was a non-porous material with a specific surface area of ​​9.8m². 2 / g.

[0029] Figure 4 The methane adsorption-desorption isotherm of the catalyst in Example 2 is shown below. Figure 5 The XPS spectrum of the catalyst in Example 2 is shown below. Figure 5 (a) Figure 5 (b) Figure 5 (c) Figure 5 (d) correspond to the W(4f), V(2p), Co(2p), and O(1s) signals, respectively. The catalyst in Example 2 can effectively adsorb methane, with an adsorption capacity of approximately 25 cm⁻¹. 3 / g. XPS indicates that the tungsten in the catalyst of Example 2 is W. 6+ Vanadium is V 4+ and V 5+ Cobalt is a mixed valence state of Co. 2+ Oxygen is O2- .

[0030] For comparison, IrO2 / CuO and Au-ZSM-5 disclosed in the references mentioned in the background of this invention were used as catalysts for Comparative Examples 1 and 2, respectively, and comparative experiments were conducted. The experimental results compared with those of Example 10 are shown in Table 5.

[0031] Table 1

[0032]

[0033] Table 2

[0034] Atom 1 Atom 2 bond length Atom 1 Atom 2 bond length W1 O5 2.083 O3 V1 1.911 W1 O5 2.113 O3 W1 1.825 W1 O2 1.819 O4 W2 1.824 W1 O1 1.824 O4 V1 1.915 W1 O3 1.825 O5 W1 2.083 W1 O7 2.091 O5 W1 2.113 V1 O4 1.915 O5 W2 2.089 V1 O1 1.919 O6 V1 1.582 V1 O2 1.931 W2 O4 1.824 V1 O6 1.582 W2 O4 1.824 V1 O3 1.911 W2 O5 2.089 O1 W1 1.824 W2 O5 2.089 O1 V1 1.919 O7 W1 2.091 O2 W1 1.819 O7 W1 2.091 O2 V1 1.931 O7 W1 2.091

[0035] Table 3

[0036]

[0037] Table 4

[0038]

[0039] Table 5

[0040] Reaction conditions Comparative Example 1 Comparative Example 2 Example 10 catalyst <![CDATA[IrO2 / CuO]]> Au-ZSM-5 <![CDATA[Co 0.4～1 H 0～1.2 [(VO)3W4O 16 ]]]> Catalyst dosage (g) 0.01 0.1 0.1 Reaction temperature (°C) 150 240 90 Reaction time (min) 180 120 1 <![CDATA[Methanol production (μmol / g cat )]]> 1937 11.1 110.1 <![CDATA[Methanol production rate (μmol g cat -1 min -1 )]]> 10.80 0.09 110.10

[0041] Comparing Examples 1, 2, and 3, it can be found that the catalyst Co 0.4～1 H 0～1.2 [(VO)3W4O 16 The catalyst with the best catalytic activity was [ ], and its methanol yield, methanol generation rate and methanol selectivity were the highest among the three catalysts.

[0042] Comparing the catalyst dosages in Examples 2, 4, 5, and 6, it can be found that reducing the catalyst dosage can increase the methanol yield. When the catalyst dosage is 1 mg, the methanol yield is 541.0 μmol / g. cat Reducing the amount of catalyst can improve methanol selectivity, up to 90.9%.

[0043] Comparing the reaction temperatures of Examples 2, 7, 8, and 9, it can be found that the catalyst exhibits the best catalytic activity and the highest methanol yield (140.0 μmol / g) when the reaction temperature is controlled at 90°C. cat Lowering the reaction temperature can improve methanol selectivity.

[0044] Comparing the reaction times of Examples 2, 10, 11, and 12, it can be found that the methanol yield is highest at 149.9 μmol / g when the reaction time is 1 hour. cat A large amount of methanol was generated after 1 minute of reaction, at which point the methanol generation rate was 110.10 μmol g. cat-1 min -1 The methanol selectivity was 83.6%.

[0045] Comparing Comparative Examples 1 and 2 with Example 10, it can be found that Example 10 showed a significant amount of methanol production after 1 minute, with the highest methanol production rate of 110.10 μmol g. cat -1 min -1 On the other hand, Example 10, compared to Comparative Examples 1 and 2, required the lowest temperature for the catalytic reaction, indicating that Co... 0.4～1 H 0～1.2 [(VO)3W4O 16 The catalytic activity of [ ] is the best.

Claims

1. Use of a vanadotungstate-based zeolite-like octahedral metal oxide catalyst in the catalytic oxidation of methane to methanol, characterized in that, The catalyst has the molecular formula X. 0.5~2 H 0~1 [(VO)3W4O 16 The crystal system is cubic, space group PA-3, and the unit cell parameters are a = 17.0971 Å, α = 90 °, V = 4997.67 Å. 3 Where X is K, Co, or Cs, [W4O 16 ] 8- As a building block, VO 2+ As connection points, there are 8 building blocks in a single cell and 8 connection points.

2. Use according to claim 1, characterized in that, X is K, the molecular formula of the catalyst is K2[(VO)3W4O 16 ].

3. Use according to claim 1, characterized in that, K2[(VO)3W4O 16 ] and Co 2+ Using chloride as raw material, a zeolite-like octahedral metal oxide catalyst based on vanadate was prepared by ion exchange. The specific preparation process is as follows: Weigh 0.5~1 g of K2[(VO)3W4O 16 The catalyst and 0.2–0.8 g of CoCl₂·6H₂O were dissolved in 30 mL of water. The resulting mixture was stirred at room temperature for 1–2 h, washed three times with water, and then centrifuged at 8000 rpm for 5 min to obtain X, where X is Co. 0.5~ 2H 0~1 [(VO)3W4O 16 ]catalyst.

4. Use according to claim 1, characterized in that, K2[(VO)3W4O 16 ] and Cs + Using chloride as raw material, a zeolite-like octahedral metal oxide catalyst based on vanadate was prepared by ion exchange. The specific preparation process is as follows: Weigh 0.5~1 g of K2[(VO)3W4O] 16 The catalyst and 0.05–0.15 g of CsCl were dissolved in 30 mL of water. The resulting mixture was stirred at room temperature for 1–2 h, washed three times with water, and then centrifuged at 8000 rpm for 5 min to obtain X, where X is Cs. 0.5~2 H 0~1 [(VO)3W4O 16 ]catalyst.

5. Use according to claim 1, characterized in that, 0.1 to 0.001 g of the vanadotungstate-based zeolite-like octahedral metal oxide catalyst and 15 mL of water are introduced into a high-pressure reaction vessel, and then the high-pressure reaction vessel is charged with oxygen and methane, wherein the pressure of the oxygen is 0.1 to 0.35 MPa and the pressure of the methane is 0.586 to 2.05 MPa, and the reaction is carried out at 60 to 150 o C for 1 to 120 min.

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