Catalyst for preparing acetic acid by selectively oxidizing ethane as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for preparing acetic acid by selectively oxidizing ethane as well as a preparation method and application of the catalyst. The catalyst comprises a composite oxide and a TiO2 carrier, wherein the composite oxide is formed by combining palladium, vanadium and oxygen; the TiO2 at least comprises anatase type TiO2. The catalyst has excellent catalytic activity and acetic acid selectivity, the preparation process is simple, and the catalyst is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a catalyst for selectively oxidizing ethane to produce acetic acid, a preparation method thereof, and an application thereof. Background Art

[0002] Acetic acid (CH3COOH) is one of the world's most important commodity chemicals, widely used in various industrial fields, such as the production of acetate esters, the synthesis of pharmaceuticals such as aspirin, as a coagulant for natural rubber, and as a solvent in various chemical processes. The traditional industrial route for acetic acid production relies primarily on methanol carbonylation, in which methanol reacts with carbon monoxide (CO) in the presence of homogeneous catalysts such as rhodium or iridium complexes. Approximately 70% of global acetic acid production uses this method. However, this technology also has significant drawbacks, including reliance on toxic iodide co-catalysts, the requirement for high pressure and temperature, and the cost and recovery issues of noble metal homogeneous catalysts.

[0003] Developing new, milder, and low-carbon pathways for producing acetic acid has become a research hotspot. Within this context, ethane (C₂H₂), a major component of natural gas, is considered an ideal feedstock for acetic acid synthesis due to its abundant reserves, low cost, and high carbon atom utilization rate. Direct, selective oxidation of ethane to acetic acid promises to significantly simplify the reaction process, reduce raw material and energy costs, and avoid the high carbon footprint associated with methanol carbonylation. However, due to ethane's stable molecular structure and high C–H bond energy, effective activation of ethane under mild conditions and high selectivity for acetic acid production remain major challenges in current catalytic conversion technologies. Previous studies have demonstrated that heterogeneous catalysts can achieve ethane oxidation to a certain extent. For example, the HPMoV₂ / TiO₂ catalyst reported in Appl. Catal. A: Gen. in 2005 can oxidize ethane to acetic acid in a fixed bed under high temperature and pressure conditions. However, the selectivity for acetic acid is low, with the selectivity for the byproduct carbon dioxide exceeding 60%. In 2024, CCS Chem reported that Fe / ZSM-5 could oxidize ethane to acetic acid in a batch reaction system using expensive hydrogen peroxide (H2O2). While this improved selectivity for the target product, the operating system was complex and economical, making it difficult to meet the requirements of industrial application. Furthermore, existing technologies for oxidizing ethane to acetic acid typically require temperatures exceeding 300°C.

[0004] Therefore, developing a catalyst system that can achieve highly selective and continuous oxidation of ethane to acetic acid under mild conditions using inexpensive oxygen (O2) as an oxidant has become a key direction for the development of green acetic acid synthesis technology. In particular, designing catalyst structures with synergistic active centers and controllable oxidation properties to improve ethane activation efficiency and acetic acid selectivity while reducing the formation of peroxidation byproducts will play a key role in promoting the industrialization of this reaction. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a catalyst for the selective oxidation of ethane to acetic acid, a preparation method and application thereof, so as to address the problems of the prior art catalysts for the production of acetic acid, such as insufficient reaction activity, product selectivity and stability, high energy consumption required for catalysis and high raw material costs.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides a catalyst for selectively oxidizing ethane to produce acetic acid, and a preparation method and application thereof.

[0007] A first aspect of the present invention provides a catalyst for the selective oxidation of ethane to acetic acid, the catalyst comprising: a composite oxide formed by the combination of palladium and vanadium with oxygen and a TiO2 carrier; the TiO2 comprises at least anatase TiO2.

[0008] Preferably, the mass ratio of Pd element to V element in the catalyst is (0.4-5):100.

[0009] Further preferably, the mass ratio of Pd element to V element in the catalyst is (0.4-2):100; for example, it can be 0.4:100, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.4:100, 1.6:100, 1.8:100 or 2:100.

[0010] Preferably, the mass ratio of the two elements Pd and V in the catalyst to TiO2 is (2-25):100.

[0011] Further preferably, the mass ratio of the two elements Pd and V in the catalyst to TiO2 is (2-10):100.

[0012] More preferably, the mass ratio of the two elements Pd and V in the catalyst to TiO2 is (5-10):100; for example, it can be 5:100, 5.5:100, 6:100, 6.5:100, 7:100, 7.5:100, 8:100, 8.5:100, 9:100, 9.5:100 or 10:100.

[0013] Preferably, the TiO2 carrier is a TiO2 carrier containing a lattice dislocation structure.

[0014] Preferably, the specific surface area of ​​the TiO2 carrier is 20 to 80 m 2 / g.

[0015] More preferably, the specific surface area of ​​the TiO2 carrier is 25 to 70 m 2 / g; for example, it can be 25m2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g, 60m 2 / g、65m 2 / g or 70m 2 / g.

[0016] Preferably, the particle size of the TiO2 carrier is 10 to 50 nm.

[0017] Further preferably, the particle size of the TiO2 carrier is 10 to 40 nm; for example, it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm or 40 nm.

[0018] Preferably, the TiO2 also includes rutile TiO2.

[0019] Further preferably, the volume ratio of anatase TiO2 to rutile TiO2 is (2-10):1.

[0020] More preferably, the volume ratio of anatase TiO2 to rutile TiO2 is (2-6):1; for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1.

[0021] In some preferred embodiments of the present invention, the TiO2 is P25 type TiO2.

[0022] The P25 type TiO2 described in the present invention includes anatase type TiO2 and rutile type TiO2.

[0023] A second aspect of the present invention provides a method for preparing a catalyst for selective oxidation of ethane to acetic acid, the method comprising dissolving soluble salts corresponding to palladium and vanadium and dihydrated oxalic acid in water to obtain a mixed solution, adding a TiO2 carrier to the mixed solution, and performing rotary evaporation, drying and a first calcination to obtain the catalyst.

[0024] Preferably, the soluble salt corresponding to vanadium is any one or more selected from ammonium metavanadate, sodium vanadate, vanadium chloride, and vanadium sulfate.

[0025] Preferably, the soluble salt corresponding to the palladium is any one or more selected from palladium chloride, palladium nitrate, palladium sulfate, and palladium acetate.

[0026] Preferably, the molar ratio of the soluble salt corresponding to vanadium to oxalic acid dihydrate is 1:(2-5); for example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0027] Preferably, based on 1 mmol of soluble salt corresponding to vanadium, the amount of water added is 20-50 mL; for example, it can be 20 mL, 25 mL, 28 mL, 30 mL, 35 mL, 40 mL, 45 mL or 50 mL.

[0028] Preferably, the concentration of palladium in the mixed solution is 0.01 to 0.05 mg / mL; for example, it can be 0.01 mg / mL, 0.015 mg / mL, 0.02 mg / mL, 0.025 mg / mL, 0.03 mg / mL, 0.035 mg / mL, 0.04 mg / mL, 0.045 mg / mL or 0.05 mg / mL.

[0029] Preferably, based on 10 mL of the mixed solution, the added amount of the TiO2 carrier is 0.1 to 0.5 g.

[0030] Further preferably, based on 10 mL of the mixed solution, the added amount of the TiO2 carrier is 0.2 to 0.4 g; for example, it can be 0.2 g, 0.22 g, 0.24 g, 0.26 g, 0.28 g, 0.3 g, 0.32 g, 0.34 g, 0.36 g, 0.38 g or 0.4 g.

[0031] Preferably, the rotary evaporation temperature is 50-80°C; for example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C.

[0032] Preferably, the rotary evaporation is performed using a rotary evaporator, and the degree of rotary evaporation is such that the evaporated product is in a dry powder form.

[0033] Preferably, the drying is carried out in an oven.

[0034] Preferably, the drying temperature is 60-150°C.

[0035] More preferably, the drying temperature is 80-120°C; for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C.

[0036] Preferably, the drying time is 10 to 15 hours.

[0037] More preferably, the drying time is 12 to 15 hours; for example, it can be 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours.

[0038] Preferably, the first calcination temperature is 400-650°C.

[0039] More preferably, the first calcination temperature is 400-600°C; for example, it can be 400°C, 450°C, 500°C, 550°C or 600°C.

[0040] Preferably, the first calcination time is 2 to 5 hours; for example, it can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0041] Preferably, the atmosphere of the first calcination is air atmosphere.

[0042] Preferably, the TiO2 carrier is obtained by a second calcination of TiO2 powder.

[0043] Preferably, the second calcination temperature is 400-550°C; for example, it can be 400°C, 420°C, 450°C, 480°C, 500°C, 520°C or 550°C.

[0044] Preferably, the second calcination time is 2 to 5 hours.

[0045] More preferably, the second calcination time is 3 to 5 hours; for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0046] A third aspect of the present invention provides a use of the above catalyst in the reaction of oxidizing ethane to produce acetic acid.

[0047] A fourth aspect of the present invention provides a method for selectively oxidizing ethane to produce acetic acid using the above catalyst, wherein the catalyst is loaded into a reactor and a mixed reaction gas is introduced to carry out the reaction.

[0048] Preferably, the mixed reaction gas includes C2H6, O2 and N2, the volume fraction of C2H6 in the mixed reaction gas is 60-80%, and the volume ratio of O2 to N2 is 1:(4-6).

[0049] Further preferably, the volume fraction of C2H6 in the mixed reaction gas is 70-80%; for example, it can be 70%, 72%, 75%, 78% or 80%.

[0050] Preferably, the flow rate of the mixed reaction gas is 20-40 mL / min; for example, it can be 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min or 40 mL / min.

[0051] Preferably, the reaction temperature is 200-250°C.

[0052] More preferably, the reaction temperature is 200-230°C; for example, it can be 200°C, 205°C, 210°C, 215°C, 220°C, 225°C or 230°C.

[0053] Preferably, the reaction pressure is 1 to 5 atm; for example, it may be 1 atm, 2 atm, 3 atm, 4 atm or 5 atm.

[0054] As described above, the catalyst for selective oxidation of ethane to acetic acid of the present invention, its preparation method and application have the following beneficial effects:

[0055] 1. The preparation method of the catalyst of the present invention has a simple process and is suitable for large-scale industrial production. The active components are evenly dispersed and the interface structure is stable, which facilitates maintaining long-term stable catalytic performance in practical applications.

[0056] 2. The catalyst of the present invention achieves efficient activation and selective oxidation of ethane by constructing a synergistic effect of a composite oxide of Pd and V on the surface of a TiO2 carrier, stably producing acetic acid under mild conditions, avoiding the problems of complex product distribution and poor selectivity in traditional ethane oxidation systems.

[0057] 3. The catalyst of the present invention has excellent catalytic activity and acetic acid selectivity under reaction conditions of 210-250°C, produces few by-products, is conducive to subsequent separation and purification, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 a shows the XRD diagram of the catalysts in Example 1 (PdVTi-400), Example 2 (PdVTi-500), Comparative Example 3 (PdVTi-600), Comparative Example 4 (PdVTi-650), Comparative Example 5 (PdVTi-A) and Comparative Example 6 (PdVTi-R) of the present invention; Figure 1 b (left) shows a schematic diagram of a high-resolution transmission electron microscope (HRTEM) of the catalyst prepared in Example 2 of the present invention; Figure 1 (i-1) is a schematic diagram showing an image after filtering the HRTEM image of the catalyst prepared in Example 2 of the present invention; Figure 1 (i-2) is a schematic diagram showing an image after inverse Fourier transformation of the HRTEM image of the catalyst prepared in Example 2 of the present invention.

[0059] Figure 2 A schematic diagram showing the catalytic productivity of the catalyst prepared in Example 2 of the present invention at different reaction times within 0 to 35 hours of continuous catalytic reaction at 210°C. DETAILED DESCRIPTION

[0060] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0061] It should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. It should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the presence of other devices / apparatuses before or after the combination device / apparatus, or the insertion of other devices / apparatuses between two explicitly mentioned devices / apparatuses. Moreover, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0062] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0063] When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the understanding of the prior art by those skilled in the art and the description of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention may also be used to implement the present invention.

[0064] Example 1

[0065] The present embodiment provides a catalyst for selective oxidation of ethane to acetic acid, and its preparation method is as follows:

[0066] 2g of P25 TiO2 powder was weighed and placed in a muffle furnace and calcined at 400°C in air for 3 hours to obtain the modified support TiO2-400. Separately, 0.29g of ammonium metavanadate (NH4VO3) and 1g of oxalic acid dihydrate (C2H2O4·2H2O) were dissolved in 70mL of deionized water to prepare a vanadium source precursor solution. 50μL of palladium nitrate (Pd(NO3)2) solution with a Pd concentration of 24.7mg / mL was then added to this solution and mixed thoroughly.

[0067] 2g of TiO2-400 carrier was slowly added to the above mixed solution, mixed evenly, and then placed in a rotary evaporator for rotary evaporation. After rotary evaporation to powder, it was taken out and placed in an oven and dried at 120°C for 12 hours to remove residual moisture. Subsequently, the dried powder was placed in a muffle furnace and calcined at 400°C in air atmosphere for 4 hours to finally obtain PdVO with a Pd content of 0.05wt% and a V content of 6wt%. x / TiO2-400 catalyst.

[0068] Example 2

[0069] The present embodiment provides a catalyst for selective oxidation of ethane to acetic acid, and its preparation method is as follows:

[0070] 2g of P25 TiO2 powder was weighed and placed in a muffle furnace and calcined at 500°C in air for 3 hours to obtain the modified support TiO2-500. Separately, 0.29g of ammonium metavanadate (NH4VO3) and 1g of oxalic acid dihydrate (C2H2O4·2H2O) were dissolved in 70mL of deionized water to prepare a vanadium source precursor solution. Subsequently, 50μL of palladium nitrate (Pd(NO3)2) solution with a Pd concentration of 24.7mg / mL was added to this solution and mixed thoroughly.

[0071] 2g of TiO2-500 carrier was slowly added to the above mixed solution, mixed evenly, and then placed in a rotary evaporator for rotary evaporation. After rotary evaporation to powder, it was taken out and placed in an oven and dried at 120°C for 12 hours to remove residual moisture. Subsequently, the dried powder was placed in a muffle furnace and calcined at 400°C in air atmosphere for 4 hours to finally obtain PdVO with a Pd content of 0.05wt% and a V content of 6wt%. x / TiO2-500 catalyst.

[0072] Example 3

[0073] The present embodiment provides a catalyst for selective oxidation of ethane to acetic acid, and its preparation method is as follows:

[0074] 2g of P25 TiO2 powder was weighed and placed in a muffle furnace and calcined at 500°C in air for 3 hours to obtain the modified support TiO2-500. Separately, 0.29g of ammonium metavanadate (NH4VO3) and 1g of oxalic acid dihydrate (C2H2O4·2H2O) were dissolved in 70mL of deionized water to prepare a vanadium source precursor solution. 100μL of palladium nitrate (Pd(NO3)2) solution with a Pd concentration of 24.7mg / mL was then added to this solution and mixed thoroughly.

[0075] 2g of TiO2-500 carrier was slowly added to the above mixed solution, mixed evenly, and then placed in a rotary evaporator for rotary evaporation. After rotary evaporation to powder, it was taken out and placed in an oven and dried at 120°C for 12 hours to remove residual moisture. Subsequently, the dried powder was placed in a muffle furnace and calcined at 400°C in air atmosphere for 4 hours to finally obtain PdVO with a Pd content of 0.1wt% and a V content of 6wt%. x / TiO2-500 catalyst.

[0076] Example 4

[0077] The present embodiment provides a catalyst for selective oxidation of ethane to acetic acid, and its preparation method is as follows:

[0078] Prepare a vanadium source precursor solution by dissolving 0.29g of ammonium metavanadate (NH4VO3) and 1g of oxalic acid dihydrate (C2H2O4·2H2O) in 70mL of deionized water. Add 50μL of a palladium nitrate (Pd(NO3)2) solution with a Pd concentration of 24.7mg / mL to this solution and mix thoroughly.

[0079] 2g of uncalcined anatase TiO2 carrier was slowly added to the above mixed solution, mixed evenly, and placed in a rotary evaporator for rotary evaporation. After rotary evaporation to powder, it was taken out and placed in an oven and dried at 120°C for 12 hours to remove residual moisture. Subsequently, the dried powder was placed in a muffle furnace and calcined at 400°C in air atmosphere for 4 hours to finally obtain PdVO with a Pd content of 0.05wt% and a V content of 6wt%. x / TiO2-A catalyst.

[0080] Comparative Example 1

[0081] The difference between Comparative Example 1 and Example 2 is that no palladium nitrate solution is added, and the rest of the preparation method is the same as that of Example 2.

[0082] Comparative Example 2

[0083] The difference between Comparative Example 2 and Example 2 is that ammonium metavanadate and oxalic acid dihydrate are not added, and only 70 mL of deionized water is added. The rest of the preparation method is the same as that of Example 2.

[0084] Comparative Example 3

[0085] The difference between Comparative Example 3 and Example 2 is that the P25 type TiO2 powder is calcined at a temperature of 600°C to obtain the modified carrier TiO2-600. The rest of the preparation method is the same as that of Example 2.

[0086] Comparative Example 4

[0087] The difference between Comparative Example 4 and Example 2 is that the P25 type TiO2 powder is calcined at a temperature of 650°C to obtain the modified carrier TiO2-650. The rest of the preparation method is the same as that of Example 2.

[0088] Comparative Example 5

[0089] The difference between this comparative example 5 and Example 2 is that single rutile TiO2 is used to replace P25 type TiO2, and the rutile TiO2 is not calcined. The rest of the preparation method is the same as that of Example 2.

[0090] Comparative Example 6

[0091] The difference between Comparative Example 6 and Example 2 is that ZrO2 powder is used to replace P25 type TiO2 powder, and the rest of the preparation method is the same as that of Example 2.

[0092] Comparative Example 7

[0093] The difference between Comparative Example 7 and Example 2 is that Al2O3 powder is used to replace P25 type TiO2 powder, and the rest of the preparation method is the same as that of Example 2.

[0094] Comparative Example 8

[0095] The difference between Comparative Example 8 and Example 2 is that 200 μL of palladium nitrate solution is added instead of 50 μL of palladium nitrate solution, and the rest of the preparation method is the same as that of Example 2.

[0096] Comparative Example 9

[0097] The difference between Comparative Example 9 and Example 2 is that the vanadium source precursor solution is replaced by a molybdenum source solution. Specifically, 0.243 g of ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 ·4H2O) was dissolved in 70 mL of deionized water to prepare a molybdenum source solution. The rest of the preparation method was the same as that in Example 2.

[0098] Comparative Example 10

[0099] The difference between this comparative example 10 and Example 2 is that a tungsten source solution is used to replace the vanadium source precursor solution. Specifically, 0.230 g of ammonium tungstate ((NH4)2WO4) is dissolved in 70 mL of deionized water to prepare a tungsten source solution. The rest of the preparation method is the same as that of Example 2.

[0100] Performance tests were conducted on the catalysts prepared in Examples 1-4 and Comparative Examples 1-10 in a fixed-bed quartz reactor (11 mm outer diameter, 8 mm inner diameter, 450 mm length). The test temperature was controlled by two thermocouples located within the reactor and the quartz tube. 50 mg of the catalyst was filled into the reactor with a quartz wool plug. The reaction gases, C₂H₂ and 20% O₂ / N₂, were introduced into the reaction system at a 3:1 ratio via a mass flowmeter controller (Brooks Instruments) at a total flow rate of 30 mL / min and a pressure of 1 atm. The temperature was raised to the reaction temperature (210°C) at a rate of 4°C / min. The acetic acid selectivity and acetic acid productivity of the catalysts at 210°C were measured. The results are shown in Table 1.

[0101] Table 1 Reaction performance of each catalyst at 210℃

[0102]

[0103]

[0104] The acetic acid productivity in Table 1 above represents the micromoles of acetic acid that can be generated per gram of catalyst per hour. The calculation formula for acetic acid productivity is:

[0105]

[0106] Where C(CH3COOH) is the concentration of acetic acid (unit: μmol / L), F is the flow rate of the reaction system (unit: L / h), and m is the mass of the catalyst (unit: g).

[0107] The calculation formula for acetic acid selectivity is:

[0108]

[0109] Where n(CH3COOH) is the number of moles of acetic acid produced, n(CO) is the number of moles of carbon monoxide produced, and n(CO2) is the number of moles of carbon dioxide produced.

[0110] According to the results in Table 1, we can see that:

[0111] The catalysts prepared in Examples 1 to 4 all exhibited excellent catalytic performance in the reaction of ethane oxidation to acetic acid, with high acetic acid productivity and acetic acid selectivity.

[0112] From the results of Examples 2 and 4, it can be seen that when single anatase TiO2 is used to replace P25 TiO2, although the selectivity of acetic acid does not decrease, the catalytic ability of the catalyst decreases.

[0113] From the results of Example 2 and Comparative Example 1, it can be seen that when palladium is not added, although the selectivity of the catalyst for acetic acid does not decrease, the productivity of acetic acid is significantly reduced and the catalytic activity is low.

[0114] It can be seen from the results of Example 2 and Comparative Example 2 that when no vanadium oxide is added, the catalyst is completely inactive and cannot produce acetic acid.

[0115] It can be seen from the results of Example 2 and Comparative Examples 3-4 that when the carrier is calcined, if the calcination temperature is too high (600° C. and above), the activity of the catalyst will continue to decrease as the temperature increases.

[0116] From the results of Example 2 and Comparative Example 5, it can be seen that when a single rutile TiO2 is used to replace the P25 TiO2, the catalyst is completely inactive and cannot produce acetic acid.

[0117] It can be seen from the results of Example 2 and Comparative Examples 6-7 that when zirconium oxide or aluminum oxide is used to replace titanium oxide, the prepared catalyst is completely inactive and cannot produce acetic acid.

[0118] The results of Example 2 and Comparative Example 8 show that when the amount of palladium added is too high (0.2 wt % of the total weight of the catalyst), the productivity of acetic acid is slightly improved, but the selectivity of acetic acid is significantly reduced, the proportion of by-products produced increases, and the target product cannot be generated specifically.

[0119] It can be seen from the results of Example 2 and Comparative Examples 9-10 that when molybdenum oxide or tungsten oxide is used to replace vanadium oxide, the prepared catalyst is completely inactive and cannot produce acetic acid.

[0120] Furthermore, the crystal phases of the catalysts in Example 1 (PdVTi-400), Example 2 (PdVTi-500), Comparative Example 3 (PdVTi-600), Comparative Example 4 (PdVTi-650), Example 4 (PdVTi-A) and Comparative Example 5 (PdVTi-R) were characterized by X-ray diffraction. Figure 1As shown in Figure 1, it can be seen from the crystal diffraction peaks of Examples 1 to 2 and Comparative Examples 3 to 4 that with the increase of calcination temperature, the XRD diffraction peaks of TiO2 undergo significant evolution: the characteristic diffraction peaks of the anatase phase gradually weaken, while the diffraction peak intensity of the rutile phase gradually increases, indicating that the TiO2 crystal phase transforms from anatase to thermodynamically more stable rutile. In particular, under calcination conditions of 500°C and above, obvious characteristic peaks of the rutile phase can be observed in the XRD pattern, while the characteristic peaks of the anatase phase are significantly attenuated, indicating that the crystal phase transformation trend is clearly visible.

[0121] The internal lattice of the catalyst prepared in Example 2 was further observed using a high-resolution transmission electron microscope (HRTEM). Figure 1 As shown in b (left), the HRTEM image shows a structural feature of alternating crystalline and disordered regions, indicating that both crystalline and amorphous regions exist in the sample. This alternating morphology is manifested as clear lattice fringes in some areas, while other areas show fuzzy, non-periodic contrast changes. Further, the HRTEM image is filtered, and the results are as follows: Figure 1 As shown in (i-1), the filtered image shows that the lattice fringes are discontinuous or bent in some areas, which indicates that the crystal phase is disturbed, confirming the dislocation phenomenon. Further inverse Fourier transform analysis is performed on the i area selected in the HRTEM image, and the results are as follows Figure 1 As shown in (i-2), after inverse Fourier transform, an irregular arrangement of diffraction spots appears, which further confirms the existence of lattice distortion or defects in the local area, that is, the existence of lattice dislocation.

[0122] The catalytic performance of the catalyst prepared in Example 2 at different temperatures was further studied, and the results are shown in Table 2.

[0123] Table 2 Reaction performance of catalyst in Example 2 at different temperatures

[0124] Reaction temperature (℃) <![CDATA[Acetic acid productivity (μmol / g cat / h)]]> Acetic acid selectivity (%) 150 0 / 210 181.4 100％ 230 349.3 63.9％ 250 564.0 50.2％

[0125] It can be seen from the data in Table 2 that when the temperature is 150°C, the reaction activity temperature of the catalyst cannot be reached, the catalyst is in an inactive state, and cannot catalyze the reaction, so no acetic acid is produced; when the temperature is increased, the catalyst is in an active state, catalyzing the oxidation of ethane to acetic acid. As the reaction temperature increases, its catalytic activity gradually increases, and the productivity of acetic acid continues to increase, but the selectivity of acetic acid decreases with increasing temperature.

[0126] The catalytic performance of the catalyst prepared in Example 2 was further studied at 210°C for different reaction times within 0 to 35 hours of continuous catalytic reaction. Figure 2The results show that the productivity of acetic acid is higher than 150 μmol / g at different reaction times within 0 to 35 h. cat / h, proving that its catalytic performance is stable and can maintain excellent catalytic activity for a long time.

[0127] In summary, the catalyst prepared in this invention for the selective oxidation of ethane to acetic acid not only significantly improves the activation efficiency of ethane's C–H bonds but also suppresses the occurrence of over-oxidation side reactions. Under relatively mild reaction conditions, the catalyst can stably convert ethane into a liquid product primarily composed of acetic acid. The resulting catalytic system offers advantages such as high structural stability, a simple synthesis process, low cost, and high product selectivity.

[0128] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A catalyst for selective oxidation of ethane to acetic acid, characterized in that: The catalyst comprises: a composite oxide formed by the combination of palladium, vanadium and oxygen and a TiO2 carrier; the TiO2 comprises at least anatase-type TiO2.

2. The catalyst according to claim 1, characterized in that The mass ratio of the Pd element to the V element in the catalyst is (0.4-5):100, and the mass ratio of the sum of the Pd and V elements in the catalyst to the TiO2 is (2-25):100; and / or, the TiO2 carrier is a TiO2 carrier containing a lattice dislocation structure; and / or, the specific surface area of ​​the TiO2 carrier is 20-80 m 2 / g; and / or, the particle size of the TiO2 carrier is 10 to 50 nm; and / or, the TiO2 also includes rutile TiO2; preferably, the volume ratio of the anatase TiO2 to the rutile TiO2 is (2 to 10):

1.

3. A method for preparing the catalyst according to any one of claims 1 to 2, characterized in that: The preparation method comprises dissolving soluble salts corresponding to palladium and vanadium and dihydrated oxalic acid in water to obtain a mixed solution, adding a TiO2 carrier into the mixed solution, and performing rotary evaporation, drying and a first calcination to obtain the catalyst.

4. The preparation method according to claim 3, characterized in that The soluble salt corresponding to the vanadium is any one or more selected from ammonium metavanadate, sodium vanadate, vanadium chloride, and vanadium sulfate; and / or, the soluble salt corresponding to the palladium is any one or more selected from palladium chloride, palladium nitrate, palladium sulfate, and palladium acetate; and / or, the molar ratio of the soluble salt corresponding to the vanadium to oxalic acid dihydrate is 1:(2-5); and / or, based on 1 mmol of the soluble salt corresponding to the vanadium, the amount of water added is 20-50 mL; and / or, the concentration of palladium in the mixed solution is 0.01-0.05 mg / mL; and / or, based on 10 mL of the mixed solution, the amount of the TiO2 carrier added is 0.1-0.5 g.

5. The preparation method according to claim 3, characterized in that The rotary evaporation temperature is 50-80°C; and / or, the drying temperature is 100-150°C, and the drying time is 10-15 hours; and / or, the first calcination temperature is 400-650°C, and the first calcination time is 2-5 hours; and / or, the first calcination atmosphere is air atmosphere.

6. The preparation method according to claim 3, characterized in that The TiO2 carrier is prepared by a second calcination of TiO2 powder.

7. The preparation method according to claim 6, characterized in that The second calcination temperature is 400-550° C.; and / or, the second calcination time is 2-5 hours; and / or, the second calcination atmosphere is air atmosphere.

8. Use of the catalyst according to claim 1 or 2 in the reaction of oxidizing ethane to produce acetic acid.

9. A method for preparing acetic acid by selectively oxidizing ethane using the catalyst according to claim 1 or 2, characterized in that: The catalyst is loaded into a reactor, and mixed reaction gas is introduced to carry out the reaction.

10. The method according to claim 9, characterized in that The mixed reaction gas includes C2H6, O2 and N2, the volume fraction of C2H6 in the mixed reaction gas is 60-80%, and the volume ratio of O2 to N2 is 1:(4-6); and / or, the flow rate of the mixed reaction gas is 20 to 40 mL / min; and / or, the reaction temperature is 200-250° C.; And / or, the reaction pressure is 1 to 5 atm.

Images