High selectivity catalyst suitable for high space velocity, and preparation method and application thereof

Abstract

The application relates to the technical field of catalyst preparation, in particular to a high-selectivity catalyst suitable for high air speed and a preparation method and application thereof. 12 Bi a Fe b Co c Ni d A e Cl f O x , A is one of sodium, potassium, rubidium and cesium; a=0.3-3, b=1-4, c=3-8, d=1-5, e=0.01-0.5, f=0.01-2, and x is a value determined by the total valence of elements in the general formula except oxygen. The catalyst prepared by the preparation method has excellent catalytic performance under high air speed conditions and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a highly selective catalyst suitable for high space velocities, its preparation method, and its application. Background Technology

[0002] In industrial production, acrylic acid is produced via a two-step oxidation process of propylene. The first step, the oxidation of propylene to acrolein, commonly employs a composite oxide catalyst composed of multiple components, including Mo, Bi, Co, Ni, Fe, and alkali metals. The reaction mechanism is generally considered to follow the Mars-van-Krevelen mechanism. In this process, Bi species promote the activation of the allylic site, responsible for the dehydrogenation process, while Mo species insert lattice oxygen, responsible for the oxidation process. The synergistic effect between Mo and Bi effectively regulates the reaction pathway and plays a crucial role in maintaining the catalyst's high activity and selectivity.

[0003] Currently widely used traditional multimetal oxide catalyst systems have significant shortcomings. The precipitation growth, drying, and calcination steps in the preparation process often fail to maintain a uniform distribution of various metal species. On the one hand, the uneven distribution of Bi leads to low utilization of active sites. For example, after 100 hours... -1 At space velocities above a certain level, it is difficult to maintain catalyst activity. Furthermore, Mo is prone to migration and even aggregation at high temperatures, leading to over-oxidation and the formation of COx. Uneven elemental distribution and aggregation disrupt the original Mo-Bi synergistic structure, affecting reaction activity and selectivity. In addition, traditional polymetallic oxide catalysts inevitably possess a certain number of non-selective acidic sites on their surface, resulting in the formation of acetaldehyde and acetic acid, further reducing the selectivity of the target product.

[0004] Therefore, developing a catalyst suitable for the oxidation of propylene to acrolein under high air velocity conditions is of great practical value. Summary of the Invention

[0005] The purpose of this invention is to provide a highly selective catalyst for the oxidation of propylene to acrolein at high space velocities, improving the selectivity and reaction space velocity of existing catalysts. This catalyst enhances the dispersion of Mo and Bi through confinement and inhibits Mo aggregation, strengthens the Mo-Bi synergistic effect to reduce COx yield, and introduces Cl to reduce the yields of acetaldehyde and acetic acid, thereby achieving high selectivity under high space velocity conditions.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a highly selective catalyst suitable for high space velocities, comprising the following steps:

[0008] S1. Bi-MOF nanosheets were synthesized by hydrothermal method by dissolving Bi-containing compounds in a mixture of N,N-dimethylformamide, methanol and trimesic acid;

[0009] S2. Mo6BiCl 15 Mo6BiCl was obtained by chemical growth on Bi-MOF nanosheets. 15 / Bi-MOF;

[0010] S3. Under heating conditions, Mo-containing compounds, A-containing compounds, Fe-containing compounds, Co-containing compounds, and Ni-containing compounds are dissolved in deionized water to obtain a slurry. Mo6BiCl... 15 Bi-MOF was added to the above slurry to obtain an active component slurry; the active component slurry was dried, pulverized, and calcined to obtain an active powder;

[0011] S4. After uniformly mixing the active powder, diluent, and graphite, the mixture is compressed into tablets and granulated to obtain a highly selective catalyst.

[0012] In some preferred embodiments, step S1 specifically involves adding trimesic acid and Bi(NO3)3·5H2O to a mixture of N,N-dimethylformamide and methanol. After stirring and dissolving at room temperature, the transparent mixture is transferred to a reactor, sealed and heated, centrifuged, and washed with methanol to collect a white powder to obtain Bi-MOF.

[0013] Further, step S1 specifically involves adding 750 mg of trimesic acid and 150 mg of Bi(NO3)3·5H2O to a mixture of N,N-dimethylformamide and methanol (60 mL, volume ratio 4:1). After dissolving by stirring at room temperature, the transparent mixture is transferred to a 100 mL polytetrafluoroethylene-lined steel reactor. The reactor is sealed and heated at 120°C for 24 hours. After centrifugation and washing with methanol, a white powder is collected to obtain Bi-MOF. In some preferred embodiments, the reaction time for chemical growth in step S2 is 5–60 min, and the reaction temperature is 0–120°C.

[0014] In some preferred embodiments, the specific steps of the chemical growth in S2 are as follows: Bi-MOF is dissolved in dimethyl sulfoxide and n-octylamine, and stirred to form a precursor solution. MoCl5 is dissolved in a mixed solution of ethanol, oleylamine, and the precursor solution, and BiCl3 is added to induce Mo6BiCl4 growth. 15 Growth on Bi-MOF. The mixed solution was stirred and centrifuged, and washed with ethanol before drying to obtain Mo6BiCl. 15 / Bi-MOF.

[0015] Further, the specific steps of the chemical growth in S2 are as follows: 40g of Bi-MOF is dissolved in 120mL of dimethyl sulfoxide and 1.3mL of n-octylamine, and stirred at room temperature for 5min to form a precursor solution. Subsequently, MoCl5 is dissolved in a mixed solution of ethanol (120mL), oleylamine (12mL), and the precursor solution (120mL), and 1.0g of BiCl3 is added to induce Mo6BiCl 15 Growth on Bi-MOF. The mixed solution was stirred at room temperature (25℃) for 60 min, the crude solution was centrifuged at 5000 rpm, and then washed three times with ethanol before drying to obtain Mo6BiCl. 15 / Bi-MOF.

[0016] In some preferred embodiments, the Mo6BiCl 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:(0.5~10).

[0017] Preferably, the Mo6BiCl 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:(1~6).

[0018] In some preferred embodiments, the Bi-MOF nanosheets have a length of 5~30μm, a width of 50~500nm, and a thickness of 10~200nm.

[0019] In some preferred embodiments, the Mo-containing compound, A-containing compound, Fe-containing compound, Co-containing compound, and Ni-containing compound are all nitrates containing the corresponding elements.

[0020] In some preferred embodiments, the diluent is selected from one or more of SiO2, α-Al2O3, and TiO2.

[0021] In some preferred embodiments, the active powder in the highly selective catalyst has a mass ratio of 30-100%, and the diluent has a mass ratio of 0-70%.

[0022] Preferably, the mass ratio of active powder in the highly selective catalyst is 60-100%, and the mass ratio of diluent is 0-40%.

[0023] In some preferred embodiments, the calcination conditions in S3 include: a temperature of 400~600℃ and a time of 0.5~10h.

[0024] Preferably, the calcination conditions in S3 include: a temperature of 450~550℃ and a time of 4~8h.

[0025] Secondly, the present invention provides a highly selective catalyst suitable for high space velocities, obtained by the aforementioned preparation method, with the general formula Mo. 12 Bi a Fe b Co c Ni d A e Cl f O x A is one of sodium, potassium, rubidium, and cesium; a = 0.3~3, b = 1~4, c = 3~8, d = 1~5, e = 0.01~0.5, f = 0.01~2, and x is a value determined by the total oxidation state of the elements other than oxygen in the general formula.

[0026] Thirdly, this invention provides an application of a highly selective catalyst suitable for high space velocities, used in the catalytic oxidation of propylene to prepare acrolein.

[0027] In some preferred embodiments, when the catalyst is applied to the oxidation of propylene to acrolein, the reaction temperature is 310-360°C and the propylene volume hourly space velocity is 80-150 h⁻¹. -1 .

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention utilizes a chemical method to grow Mo6BiCl on the surface of Bi-MOF nanosheets. 15 Mo6BiCl 15 Confining the Bi and Mo species to the surface of Bi-MOF nanosheets achieves high dispersion and effectively inhibits Mo aggregation, strengthening the synergistic effect between Mo and Bi, thereby reducing COx formation. Furthermore, through Mo6BiCl... 15 Introducing Cl element to regulate the surface properties of the catalyst can effectively suppress non-selective reaction pathways and reduce the formation of acetaldehyde and acetic acid. The catalyst prepared by the method of this invention maintains excellent catalytic performance under high space velocity conditions and has good application prospects.

[0030] 2. In Example 5 of this invention, the propylene space velocity was 80 h⁻¹. -1 At a reaction temperature of 340°C, a propylene conversion rate of 99.7%, an acrolein yield of 87.0%, and an acrylic acid yield of 7.0% (total yield 94.0%) were achieved, with good reaction stability. Example 13 showed a reaction at a propylene space velocity of 140 h⁻¹. -1 It still achieves a propylene conversion rate of 99.7%, an acrolein yield of 87.5%, and an acrylic acid yield of 6.5% (total yield 94.0%). Attached Figure Description

[0031] Figure 1These are XRD patterns of Embodiments 1 and 5 of the present invention;

[0032] Figure 2 This is a SEM image of Bi-MOF in Embodiment 1 of the present invention;

[0033] Figure 3 The Mo6BiCl obtained by the chemical method in Example 5 of this invention 15 SEM image of / Bi-MOF. Detailed Implementation

[0034] The present invention can be better understood through the following examples.

[0035] Example 1:

[0036] This embodiment provides a method for synthesizing Bi-MOF nanosheets, including the following steps:

[0037] Tristyric acid (750 mg) and Bi(NO3)3·5H2O (150 mg) were added to a mixture of N,N-dimethylformamide and methanol (60 mL, volume ratio 4:1). After dissolving by stirring at room temperature, the transparent mixture was transferred to a 100 mL polytetrafluoroethylene-lined steel reactor. The reactor was sealed and heated at 120 °C for 24 hours. After centrifugation and washing with methanol, the white powder was collected to obtain Bi-MOF.

[0038] Example 2:

[0039] 40 g of Bi-MOF from Example 1 was dissolved in 120 mL of dimethyl sulfoxide and 1.3 mL of n-octylamine, and stirred at room temperature for 5 min to form a precursor solution. Subsequently, MoCl5 (13.2 g) was dissolved in a mixture of ethanol (120 mL), oleylamine (12 mL), and the precursor solution (120 mL), and 1.0 g of BiCl3 was added to induce Mo6BiCl4. 15 Growth on Bi-MOF. The mixed solution was stirred at room temperature (25℃) for 60 min, the crude solution was centrifuged at 5000 rpm, and then washed three times with ethanol before drying to obtain Mo6BiCl. 15 / Bi-MOF, where the molar ratio of Mo to Bi is 1:1.4.

[0040] An active component slurry was obtained by dissolving 113.6 g ammonium heptamolybdate, 0.738 g potassium nitrate, 22.7 g ferric nitrate, 91.5 g cobalt nitrate, and 45.7 g nickel nitrate in 350 mL of deionized water at 80 °C. Mo6BiCl... 15 / Bi-MOF was added to the above active component slurry, stirred evenly, and dried at 130℃ for 24h. The dried powder was calcined in a muffle furnace at 500℃ for 5h to obtain catalyst powder. 40g of the obtained catalyst powder, 20g of α-Al2O3 and 1.0g of graphite were mixed evenly, and then pressed into tablets and granulated to obtain a catalyst with a mesh size of 20~40.

[0041] Example 3:

[0042] The difference between this embodiment and Embodiment 2 is that 1.0g of BiCl3 was added to induce Mo6BiCl 15 During growth on Bi-MOF, the mixed solution was stirred at 80°C for 10 min.

[0043] Example 4:

[0044] The difference between this embodiment and Example 2 is that 4.4 g of MoCl5 was dissolved in a mixed solution of ethanol (120 mL), oleylamine (12 mL), and precursor solution (120 mL), and Mo6BiCl... 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:4.

[0045] Example 5:

[0046] The difference between this embodiment and Example 2 is that 8.8 g of MoCl5 was dissolved in a mixed solution of ethanol (120 mL), oleylamine (12 mL), and precursor solution (120 mL), and Mo6BiCl... 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:2.

[0047] Example 6:

[0048] The difference between this embodiment and Example 2 is that 17.6 g of MoCl5 was dissolved in a mixed solution of ethanol (120 mL), oleylamine (12 mL), and precursor solution (120 mL), and Mo6BiCl... 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:1.

[0049] Example 7:

[0050] The difference between this embodiment and embodiment 5 is that the dried powder was calcined in a muffle furnace at 470°C for 5 hours to obtain catalyst powder.

[0051] Example 8:

[0052] The difference between this embodiment and Example 5 is that the dried powder was calcined in a muffle furnace at 530°C for 5 hours to obtain catalyst powder.

[0053] Example 9:

[0054] The difference between this embodiment and Example 5 is that the dried powder was calcined in a muffle furnace at 500°C for 10 hours to obtain catalyst powder.

[0055] Example 10:

[0056] The difference between this embodiment and Example 5 is that 113.6g of ammonium heptamolybdate, 0.738g of potassium nitrate, 22.7g of ferric nitrate, 83.3g of cobalt nitrate, and 45.7g of nickel nitrate were dissolved in 350mL of deionized water at 80℃ to obtain an active component slurry.

[0057] Example 11:

[0058] The difference between this embodiment and embodiment 5 is that 20g of α-Al2O3 is replaced with 20g of SiO2.

[0059] Example 12:

[0060] The difference between this embodiment and Example 5 is that 40g of the obtained catalyst powder and 20g of α-Al2O3 are replaced with 50g of the obtained catalyst powder and 10g of α-Al2O3.

[0061] Example 13:

[0062] The difference between this embodiment and Example 5 is that 40g of the obtained catalyst powder and 20g of α-Al2O3 are replaced with 60g of the obtained catalyst powder.

[0063] Comparative Example 1:

[0064] An active component slurry was obtained by dissolving 118.9 g of ammonium heptamolybdate, 0.738 g of potassium nitrate, 22.7 g of ferric nitrate, 91.5 g of cobalt nitrate, and 45.7 g of nickel nitrate in 350 mL of deionized water at 80 °C. Solution I was obtained by dissolving 32.7 g of bismuth nitrate in a solution prepared with 4 mL of deionized water and 1 mL of nitric acid. Solution I was added dropwise to the above active component slurry. After stirring evenly, the mixture was dried at 130 °C for 24 h. The dried powder was then calcined in a muffle furnace at 500 °C for 5 h to obtain catalyst powder. 60 g of the obtained catalyst powder was mixed evenly with 1.0 g of graphite, and then granulated into tablets to obtain a catalyst with a mesh size of 20–40 mesh.

[0065] Comparative Example 2:

[0066] 8.8 g MoCl₅, 1.7 g BiCl₃, and 1.3 mL n-octylamine were dissolved in 120 mL dimethyl sulfoxide under an argon atmosphere at 60 °C to form a clear precursor solution. This precursor solution was then slowly added dropwise to a mixture of 120 mL ethanol and 12 mL oleylamine, and the mixture was stirred vigorously at 80 °C. The reaction solution was collected by centrifugation at 7000 rpm for 8 min, yielding Mo₆BiCl₃ from the solution. 15Add 10.5g of Mo6BiCl to the ball mill jar. 15 Add 40g Bi-MOF, then grind the mixture for 15 minutes to obtain the physical method Mo6BiCl. 15 @Bi-MOF.

[0067] An active component slurry was obtained by dissolving 113.6 g ammonium heptamolybdate, 0.738 g potassium nitrate, 22.7 g ferric nitrate, 91.5 g cobalt nitrate, and 45.7 g nickel nitrate in 350 mL of deionized water at 80 °C. The active component slurry was then prepared by physical method using Mo6BiCl. 15 @Bi-MOF was added to the above active component slurry, stirred evenly, and dried at 130℃ for 24 hours. The dried powder was calcined in a muffle furnace at 500℃ for 5 hours to obtain catalyst powder. 40g of the obtained catalyst powder, 20g of α-Al2O3 and 1.0g of graphite were mixed evenly, and then pressed into tablets and granulated to obtain a catalyst with a mesh size of 20~40.

[0068] Comparative Example 3:

[0069] Bi-MOF and Na2MoO4 were dispersed in 60 mL of anhydrous ethanol and stirred at 35 °C for 30 h. Mo / Bi-MOF was obtained by centrifugation at 5000 rpm.

[0070] An active component slurry was obtained by dissolving 79.4 g of ammonium heptamolybdate, 0.738 g of potassium nitrate, 22.7 g of ferric nitrate, 91.5 g of cobalt nitrate, and 45.7 g of nickel nitrate in 350 mL of deionized water at 80 °C. Mo / Bi-MOF was added to the slurry, stirred until homogeneous, and then dried at 130 °C for 24 h. The dried powder was calcined in a muffle furnace at 500 °C for 5 h to obtain catalyst powder. 40 g of the obtained catalyst powder, 20 g of α-Al₂O₃, and 1.0 g of graphite were mixed evenly, and then granulated into tablets to obtain a catalyst with a mesh size of 20–40 mesh.

[0071] Performance testing

[0072] 1. Catalyst characterization:

[0073] The catalysts prepared in Examples 1 and 5 were analyzed by XRD in the range of 5–45° at a double-angle scanning rate of 5° / min. The results are shown in the figure. Figure 1 .from Figure 1 It can be seen that the diffraction peaks at 8.1°, 9.5° and 10.3° represent the (002), (110) and (003) crystal planes of Bi-MOF, respectively. The XRD pattern of the synthesized Bi-MOF in the sample is similar to the simulated XRD pattern of the standard Bi-MOF. Figure 1 The result indicates that Bi-MOF was successfully synthesized. When MoCl5 was introduced, Mo6BiCl3 appeared at 17.1° in Example 5.15 The new peak at (114) indicates the formation of Mo6BiCl. 15 / Bi-MOF.

[0074] The morphology of the samples in Examples 1 and 5 was observed by SEM, and the results are shown in the figure. Figure 2 , Figure 3 .like Figure 2 As shown, the Bi-MOF in Example 1 has a uniform lamellar structure with a length of 5-30 μm, a width of 50-500 nm, and a thickness of 10-200 nm. The synthesized Bi-MOF exhibits good crystallinity and structural integrity, with no obvious aggregation or structural collapse observed. Figure 3 As shown, Example 5 introduces Mo6BiCl by chemical method. 15 Afterwards, the obtained Mo6BiCl 15 The morphology of / Bi-MOF did not change significantly.

[0075] 2. Catalyst evaluation:

[0076] The catalysts prepared according to the above embodiments and comparative examples were evaluated in a fixed-bed reactor. The evaluation methods are as follows:

[0077] 10 mL each of granulated catalyst particles and inert diluted microspheres were thoroughly mixed and placed in the constant temperature zone of the reaction tube. A mixed reaction gas was introduced, in which the volume flow ratio of propylene, oxygen, water vapor and nitrogen was 1:8.1:1:2.4. The reaction pressure was atmospheric pressure and the reaction temperature was 340℃. The reaction of acrolein to acrylic acid was simulated in an industrial setting under different space velocities and reaction times. The reaction conversion rate and yield were analyzed by gas chromatography. Data with carbon balance of 95-105% were selected as valid data. The evaluation results are shown in Tables 1-3.

[0078] Table 1 shows some of the examples and comparative examples at 340°C for 80 hours. -1 Catalytic performance of propylene at space velocity

[0079]

[0080] As shown in Table 1, Examples 2 and 3 were carried out at different reaction temperatures and times for the Mo6BiCl reaction. 15 The catalysts grown on Bi-MOF achieved propylene conversions of 99.2% and 99.1%, acrolein yields of 84.1% and 84.0% (total yields of acrolein and acrylic acid were 93.2% and 93.1%), and COx yields of 4.6% and 4.8%, respectively. (Mo6BiCl) 15The growth conditions on Bi-MOF have little impact on catalytic performance, indicating that the chemical growth method in this invention has good reproducibility. Examples 4-6 changed the Mo6BiCl content by adjusting the amount of MoCl5 added. 15 The ratio of Mo to Bi in the / Bi-MOF was as follows: the acrolein yields in Examples 4, 5, and 6 were 84.3%, 87.0%, and 83.0% (total yields of 93.1%, 94.0%, and 92.6%), and the COx yields were 4.4%, 4.5%, and 5.0%, respectively. In Example 5, Mo and Bi exhibited the best synergistic effect and the best catalytic performance. In Example 4, the amount of Mo was relatively small, while in Example 6, the amount of Mo was relatively large, resulting in a slight increase in the deep oxidation reaction and a slight increase in the COx yield.

[0081] The catalyst prepared by the conventional coprecipitation method (Comparative Example 1) achieved a propylene conversion of 99.5% under the same conditions, but its COx yield was as high as 6.3%, and its acetaldehyde and acetic acid yields were as high as 2.3%, higher than those of Examples 2-6. This resulted in an acrolein yield of only 79.7%, an acrylic acid yield of 11.2%, and an overall yield of 90.9%. The high COx yield of Comparative Example 1 is due to the uneven distribution of active sites and severe deep oxidation in the catalyst obtained by the conventional coprecipitation method. Compared to Comparative Example 1, the acetaldehyde and acetic acid yields in the examples of this invention are low because the Cl element in the formulation inhibits non-selective acid sites. To verify the role of the Cl element, a Cl-free Mo / Bi-MOF and the final catalyst were synthesized in Comparative Example 3. The propylene conversion of Comparative Example 3 was 99.7%, the acrolein yield was 86.3% (overall yield 93.4%), and the COx yield was a normal 4.1%, but the acetaldehyde and acetic acid yields were as high as 2.4%. The data from Comparative Examples 1 and 3 verify the beneficial effect of the catalyst preparation method in this invention on reducing COx yield, and the beneficial effect of Cl element on reducing acetaldehyde and acetic acid yield. Comparative Example 2 uses Mo6BiCl... 15 Physical mixing with Bi-MOF failed to form an effective Mo-Bi synergistic structure, resulting in a propylene conversion rate of only 70.4%. This verifies the effectiveness of the method in this invention, which utilizes Mo6BiCl... 15 The beneficial effects of chemical growth on Bi-MOF.

[0082] Examples 7-9 investigate the effect of calcination conditions on catalytic performance based on Example 5. In Example 7, the calcination temperature was lowered to 470℃, and the COx yield slightly increased to 5.2%. In Example 8, the calcination temperature was increased to 530℃, and the propylene conversion rate decreased to 97.7%, but the COx yield also decreased to 3.8%, with an acrolein yield of 86.0% (total yield 92.5%). In Example 9, the calcination time was extended, and both the propylene conversion rate and COx yield slightly decreased, with an acrolein yield of 85.6% (total yield 93.3%). In the technical solution of this invention, appropriate calcination conditions need to be selected. Example 10, based on Example 5, adjusted the Fe and Co element ratio, slightly increasing the COx yield to 5.0%, while the acrolein yield remained at 87.0% (total yield 93.3%), still demonstrating the beneficial effects of the technical solution of this invention. Example 11 is based on Example 5, but the diluent is replaced by SiO2 instead of α-Al2O3. The catalytic performance is not significantly changed. In the technical solution of the present invention, SiO2 can also be selected as the diluent.

[0083] Table 2 shows some examples and comparative examples at 340℃ for 110 hours. -1 With 140h -1 Catalytic performance of propylene at space velocity

[0084]

[0085] In the technical solution of this invention, by reducing the proportion of diluent, the space velocity of the reaction can be increased. In Example 5, the proportion of diluent was 33.3%, and when the propylene space velocity was increased to 110 h⁻¹, the reaction space velocity was increased. -1 140h -1 At that time, the propylene conversion rates decreased to 96.4% and 91.2%, respectively, and the acrolein yields decreased to 79.3% and 74.3%, respectively (the total yields of acrolein and acrylic acid decreased to 93.3% and 91.9%, respectively). Example 12 reduced the diluent ratio to 16.7%, suitable for a higher reaction space velocity, preferably 110 h⁻¹. -1 The propylene conversion rate was 99.7%, and the acrolein yield was 86.9% (total yield 93.9%). Example 13 is diluent-free and suitable for higher reaction space velocities, preferably 140 h⁻¹. 1 The propylene conversion rate was 99.7%, and the acrolein yield was 87.5% (total yield 94.0%). Comparative Example 1, prepared via a traditional co-precipitation method, exhibited uneven distribution of active sites and low utilization. Its formulation did not contain diluent. When the propylene space velocity was increased to 110 h⁻¹, [further improvements were observed]. -1 At that time, the propylene conversion rate decreased to 96.4%, and the acrolein yield decreased to 79.3% (total yield decreased to 88.6%). When the propylene space velocity was increased to 140 h⁻¹, the propylene conversion rate decreased to 96.4%, and the acrolein yield decreased to 79.3% (total yield decreased to 88.6%). -1At that time, the propylene conversion rate and product yield further decreased, while the COx yield, acetaldehyde yield, and acetic acid yield increased, indicating that the catalyst had a severe lack of active sites, and the excess propylene was converted into other by-products. According to the technical solution of the present invention, by changing the ratio of active powder and diluent, the obtained catalyst is applicable to a wide range of propylene space velocities.

[0086] Table 3 shows some of the examples and comparative examples at 340℃ for 80 hours. -1 propylene space velocity and catalytic performance at different reaction times

[0087]

[0088] As shown in Table 3, Comparative Example 1 exhibited a gradual decline in catalytic performance during long-term testing. This is because the traditional multi-metal co-precipitation system easily causes Mo to migrate and aggregate at high temperatures, disrupting the Mo-Bi synergistic effect and resulting in a decrease in propylene conversion and an increase in COx yield. In contrast, Example 5 maintained stable catalytic performance during long-term testing, demonstrating the beneficial effect of the present invention's technical solution on improving catalyst stability.

[0089] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Within the principles of the present invention, any person skilled in the art can modify or make equivalent substitutions to the described embodiments, and such modifications and variations should be considered to fall within the protection scope of the present invention.

Claims

1. A method for preparing a high space velocity and high selectivity catalyst suitable for the catalytic oxidation of propylene to acrolein, characterized in that, Includes the following steps: S1. Dissolve the Bi-containing compound in... N , N Bi-MOF nanosheets were synthesized via a hydrothermal method from a mixture of dimethylformamide, methanol and trimesic acid. S2. Mo6BiCl 15 Mo6BiCl was obtained by chemical growth on Bi-MOF nanosheets. 15 / Bi-MOF; S3. Under heating conditions, Mo-containing compounds, A-containing compounds, Fe-containing compounds, Co-containing compounds, and Ni-containing compounds are dissolved in deionized water to obtain a slurry. Mo6BiCl... 15 / Bi-MOF is added to the above slurry to obtain an active component slurry; the active component slurry is dried, pulverized, and calcined to obtain an active powder; A is one of sodium, potassium, rubidium, and cesium; S4. After uniformly mixing the active powder, diluent, and graphite, the mixture is compressed into tablets and granulated to obtain the catalyst; the diluent is selected from one or more of SiO2, α-Al2O3, and TiO2.

2. The preparation method according to claim 1, characterized in that, The specific steps of S1 are as follows: In N , N A mixture of dimethylformamide and methanol was added with pyromellitic acid and a Bi-containing compound. After stirring and dissolving at room temperature, the mixture was transferred to a reactor, sealed and heated, centrifuged and washed with methanol. The white powder was collected to obtain Bi-MOF nanosheets.

3. The preparation method according to claim 1, characterized in that, The reaction time for the chemical growth in step S2 is 5-60 min, and the reaction temperature is room temperature to 120℃. Specifically, step S2 involves: dissolving Bi-MOF nanosheets in dimethyl sulfoxide and n-octylamine, stirring to form a precursor solution; dissolving MoCl5 in a mixed solution of ethanol, oleylamine, and the precursor solution; and adding BiCl3 to induce the growth of Mo6BiCl3. 15 For growth on Bi-MOF, the mixed solution was stirred and centrifuged, and washed with ethanol before drying to obtain Mo6BiCl. 15 / Bi-MOF.

4. The preparation method according to claim 1, characterized in that, The Mo6BiCl 15 In / Bi-MOF, the molar ratio of Mo to Bi is 1:(0.5~10).

5. The preparation method according to claim 1, characterized in that, The Bi-MOF nanosheets have a length of 5~30μm, a width of 50~500nm, and a thickness of 10~200nm.

6. The preparation method according to claim 1, characterized in that, The catalyst contains 30-100% active powder by mass and 0-70% diluent by mass.

7. The preparation method according to claim 1, characterized in that, The calcination conditions described in S3 include: a temperature of 400~600℃ and a time of 0.5~10h.

8. A high-space-velocity, high-selectivity catalyst suitable for the catalytic oxidation of propylene to acrolein, characterized in that, Obtained by the preparation method according to any one of claims 1-7, with the general formula Mo 12 Bi a Fe b Co c Ni d A e Cl f O x A is one of sodium, potassium, rubidium, and cesium; a = 0.3~3, b = 1~4, c = 3~8, d = 1~5, e = 0.01~0.5, f = 0.01~2, and x is a value determined by the total oxidation state of the elements other than oxygen in the general formula.

9. The application of the high space velocity and high selectivity catalyst of claim 8 for the catalytic oxidation of propylene to acrolein, characterized in that, It is used in the catalytic oxidation of propylene to prepare acrolein.

10. The application according to claim 9, characterized in that, When the catalyst is applied to the oxidation of propylene to acrolein, the reaction temperature is 310-360℃ and the propylene volume hourly space velocity is 80-150 h⁻¹. -1 .

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