Catalyst for preparing isophthalonitrile by ammoxidation method and preparation method and application thereof

Abstract

The invention discloses a catalyst for preparing isophthalonitrile through an ammoxidation method and a preparation method and application thereof.The catalyst is used for preparing isophthalonitrile through low-temperature efficient ammoxidation, and the preparation method comprises the steps that an aqueous solution of Fe, Co and Mn salt is adopted to be loaded on a-BNC, and sub-nano Fe-Co-Mn ternary nitride clusters are obtained; and nitriding the sub-nano Fe-Co-Mn ternary nitride cluster in a mixed gas of NH3 and H2 at the temperature of 300-340 DEG C to obtain the catalyst. Nitrogen vacancies on the surface of the nitride are used for activating NH3 to generate. NH2 free radicals, and high-selectivity C-H amination is achieved. The sub-nanocluster is anchored at the B-N defect site of the a-BNC carrier; limited elements such as V / Mo are not contained in the whole process. When the catalyst is used at the temperature of 300 DEG C, the yield of isophthalonitrile reaches 90.00%, the selectivity reaches 91.20%, and a new path is provided for green synthesis of high-end nitrile compounds.

Description

Technical Field

[0001] This invention relates to the field of non-precious metal catalysis and green fine synthesis technology, specifically to a catalyst based on iron-cobalt-manganese nitride / amorphous boron-nitrogen-carbon heterostructure interface for the synthesis of isophthalonitrile, its preparation method, and its application. Background Technology

[0002] isophthalonitrile is a key intermediate in the synthesis of high-performance polyimides, antidepressants, and the fluorescent whitening agent CBS-X, with a global annual demand exceeding 12,000 tons and growing at an annual rate of 8%. Its primary industrial synthesis route is the gas-phase ammonia oxidation method (using m-xylene as a raw material, a one-step reaction): .

[0003] This route achieves an atom economy of 82% and produces no wastewater, making it a key area for research and development in green processes.

[0004] However, its industrialization faces three major technological barriers: (1) The catalyst system is highly dependent on precious metal materials such as V / Mo, posing risks to the environment and supply chain. V-Sb-O system: Existing technology uses V2O5-Sb2O4 / C catalyst, with an IPN yield of 65–70% at 385℃; however, V2O5 is listed in the "Priority Controlled Chemicals List (Second Batch)" and its leaching toxicity exceeds the standard (V 5+ Release rate 0.6–1.2 mg / L > national standard 0.5 mg / L; during long-term operation, the volatilization of component V leads to severe activity decay (yield decrease of 25% after 1000 h).

[0005] (2) It is difficult to achieve both activity and selectivity in non-V / Mo systems. Using Co-Mn-Al spinel as a catalyst, the IPN selectivity was 68.2% at 380℃, and the yield was 61.5%; Co 3+ / Mn 4+ It has strong oxidizing power and easily initiates the opening of aromatic rings; CO x Selectivity > 8%. Using Fe-Bi-O composite oxide as a catalyst: introducing Bi enhances NH3 adsorption, but Bi is easily reduced to the metallic state; after 500 h, 32% of Bi is lost, and the yield decreases to 54% of the initial value. The fundamental problem is that existing non-V / Mo catalysts still rely on the Mars–van Krevelen mechanism (lattice oxygen involvement), and lattice oxygen activity is negatively correlated with selectivity—highly active lattice oxygen easily leads to C–C bond breakage.

[0006] In summary, existing ammonia oxidation catalysts, when applied to the synthesis of isophthalonitrile, still face three major technical bottlenecks: high toxicity, high energy consumption, and insufficient selectivity. Vanadium / molybdenum-containing systems pose environmental risks and are prone to over-oxidation; while non-vanadium / molybdenum systems lack efficient ammonia activation pathways, making it difficult to achieve both high yield and long lifespan. Therefore, there is an urgent need to develop a catalyst that does not rely on traditional ammonia oxidation active elements and can achieve highly selective conversion at low temperatures through a novel reaction mechanism, in order to overcome existing technological limitations and meet the pressing needs of green chemistry and high-end materials industries. Summary of the Invention

[0007] The purpose of this invention is to address the above-mentioned problems. This invention relates to the use of metal nitrides or nitrogen vacancy radical pathways for the ammoxidation of aromatics to synthesize nitrile substances, and provides a novel catalyst system that breaks through V / Mo dependence, achieving MPN selectivity ≥90%, reaction temperature ≤340℃, non-toxic elemental composition, and stability decay <15% over 2000 h.

[0008] This invention is mainly achieved through the following technical solutions: A catalyst for the preparation of isophthalonitrile by ammonia oxidation method is obtained by supporting an aqueous solution of Fe, Co, and Mn nitrates on a-BNC to obtain sub-nanometer Fe-Co-Mn ternary nitride clusters; the sub-nanometer Fe-Co-Mn ternary nitride clusters are nitrided in a mixture of NH3 and H2 at 300-340℃ to obtain the catalyst. (1) The a-BNC is an amorphous boron-nitrogen co-doped carbon support, wherein the B:N:C atomic ratio is 1:(1.8-2.5):(8-12). (2) The sub-nanometer Fe-Co-Mn ternary nitride cluster has the chemical formula Fe a Co b Mn c N, where a=1.0, b=1.0, c=1.0, and the cluster size is 0.8-1.6 nm; (3) The nitrogen vacancy concentration on the catalyst surface is ≥1.8×10 19 cm -3 .

[0009] A method for preparing a catalyst for the ammonia oxidation process to prepare isophthalonitrile includes the following steps: (1) Boric acid, melamine and glucose were measured according to the above atomic ratio and mixed in deionized water to prepare a suspension with a total solid content of 15~20wt.%; the suspension was transferred to a reaction vessel and hydrothermally reacted at 180℃ for 10~14h; after the reaction was completed, the product was naturally cooled to room temperature, washed 3 times with deionized water and 2 times with anhydrous ethanol, and vacuum dried at 80℃ for 12h; the dried product was placed in a tube furnace and carbonized at 600℃ for 2~3h with nitrogen flow rate of 50 mL / min and temperature increased at 3℃ / min; after natural cooling to room temperature, the product was ground through a 60-mesh sieve to obtain amorphous boron-nitrogen co-doped carbon support a-BNC; (2) Prepare a metal salt solution with a total metal concentration of 15wt.% by mixing Fe, Co and Mn salts in a metal molar ratio of 1:1:1. Load the solution onto an amorphous boron-nitrogen co-doped carbon support a-BNC using an equal volume impregnation method and dry at 120℃ for 4h to obtain sub-nanometer Fe-Co-Mn ternary nitride clusters. (3) Place the sub-nanometer Fe-Co-Mn ternary nitride clusters obtained in step (2) in a tube furnace, introduce a mixture of NH3 and H2 with a volume ratio of 9:1 and a flow rate of 80~120mL / min, and treat at a constant temperature of 300~340℃ for 3~5h; after the reaction is completed, cool naturally to below 100℃, and then switch to nitrogen protection to cool to room temperature to obtain the catalyst.

[0010] The hydrothermal reaction temperature in step (1) is 180℃ and the reaction time is 12h; the carbonization temperature is 600℃ and the carbonization time is 2h; the metal salt solution in step (2) is one or more of nitrate, acetate or hydrochloride; the nitriding temperature in step (3) is 320℃ and the nitriding time is 4h, and the volume ratio of NH3 to H2 is 9:1.

[0011] An application of a catalyst for the ammonia oxidation process to prepare isophthalonitrile is disclosed. The catalyst is used for the gas-phase ammonia oxidation of m-xylene to isophthalonitrile at a reaction temperature of 280-340℃, a molar ratio of m-xylene:ammonia:hydrogen of 1:3.0:5.0, and a gas hourly space velocity (GHSV) of 1300 h⁻¹. -1 .

[0012] The advantages of this invention over the prior art are: (1) High selectivity: IPN selectivity reaches 91.20%, and IPA byproducts <1%; (2) Low temperature and high efficiency: high yield reaction can be achieved at 300℃, with energy saving >20%; (3) Green and safe: All Fe / Co / Mn / B / N / C system, non-toxic, free of precious metals and strategically restricted elements; (4) Long lifespan: ≥96% yield retention rate after 2000 hours of operation (initial yield is 90.0%, and yield is 86.4% after 2000 hours of operation).

[0013] In summary, by leveraging the anchoring effect of the α-BNC support, this invention precisely controls the size of Fe-Co-Mn ternary nitride clusters between 0.8 and 1.6 nm, ensuring high exposure and size consistency of active sites. Simultaneously, it is the first to utilize nitrogen vacancies on the nitride surface to activate NH3 and generate ·NH2 radicals, achieving highly selective C–H amination via a radical relay pathway. This avoids excessive oxidation caused by lattice oxygen, overcoming the dual challenges of nitrides easily sintering and losing activity at temperatures above 400℃ and clusters larger than 10 nm, as well as the difficulty in stabilizing nitrogen vacancies due to the lack of an anchorable support. The isophthalonitrile obtained at 300℃ exhibits a selectivity of 91.20%, while the selectivity of the byproduct isophthalic acid is less than 1%, breaking the limitations of high-temperature reactions. This reduces the reaction temperature by 85℃ compared to conventional industrial reactions, resulting in overall energy savings of over 20% in the production process. Detailed Implementation

[0014] The following examples further illustrate the present invention, but the invention is not limited to these examples. The catalyst of the present invention is prepared using the approach of "support anchoring + low-temperature confined nitriding".

[0015] Example 1 (Optimal Example): A catalyst for the preparation of isophthalonitrile via ammonia oxidation method was prepared by adding 10.0 g boric acid, 7.7 g melamine, and 44.5 g glucose to 300 mL deionized water and stirring for 30 min to form a homogeneous suspension. The suspension was then transferred to a 500 mL reactor and hydrothermally reacted at 180 °C for 12 h. After the reaction, the mixture was allowed to cool naturally to room temperature. The product was washed with deionized water until the pH of the filtrate reached 7.1, then washed twice with anhydrous ethanol and vacuum dried at 80 °C for 12 h. The dried product was placed in a tube furnace and carbonized at 600 °C for 2 h under a high-purity nitrogen atmosphere at a flow rate of 50 mL / min, with the temperature increased at 3 °C / min. After cooling naturally to room temperature, the product was ground through a 60-mesh sieve to obtain approximately 50.3 g of α-BNC support. XRD analysis showed no sharp diffraction peaks, and the B:N:C atomic ratio was 1:2.2:10. 4.84 g of ferric nitrate, 3.66 g of cobalt nitrate and 3.58 g of manganese nitrate were dissolved in 40 mL of deionized water to prepare a metal salt solution. The solution was loaded onto an a-BNC support using an equal-volume impregnation method, allowed to stand at room temperature for 12 h, and dried at 120 °C for 4 h to obtain sub-nanometer Fe-Co-Mn ternary nitride clusters.

[0016] Sub-nanometer Fe-Co-Mn ternary nitride clusters were packed into a quartz boat and placed in a tube furnace. Under an atmosphere of ammonia to hydrogen (volume ratio 9:1, flow rate 100 mL / min), the temperature was increased to 320℃ at a rate of 2℃ / min and held constant for 4 h. After natural cooling to 80℃, nitrogen gas was switched to cool to room temperature, yielding the FeCoMnN / a-BNC catalyst (denoted as catalyst 1). The cluster size was 1.2 nm, and the nitrogen vacancy concentration was 2.1 x 10⁻⁶. 19 cm -3 The pore volume is 0.45 cm³. 3 / g.

[0017] Example 2 (Carrier Comparison: Boron-free Carrier): A catalyst for the ammonia oxidation process to prepare isophthalonitrile was developed, except that the α-BNC support was replaced with nitrogen-doped carbon (NC, without boron) prepared from urea / glucose. 20.0 g of urea and 110.0 g of glucose were dissolved in 300 mL of deionized water, hydrothermally heated at 180°C for 12 h, and then carbonized under nitrogen at 600°C for 2 h to obtain the NC support with an N:C atomic ratio of 1:6. Subsequent iso-volume impregnation loading of the NC support and nitriding in a tube furnace were performed as in Example 1, yielding a FeCoMnN / NC catalyst (denoted as catalyst 2) with a cluster size of 2.9 nm.

[0018] Example 3 (Nitriding Temperature Optimization): A catalyst for the preparation of isophthalonitrile by ammonia oxidation method is obtained by raising the nitriding temperature in the tube furnace to 360°C, and the other steps are the same as in Example 1, resulting in a FeCoMnN / a-BNC (360°C) catalyst (denoted as catalyst 3) with a cluster size of 3.5 nm.

[0019] Example 4 (Metal composition optimization: iron-free): A catalyst for the ammonia oxidation method to prepare isophthalonitrile, except that ferric nitrate is not added when preparing the metal salt solution, and only 3.66 g of cobalt nitrate and 3.58 g of manganese nitrate (Co:Mn molar ratio = 1:1) are used, the remaining steps are the same as in Example 1, yielding Co. 1.0 Mn 1.0 The N / a-BNC catalyst (denoted as catalyst 4) has a cluster size of 1.3 nm.

[0020] Example 5 (Comparison of Metal Salt Types): A catalyst for the preparation of isophthalonitrile by ammonia oxidation method is obtained by replacing the metal salt in the preparation of the metal salt solution with acetate: 4.66 g ferric acetate, 4.98 g cobalt acetate and 4.90 g manganese acetate. The remaining steps are the same as in Example 1, resulting in FeCoMnN / a-BNC (acetate) catalyst (denoted as catalyst 5).

[0021] Example 6 (Minimum Material Ratio): A catalyst for the preparation of isophthalonitrile by ammonia oxidation method is obtained by changing the amount of boric acid, melamine and glucose to make the B:N:C atomic ratio in the a-BNC support = 1:1.8:8. The remaining steps, as well as the subsequent metal loading and nitriding steps, are the same as in Example 1, and the resulting catalyst (denoted as catalyst 6) has a cluster size of 1.2 nm.

[0022] Example 7 (Highest Material Ratio): A catalyst for the preparation of isophthalonitrile by ammonia oxidation method is obtained by changing the amount of boric acid, melamine and glucose to make the B:N:C atomic ratio in the a-BNC support = 1:2.5:12. The remaining steps, as well as the subsequent metal loading and nitriding steps, are the same as in Example 1, and the resulting catalyst (denoted as catalyst 7) ​​has a cluster size of 1.3 nm.

[0023] Comparative Example 1 (non-nitriding treatment): A catalyst for the preparation of isophthalonitrile by ammonia oxidation method was obtained by calcining the metal salt / a-BNC precursor obtained in Example 1 in air atmosphere at a temperature increase of 2℃ / min to 400℃ for 4 h (non-nitriding treatment) to obtain the FeCoMnO / a-BNC catalyst (referred to as Comparative Example 1).

[0024] Comparative Example 2 (Commercial V-Sb-O / C catalyst): React at 385°C using a commercial V-Sb-O / C catalyst (8 wt.% V content).

[0025] Catalytic performance evaluation: Catalysts 1-5 and Comparative Examples 1 and 2 (3.0 g, 20-40 mesh) were packed into the isothermal zone of a φ10 mm*300 mm stainless steel fixed-bed reactor. Quartz wool and inert ceramic rings were placed above and below the catalysts. Pre-reduction was performed at 350℃ for 2 h under H2 (50 mL / min). The feed consisted of m-xylene (99.5%), high-purity ammonia (99.9%), and compressed air, with the feed precisely controlled by a mass flow controller. Reaction conditions: temperature 300℃ (385℃ for Comparative Example 2), m-xylene:ammonia:oxygen = 1:3.0:5.0, gas hourly space velocity 1300 h⁻¹. -1 The reaction products were separated using a condenser at 0–5 °C. The liquid products were quantitatively analyzed by gas chromatography with external standard correction. The gas products were monitored by online mass spectrometry. Sampling and analysis began 2 hours after the reaction stabilized. The results are shown in Table 1.

[0026] Stability test: The catalyst from Example 1 was subjected to an incubation period of 300°C and a space velocity of 1300 h⁻¹. -1The catalyst was continuously run for 2000 h under the specified conditions, with samples taken for analysis every 200 h. The results showed that the initial IPN yield was 90.00%, and after 2000 h, the yield was 86.4%, maintaining a yield of 96.0%. The selectivity of the byproduct IPA remained <1.5%. XPS analysis of the catalyst after the reaction showed that the surface Fe, Co, and Mn elemental contents decreased by <8%, while the nitrogen vacancy concentration remained at 1.9 × 10⁻⁶. 19 cm -3 This demonstrates that the catalyst exhibits excellent long-term stability.

[0027] Mechanism verification experiment: To verify the mechanism of "nitrogen vacancy activation of NH3 to generate NH2 radicals", the following control experiment was conducted: (1) NH3 TPD-MS test: The catalyst in Example 1 showed a strong NH3 desorption peak at 150℃ (corresponding to chemisorption), and an NH2 fragment signal at 250℃ (m / z=16); Comparative Example 1 did not have this signal; (2) In-situ EPR test: After NH3 was introduced at 300℃, the signal intensity of the catalyst in Example 1 increased by 3.2 times at g=2.003 (corresponding to the formation of NH2 by capturing electrons from nitrogen vacancies). (3) Isotope labeling experiment: using 15 NH3 reacts, and GC-MS detects the presence of NH3 in the IPN molecule. 15 The N labeling rate is >95%, proving that the N atoms come directly from NH3 rather than lattice nitrogen.

[0028] Table 1 Results of the reaction for the preparation of isophthalonitrile by ammoxidation of m-xylene.

[0029] serial number Catalyst type Key preparation differences Cluster size IPN selectivity at 300℃ IPN yield Example 1 FeCoMnN / a-BNC a-BNC carrier + nitriding at 320℃ 1.2 nm 91.20% 90.00% Example 2 FeCoMnN / NC (Nitrogen and Carbon, Boron-Free) Replace α-BNC with NC carriers made from urea / glucose. 2.9 nm 83.50% 79.10% Example 3 FeCoMnN / a-BNC (nitrided at 360℃) Everything else is the same as in Example 1, except that the nitriding temperature is increased to 360°C. 3.5 nm 82.10% 78.30% Example 4 <![CDATA[Co 1.0 Mn 1.0 N / a-BNC (Fe-free) No Fe salt added 1.3 nm 85.40% 82.00% Example 5 FeCoMnN / a-BNC (acetate) Comparison of metal salt types 1.4nm 90.95% 89.80% Example 6 FeCoMnN / a-BNC a-BNC carrier + nitriding at 320℃ 1.2 nm 91.17% 90.00% Example 7 FeCoMnN / a-BNC a-BNC carrier + nitriding at 320℃ 1.3 nm 91.15% 90.00% Comparative Example 1 <![CDATA[FeCoMnO x / a-BNC]]> Same precursor, air-roasted (non-nitrided) microcrystalline oxides 62.40% 58.70% Comparative Example 2 Commercial V–Sb–O / C Reproduction using commercial catalysts >50 nm 86.6%（385℃） 84.30%

[0030] From Table 1 and the above experiments, we can see that:

[0031] (1) The catalyst in Example 1, which adopts sub-nano clusters and a-BNC anchoring, has high selectivity and low temperature activity. It achieves a high yield of 90.00% and a high selectivity of 91.20% at a low temperature of 300℃, which is significantly better than Comparative Example 2 (84.30% yield at 385℃).

[0032] (2) In the catalyst of Example 2, the sub-nano clusters grew and the selectivity decreased. The cluster size increased to 2.9 nm and the selectivity decreased by 7.7%. The BN defect sites of the a-BNC support are crucial for anchoring the sub-nano clusters.

[0033] (3) For the catalyst in Example 3, increasing the temperature led to cluster sintering and a decrease in yield. 320℃ is the optimal temperature for the formation of sub-nano structures.

[0034] (4) The catalyst in Example 4 lacked Fe-Co-Mn ternary synergy, resulting in a 5.8% decrease in selectivity.

[0035] (5) The catalyst in Example 5, wherein the metal salt solution is one or more of nitrate or acetate, has little effect on the final result.

[0036] (6) Catalysts of Examples 6 and 7, wherein the a-BNC support is preferably B:N:C atomic ratio of 1:(1.8-2.5):(8-12).

[0037] (7) Comparative Example 1 demonstrates that the nitride phase and nitrogen vacancies are prerequisites for high selectivity; without nitrides, the IPA selectivity reaches as high as 18.7%.

[0038] This invention successfully overcomes the limitations of the traditional lattice oxygen mechanism by employing a novel pathway of "nitrogen vacancy activation of NH3 to generate NH2 radicals," demonstrating the feasibility of a low-temperature, high-efficiency synthesis route for isophthalonitrile at 300℃. The catalyst prepared in this invention exhibits high selectivity and high yield in the amination of m-xylene to isophthalonitrile at relatively low reaction temperatures. Furthermore, the catalyst used is inexpensive and environmentally friendly, avoiding the use of precious metals. This provides a new approach for the green synthesis of high-end nitrile compounds and shows promising prospects for industrial application.

Claims

1. A catalyst for the preparation of isophthalonitrile by ammonia oxidation, characterized in that: Subnanometer Fe-Co-Mn ternary nitride clusters were obtained by loading an aqueous solution of Fe, Co, and Mn salts onto a-BNC; the subnanometer Fe-Co-Mn ternary nitride clusters were then nitrided in a mixture of NH3 and H2 at 300-340℃ to obtain a catalyst. The a-BNC is an amorphous boron-nitrogen co-doped carbon support, wherein the B:N:C atomic ratio is 1:(1.8-2.5):(8-12). The sub-nanometer Fe-Co-Mn ternary nitride cluster has the chemical formula Fe. a Co b Mn c N, where a=1.0, b=1.0, c=1.0, and the cluster size is 0.8-1.6 nm; The nitrogen vacancy concentration on the catalyst surface is ≥1.8×10⁻⁶. 19 cm -3 .

2. A method for preparing a catalyst for the ammonia oxidation process to prepare isophthalonitrile as described in claim 1, characterized in that, Includes the following steps: (1) Boric acid, melamine and glucose were measured according to the above atomic ratio requirements and mixed in deionized water to prepare a suspension with a total solid content of 15~20wt.%; the suspension was transferred to a reaction vessel and hydrothermally reacted at 180℃ for 10~14h; after the reaction was completed, the product was naturally cooled to room temperature, washed 3 times with deionized water and 2 times with anhydrous ethanol, and vacuum dried at 80℃ for 12h; the dried product was placed in a tube furnace and carbonized at 600℃ for 2~3h with nitrogen flow rate of 50 mL / min and temperature increased at 3℃ / min, and then naturally cooled to room temperature, and ground through a 60-mesh sieve to obtain amorphous boron-nitrogen co-doped carbon support a-BNC; (2) Prepare a metal salt solution with a total metal concentration of 15wt.% by mixing Fe, Co and Mn salts in a metal molar ratio of 1:1:

1. Load the solution onto an amorphous boron-nitrogen co-doped carbon support a-BNC using an equal volume impregnation method and dry at 120℃ for 4h to obtain sub-nanometer Fe-Co-Mn ternary nitride clusters. (3) Place the sub-nanometer Fe-Co-Mn ternary nitride clusters obtained in step (2) in a tube furnace, introduce a mixture of NH3 and H2 with a volume ratio of 9:1 and a flow rate of 80~120mL / min, and treat at a constant temperature of 300~340℃ for 3~5h; after the reaction is completed, cool naturally to below 100℃, and then switch to nitrogen protection to cool to room temperature to obtain the catalyst.

3. The method for preparing a catalyst for the ammonia oxidation process to prepare isophthalonitrile according to claim 2, characterized in that: The hydrothermal reaction temperature in step (1) is 180℃ and the reaction time is 12h; the carbonization temperature is 600℃ and the carbonization time is 2h; the metal salt solution in step (2) is one or more of nitrate, acetate or hydrochloride; the nitriding temperature in step (3) is 320℃ and the nitriding time is 4h, and the volume ratio of NH3 to H2 is 9:

1.

4. The application of a catalyst for the preparation of isophthalonitrile by ammonia oxidation as described in any one of claims 1-3, characterized in that: This method is used for the gas-phase ammoxidation of m-xylene to isophthalonitrile, with a reaction temperature of 280-340℃, a molar ratio of m-xylene:ammonia:hydrogen of 1:3.0:5.0, and a gas hourly space velocity of 1300 h⁻¹. -1 .