A method for improving the performance of propane dehydrogenation to propylene by hydrothermal treatment of transition metal catalysts and introduction of CO2.

Abstract

This invention discloses a method for improving the performance of propane dehydrogenation to propylene by hydrothermal treatment of a transition metal catalyst and the introduction of CO2. The method involves a two-step process with synergistic effects. The first step modifies the transition metal catalyst through a hydrothermal process. This invention hydrothermally treats the catalyst with transition metals supported on a molecular sieve, transforming the metal species on the catalyst into single, highly dispersed active species, thereby promoting the propane dehydrogenation reaction. The second step introduces CO2 into the propane dehydrogenation reaction system. This method co-feeds CO2 with propane, utilizing the weak oxidizing properties of CO2 to protect the active species in the catalyst from reduction, further enhancing the propane dehydrogenation performance. This invention achieves high propane dehydrogenation activity, high propylene selectivity, and low catalyst deactivation rate through hydrothermal modification of the catalyst and utilization of the weak oxidizing properties of CO2, optimizing the catalytic performance of the transition metal catalyst and reducing carbon emissions.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a transition metal catalyst for propane dehydrogenation to propylene and its preparation method, as well as a method for protecting the active sites of the transition metal by introducing CO2. Background Technology

[0002] Propylene is a major raw material in the chemical industry, used in the production of bulk chemicals such as polypropylene, acrylic acid, acrylonitrile, propylene oxide, and acetone. Traditional propylene production mainly relies on fluidized bed catalytic cracking and steam cracking of naphtha and light diesel oil. Propane dehydrogenation (PDH) technology is an emerging and promising route for propylene production. Due to the maturity of shale gas and natural gas exploration technologies, which have lowered propane prices, it has been extensively studied by academia and industry over the past decade. Catofin and Oleflex are two PDH technologies that have been successfully industrialized globally. However, the Pt-based catalysts currently used in Oleflex technology suffer from high costs due to precious metals, easy sintering of active sites, and coke deposition at high temperatures, leading to rapid catalyst deactivation and limiting its further development. Furthermore, the Cr-based catalysts used in Catofin technology are also limited by their sintering tendency and the need for frequent regeneration due to the large amount of coke deposits. Therefore, the development of low-cost, stable PDH catalysts is urgently needed.

[0003] Due to their excellent CH bond activation capabilities and low cost, transition metals (Fe, Co, Ni, Zn, Zr, Mn, Cu, Cr, etc.) have attracted widespread attention from researchers in recent years for alkane dehydrogenation, particularly propane and ethane dehydrogenation. To achieve high-performance transition metal catalysts, researchers have conducted extensive studies using strategies such as in-situ hydrothermal synthesis or post-processing modification, including adjusting the metal-support interaction, utilizing the confinement effect of zeolite molecular sieve channels, and embedding metals into the molecular sieve framework. Although researchers have tried many strategies to improve the PDH catalytic performance of transition metal catalysts, the synthesized catalysts exhibit low activity, low propylene selectivity, and high deactivation rates due to the presence of multiple active species and poor dispersion, thus limiting their further application.

[0004] Meanwhile, the propane dehydrogenation process takes place at high temperatures and in the presence of reducing gases such as propane, propylene, and hydrogen. This can cause the active sites of the transition metal catalyst to be reduced to metal particles, leading to side reactions such as propane and propylene cracking, and ultimately resulting in rapid catalyst deactivation. Therefore, how to synthesize transition metal catalysts with a single active site and maintain the stability of this active site during the catalytic process is a major challenge that urgently needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a transition metal catalyst for propane dehydrogenation to propylene. This method modifies the transition metal in a molecular sieve through hydrothermal treatment, thereby forming highly dispersed transition metal active sites with uniform valence states. Furthermore, the weak oxidizing property of CO2 is utilized to protect the transition metal active sites, thus ensuring the stability of the catalyst in the propane dehydrogenation reaction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A transition metal catalyst for propane dehydrogenation to propylene, comprising 0.5-3.0 wt% of a transition metal element, preferably 1.6 wt% of the transition metal element.

[0008] Furthermore, the transition metal element is any one of Fe, Co, Ni, Zn, Zr, Mn, Cu, and Cr.

[0009] The preparation method of the transition metal catalyst includes the following steps:

[0010] 1) A mixture of transition metal precursor and molecular sieve is calcined at high temperature to obtain a molecular sieve containing transition metal in the pores;

[0011] 2) The catalyst obtained in step 1) is subjected to hydrothermal treatment in an aqueous solution, followed by calcination, to obtain a highly dispersed and uniformly valence transition metal supported catalyst in the molecular sieve channels, thereby improving the activity of the transition metal catalyst in the propane dehydrogenation reaction.

[0012] 3) When the transition metal supported catalyst obtained in step 2) is used for propane dehydrogenation, CO2 co-feed is used to protect the active sites in the transition metal catalyst, thereby further improving the catalytic activity and stability of the transition metal catalyst for propane dehydrogenation.

[0013] Further, the transition metal precursor mentioned in step 1) is a chloride or nitrate of any one of Fe, Co, Ni, Zn, Zr, Mn, Cu, and Cr.

[0014] Furthermore, the molecular sieve mentioned in step 1) is any one of MFI, MWW, CHA, and BEA.

[0015] Furthermore, the roasting temperature in steps 1) and 2) is 300-800 ℃ and the time is 6 h.

[0016] Furthermore, the roasting atmosphere in steps 1) and 2) includes any one of air, oxygen, nitrogen, argon, helium, or vacuum atmosphere.

[0017] Further, the aqueous solution mentioned in step 2) is an H2O or H2O-C2H5OH or H2O-C2H5OH-TPAOH or H2O-TPAOH system.

[0018] Furthermore, the hydrothermal temperature described in step 2) is 100-250 ℃, and the time is 1-72 h.

[0019] Furthermore, in step 3), the concentration of the co-feed CO2 is 1-50 vol%, and the reaction temperature for propane dehydrogenation is 400-700℃.

[0020] The significant advantages of this invention are:

[0021] (1) This invention prepares a transition metal supported catalyst with highly dispersed and uniformly valence active sites by hydrothermal treatment of conventionally prepared transition metal catalysts in the art. Taking Co-based catalysts as an example, after hydrothermal treatment, Co3O4 in the Co-based catalyst is transformed into highly dispersed tetracoordinated divalent cobalt (T3O4). d -Co(II)) is added, thereby improving the performance of Co-based catalysts in catalyzing propane dehydrogenation; further, by introducing CO2 into the reaction system, the effect of CO2 on T d -Co(II) is used for protection, allowing T d -Co(II) can exist stably during propane dehydrogenation, thereby further enhancing the catalytic activity and reducing the deactivation rate of the catalyst.

[0022] (2) Studies have shown that the transition metal catalyst synthesized in this invention exhibits extremely high catalytic activity when applied to propane dehydrogenation to propylene. Taking the Co-based catalyst as an example, a comparison of the propane dehydrogenation performance of the Co-based catalyst before and after hydrothermal treatment reveals that the propylene yield increased from 0.46 mol C3H6·g Co -1 ·h -1 Furthermore, its catalytic stability was improved. When CO2 was introduced into the reaction system, the yield of propylene was further increased to 0.97 mol C3H6·g. Co -1 ·h -1 Its TOF reached 700 h -1 This catalyst exhibits higher catalytic activity than previously reported Co-based catalysts.

[0023] (3) The transition metal catalyst prepared by the present invention exhibits extremely high propane dehydrogenation activity, providing a highly efficient catalyst for propane dehydrogenation, thereby promoting the further development of propane dehydrogenation technology. Attached Figure Description

[0024] Figure 1 TEM images of the catalysts obtained in Comparative Example 1(a) and Example 1(b).

[0025] Figure 2 The images show the H2-TPR (a) and UV-Raman (b) plots of the catalysts obtained in Example 1 and Comparative Example 1.

[0026] Figure 3 The UV-Vis(a) spectra and Co spectra of Example 1 and Comparative Example 1 2p XPS(b) diagram.

[0027] Figure 4 The images show the catalytic activity spectra of the catalysts obtained in Example 1 and Comparative Example 1.

[0028] Figure 5 This is a graph showing the catalyst regeneration cycle performance of Example 1.

[0029] Figure 6 Co after 1 h (a) and 8 h (b) of PDH and CO2-PDH reactions with the catalyst obtained in Example 1 2p XPS diagram.

[0030] Figure 7 The image shows a TEM image of PDH (a) and CO2-PDH (b) reactions in Example 1. Detailed Implementation

[0031] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0032] Example 1

[0033] 0.158 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Co / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O, 0.12 g TPAOH, and 2.8 g C2H5OH and stirred for 12 h. The resulting suspension was then heated at 180 ℃. oThe catalyst was hydrothermally dried in a dynamic oven for 1 day. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Co / S-1-HTS catalyst (with a Co content of 1.6 wt%).

[0034] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions (PDH), and the initial propane conversion was measured to be 52.8%, with a deactivation rate of 0.148 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the following conditions (CO2-PDH), and the initial propane conversion was measured to be 62.6%, with a deactivation rate of 0.127 h after 8 h. -1 .

[0035] Example 2

[0036] 0.316 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Co / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O, 0.12 g TPAOH, and 2.8 g C2H5OH and stirred for 12 h. The resulting suspension was then heated at 180 ℃. o The catalyst was hydrothermally dried in a dynamic oven for 1 day. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Co / S-1-HTS catalyst (with a Co content of 3.2 wt%).

[0037] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 59.8%, with a deactivation rate of 0.248 h after 8 h. -1Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 69.4%, with a deactivation rate of 0.176 h⁻¹. -1 .

[0038] Example 3

[0039] 0.079 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Co / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O, 0.12 g TPAOH, and 2.8 g C2H5OH and stirred for 12 h. The resulting suspension was then heated at 180 ℃. o The catalyst was hydrothermally dried in a dynamic oven for 1 day. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Co / S-1-HTS catalyst (with a Co content of 0.8 wt%).

[0040] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 37.5%, with a deactivation rate of 0.108 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 48.7%, with a deactivation rate of 0.089 h⁻¹. -1 .

[0041] Example 4

[0042] 0.289 g of Fe(NO3)3·9H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. oAfter static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Fe / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O and 2.8 g C2H5OH and stirred for 12 h. The resulting suspension was then heated at 180 ℃. o The catalyst was hydrothermally dried in a dynamic oven at C for 1 day. The resulting solid was then washed with deionized water until neutral, dried in an oven at 80°C for 10 h, and then calcined at 550°C for 6 h under an argon atmosphere to obtain the Fe / S-1-HTS catalyst (with a Fe content of 2 wt%).

[0043] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 19.5%, with a deactivation rate of 0.198 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 29.4%, with a deactivation rate of 0.174 h⁻¹. -1 .

[0044] Example 5

[0045] 0.228 g of Cu(NO3)2·3H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Beta (BEA topology, Si / Al=60) molecular sieve using an equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain a Cu / Beta catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H₂O and 0.12 g TPAOH and stirred for 12 h. The resulting suspension was then heated at 150 °C. o The catalyst was hydrothermally dried in a dynamic oven for 2 days. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Cu / Beta-HTS catalyst (with a Cu content of 3 wt%).

[0046] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 15.7%, with a deactivation rate of 0.176 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 23.8%, with a deactivation rate of 0.153 h⁻¹ after 8 hours. -1 .

[0047] Example 6

[0048] 0.279 g of Cr(NO3)3·9H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of MCM-22 (MWW topology, Si / Al=30) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined in air at 550 °C for 6 h to obtain the Cr / MCM-22 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H₂O and 0.12 g TPAOH and stirred for 12 h. The resulting suspension was then heated at 190 °C. o The catalyst was hydrothermally dried in a dynamic oven for 2 days. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined in air at 550 °C for 6 h to obtain the Cr / MCM-22-HTS catalyst (with a Cr content of 3 wt%).

[0049] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 34.4%, with a deactivation rate of 0.156 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 51.2%, with a deactivation rate of 0.132 h after 8 hours. -1 .

[0050] Example 7

[0051] 0.296 g of Ni(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of MCM-22 (MWW topology, Si / Al=30) molecular sieve using an equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Ni / MCM-22 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O and 0.12 g TPAOH and stirred for 12 h. The resulting suspension was then heated at 190 °C. o The catalyst was hydrothermally dried in a dynamic oven for 2 days. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Ni / MCM-22-HTS catalyst (with a Ni content of 3 wt%).

[0052] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 32.3%, with a deactivation rate of 0.142 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 39.3%, with a deactivation rate of 0.122 h⁻¹. -1 .

[0053] Example 8

[0054] 0.274 g of Mn(NO3)2·4H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of SAPO-34 (CHA topology, Si / Al=0.8 / 1.0) molecular sieve using an equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under an argon atmosphere to obtain the Cr / SAPO-34 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H₂O and 0.12 g TPAOH and stirred for 12 h. The resulting suspension was then heated at 190 °C. oThe catalyst was hydrothermally dried in a dynamic oven for 2 days. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C for 6 h under an argon atmosphere to obtain the Cr / SAPO-34-HTS catalyst (with a Mn content of 3 wt%).

[0055] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 16.4%, with a deactivation rate of 0.144 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 3:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 26.4%, with a deactivation rate of 0.112 h after 8 hours. -1 .

[0056] Example 9

[0057] 0.102 g of ZrCl4 was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under a nitrogen atmosphere to obtain the Zr / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O and stirred for 12 h. The resulting suspension was then heated at 250 ℃. o The catalyst was hydrothermally dried in a dynamic oven at C for 12 h. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under a nitrogen atmosphere to obtain the Zr / S-1-HTS catalyst (with a Zr content of 2 wt%).

[0058] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 600 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 16.4%, with a deactivation rate of 0.157 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 600 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 28.3%, with a deactivation rate of 0.122 h⁻¹. -1 .

[0059] Example 10

[0060] 0.182 g of Zn(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined at 550 °C under vacuum for 6 h to obtain the Zn / S-1 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O and stirred for 12 h. The resulting suspension was then heated at 250 °C. o The catalyst was hydrothermally dried in a dynamic oven at C for 12 h. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined in a vacuum atmosphere at 550 ℃ for 6 h to obtain the Zn / S-1-HTS catalyst (with a Zn content of 2 wt%).

[0061] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 580 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 20.4%, with a deactivation rate of 0.173 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 580 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 36.5%, with a deactivation rate of 0.130 h⁻¹. -1 .

[0062] Example 11

[0063] 0.158 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of MCM-22 (MWW topology, Si / Al=30) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After static aging at C for 1 h, the catalyst was dried in an oven at 80 ℃ for 10 h. The dried catalyst was then calcined at 550 ℃ for 6 h under a hydrogen atmosphere to obtain the Co / MCM-22 catalyst. 2 g of the obtained catalyst was then dispersed in a mixed solution containing 16.8 g H2O and stirred for 12 h. The resulting suspension was then heated at 180 ℃.o The catalyst was hydrothermally dried in a dynamic oven for 1 day. The resulting solid was then washed with deionized water until neutral and dried in an oven at 80 °C for 10 h. The dried catalyst was then calcined in a hydrogen atmosphere at 550 °C for 6 h to obtain the Co / MCM-22-HTS catalyst (with a Co content of 1.6 wt%).

[0064] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 34.2%, with a deactivation rate of 0.159 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 2:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 46.5%, with a deactivation rate of 0.103 h⁻¹. -1 .

[0065] Comparative Example 1:

[0066] 0.158 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80°C for 10 hours. Then, the dried catalyst was calcined at 550°C under an argon atmosphere for 6 hours to obtain the Co / S-1 catalyst (with a Co content of 1.6 wt%).

[0067] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 36.1%, with a deactivation rate of 0.186 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 25.3%, with a deactivation rate of 0.084 h after 8 hours. -1 .

[0068] Comparative Example 2:

[0069] 0.316 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80°C for 10 hours. Then, the dried catalyst was calcined at 550°C under an argon atmosphere for 6 hours to obtain the Co / S-1 catalyst (with a Co content of 3.2 wt%).

[0070] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 40.3%, with a deactivation rate of 0.266 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 37.6%, with a deactivation rate of 0.154 h after 8 hours. -1 .

[0071] Comparative Example 3:

[0072] 0.079 g of Co(NO3)2·6H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80°C for 10 hours. Then, the dried catalyst was calcined at 550°C under an argon atmosphere for 6 hours to obtain the Co / S-1 catalyst (with a Co content of 0.8 wt%).

[0073] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 19.3%, with a deactivation rate of 0.126 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 15.2%, with an 8-hour deactivation rate of 0.113 h. -1 .

[0074] Comparative Example 4:

[0075] 0.289 g of Fe(NO3)3·9H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Silicalite-1 (MFI topological structure) molecular sieve using an equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80°C for 10 hours. Then, the dried catalyst was calcined at 550°C under an argon atmosphere for 6 hours to obtain the Fe / S-1 catalyst (with a Fe content of 2 wt%).

[0076] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 15.9%, with a deactivation rate of 0.187 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 13.5%, with a deactivation rate of 0.146 h after 8 hours. -1 .

[0077] Comparative Example 5:

[0078] 0.228 g of Cu(NO3)2·3H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of Beta (BEA topology, Si / Al=60) molecular sieve using an equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80°C for 10 hours. Then, the dried catalyst was calcined at 550°C under an argon atmosphere for 6 hours to obtain the Cu / Beta catalyst (with a Cu content of 3 wt%).

[0079] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 12.7%, with a deactivation rate of 0.126 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 11.9%, with a deactivation rate of 0.093 h⁻¹. -1 .

[0080] Comparative Example 6:

[0081] 0.279 g of Cr(NO3)3·9H2O was dissolved in 1.2 mL of deionized water and added dropwise to 2 g of MCM-22 (MWW topology, Si / Al=30) molecular sieve using the equal-volume impregnation method. The solution was then heated to 25 °C. o After being allowed to stand for 1 hour, the catalyst was dried in an oven at 80 °C for 10 hours. Then, the dried catalyst was calcined in air at 550 °C for 6 hours to obtain the Cr / MCM-22 catalyst (with a Cr content of 3 wt%).

[0082] 100 mg of the obtained catalyst was loaded into a fixed-bed reactor and pretreated at 550 °C under an argon atmosphere for 1 h. Then, propane was used as the reactant, and the reactor was subjected to reaction at 550 °C, atmospheric pressure, and a mass hourly space velocity (WHSV) of 1.2 h. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 25.4%, with a deactivation rate of 0.199 h after 8 h. -1 Carbon dioxide and propane were introduced into the reactor at a molar ratio of 1:1, and the reactor was kept at 550 °C, atmospheric pressure, and a mass hourly space velocity of 1.2 h⁻¹. -1 The reaction was carried out under the specified conditions, and the initial conversion rate of propane was measured to be 22.0%, with an 8-hour deactivation rate of 0.123 h. -1 .

[0083] To more clearly compare the catalyst reaction performance of the examples and comparative examples, the performance of the above examples and comparative examples is summarized in Table 1 below.

[0084] Table 1 Comparison of catalytic performance between the examples and comparative examples

[0085]

[0086] Figure 1 TEM images of the catalysts obtained in Comparative Example 1(a) and Example 1(b). Figure 1 As shown in (a), the cobalt species exhibit an aggregated state before hydrothermal treatment. Measurements of the interplanar spacing of the cobalt species revealed the presence of the 311 crystal plane of Co3O4, indicating that the cobalt species of the catalyst before hydrothermal treatment aggregated on the support in the form of Co3O4. However, the corresponding TEM, STEM, and mapping images of Co / S-1-HTS in Example 1 show that the cobalt species exhibit a uniformly dispersed state after hydrothermal treatment, indicating that the hydrothermal process promotes the transformation of Co3O4 into a more dispersed cobalt species.

[0087] Figure 2The images show the H2-TPR (a) and UV-Raman (b) spectra of the catalysts obtained in Example 1 and Comparative Example 1. In the H2-TPR, the Co / S-1 ratio in Comparative Example 1 (a) is 450 °C. o There are two reduction peaks before C. By comparing the position of the reduction peak of Co3O4, it can be inferred that these are the reduction peaks of Co3O4 in Co / S-1 first being reduced to CoO and CoO being reduced to metallic Co. In contrast, the reduction peak at the corresponding position of Co / S-1-HTS in Example 1 almost completely disappears. At 800 o At position C, both exhibited reduction peaks, but the reduction peak intensity of Co / S-1-HTS was significantly enhanced, indicating that hydrothermal treatment promoted the transformation of Co3O4 in Co / S-1 into cobalt species with stronger interactions with the support. The presence of Co3O4 in Example 1 and Comparative Example 1 was verified by UV-Raman spectroscopy analysis, with both showing a peak intensity at 381 cm⁻¹. -1 All peaks showed characteristic features of the molecular sieve MFI configuration, but Co / S-1 in Comparative Example 1 showed peaks at 476, 521, and 688 cm⁻¹. -1 The Co3O4 characteristic peak was observed at the point, while the Co / S-1-HTS in Example 1 did not show the Co3O4 characteristic peak, further indicating that the hydrothermal treatment process caused Co3O4 to be transformed into a Co species that has a strong interaction with the support.

[0088] Figure 3 The UV-Vis(a) spectra and Co spectra of Example 1 and Comparative Example 1 2p XPS (b) spectrum. From the UV-Vis spectrum, it can be seen that the characteristic peak of Co / S-1 at 756 nm in Comparative Example 1 can be attributed to O in CO3O4. 2- →Co 3+ The charge transfer between the ligand and the metal. Both Co / S-1 in Comparative Example 1 and Co / S-1-HTS in Example 1 showed three characteristic peaks at 662, 590, and 524 nm, which is due to the four-coordinated Co(II) (T d -Co(II)) of V3( 4 A2→ 4 The T1(P)) transfer characteristics were observed, and the characteristic peak intensity of Co / S-1-HTS was significantly enhanced. Based on this, combined with H2-TPR, it can be inferred that the hydrothermal process induced the transformation of Co3O4 in Co / S-1 into T1(P). d -Co(II) species, thus making the cobalt species completely T d The presence of -Co(II) in the support leads to an increase in catalytic activity. 2pThe XPS(b) spectra reveal two broad and asymmetric main peaks at 775-792 eV and 792-807 eV, respectively, corresponding to Co₂. p 3 / 2 With Co 2 p 1 / 2 By comparing the Co2 of the two... p The spectra revealed that both exhibited a characteristic peak of Co(II) at BE=781.9 eV and a satellite peak at BE=786.2 eV. However, only Co / S-1 in Comparative Example 1 showed a characteristic peak of Co(III) at BE=779.9 eV. This further indicates that the hydrothermal process induced the transformation of Co3O4 into a tetracoordinated Co(II) species.

[0089] Figure 4 The figures show the catalytic activity spectra of the catalysts obtained in Example 1 and Comparative Example 1. It can be seen from the figures that the Co / S-1-HTS catalyst in Example 1 exhibited significantly improved catalytic activity during the PDH reaction after hydrothermal treatment. Furthermore, when propane and carbon dioxide were co-fed (C3H8: CO2 = 1:1), the Co / S-1-HTS catalyst showed the highest catalytic activity.

[0090] Figure 5 The figure shows the regeneration activity of Co / S-1-HTS in Example 1. As can be seen from the figure, the propane conversion rate of the Co / S-1-HTS catalyst in Example 1 can still reach 49.2% after three cycles, indicating that the catalyst exhibits good catalyst regeneration ability under the conditions of hydrothermal treatment and co-feeding with carbon dioxide.

[0091] Figure 6 Co after PDH and CO2-PDH reactions of Co / S-1-HTS in Example 1 2p XPS spectra. After 1 h of CO2-PDH reaction ( Figure 6 (a) From the catalyst Co2 p The XPS spectrum reveals Co(II) at BE = 781.9 eV. 2p 3 / 2 Peak. In contrast, after 1 h of PDH reaction ( Figure 6 (a) In Co 2 p The XPS spectrum not only shows Co(II) at BE=778.23 eV 2p 3 / 2 A peak was observed, and metallic Co appeared at BE = 778.23 eV. 2p 3 / 2Peak. After 8 h of PDH and CO2-PDH reactions ( Figure 6 The same results were observed in b), indicating that the initial decrease in catalytic performance of the Co / S-1-HTS in Example 1 during the PDH catalytic reaction was due to the reduction of Co(II) to metallic Co. However, when CO2 was introduced into the PDH reaction as a weak oxidant, it inhibited the reduction of Co(II) to metallic Co, thus maintaining a higher level of catalytic activity.

[0092] Figure 7 TEM images of PDH (a) and CO2-PDH (b) reactions in Example 1 are shown. After 8 h of PDH reaction, significant aggregation of metallic Co and the formation of a large number of carbon nanotubes were observed. When CO2 was introduced into the reaction system, both the aggregation of cobalt species and the formation of carbon nanotubes were inhibited. This further indicates that the introduction of CO2 into the reaction system can suppress T... d -Co(II) is reduced to metallic Co, and the formation of carbon deposits is further suppressed.

[0093] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A process for the dehydrogenation of propane to propylene using a transition metal catalyst, characterized in that, The method comprises the following steps: 1) calcining a mixture of a transition metal precursor and a molecular sieve at a high temperature to obtain a molecular sieve catalyst containing a transition metal in the pore channel; 2) hydrothermally treating the catalyst obtained in step 1) in an aqueous solution, converting Co3O4 in the Co-based catalyst into highly dispersed tetracoordinated divalent cobalt after the hydrothermal treatment, and then performing calcination treatment to obtain a transition metal supported catalyst with high dispersion and uniform valence state in the pore channel of the molecular sieve, thereby improving the activity of the transition metal catalyst in the propane dehydrogenation reaction; 3) when the transition metal supported catalyst obtained in step 2) is used in the propane dehydrogenation reaction, CO2 is co-fed to protect the active sites in the transition metal catalyst, thereby further improving the catalytic activity and stability of the transition metal catalyst in the propane dehydrogenation reaction; The transition metal precursor in step 1) is a chloride or nitrate of Co; The molecular sieve in step 1) is Silicalite-1; The calcination atmosphere in steps 1) and 2) is any one of nitrogen, argon, helium, and vacuum atmosphere; The temperature of the hydrothermal treatment in step 2) is 100-250 ℃, and the hydrothermal time is 1-72 h; The content of CO2 in the reaction system in step 3) is 1-50 vol%, and the temperature for the propane dehydrogenation reaction is 400-700 ℃.

2. The method of claim 1, wherein, The content of the transition metal in the catalyst obtained in step 2) is 0.5-3 wt%.

3. The method of claim 1, wherein, The temperature of the calcination in step 1) is 300-800 ℃, and the time is 6-12 h.

4. The method of claim 1, wherein, The aqueous solution in step 2) is H2O or H2O-C2H5OH or H2O-C2H5OH-TPAOH or H2O-TPAOH system.

5. The method of claim 1, wherein, The temperature of the calcination in step 2) is 300-800 ℃, and the time is 6-12 h.

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