Mo-containing catalysts, methods for their preparation and use

Abstract

This invention relates to the technical field of catalysts, and discloses a Mo-containing catalyst, its preparation method, and its application. The catalyst contains active metal elements Mo, Zr, Ce, Y, and Al, wherein the active metal elements are in an oxidized state. The molar percentages of Mo, Zr, Ce, Y, and Al in the total active metal elements are each independently 10-30%, preferably 15-25%. By rationally designing the ratio of active metal elements in the catalyst, a fluorite phase structure is formed, improving the structural stability of the catalyst. When this catalyst is applied to the catalytic cracking of alkane to olefins, the olefin yield is significantly improved compared to traditional steam cracking under the same conditions.

Description

Technical Field

[0001] This invention relates to the technical field of catalysts, specifically to a Mo-containing catalyst, its preparation method, and its application. Background Technology

[0002] Light olefins play a crucial role in the chemical synthesis industry, and market demand for them is increasing. Currently, the main source of low-carbon olefins is the traditional steam cracking process, a thermal cracking reaction that often suffers from problems such as high reaction temperatures (>800℃), high energy consumption, large CO2 emissions, low olefin yield, and difficulty in regulating product distribution. Naphtha catalytic cracking refers to the process of cracking hydrocarbons to produce low-carbon olefins under the action of a catalyst. Compared with steam cracking technology, this technology has advantages such as improved selectivity for low-carbon olefins; lower cracking reaction temperature and energy consumption; increased flexibility in product distribution and improved olefin yield; reduced coking and CO2 emissions; and extended stable operation time of the unit. Therefore, naphtha catalytic cracking technology for producing low-carbon olefins is highly competitive.

[0003] Catalytic cracking catalysts commonly fall into two categories: metal oxides and molecular sieves. Molecular sieves utilize Brønsted acid sites to activate CH bonds, following a carbocation mechanism, effectively lowering the reaction temperature by 100-200℃ and producing a high-yield propylene product. However, molecular sieves exhibit high Brønsted acid activity, leading to severe carbon deposition and deactivation, poor structural stability, and poor resistance to high temperatures and moisture. Metal oxides catalyze alkane activation via a free radical mechanism, where surface lattice oxygen catalyzes alkane dehydrogenation, initiating a free radical reaction and producing a high-yield ethylene product. Their main advantages are high mechanical strength, resistance to high temperatures and moisture, and low carbon deposition. However, traditional oxides have limited surface lattice oxygen concentration, resulting in low intrinsic activity and requiring higher reaction temperatures, which in turn leads to the loss of active species and a decrease in activity.

[0004] High-entropy oxides are emerging multi-cationic solid solutions composed of five or more metallic elements, with each element accounting for 5%-35% of the total metallic content. They possess unique geometric compatibility and electronic structure, abundant multi-metallic active sites, high oxygen vacancy concentration, adjustable specific surface area, and high-temperature stable crystal structure. Through rational design of the multi-component structure of high-entropy oxides, it is hoped that the activity and stability of catalysts can be improved, achieving efficient and stable catalytic cracking of alkanes. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and to provide a Mo-containing catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the first aspect of the present invention provides a Mo-containing catalyst, wherein the catalyst contains active metal elements Mo, Zr, Ce, Y and Al, and the active metal elements are in an oxidized state; The molar percentages of Mo, Zr, Ce, Y, and Al in the total active metal elements are each independently 10-30%.

[0007] A second aspect of the present invention provides a method for preparing a Mo-containing catalyst, the method comprising: (1) The precursor is ball-milled to obtain precursor powder, wherein the precursor is a precursor providing five active metal elements: Mo, Zr, Ce, Y and Al; wherein, based on the metal elements, the molar percentage of Mo, Zr, Ce, Y and Al in the total amount of the precursor is independently 10-30%; (2) The obtained powder is roasted.

[0008] A third aspect of the present invention provides a catalyst prepared by the preparation method of the second aspect of the present invention.

[0009] The fourth aspect of this invention provides the application of the catalyst described in the first aspect, the catalyst prepared by the method described in the second aspect, or the catalyst described in the third aspect in the catalytic cracking of alkane to olefins.

[0010] Through the above technical solution, the present invention has at least the following beneficial effects: (1) The present invention improves the structural stability of the catalyst by rationally designing the ratio of active metal elements in the catalyst to form a fluorite phase structure.

[0011] (2) The preparation method of the present invention is simple. The catalyst with excellent performance can be obtained by ball milling and calcining the precursor.

[0012] (3) The Mo-containing catalyst prepared in this invention significantly improves the olefin yield in alkane catalytic cracking reaction compared with traditional steam cracking under the same conditions. Attached Figure Description

[0013] Figure 1 This is the XRD pattern of the catalyst obtained in Example 1; Figure 2 These are the SEM and EDS images of the catalyst obtained in Example 1. Figure 3 This is the XRD pattern of the catalyst obtained in Example 3; Figure 4 This is the XRD pattern of the catalyst obtained in Example 4; Figure 5 This is the XRD pattern of the catalyst obtained in Example 5. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] The first aspect of the present invention provides a Mo-containing catalyst, wherein the catalyst contains active metal elements Mo, Zr, Ce, Y and Al, wherein the active metal elements are in an oxidized state.

[0016] According to the present invention, the molar content of Mo, Zr, Ce, Y and Al as a percentage of the total active metal elements is independently 10-30%, for example, it can be 10%, 15%, 20%, 25%, 30%, or any two of the above values; preferably 15-25%, that is, the molar content of Mo as a percentage of the total active metal elements is 10-30%, preferably 15-25%; the molar content of Zr as a percentage of the total active metal elements is 10-30%, preferably 15-25%, and so on and may be the same or different.

[0017] According to the present invention, the preferred structural formula of the catalyst is (MoZrCeYAl)O. 2-δ , where δ represents the number of oxygen vacancies, 0 < δ ≤ 2.

[0018] According to the present invention, the catalyst is preferably a high-entropy oxide.

[0019] This invention optimizes the proportion of active metal elements to form a fluorite phase structure in the catalyst, thereby improving the structural stability of the catalyst. Therefore, preferably, the catalyst has a fluorite phase structure.

[0020] According to a preferred embodiment of the present invention, the catalyst has an average particle size of 100-300 μm.

[0021] A second aspect of the present invention provides a method for preparing a Mo-containing catalyst, the method comprising: (1) The precursor is ball-milled to obtain precursor powder, wherein the precursor is a precursor providing five active metal elements: Mo, Zr, Ce, Y and Al; wherein, based on the metal elements, the molar percentage of Mo, Zr, Ce, Y and Al in the total amount of the precursor is independently 10-30%, preferably 15-25%; (2) The obtained powder is roasted.

[0022] According to the present invention, the precursor can be a substance commonly used in the art that can provide Mo, Zr, Ce, Y and Al. Preferably, the precursor is an oxide, more preferably MoO3, ZrO2, CeO2, Y2O3 and Al2O3.

[0023] In a specific implementation, in step (1), the ball milling is carried out in a ball mill, which is one of a planetary ball mill, a vibratory ball mill, a stirred ball mill, or a drum ball mill.

[0024] In a specific implementation, in step (1), the precursor is mixed in a ball mill jar and then fed into a ball mill for ball milling. The ball mill jar is one of agate ball mill jar, zirconia ball mill jar, stainless steel ball mill jar, or corundum ball mill jar.

[0025] In a specific embodiment, in step (1), the ball milling conditions include a ball milling speed of 200-400 r / min, preferably 300-400 r / min, and a ball milling time of 5-30 h, preferably 10-20 h.

[0026] In a specific embodiment, in step (1), the number of grinding balls is 20-100, preferably 50-100, relative to 50g of material to be milled. The cross-sectional diameter of the grinding balls is 2-12mm. Preferably, the ratio of grinding balls with a cross-sectional diameter greater than or equal to 5mm to grinding balls with a cross-sectional diameter less than 5mm is 0.5-1.5.

[0027] In a specific implementation, in step (1), the ball milling method is alternating forward and reverse ball milling, and the alternation switching time is 2-30 minutes.

[0028] In a specific implementation, in step (2), the high-temperature calcination temperature is 800-1000℃, preferably 800-900℃, and the calcination time is 5-20 h, preferably 8-16 h. The calcination time refers to the time maintained at the calcination temperature. Further, the heating rate during calcination can be 2-20℃ / min.

[0029] A third aspect of the present invention provides a catalyst prepared by the preparation method of the second aspect of the present invention.

[0030] The fourth aspect of this invention provides the application of the catalyst described in the first aspect, the catalyst prepared by the method described in the second aspect, or the catalyst described in the third aspect in the catalytic cracking of alkane to olefins.

[0031] According to the present invention, the alkane can be a common alkane used for cracking to produce olefins. In a specific embodiment, the alkane is n-hexane. Correspondingly, when n-hexane is used as a cracking feedstock, the olefins obtained are mainly ethylene, propylene, and butadiene.

[0032] In a further embodiment, the reaction conditions include: a reaction temperature of 600-840°C, a reaction time of at least 1 h, and a weight hourly space velocity (WHSV) of 1-10 h⁻¹ for the alkane. -1 The weight ratio of water to alkanes is 0.5-5.

[0033] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0034] Unless otherwise specified, all reagents and materials used in the following examples were purchased from reputable chemical reagent suppliers and were of analytical purity.

[0035] Preparation Example 1 Five precursors—MoO3, ZrO2, CeO2, Y2O3, and Al2O3—each with a molar content of 20%, were weighed out and placed in a 100 mL ball mill jar. Five 10 mm diameter agate balls, 35 6 mm diameter agate balls, and 40 3 mm diameter agate balls were added. The ball mill jar was then fed into a planetary ball mill for high-energy ball milling. The milling mode was alternating between forward and reverse rotation, alternating every 15 minutes, at a rotation speed of 400 r / min, for a total milling time of 10 h. The resulting powder was then placed in a muffle furnace for high-temperature calcination, increasing the temperature by 5 °C / min to 900 °C and maintaining it for 12 h to obtain the Mo-containing catalyst.

[0036] Preparation Example 2 Same as preparation example 1, except that the calcination temperature is 800℃.

[0037] Preparation Example 3 Same as Preparation Example 1, except that the molar contents of MoO3, ZrO2, CeO2, Y2O3 and Al2O3 are 5%, 20%, 20%, 20% and 35%, respectively.

[0038] Preparation Example 4 Same as Preparation Example 1, except that the molar contents of MoO3, ZrO2, CeO2, Y2O3 and Al2O3 are 35%, 20%, 20%, 20% and 5%, respectively.

[0039] Preparation Example 5 Same as preparation example 1, except that the calcination temperature is 600℃.

[0040] Example 1 The catalyst prepared in Example 1 was evaluated for its performance in the catalytic cracking of hexane, specifically including the following steps: 20g of catalyst was weighed and loaded into a small-scale catalytic cracking reaction tube (the catalyst was filled with ceramic balls on both sides). The reaction tube was then sealed, and the temperature was raised to 750℃ under N2 purging. After 1 h, n-hexane was introduced into the reaction tube. The weight ratio of water to alkane was 1:1, and the weight hourly space velocity (WHSV) was 5 h⁻¹. -1 The reaction time was 1 h, and the reaction pressure was atmospheric pressure. The gaseous and liquid products were collected separately, and the reaction yield was calculated by chromatographic analysis. The results are shown in Table 1.

[0041] Example 2 Same as Example 1, except that the reaction temperature is 700°C.

[0042] Example 3 Same as Example 1, except that Preparation Example 2 is evaluated.

[0043] Comparative Example 1 Same as Example 1, except that Preparation Example 3 is evaluated.

[0044] Comparative Example 2 Same as Example 1, except that Preparation Example 4 is evaluated.

[0045] Comparative Example 3 Same as Example 1, except that Preparation Example 5 is evaluated.

[0046] Comparative Example 4 The catalytic cracking test tube was filled with ceramic balls, then sealed. The tube was heated to 750°C under N2 conditions. After 1 hour, n-hexane was introduced into the tube. The weight ratio of water to alkane was 1:1, and the weight hourly space velocity (WHSV) was 5 h⁻¹. -1 The reaction time was 1 h, and the reaction pressure was atmospheric pressure. The gaseous and liquid products were collected separately, and the reaction yield was calculated by chromatographic analysis. The results are shown in Table 1.

[0047] Test case The crystal structure of the catalyst prepared by X-ray diffraction was determined, and the results are as follows: Figure 1 (Preparation Example 1) and Figure 3-5 As shown in (Preparation Examples 3-5).

[0048] The surface morphology and elemental composition of the catalyst prepared in Example 1 were analyzed by scanning electron microscopy and X-ray energy dispersive spectroscopy. The results are as follows: Figure 2 As shown.

[0049] Table 1

[0050] Depend on Figure 1 and Figure 3-5 It can be seen that the catalyst prepared by this invention has a fluorite phase structure.

[0051] As shown in Table 1, the catalyst described above can effectively catalyze the cracking of n-hexane to olefins, and the yield of trienes continuously increases with increasing reaction temperature. At 750°C, the yield of trienes is about 10% higher than that of pure steam cracking at the same temperature, demonstrating the high activity and high-temperature stability of the prepared catalyst.

[0052] Depend on Figure 2 It can be seen that the average particle size of the catalyst is between 100-300 μm, and each particle is composed of crystals of about 100 nm in size, with the elements in the particle being evenly distributed.

[0053] The crystal structure and catalytic performance are optimal when the molar percentage of each metal element is between 10% and 30%; beyond this range, the catalytic performance deteriorates. Figure 1 , Figure 3 and Figure 4 XRD characterization results suggest that the catalyst structure may have split due to improper stoichiometry, failing to form a single-phase high-entropy oxide. The catalyst obtained under calcination at 600℃ exhibited poor catalytic performance. Figure 1 and Figure 5 Based on the XRD characterization results, this may be due to the failure to form a single-phase high-entropy oxide during low-temperature calcination.

[0054] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A Mo-containing catalyst, characterized in that, The catalyst contains an active metal element, which is Mo, Zr, Ce, Y and Al, and the active metal element is in an oxidized state; The molar content of Mo, Zr, Ce, Y and Al as a percentage of the total active metal elements is 10-30%, preferably 15-25%.

2. The catalyst according to claim 1, wherein, The structural formula of the catalyst is (MoZrCeYAl)O 2-δ wherein δ represents the number of oxygen vacancies, 0 < δ ≤ 2.

3. The catalyst according to claim 1, wherein, The catalyst is a high-entropy oxide; And / or, the catalyst has a fluorite phase structure; And / or, the average particle size of the catalyst is 100-300 μm.

4. A method for preparing a Mo-containing catalyst, wherein, The method includes: (1) The precursor is ball-milled to obtain precursor powder, wherein the precursor is a precursor that provides active metal elements Mo, Zr, Ce, Y and Al, wherein, based on the metal elements, the molar percentage of Mo, Zr, Ce, Y and Al in the total amount of the precursor is independently 10-30%, preferably 15-25%; (2) The obtained powder is calcined at a temperature greater than 600°C.

5. The preparation method according to claim 4, wherein, The precursor is an oxide that provides active metal elements such as Mo, Zr, Ce, Y and Al, preferably MoO3, ZrO2, CeO2, Y2O3 and Al2O3.

6. The preparation method according to claim 4, wherein, The ball milling is carried out in a ball mill, which is one of a planetary ball mill, a vibratory ball mill, a stirred ball mill, or a drum ball mill. And / or, the precursor is mixed in a ball mill jar and then fed into a ball mill for ball milling, wherein the ball mill jar is one of agate ball mill jar, zirconia ball mill jar, stainless steel ball mill jar, or corundum ball mill jar; And / or, the ball milling conditions include a ball milling speed of 200-400 r / min, a ball milling time of 5-30 h, a number of 20-100 ball milling balls relative to 50 g of material to be milled, and a cross-sectional diameter of 2-12 mm for the ball milling balls. Preferably, the ratio of the number of ball milling balls with a cross-sectional diameter greater than or equal to 5 mm to the number of ball milling balls with a cross-sectional diameter less than 5 mm is 0.5-1.

5. And / or, the ball milling method is alternating forward and reverse ball milling, with an alternation switching time of 2-30 minutes.

7. The preparation method according to claim 4, wherein, In step (2), the roasting temperature is 800-1000℃ and the roasting time is 5-20h.

8. The catalyst prepared by the method according to any one of claims 4-7.

9. The use of the catalyst according to any one of claims 1-3 or claim 8 in the catalytic cracking of alkane to olefins.

10. The application according to claim 9, wherein, The alkane is n-hexane; and / or, the catalytic cracking conditions include a reaction temperature of 600-840°C, a reaction time of at least 1 h, a weight hourly space velocity of the alkane of 1-10 h -1 , a weight ratio of water to alkane of 0.5-5.

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