Low-defect molecular sieve supported cobalt catalyst for propane dehydrogenation and preparation method thereof

Abstract

The invention discloses a low-defect molecular sieve supported cobalt catalyst for propane dehydrogenation and a preparation method thereof. The cobalt-based molecular sieve catalyst comprises a low-defect molecular sieve (L-Zeoliite) carrier and an active component cobalt loaded on the molecular sieve carrier. The preparation method of the Co / L-Zeoliite catalyst comprises the following steps: repairing defects of the defective molecular sieve carrier, and loading the active component cobalt on the low-defect molecular sieve. According to the method, various commodities or self-made molecular sieves are adopted, the low-defect molecular sieve carrier is synthesized through innovative alkali liquor repairing, monatomic Co or ultra-small CoO clusters can be limited to the low-defect molecular sieve through the method, and the activity of the molecular sieve catalyst is far higher than that of a conventional defect (silicon hydroxyl nest) limited Co molecular sieve catalyst and is higher than that of most noble metal-based catalysts. In addition, the invention further provides a process for synthesizing the catalyst through a one-pot method, the dosage of active metal is greatly reduced, the synthesis process is simplified, the applicability to raw materials and carriers is high, and the application prospect is good.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, specifically relating to a low-defect molecular sieve supported cobalt catalyst for propane dehydrogenation and its preparation method. Background Technology

[0002] Propylene, as a cornerstone of modern chemical industry, is in ever-increasing demand. Currently, the main production methods for propylene rely on byproducts such as naphtha cracking and petroleum catalytic cracking. These traditional processes are no longer sufficient to meet the growing market demand; therefore, developing more efficient propylene production technologies is urgently needed. Propane dehydrogenation (PDH) technology has attracted much attention due to its ability to directly produce propylene from propane, its single product, and its directional production capabilities. It is considered a highly promising propylene production route and has become the world's third-largest source of propylene. The abundant and inexpensive propane resources brought about by the shale gas revolution provide a cost advantage for PDH technology. Furthermore, the PDH process exhibits high propylene selectivity and ease of separation, making it an ideal propylene production route.

[0003] Currently, Pt-based and Cr-based catalysts are mainly used in industry for propane dehydrogenation. While Pt-based catalysts exhibit excellent CH bond activation ability and high selectivity, their sintering and carbon deposition characteristics lead to poor catalytic stability. Although Cr-based catalysts show high activity at low temperatures, they are prone to initiating side reactions, and their toxicity limits their application. Therefore, developing environmentally friendly catalysts with superior performance is crucial for the development of PDH technology.

[0004] In recent years, transition metal oxides have gained popularity due to their excellent dehydrogenation performance and cost advantages. Transition metal oxides, including vanadium, nickel, and zinc, have all exhibited certain dehydrogenation activities. Among them, cobalt, as a common transition metal, has attracted widespread attention for its ability to efficiently activate CH bonds and selectively generate alkenes.

[0005] Although the catalytic activity of Co-based catalysts is widely recognized, they have not yet been commercially applied because their catalytic activity, production cost, and catalyst lifetime are significantly lower than those of commercially available Pt-based and Cr-based catalysts, making them uncompetitive. The performance of Co-based catalysts is highly dependent on preparation conditions, such as the loading method and loading amount. Furthermore, differences in the specific surface area, acidity, and crystal planes of different supports all affect the interaction between Co particles and the support, thereby altering the dehydrogenation active sites and dehydrogenation capacity on the surface. Chinese patent CN106391073A discloses a cobalt-based catalyst for olefin production from syngas. This catalyst is prepared by precipitation or impregnation methods and uses alkali metal promoters to enhance its performance. Although it exhibits high olefin selectivity and conversion, its catalytic stability is poor due to the high cobalt loading and poor dispersibility. Chinese patent CN111589449A discloses a Co-based catalyst on a sheet-like Al2O3 support prepared by a one-step hydrothermal synthesis method. This catalyst has high dehydrogenation activity and stability, but its olefin selectivity is insufficient. Chinese patent CN111672529A discloses a cobalt-nitrogen-carbon catalyst supported on nano-carbon. This catalyst is prepared through a complex process of complexation, impregnation, calcination, and acid washing. It exhibits high activity and selectivity under anhydrous and oxygen-free conditions, but its cumbersome process is unsuitable for industrial applications. Although these preparation methods use simple supports, reducing costs, their synthesis is complex, and their catalytic activity is far lower than that of industrially available precious metals, resulting in low commercial competitiveness. Furthermore, using alumina or other amorphous supports easily leads to sintering, causing active sites to agglomerate and form large cobalt particles, resulting in reduced activity and propane cracking. Therefore, besides improving catalytic activity and controlling costs, another challenge for cobalt-based catalysts is improving their regeneration performance and reducing the loading.

[0006] Traditional cobalt-based catalysts still face bottlenecks in terms of cost, activity, selectivity, and lifetime. To overcome these limitations, molecular sieve-confined catalysts have emerged. Chinese patent CN115007200A reports a method and strategy for loading Co onto dealullated beta molecular sieves and anchoring confined active sites using defect sites (silanol nests) generated during dealullation. This method exhibits high activity and good regeneration performance. However, these strategies result in high concentrations of defects within the molecular sieve, often affecting its hydrothermal stability. Furthermore, the activity of these defect-anchored sites is difficult to achieve the levels of most precious metals. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) that is simple to prepare, has ultra-high activity and ultra-high stability, and its application in propane dehydrogenation reaction.

[0008] The low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) provided by the present invention includes a low-defect molecular sieve support (L-Zeolite) and an active component cobalt supported on the molecular sieve support;

[0009] The low-defect molecular sieve carrier is prepared by repairing defects in a molecular sieve carrier (H-Zeolite).

[0010] Specifically, the defective molecular sieve support (H-Zeolite) is repaired using a dilute alkaline solution.

[0011] The defective molecular sieve carrier (H-Zeolite) is a self-made or commercial molecular sieve carrier, including but not limited to Silicalite-1, Silicalite-2, ZSM-5, β molecular sieve, X molecular sieve, and Y molecular sieve.

[0012] The active component, cobalt, accounts for 0.01 to 5% of the total mass of the low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite).

[0013] The low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) may further include alkali metals and / or alkaline earth metals;

[0014] The alkali metal and / or alkaline earth metal account for 0-2% of the total mass of the low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite).

[0015] The aforementioned low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) was prepared by a method comprising the following steps:

[0016] 1) Preparation of low-defect molecular sieve support L-Zeolite

[0017] A dilute alkaline solution was mixed with H-Zeolite support, heated and stirred, filtered, dried, and calcined to obtain the low-defect molecular sieve support L-Zeolite.

[0018] 2) Preparation of Co-L-Zeolite catalyst

[0019] The Co precursor solution was impregnated onto the low-defect molecular sieve support L-Zeolite obtained in step 1), stirred, filtered, dried, and calcined to obtain the low-defect molecular sieve supported cobalt catalyst Co / L-Zeolite.

[0020] In step 1) of the above method, the dilute alkaline solution is a dilute aqueous solution or alcoholic solution of an organic or inorganic base, such as an aqueous solution of dilute sodium hydroxide, sodium bicarbonate, ammonium bicarbonate, ammonia, ethylenediamine, trimethylamine, tetrapropylammonium hydroxide, n-butylamine, etc., specifically an aqueous solution of ethylenediamine.

[0021] The mass ratio of solute, solvent and H-Zeolite carrier in the dilute alkaline solution can be (0.0001-0.01):(1-100):(1-15), specifically 0.01:30:1;

[0022] The heating and stirring temperature can be 65-150℃, specifically 80-150℃, more specifically 85℃, and the time can be 0.5-96h, specifically 10h;

[0023] The drying process involves drying at 40-200℃ for 4-24 hours, specifically drying at 60℃ for 8 hours.

[0024] The calcination is carried out by heating to 200-650℃ at a heating rate of 0.5-20℃ / min and holding at that temperature for 0.5-12 hours, specifically calcining at 550℃ for 6 hours at a heating rate of 2℃ / min.

[0025] In step 2) of the above method, the Co precursor solution includes cobalt salt, ligand, and water;

[0026] The cobalt salt is at least one of cobalt chloride, cobalt nitrate, cobalt acetate, and their hydrates;

[0027] The mass ratio of the cobalt salt to the molecular sieve support L-Zeolite can be (0.001-0.005):1, specifically 0.0015:1;

[0028] The ligand may be at least one of the following: ammonia gas, ammonia water, trimethylamine, ethylamine, ethylenediamine, ethanolamine, triethylenediamine, etc., in solution or hydrate, or may be omitted; specifically, it may be ethylenediamine.

[0029] The molar ratio of cobalt salt to ligand in the Co precursor solution can be 0.01-3:1, specifically 0.3:1;

[0030] The stirring temperature can be 10-50℃, specifically 30℃, and the time can be 0-96h, with the endpoint 0 being undesirable; specifically, it can be 1-24h or 12h.

[0031] The drying process involves drying at 40-200℃ for 4-24 hours, specifically drying at 60℃ for 10 hours.

[0032] The calcination is carried out by heating to 200-650℃ at a heating rate of 0.5-20℃ / min and holding at that temperature for 0.5-12 hours, specifically calcining at 550℃ for 6 hours at a heating rate of 2℃ / min.

[0033] In step 2) of the above method, when the basic ligand is an organic amine, the basic ligand can also be used as a dilute alkali. Steps 1) and 2) of the above method can be combined, that is, the cobalt salt solution is heated and stirred together with the molecular sieve and the basic ligand at room temperature, stirred, filtered, dried and calcined, which is a one-pot method for preparing catalyst.

[0034] The heating and stirring temperature can be 65-150℃, specifically 80-150℃, or more specifically 85℃, and the time can be 0.5-96h, specifically 10h.

[0035] The stirring temperature at room temperature can be 30℃, and the time can be 0 to 96 hours. The endpoint of 0 is not advisable. Specifically, it can be 1 to 24 hours or 12 hours.

[0036] Basic ligands (i.e., organic amines) can repair defects while loading metals. The heating process can both repair defects and load metals, thus obtaining a low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite).

[0037] The above method can be further improved by adding a third auxiliary precursor, such as soluble salts of alkali metals and / or alkaline earth metals (e.g., potassium chloride, cesium chloride, calcium chloride, indium nitrate, etc.) to the Co precursor solution in step 2) to increase propylene selectivity.

[0038] The aforementioned low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) is used in the oxygen-free dehydrogenation of low molecular weight alkanes to olefins.

[0039] The low molecular weight alkane can be selected from: ethane, propane, and butane.

[0040] Specifically, the aforementioned low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) is used in the oxygen-free dehydrogenation of ethane, propane, and butane to produce ethylene, propylene, and butadiene.

[0041] Compared with cobalt molecular sieve catalysts prepared by the traditional defect anchoring method, the low-defect molecular sieve supported cobalt catalyst prepared by this invention has significantly higher dehydrogenation activity, stronger Lewis acidity at the sites, and the surface metal sites are more inclined to form strained single-atom Lewis acidic cobalt active centers. By repairing the defects of the molecular sieve, its acidity and hydrothermal stability are significantly improved, the conversion frequency per unit active site is significantly higher, it is suitable for reactions at ultra-high space velocities, its activity exceeds that of most noble metals, and it has slow deactivation and low price.

[0042] This invention repairs defects in conventional defective molecular sieves using a low-alkalinity hydrothermal-mediated method to synthesize a low-defect molecular sieve support. Subsequently, strained cobalt Lewis acid active sites are formed by impregnating a cobalt precursor solution. The preparation method is simple and exhibits excellent activity, stability, and propylene selectivity at low loading (0.1 wt%) and ultra-high space velocities. Compared with molecular sieve catalysts that have not undergone defect repair, the activity is improved by orders of magnitude.

[0043] To further enhance the stability and activity of Co-based catalysts, this invention makes the following innovations: First, regarding the molecular sieve support, this invention utilizes various commercial or self-made molecular sieves, synthesizing low-defect molecular sieves through innovative alkaline repair. Using these as supports, this invention provides a method for confining single-atom Co or ultrasmall CoO clusters within the strain sites of the molecular sieve. Compared to conventional molecular sieve catalysts with defect (silanol nests) confining Co, the active sites synthesized in this invention form stronger Lewis acidic cobalt, resulting in an order of magnitude higher dehydrogenation activity at low loading (0.1 wt%) and high space velocities (from...). Figure 5 The difference in acidity can be seen from the high air velocity. Figure 7 The difference in intrinsic activity is evident (it's an order of magnitude), even surpassing most noble metal-based catalysts. Furthermore, the low-defect support exhibits higher hydrothermal stability, which improves the catalyst's regeneration stability. Attached Figure Description

[0044] Figure 1 Transmission electron microscope (TEM) images of (a) Co / H-Zeolite prepared in Comparative Example 1 and (b) Co / L-Zeolite prepared in Example 2.

[0045] Figure 2 The in-situ FTIR images are of H-Zeolite and L-Zeolite prepared in Example 1, Co / L-Zeolite prepared in Example 2, and Co / H-Zeolite prepared in Comparative Example 1.

[0046] Figure 3 The images show the H2-TPR diagrams of Co / L-Zeolite prepared in Example 2, Co / H-Zeolite prepared in Comparative Example 1, and Co-H-Zeolite (IM) prepared in Comparative Example 2.

[0047] Figure 4 XRD patterns of H-Zeolite and L-Zeolite prepared in Example 1, Co / L-Zeolite prepared in Example 2, and Co / H-Zeolite prepared in Comparative Example 1.

[0048] Figure 5The images show in-situ FTIR images of deuterated acetonitrile adsorption of Co / L-Zeolite prepared in Example 2 and Co / H-Zeolite prepared in Comparative Example 1.

[0049] Figure 6 The propane conversion and propylene selectivity of Co / L-Zeolite prepared in Example 2 and Co / H-Zeolite prepared in Comparative Example 1 are shown.

[0050] Figure 7 Propane conversion and propylene selectivity of Co / L-Zeolite (YG) prepared in Example 3.

[0051] Figure 8 Propane conversion and propylene selectivity of Co / L-Zeolite (Z5) prepared in Example 4.

[0052] Figure 9 The propane conversion and propylene selectivity of Co / H-Zeolite (IM) prepared in Comparative Example 2 are given.

[0053] Figure 10 The figures show the propylene formation rates at high propane space velocities for the Co / H-Zeolite catalyst prepared in Comparative Example 1 and the Co / L-Zeolite catalyst prepared in Example 2, respectively.

[0054] Figure 11 The image shows the water resistance test results for Co / L-Zeolite in Example 7. Detailed Implementation

[0055] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0056] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0057] In the following examples, the defective homemade molecular sieve or commercially available molecular sieve carrier is referred to as: H-Zeolite;

[0058] The defect-repaired molecular sieve carrier is represented as: L-Zeolite;

[0059] Defective catalysts containing cobalt, alkali metals, etc., are represented as: Co / H-Zeolite;

[0060] Low-defect catalysts containing cobalt, alkali metals, etc., are denoted as Co / L-Zeolite.

[0061] Example 1: Preparation of low-defect molecular sieve support L-Zeolite

[0062] Weigh 0.01 g of ethylenediamine monohydrate and dissolve it in 30 mL of deionized water to prepare two identical solutions. Weigh 1 g of high-defect molecular sieve H-Zeolite molecular sieve powder (prepared in the laboratory; synthesis method: stir 60 g of 40% tetrapropylammonium hydroxide aqueous solution, 85 g of tetraethyl silicate and 250 g of water at room temperature for 20 hours, then reflux the mixture at 85 °C for 2 days, then centrifuge and wash, dry the solid at 60 °C for 8 hours, and then calcine at 550 °C for 6 hours at a heating rate of 2 °C / min to obtain Silicalite-1 powder, named H-Zeolite). Add the powder to the two solutions respectively, heat and stir (heat and stir at 85 °C for 10 hours), then filter, dry the powder at 60 °C for 8 hours, and calcine at 550 °C for 6 hours at a heating rate of 2 °C / min to obtain the low-defect molecular sieve support L-Zeolite.

[0063] Example 2: Preparation of Co / L-Zeolite Samples

[0064] 0.005 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.005 g of ethylenediamine monohydrate were dissolved in 30 mL of deionized water to prepare a solution. 1 g of the low-defect molecular sieve L-Zeolite powder synthesized in Example 1 was added to the above solution. The mixture was stirred overnight at room temperature under sealed conditions. Then, Co / L-Zeolite was synthesized through the same filtration, drying, and calcination process as in Example 1. The loading was 0.1 wt%.

[0065] Example 3: One-pot preparation of Co / L-Zeolite (YG) samples (alternative synthesis method)

[0066] 0.005 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.005 g of ethylenediamine monohydrate were dissolved in 30 mL of deionized water to prepare a solution. 1 g of H-Zeolite powder (prepared in Example 1) was added to the solution, and the mixture was heated and stirred at 85°C for 10 h. The mixture was then stirred overnight at room temperature under sealed conditions. Co / L-Zeolite was obtained by filtration, drying, and calcination as in Example 1. This one-pot synthesized highly active sample is called Co / L-Zeolite (YG). The loading was 0.1 wt%.

[0067] Example 4: Preparation of Co / L-Zeolite (Z5 YG) Samples (One-Pot Method)

[0068] 0.028 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.03 g of ethylenediamine monohydrate were dissolved in 30 mL of deionized water to prepare a solution. 1 g of ZSM-5 powder (purchased from Nankai University Chemical Reagent Factory, trade name NKF-5-800H, silicon-to-aluminum atomic ratio 430, https: / / www.nkcatalyst.com / productinfo / 797562.html) was added to the above solution. The mixture was heated and stirred at 85°C for 10 h; then stirred overnight at room temperature under sealed conditions. Co / L-Zeolite was then synthesized by filtration, drying, and calcination as in Example 1. This sample was named Co / L-Zeolite (Z5 YG). The loading was 0.5 wt%.

[0069] Comparative Example 1: Preparation of Co / H-Zeolite Samples

[0070] 0.005 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and 0.008 g of ethylenediamine monohydrate were dissolved in 30 mL of deionized water to prepare a solution. 1 g of H-Zeolite powder (prepared in Example 1) was added to the solution, and the mixture was stirred overnight at room temperature under a sealed container. Then, Co / H-Zeolite was synthesized through the same filtration, drying, and calcination process as in Example 1. The loading was 0.1 wt%.

[0071] Comparative Example 2: Sample Preparation by Co / H-Zeolite (IM) Impregnation Method

[0072] The catalyst Co / H-Zeolite(IM) was prepared using an equal-volume impregnation method. 0.005 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in an appropriate amount of deionized water to prepare a solution with a volume equal to that of 1 g of molecular sieve with the same water absorption rate. 1 g of H-Zeolite molecular sieve powder (prepared in Example 1) was added to the above solution and stirred until homogeneous. Then, Co / H-Zeolite(IM) was synthesized through the same drying and calcination process as in Example 1. The loading was 0.1 wt%.

[0073] Example 5

[0074] The defects and morphology of Co / L-Zeolite prepared in Example 2 and Co / H-Zeolite prepared in Comparative Example 1 were observed using high-resolution transmission electron microscopy (HRTEM). The crystal phase composition of the catalysts was analyzed using X-ray diffraction (XRD). The redox performance of the catalysts was analyzed using hydrogen temperature-programmed reduction (H2-TPR). The concentration and distribution of defects (silanol groups) in the catalysts were analyzed using in-situ FTIR, and the acidity properties of the catalysts were analyzed using deuterated acetonitrile adsorption infrared spectroscopy.

[0075] Figure 1 High-resolution transmission electron microscopy (HRTEM) images of Co / L-Zeolite prepared in Example 2 and Co / H-Zeolite prepared in Comparative Example 1 are shown. The results indicate that the prepared molecular sieve catalysts possess spherical nanostructures, with particle sizes of approximately 100-200 nm. Co / H-Zeolite has rougher edges, while Co / L-Zeolite has smoother edges, indicating that defects on the outer surface of the molecular sieve were reduced after defect repair, and that silicon rearrangement and annealing occurred. Furthermore, there was no significant aggregation of Co species on the surface, indicating a highly dispersed active phase.

[0076] Figure 2 The in-situ hydroxyl infrared spectra of the H-Zeolite, L-Zeolite, and Co / H-Zeolite and Co / L-Zeolite catalysts prepared in Examples 1 and 2 and Comparative Example 1 are shown. Some defects in the molecular sieve exist in the form of silanol groups. H-Zeolite and Co / H-Zeolite have a large number of silanol groups, while the peak areas of L-Zeolite and Co / L-Zeolite are significantly reduced, indicating that defect repair reduces the concentration of silanol groups.

[0077] Figure 3 The H2-TPR curves of the Co / L-Zeolite catalyst prepared in Example 2 and the Co / H-Zeolite catalyst prepared in Comparative Example 1 show that neither of them has a significant reduction peak in the range of 300–890 °C, indicating that the Co species are tightly bound to the support in the form of single atoms and are difficult to be reduced.

[0078] Figure 4 The XRD patterns of H-Zeolite and L-Zeolite prepared in Example 1, Co / L-Zeolite catalyst prepared in Example 2, and Co / H-Zeolite catalyst prepared in Comparative Example 1 show that all four exhibit obvious diffraction peaks of MFI molecular sieves and are highly crystalline without any impurity phases. This indicates that defect repair and cobalt loading did not change the structure of the molecular sieves, and that cobalt is highly dispersed on the surface of the molecular sieves.

[0079] Figure 5 The in-situ deuterated acetonitrile infrared spectra of the Co / L-Zeolite catalyst prepared in Example 2 and the Co / H-Zeolite catalyst prepared in Comparative Example 1 were obtained at 2275 cm⁻¹. -1 The nearby peaks represent the signal of deuterated acetonitrile adsorbed on the silanol groups, indicating that the Co / L-Zeolite catalyst has a lower concentration of silanol groups. No CoO or Co clusters were observed in the spectrum. 3+ The signal indicates that the Co species on the catalyst are mainly in the form of single-atom Co. 2+ Mainly. At 2308cm -1The signal is attributed to deuterated acetonitrile in a single-atom Lewis acidic Co 2+ The adsorption at the site can be seen from the peak area comparison of Co / L-Zeolite. 2+ The single atom exhibits stronger Lewis acidity due to the structural strain of the low-defect molecular sieve synthesized by this method.

[0080] Example 6

[0081] The performance evaluation of each catalyst is as follows:

[0082] Catalyst activity testing method: The catalytic experiment was conducted in a quartz tube reactor with an inner diameter of 8 mm. The quartz tube contained 0.1 g of catalyst, fixed at both ends with quartz wool, and approximately 1 g of quartz sand was added to the top. Before the reaction, a 1-hour pre-treatment was performed (from room temperature to 600℃ over one hour, with nitrogen gas introduced during the heating process at a total flow rate of 10 ml / min). The reaction was then carried out at 600℃, atmospheric pressure, and a total flow rate of 15 ml / min (propane content 100%). The catalytic products were analyzed online using gas chromatography, and the catalyst conversion and selectivity were analyzed using computer software and formulas. The propane conversion rate X (C3H8) and propylene selectivity S (C3H6) were calculated using the following formulas.

[0083]

[0084] The activity test results are attached. Figure 6-11 As shown.

[0085] The activity of the Co / L-Zeolite and Co / H-Zeolite catalysts prepared in Example 2 and Comparative Example 1 was evaluated, and the results are as follows: Figure 6 As shown, Co / L-Zeolite achieves a propane conversion of approximately 40% and a propylene selectivity exceeding 90%. During high-space-velocity, long-duration reactions, the low-defect catalyst Co / L-Zeolite deactivates slowly, maintaining near-equilibrium conversion, and its propylene selectivity remains almost unchanged. The intrinsic activity of Co / L-Zeolite surpasses that of most noble metal catalysts, achieving high-space-velocity (HSV) conversion of pure propane (15 h⁻¹) at 600 °C. -1 In this process, the conversion rate is close to the equilibrium conversion rate of propane dehydrogenation, at which point the propylene formation rate exceeds 140 mol / g. Co / h. Co / H-Zeolite exhibits almost no activity, and its propylene selectivity is below 70%, nearly matching that of propane thermal cracking. This indicates that the Co single-atom catalyst synthesized under low-defect conditions possesses higher activity than single-atom cobalt confined within a hydroxyl nest.

[0086] Furthermore, the catalyst Co / L-Zeolite(YG) synthesized by the alternative synthesis method in Example 3 was tested, and the results are as follows: Figure 7 As shown, the one-pot synthesized catalyst Co / L-Zeolite (YG) has an activity close to that of Co / L-Zeolite, and it operates stably at near-equilibrium conversion rate under high space velocity. The one-pot method combines defect repair and cobalt loading into one step, which greatly simplifies the operation and saves time.

[0087] like Figure 8 As shown, the catalyst prepared in Example 4 was applied to the propane dehydrogenation reaction and achieved performance close to that of Co / L-Zeolite, demonstrating that commercial supports and aluminous molecular sieves can also be used in the method of this invention, indicating the universality of this method.

[0088] Figure 9 To compare the propane dehydrogenation performance of the Co / H-Zeolite (IM) catalyst synthesized by the high-defect molecular sieve impregnation method prepared in Comparative Example 2, the results show that, under the same loading (0.1 wt%), the performance of the catalyst synthesized by the conventional hydroxyl nest anchoring and impregnation methods is far lower than that of the Co / L-Zeolite catalyst obtained in this invention.

[0089] Similarly, the intrinsic activity of the catalyst Co / H-Zeolite prepared in Comparative Example 1 and the catalyst Co / L-Zeolite prepared in Example 2 for increasing high space velocities was tested, and the results are as follows: Figure 10 As shown, the results indicate that Co / L-Zeolite exhibits an intrinsic activity one order of magnitude higher than that of the traditional hydroxyl-confined catalyst Co / H-Zeolite, further demonstrating the reliability of this method.

[0090] Example 7: Water resistance test of sample Co / L-Zeolite

[0091] Except for changing the propane space velocity to 22.5 h⁻¹ -1 Except for the propane dehydrogenation test, the other test conditions were completely consistent with those in Example 6. After testing Co / L-Zeolite at 600°C for 20 minutes, 100 times the mass of the catalyst was uniformly vaporized in a gasifier, and nitrogen was used to introduce it into the catalyst bed for hydrothermal treatment.

[0092] Activity results before and after treatment are as follows Figure 11 As shown, since the zeolite framework is prone to collapse under high-temperature hydrothermal conditions, water resistance is an important indicator for evaluating industrial zeolite catalysts. It is evident that the low-defect Co / L-Zeolite catalyst maintains high performance even after treatment with hot water steam equivalent to 100 times its own mass, indicating that this catalyst has good water resistance.

[0093] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite), comprising a low-defect molecular sieve support (L-Zeolite) and an active component cobalt supported on the molecular sieve support; The low-defect molecular sieve carrier is prepared by repairing defects in a molecular sieve carrier (H-Zeolite).

2. The catalyst according to claim 1, characterized in that, The defective molecular sieve support (H-Zeolite) was repaired using a dilute alkaline solution.

3. The catalyst according to claim 1, characterized in that... The molecular sieve support is selected from at least one of the following: Silicalite-1, Silicalite-2, ZSM-5, ZSM-11, ZSM-22, β molecular sieve, Y molecular sieve, and USY molecular sieve; The active component, cobalt, accounts for 0.01 to 5% of the total mass of the low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite); The low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite) further comprises alkali metals and / or alkaline earth metals; The alkali metal and / or alkaline earth metal constitute 0-2% of the total mass of the low-defect molecular sieve supported cobalt catalyst (Co / L-Zeolite).

4. A method for preparing the Co / L-Zeolite catalyst according to any one of claims 1-3, comprising the following steps: 1) Preparation of low-defect molecular sieve support L-Zeolite A dilute alkaline solution was mixed with H-Zeolite support, heated and stirred, filtered, dried, and calcined to obtain the low-defect molecular sieve support L-Zeolite. 2) Preparation of Co-L-Zeolite catalyst The Co precursor solution was impregnated onto the low-defect molecular sieve support L-Zeolite obtained in step 1), stirred, filtered, dried, and calcined to obtain the low-defect molecular sieve supported cobalt catalyst Co / L-Zeolite.

5. The method according to claim 4, characterized in that: In step 1), the dilute alkaline solution is a dilute aqueous solution or alcoholic solution of an organic or inorganic base, and the base is at least one of sodium hydroxide, sodium bicarbonate, ammonium bicarbonate, ammonia, ethylenediamine, trimethylamine, and tetrapropylammonium hydroxide. The mass ratio of solute, solvent, and H-Zeolite carrier in the dilute alkaline solution is (0.0001-0.01):(1-100):(1-15); The heating and stirring temperature is 65-150℃, and the time is 0.5-96h; The drying process involves drying at 40-200℃ for 4-24 hours. The roasting process involves heating the temperature to 200-650℃ at a rate of 0.5-20℃ / min and holding the temperature for 0.5-12 hours.

6. The method according to claim 4, characterized in that: In step 2), the Co precursor solution comprises a cobalt salt, a ligand, and water; The cobalt salt is at least one of cobalt chloride, cobalt nitrate, cobalt acetate, and their hydrates; The mass ratio of the cobalt salt to the molecular sieve support L-Zeolite is (0.001-0.005):1; The ligand is at least one of the following: ammonia gas, ammonia water, trimethylamine, ethylamine, ethylenediamine, ethanolamine, and triethylenediamine, or none of these are added; The molar ratio of cobalt salt to ligand in the Co precursor solution is 0.01-3:1; The stirring temperature is 10-50℃, and the time is 0-96h. The roasting process involves heating the temperature to 200-650℃ at a rate of 0.5-20℃ / min and holding the temperature for 0.5-12 hours.

7. The method according to claim 4, characterized in that: In step 2), the basic ligand is an organic amine, and the method is as follows: the cobalt salt solution is heated and stirred together with the molecular sieve and the basic ligand at room temperature, then filtered, dried, and calcined, which is a one-pot method for preparing the catalyst. The heating and stirring temperature is 65-150℃, and the time is 0.5-96h. Stirring at room temperature for 0–96 hours.

8. The method according to claim 4, characterized in that: A third auxiliary precursor is added to the Co precursor solution in step 2). The precursor of the third auxiliary agent is a soluble salt of alkali metal and / or alkaline earth metal.

9. The application of the Co / L-Zeolite catalyst according to any one of claims 1-3 in the reaction of oxygen-free dehydrogenation of low molecular weight alkanes to olefins.

10. The application according to claim 9, characterized in that, The low molecular weight alkane is selected from: ethane, propane, and butane.

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