A composite phase molybdenum carbide catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts and relates to a preparation method of a composite-phase molybdenum carbide catalyst, which comprises the following steps: S1, weighing molybdenum salt and dissolving the molybdenum salt in deionized water to obtain a molybdenum solution; adding Mo2N into the molybdenum solution to obtain a suspension; heating and stirring the suspension in a water bath to a gel state, drying at 50-120 DEG C, and preparing a precursor; carbonizing the precursor under a reducing atmosphere to prepare a composite-phase molybdenum carbide material containing alpha-MoC and beta-Mo2C; and the carbonization conditions are as follows: heating to 500-680 DEG C in 1-5 h, and carbonization time is 2-10 h. The molybdenum salt solution is loaded to Mo2N to obtain a precursor, and the precursor is carbonized at 500-680 DEG C to obtain a composite-phase molybdenum carbide catalyst with a controllable ratio.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a composite phase molybdenum carbide catalyst, its preparation method, and its application. Background Technology

[0002] The massive consumption of fossil fuels has led to significant carbon dioxide (CO2) emissions, inducing a severe greenhouse effect. Therefore, CO2 capture, storage, and utilization (CCU) has received widespread attention as a potential pathway to control the greenhouse effect. To date, the catalytic reduction of CO2 to value-added products is widely considered a compelling solution to reduce atmospheric CO2 concentrations, thereby mitigating global warming and providing a sustainable solution to the energy crisis. Reverse water gas shift reaction (RWGS) is one of the most studied CO2 utilization processes for producing carbon monoxide (CO). Besides being a potential sustainable alternative to traditional petrochemical feedstocks, it is also one of the most relevant and versatile C1 structural units in the fine chemical industry. It is a key component of industrial processes such as Fischer-Tropsch synthesis of hydrocarbons and alcohols, methanol carbonylation for large-scale acetic acid production, polymer production, and the synthesis of fine chemicals (e.g., olefin and alkyne carbonylation, olefin hydrogenation, carbonylation cross-coupling, and CH bond carbonylation, to name a few).

[0003] In reverse water-gas shift (RWGS) reactions, the performance of the catalyst plays a crucial role. Traditional RWGS catalysts, such as copper, platinum, and other noble metal-based catalysts, are known to effectively promote RWGS. The high CO selectivity of copper catalysts, coupled with their relatively low cost (alongside non-critical elements), makes them valuable candidates for this method. However, while exhibiting certain activity under specific conditions, they often suffer from low activity, unsatisfactory selectivity, and poor stability.

[0004] Transition metal carbides (TMCs) are a special class of abundant and relatively inexpensive materials with excellent physical properties, such as extremely high hardness, simple crystal structure, electrical and thermal conductivity, and good chemical and thermal stability. They also exhibit excellent activity and selectivity in many catalytic reactions. However, pure-phase molybdenum carbide also has shortcomings. β-Mo2C surfaces have strong adsorption and dissociation capabilities for H2, but their selectivity for CO is not high. Currently, the preparation of α-MoC and β-Mo2C composite molybdenum carbide catalysts mainly involves high-temperature calcination to partially convert the α-Mo2C phase into the α-MoC phase or vice versa, thereby obtaining the composite molybdenum carbide. This route is costly, and the composite phase ratio is difficult to control precisely. Summary of the Invention

[0005] The purpose of this invention is to provide a composite phase molybdenum carbide catalyst, its preparation method and application, which solves the problems of high preparation cost and difficulty in accurately controlling the composite phase ratio of existing composite phase molybdenum carbide catalysts.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a composite phase molybdenum carbide catalyst includes the following steps:

[0008] S1. Weigh out molybdenum salt and dissolve it in deionized water to obtain a molybdenum solution;

[0009] S2. Add Mo2N to the molybdenum solution to obtain a suspension;

[0010] S3. Heat and stir the suspension in a water bath until it reaches a gel state, and dry it at 50-120℃ to obtain the precursor.

[0011] S4. The precursor is carbonized in a reducing atmosphere to obtain a composite molybdenum carbide material containing α-MoC and β-Mo2C.

[0012] The carbonization conditions are as follows: heating to 500-680℃ in 1-5 hours, and carbonization time of 2-10 hours.

[0013] Furthermore, in S1, the molybdenum salt is one or more of ammonium molybdate, molybdic acid, molybdenum oxide, and molybdenum pentachloride.

[0014] Furthermore, in S3, the water bath temperature is 40-90℃.

[0015] Furthermore, in S4, the carbon source used for carbonization is CH4, urea, sucrose, glucose, or aniline.

[0016] Furthermore, in S2, the preparation process of the Mo2N is as follows:

[0017] MoO3 was prepared from ammonium molybdate using a template method; the MoO3 was then nitrided in a flowing nitrogen source to obtain Mo2N.

[0018] Furthermore, the nitriding conditions are as follows: heating to 500-700℃ in 1-3 hours and holding at that temperature for 1-3 hours.

[0019] Furthermore, the nitrogen source is ammonia or carbon nitride.

[0020] This invention discloses a composite phase molybdenum carbide catalyst prepared by the above preparation method. The composite phase molybdenum carbide catalyst contains α-MoC and β-Mo2C, and the ratio of α-MoC and β-Mo2C is controlled by the mass ratio of molybdenum salt and Mo2N.

[0021] This invention discloses the application of the aforementioned composite phase molybdenum carbide catalyst as a reverse water-gas shift catalyst in the reverse water-gas shift reaction.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] This invention discloses a method for preparing a composite phase molybdenum carbide catalyst. The method involves loading molybdenum salt onto Mo₂N via impregnation, followed by drying and carbonization to obtain the composite phase molybdenum carbide catalyst. This preparation method is reported for the first time and has advantages such as simple steps, readily available raw materials, and safe operation. Existing composite phase molybdenum carbide is obtained by high-temperature (≥800℃) carbonization of Mo₂N, and the composite phase ratio is uncontrollable. In contrast, this invention first prepares an AM / Mo₂N precursor, then carbonizes Mo₂N in a reducing atmosphere to obtain α-MoC, and the molybdenum salt provided by the molybdenum solution is carbonized to obtain β-Mo₂C. Therefore, by loading a molybdenum salt solution onto Mo₂N to obtain the precursor, and then carbonizing at 500-680℃, a composite phase molybdenum carbide catalyst with a controllable ratio is obtained.

[0024] This invention also discloses a composite phase molybdenum carbide catalyst containing α-MoC and β-Mo2C. The ratio of α-MoC to β-Mo2C in the composite phase can be precisely controlled by adjusting the mass ratio of molybdenum salt to Mo2N. The composite phase molybdenum carbide catalyst prepared by this invention exhibits improved CO2 conversion efficiency compared to single-phase molybdenum carbide.

[0025] The present invention also discloses the application of the composite phase molybdenum carbide catalyst as a reverse water gas shift catalyst in the reverse water gas shift reaction. The catalyst obtained by the present invention has excellent CO2 conversion rate and CO selectivity of more than 95%. Attached Figure Description

[0026] Figure 1 The image shows the XRD pattern of the composite phase molybdenum carbide catalyst prepared in this invention.

[0027] Figure 2 This is a graph showing the CO2 conversion rate of the composite phase molybdenum carbide catalyst prepared in this invention.

[0028] Figure 3 The graph shows the rate and selectivity of the composite phase molybdenum carbide catalyst prepared in this invention.

[0029] Figure 4 This is a stability test diagram of the composite phase molybdenum carbide catalyst prepared in this invention;

[0030] Figure 5 This is a flowchart of the preparation method of the composite phase molybdenum carbide catalyst of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0032] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0033] This invention discloses a method for preparing a composite phase molybdenum carbide catalyst, comprising the following steps:

[0034] S1. Weigh out molybdenum salt and dissolve it in deionized water to obtain a molybdenum solution;

[0035] S2. Add Mo2N to the molybdenum solution to obtain a suspension;

[0036] S3. Heat and stir the suspension in a water bath until it reaches a gel state, and dry it overnight at 50-120℃ to obtain the precursor.

[0037] S4. The precursor is carbonized in a reducing atmosphere to obtain a composite molybdenum carbide material containing α-MoC and β-Mo2C.

[0038] Preferably, in S1, the molybdenum salt is one or more of ammonium molybdate tetrahydrate, molybdic acid, molybdenum oxide, and molybdenum pentachloride.

[0039] Preferably, in S3, the water bath temperature is 40-90℃.

[0040] Preferably, in S4, the carbon source used for carbonization is CH4, urea, sucrose, glucose, or aniline.

[0041] The carbonization process involves heating the temperature to 500-680℃ over 1-5 hours, with a carbonization time of 2-10 hours.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1

[0044] like Figure 5 As shown, this invention discloses a method for preparing a composite phase molybdenum carbide catalyst, comprising the following steps:

[0045] S1. Weigh 0.045g of ammonium molybdate tetrahydrate and dissolve it in 20mL of deionized water to obtain a molybdenum solution;

[0046] S2. Weigh 0.1g of the carrier Mo2N and add it to the molybdenum solution. Stir in a water bath at 75℃ until it reaches a gel state. Transfer it to a mixing oven and dry at 80℃ for 6 hours to obtain an AM / Mo2N mixture as a precursor.

[0047] S3. 0.055g of precursor is loaded into a quartz tube, and then a CH4 / H2 mixed gas (CH4:H2=1:3) is introduced with a total flow rate of 60mL / min. The temperature is then increased to 680℃ at 2℃ / min and held for 3h. After natural cooling, the composite phase molybdenum carbide catalyst is obtained, denoted as (75%)MoC / Mo2C.

[0048] Example 2

[0049] The same process was carried out as in Example 1. The similarities will not be repeated here. Only the differences will be explained below: 0.09 g of ammonium molybdate tetrahydrate was weighed to prepare a composite phase molybdenum carbide catalyst, denoted as (50%)MoC / Mo2C.

[0050] Example 3

[0051] The same process was carried out as in Example 1. The similarities will not be repeated here. Only the differences will be explained below: 0.135g of ammonium molybdate tetrahydrate was weighed to prepare a composite phase molybdenum carbide catalyst, denoted as (25%)MoC / Mo2C.

[0052] The 25%, 50%, and 75% figures above represent the proportion of α-MoC in the composite phase molybdenum carbide.

[0053] Example 4

[0054] Based on Example 3, ammonium molybdate tetrahydrate was replaced with molybdenum pentachloride, and the carbonization temperature was adjusted to 500℃ to prepare (25%) MoC / Mo2C.

[0055] Example 5

[0056] Based on Example 3, ammonium molybdate tetrahydrate was replaced with molybdenum oxide, and the carbonization temperature was adjusted to 600℃ to prepare (25%) MoC / Mo2C.

[0057] Example 6

[0058] Based on Example 3, ammonium molybdate tetrahydrate was replaced with molybdic acid, and the carbonization temperature was adjusted to 550℃ to prepare (25%) MoC / Mo2C.

[0059] Comparative Example 1

[0060] Weigh 0.1g of Mo2N precursor, place it in a quartz tube, and carbonize it at 680℃ for 3h. After natural cooling, the catalyst α-MoC can be obtained, but β-Mo2C is not obtained.

[0061] Comparative Example 2

[0062] Weigh 0.1g of MoO3 precursor, place it in a quartz tube, and carbonize it at 680℃ for 3h. Then wait for natural cooling to obtain the catalyst β-Mo2C. α-MoC was not obtained.

[0063] In the above embodiments, Mo2N was prepared by a template method, specifically:

[0064] First, dissolve 2.0g of P123 surfactant in 30mL of ethanol and 10mL of water;

[0065] Subsequently, 1.0 g of ammonium molybdate tetrahydrate was added to the solution;

[0066] Then add 3.0g of urea and stir for another hour. Transfer the resulting solution to a 100mL container with Teflon tubing and place it in an oven for hydrothermal treatment at 160℃ for 20h.

[0067] The resulting gel was then centrifuged at 5000 rpm for 30 min, rinsed three times with pure water, and then dried in an oven at 110 °C for 24 h.

[0068] Finally, the dried gel was calcined at 550°C for 6 hours in an air-filled furnace to obtain MoO3 material. The specific surface area of ​​the MoO3 material was 113.8 m². 2 g -1 A larger specific surface area can promote CO2 adsorption.

[0069] Weigh 0.5g of the obtained MoO3 material and add it to a quartz tube. Nitride it in a tube furnace with a flowing nitrogen source at a flow rate of 40mL / min. Wait for it to cool to room temperature and then remove it to obtain Mo2N.

[0070] The nitriding temperature is 500-700℃, the heating time is 1-3h, and the temperature holding time is 1-3h.

[0071] More specifically, the nitrogen source is ammonia or carbon nitride.

[0072] The materials prepared in Examples 1-3 and the two comparative examples were subjected to diffraction analysis to obtain XRD patterns, as shown below. Figure 1 As shown, the characteristic peaks increase significantly with the increase of the α-MoC ratio, indicating that the composite phase molybdenum carbide was successfully synthesized.

[0073] like Figure 2As shown, the materials prepared in Examples 1-3 and the two comparative examples were used as catalysts for reverse water-gas shift reaction to test the CO2 conversion rate. With increasing reaction temperature, the composite phase molybdenum carbide catalyst exhibited higher activity compared to the single phase molybdenum carbide catalyst. The carbon monoxide selectivity of Comparative Example 2 was 95%, not significantly different from the examples, but its conversion rate was lower, only 0.81 times that of Example 3. The selectivity of Comparative Example 2 was only 84%, and its conversion rate was only 0.77 times that of Example 3.

[0074] The process of applying it as a catalyst for reverse water-gas shift reaction is as follows:

[0075] After crushing the catalyst to 40-80 mesh, take 0.05-1g and fill it into a quartz tube, then place it in a fixed-bed reactor for reaction evaluation.

[0076] Carbon dioxide and hydrogen are used as reactants, with a molar ratio of CO2:H2 = (1:1, 1:2, 1:3, 1:4). The gas hourly space velocity (GHSV) is 1000-200000 mL·g. -1 ·h -1 ,

[0077] The reaction pressure is at or near atmospheric pressure, and the reaction temperature is 200℃-400℃.

[0078] like Figure 3 As shown, the catalytic rate and selectivity of the reverse water-gas shift catalysts prepared in the embodiments and comparative examples of the present invention were tested. With the increase of the α-MoC ratio, the selectivity of the catalyst for CO gradually increased. However, in Comparative Example 1, the α-MoC showed weak hydrogen dissociation ability, resulting in a decreased conversion rate. In Comparative Example 2, the hydrogen dissociation ability was relatively strong, but the selectivity for CO was not high. The composite phase molybdenum carbide catalyst exhibited a superior catalytic rate compared to the single phase molybdenum carbide catalyst, and the CO selectivity increased with increasing α-MoC ratio.

[0079] like Figure 4 As shown, the stability of the reverse water gas shift catalysts prepared in the embodiments and comparative examples of the present invention was tested. During the 30-hour stability test, no deactivation was observed, indicating that the composite phase molybdenum carbide has excellent stability.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a composite phase molybdenum carbide catalyst for reverse water gas shift reaction, characterized by, The method comprises the following steps: S1, weighing molybdenum salt and dissolving it in deionized water to obtain a molybdenum solution; S2, adding Mo2N into the molybdenum solution to obtain a suspension; S3, heating and stirring the suspension in a water bath to a gel state, drying at 50-120 ℃ to obtain a precursor; S4, carbonizing the precursor in a CH4 / H2 mixed atmosphere to obtain a composite-phase molybdenum carbide material containing α-MoC and β-Mo2C; the ratio of α-MoC and β-Mo2C is regulated by the mass ratio of molybdenum salt and Mo2N; The carbonization conditions are: heating to 500-680 ℃ in 1-5 h, and carbonization time is 2-10 h.

2. The method for preparing a composite phase molybdenum carbide catalyst for reverse water gas shift reaction according to claim 1, characterized in that, In S1, the molybdenum salt is ammonium molybdate and / or molybdenum pentachloride.

3. The method for preparing a composite phase molybdenum carbide catalyst for a reverse water-gas shift reaction according to claim 1, characterized in that, In S3, the water bath temperature is 40-90 ℃.

4. The method for preparing a composite phase molybdenum carbide catalyst for reverse water-gas shift reaction according to claim 1, characterized in that, In S2, the preparation process of Mo2N is: Using a template method to prepare MoO3 from ammonium molybdate; nitriding MoO3 in a flowing nitrogen source to obtain Mo2N.

5. The process for the preparation of a composite phase molybdenum carbide catalyst for reverse water gas shift reaction as claimed in claim 4 wherein, The nitriding conditions are: heating to 500-700 ℃ in 1-3 h, and holding for 1-3 h.

6. A method for preparing a composite phase molybdenum carbide catalyst for reverse water gas shift reaction according to claim 4, characterized in that, The flowing nitrogen source is ammonia.

7. A composite phase molybdenum carbide catalyst for reverse water gas shift reaction prepared by the production method according to any one of claims 1 to 6, characterized in that, The composite-phase molybdenum carbide catalyst contains α-MoC and β-Mo2C.

8. Use of the catalyst of claim 7 as a reverse water gas shift catalyst in a reverse water gas shift reaction.

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