Preparation method and application of oligomeric vanadium (V)-based catalyst for preparing acetic acid through selective catalytic oxidation of ethyl acetate

Abstract

The invention discloses a preparation method and application of an oligomeric vanadium (V)-based catalyst for preparing acetic acid through selective catalytic oxidation of ethyl acetate. A series of V-doped catalysts are prepared by taking an oxide as a carrier and V precursors with different masses through an impregnation method. The catalyst carrier comprises TiO2 (titanium dioxide), gamma-Al2O3 (aluminum oxide), SiO2 (silicon dioxide), CeO2 (cerium dioxide) and ZrO2 ( The mass range of the V element is 0.5 to 10.0 weight percent, preferably 2.0 weight percent. Precise regulation and control of different VOx aggregation state structures are realized by screening carriers and controlling V loading capacity. The catalyst is simple in preparation process and has good selective catalytic performance on ester VOCs (such as ethyl acetate), the conversion rate of ethyl acetate can reach 20% while the selectivity of acetic acid reaches up to 93%, and the catalyst can stably and continuously run for 300 h.

Description

Technical Field

[0001] This invention relates to a method for preparing an oligomeric V-based catalyst and its application in the selective catalytic oxidation of ethyl acetate to acetic acid. Background Technology

[0002] VOCs, as major precursors to air pollution, seriously threaten the ecological environment and human health. Traditional VOCs treatment technologies (such as thermal incineration and catalytic complete oxidation) are mostly "end-of-pipe treatments," converting VOCs into CO2 and H2O, which suffer from high energy consumption and carbon resource waste. Developing VOCs resource-based conversion technologies to convert them into high-value chemicals is a preferred solution that combines environmental and economic benefits.

[0003] Ethyl acetate (EA), a typical ester-based VOC, is widely used in industries such as coatings, inks, and adhesives, resulting in substantial emissions. Its molecular structure contains easily activated C–O and C=O bonds, theoretically allowing for selective catalytic oxidation to convert it into chemicals such as acetic acid. However, the core challenge lies in precisely controlling the reaction pathway to preferentially achieve selective ester bond cleavage and oxidation, while inhibiting C–C bond cleavage and deep oxidation to generate CO. x .

[0004] V-based catalysts have attracted much attention in the catalytic oxidation of VOCs due to their excellent redox properties. Studies have shown that the catalytic performance of V-based catalysts is related to the surface VOCs... x The polymerization state of a species (monomer, oligomer, polymer, crystalline V₂O₅) is closely related, while the aggregation state is mainly determined by the V loading, support properties, and preparation process. In existing technologies, V-based catalysts are mostly used for the complete oxidation of VOCs or other selective oxidation reactions, such as the production of ethylene, ethanol, and formic acid. Research on the selective conversion of ethyl acetate to acetic acid is limited, and these catalysts suffer from low selectivity and unclear active site structures. For example, existing V-based catalysts are prone to degradation due to V₂O₅ oxidation. x Excessive polymerization or the formation of crystalline V₂O₅ leads to decreased product selectivity; conversely, insufficient interaction between the support and V species results in poor catalyst stability. Therefore, developing a catalyst capable of precisely controlling V₂O₅ is crucial. x V-based catalysts, which are oligomers and have strong interactions with the support, are crucial for the efficient conversion of ethyl acetate to acetic acid. Summary of the Invention

[0005] The purpose of this invention is to address the problems of selective ester bond cleavage and oxidation, and suppression of C–C bond cleavage during the selective oxidation of ethyl acetate to acetic acid. This invention provides a method for the selective catalytic oxidation of ethyl acetate to acetic acid using an oligomeric vanadium (V)-based catalyst (oligomeric vanadium (V)-based catalyst) with high efficiency. This catalyst exhibits high selectivity and high stability, enabling the resource utilization of ester-based VOCs.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: S1) Preparation of V-based catalysts with different oxide supports 1) Five V source solutions of the same concentration were prepared using oxalic acid dihydrate and ammonium metavanadate as raw materials and deionized water as solvent; 2) Take TiO2, γ-Al2O3, SiO2, CeO2 and ZrO2 and disperse them in five V source solutions of the same concentration respectively. Heat and stir each solution until it becomes viscous, dry and calcine to obtain five catalysts with a V loading of 2.0 wt% (denoted as 2% V-support; that is, 2.0% V-TiO2, 2.0% V-γ-Al2O3, 2.0% V-SiO2, 2.0% V-CeO2 and 2.0% V-ZrO2).

[0007] S2) Preparation of V-based catalysts with different loadings Using TiO2 oxide as a support, catalysts with different V loadings were prepared according to step S1) by using different ratios of oxalic acid dihydrate C2H2O4・2H2O to ammonium metavanadate NH4VO3; that is, a) using oxalic acid dihydrate and ammonium metavanadate as raw materials, different V source solutions of different concentrations were prepared by using different ratios of oxalic acid dihydrate C2H2O4・2H2O to ammonium metavanadate NH4VO3, and deionized water as solvent; b) a certain amount of TiO2 oxide was dispersed in the V source solutions of different concentrations obtained in step 1), and each was heated and stirred until it became viscous, dried, and calcined to obtain catalysts with different V loadings.

[0008] Furthermore, the preparation method is characterized in that: in step S1), the molar ratio of NH4VO3 to C2H2O4・2H2O is 1:1 to 1:3, the content of V is 2.0 wt%, the remainder is the carrier, and the amount of deionized water used is no more than 100 mL.

[0009] Furthermore, the preparation method is characterized in that the molar ratio of NH4VO3 to C2H2O4・2H2O in step S2) is 1:1 to 1:3.

[0010] Furthermore, the preparation method is characterized in that: during stirring in step S1), the temperature is controlled to not exceed 100 °C; the drying time is 10~24 h; and during calcination, the temperature is controlled to be 400~600 °C and the time is 1~4 h.

[0011] Furthermore, the preparation method is characterized in that: in step S2), the different V loading amounts are 0.5%~10.0%, and the rest are heated, stirred, dried, and calcined in the same manner as in step S1); that is, the heating and stirring are controlled at a temperature not exceeding 100 °C; the drying time is 10~24 h; and during calcination, the temperature is controlled at 400~600 °C and the time is 1~4 h.

[0012] Furthermore, the application of the V-based catalyst prepared by the above method in the selective oxidation of ethyl acetate to acetic acid is characterized by: setting the molar ratio of ethyl acetate to O2 to 1:0~1:3, the concentration of ethyl acetate to O2 to 3.0 vol%~10.0 vol%, the inert gas to be the equilibrium gas; the reaction temperature to 200~240 ℃; and the GHSV to be 5000~20000 mL g. -1 h -1 .

[0013] This invention provides a method for preparing an oligomeric V-based catalyst and its application in the selective catalytic oxidation of ethyl acetate to acetic acid. Compared with traditional catalysts, this method has the following advantages: Under mild reaction conditions, the oligomeric V-based catalyst prepared by this method exhibits good catalytic performance for the selective catalytic oxidation of ethyl acetate to acetic acid. It achieves an acetic acid selectivity of up to 93% while maintaining an ethyl acetate conversion of 20%, and can operate stably and continuously for 300 h. Furthermore, this method offers advantages such as simple catalyst preparation, readily available and inexpensive raw materials, high atom utilization, and environmental friendliness. Attached Figure Description

[0014] Figure 1 The performance of the different supported catalysts prepared in Example 1; Figure 2 The catalytic performance diagram is shown for the sample prepared in Example 2; Figure 3 The catalytic performance of the sample prepared in Example 3 under different oxygen atmospheres is shown in the graph. Figure 4 The above are aggregate state analysis diagrams of the sample prepared in Example 1. In the diagram: a is the XRD pattern; b is the Raman pattern; c is the UV-Raman pattern; d is the UV-vis DRS pattern; e is the E value calculated based on UV-vis DRS. g Value diagram; Figure 5The sample prepared for Example 1 was subjected to an atmosphere containing 5.0 vol% EA, 5.0 vol% O2, and a space velocity of 10000 mL g. -1 h -1 The stable test performance under the test condition of T=220 °C is shown in the figure. Detailed Implementation

[0015] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0016] Example 1 (Preparation of different oxide supports) (1) Weigh 0.24 g of oxalic acid and 0.12 g of ammonium metavanadate and add them to a beaker to dissolve in 50 mL of water. Stir at room temperature until dissolved to prepare V source solutions. Prepare 5 identical V source solutions in total. (2) Add 2.5 g of TiO2, γ-Al2O3, SiO2, CeO2 and ZrO2 to the 5 V source solutions prepared in step (1), respectively. Then heat to 80 °C with continuous stirring until 5 viscous slurries are formed. Then dry the 5 viscous slurries in an 80 °C oven for 12 h. Calcine the 5 dried samples in a muffle furnace in static air at 500 °C for 4 h to obtain 5 catalysts of 2.0% V-TiO2, 2.0% V-γ-Al2O3, 2.0% V-SiO2, 2.0% V-CeO2 and 2.0% V-ZrO2, respectively.

[0017] Figure 1 The figure shows the catalytic performance spectrum of the catalyst prepared in Example 1. It can be seen from the figure that, under the same reaction conditions, the anatase TiO2 support exhibits superior catalytic performance compared to other oxide supports. This highlights the role of TiO2 in stabilizing specific VOCs. x The unique role of the structure. This result mainly stems from the interaction between TiO2 and VO. x Strong metal-carrier interactions between species contribute to the stabilization of active VO. x Structure and regulate its electronic properties.

[0018] Example 2 (TiO2 catalysts with different V loadings) The same synthesis steps as the optimal 2% V-TiO2 catalyst in Example 1 were adopted. The difference in the synthesis process was that the support was fixed as TiO2 and the loading of V ranged from 0.5% to 10.0 wt%. The specific steps were as follows: (1) 0.07 g, 0.13 g, 0.24 g, 0.34 g, 0.62 g, 0.9 g and 1.23 g of oxalic acid were weighed and added to a beaker of 50 ml water and stirred at room temperature for 10 min to obtain 7 different oxalic acid solutions. (2) Weigh out 0.03 g, 0.06 g, 0.12 g, 0.16 g, 0.28 g, 0.42 g and 0.57 g of ammonium metavanadate respectively, and add them to the beakers of the seven different oxalic acid solutions obtained above under stirring. After stirring at room temperature for 20 min, add 2.5 g of anatase TiO2 to each, and then heat to 80 °C under continuous stirring until a viscous slurry is formed. Then place the seven slurries obtained in an 80 °C oven to dry for 12 h. The dried sample was calcined in a muffle furnace at 500 °C in static air for 4 h to obtain catalysts of 0.5% V-TiO2, 1.0% V-TiO2, 2.0% V-TiO2, 3.0% V-TiO2, 5.0% V-TiO2, 7.0% V-TiO2 and 10.0% V-TiO2 (also referred to as oligomeric vanadium (V)-based catalysts in this invention).

[0019] Figure 2 The figure shows the catalytic performance of the sample prepared in Example 2 for the selective oxidation of ethyl acetate to acetic acid. As can be seen from the figure, the TiO2 support without vanadium loading exhibits only negligible catalytic activity, consistent with its catalytic inertness as a support reported in the literature. With the introduction of V, the catalytic activity and selectivity strongly depend on the V loading. At a low loading of 0.5%, the catalyst achieved the highest ethyl acetate conversion, but the lowest acetic acid selectivity, which is likely related to the highly dispersed, isolated V₂O₃. x Species-related, such species have been reported to readily promote deep oxidation side reactions. When the V loading increased from 1% to 3%, the ethyl acetate conversion significantly improved from 7% to 22%. Notably, the selectivity for acetic acid peaked at a loading of 2% (93%). However, when the loading further increased to 5%–10%, both conversion and selectivity decreased. This trend is consistent with the effect of V loading. x The evolution of species from isolated states to oligomeric states and crystalline V₂O₅ phases with increasing loading is consistent with this trend. In summary, on the preferred TiO₂ support, the 2% V-TiO₂ catalyst achieves the best balance between activity and selectivity, realizing a 20% ethyl acetate conversion and a 93% acetic acid selectivity.

[0020] Example 3 (The effect of different oxygen atmospheres on catalytic performance) The optimal 2% V-TiO2 catalyst (vanadium loading 2.0%, anatase TiO2 as support) from Example 2 was used for testing, focusing on the effect of oxygen atmosphere on catalytic performance. The specific steps are as follows: the volume fraction of ethyl acetate was fixed at 5.0 vol%, nitrogen was used as the balance gas, and the total gas flow rate was maintained at 33.3 mL / min (ensuring a space velocity of 10000 mL g). ⁻1 h ⁻1 Only the oxygen volume fraction was adjusted, set to 0 vol%, 5.0 vol%, and 10.0 vol%, for a total of 3 variables; the reaction temperature was 220 °C, and sampling and analysis were started after the reaction was running stably.

[0021] Figure 3 The results showed that under anaerobic conditions, the conversion of ethyl acetate was less than 3%, with the main products being acetic acid and ethanol generated by hydrolysis. When a small amount of oxygen was introduced (EA to O2 molar ratio = 1:1), the conversion of ethyl acetate significantly increased to 34%, while maintaining a high acetic acid selectivity of 82%. However, further increasing the oxygen concentration to an oxygen-enriched state did not lead to a significant improvement in catalytic performance.

[0022] Figure 4 XRD in (a) shows that when the loading is ≥ 7.0%, two weak diffraction peaks appear at 2θ = 31.0° and 26.1°, corresponding to the (301) and (110) crystal planes of crystalline V2O5, respectively (PDF#41-1426). When the loading increases to 10.0%, the intensity of the V2O5 diffraction peaks significantly increases, indicating that crystalline V2O5 nanoparticles have formed on the TiO2 surface. Raman spectral results Figure 4 (b) indicates that when the loading is < 5%, only five characteristic peaks (142, 196, 394, 514, 638 cm⁻¹) belonging to the anatase TiO₂ vibrational mode were detected. -1 No characteristic peak of V2O5 crystal phase (approximately 995 cm⁻¹) was observed. -1 ), indicating VO x Species are dispersed in isolated or oligogregate states. Loading ≥ 7% at 995 cm² -1 A distinct peak belonging to the V=O stretching vibration in crystalline V₂O₅ appears at this location; Figure 4 The UV-Raman result in (c) shows that at a 3% content, at 280 cm⁻¹ -1 The location corresponds to the aggregate VO. x The vibrational peaks of the V–O–V bonds in the species, while when the content is 5%, it is the polymeric state of VO. xIt coexists with V2O5 microcrystals. Figure 4 The UV-Vis DRS of (d) in 4 and (e) in 4 show a polyvanadate absorption band at 425 nm and E g The value decreased significantly, indicating that the polymerized VO x It begins to form and coexist with the oligomeric state; the characteristic absorption band of the crystalline phase V₂O₅ appears at ~497 nm, E g The value continued to decrease to the 2.3–2.4 eV range, confirming that crystalline V2O5 nanoparticles had formed and were gradually increasing in number.

[0023] Table 1 shows the vanadium loading and surface V density of the xV-TiO2 catalyst.

[0024] Based on the V loading measured by XRF and the specific surface area of ​​the TiO2 support, the surface vanadium density of the catalyst was calculated (see Table 1). Analysis revealed that as the V loading increased from 0.5% to 10.0%, the surface V density increased from 1.1 V atoms·nm. -2 Significantly increased to 22.5 V atoms·nm -2 According to the theoretical monolayer density (isolated VO), x 2.3 V atoms·nm -2 ; Gathering VO x 7.5 V atoms·nm -2 It can be used to infer VO under different loads. x The state of existence of species: when the V density is less than 2.3 V atoms·nm -2 At that time, VO x It mainly exists in isolated states; in the range of 2.3–7.5 V atoms·nm -2 Within the range, low degree of polymerization and high degree of polymerization VO x Species coexistence; when above 7.5V atoms·nm -2 At this point, V₂O₅ crystals begin to form in the system. Calculation results show that V₂O₅ crystals appear when the loading exceeds 5%, a conclusion that corroborates previous characterization results.

[0025] Figure 5 2% V-TiO2 in 5.0 vol% EA, 5.0 vol% O2, space velocity 10000 mL h -1 g -1 The stability test performance is shown in the graph under the test condition of T=220 °C. The results show that the performance remains unchanged after 300 h of operation, indicating that the catalyst has good stability. Unless otherwise specified (e.g., vol%), all percentages mentioned above refer to weight percentage (wt%).

[0026] 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 method for preparing an oligomeric vanadium (V)-based catalyst for the selective catalytic oxidation of ethyl acetate to acetic acid, characterized in that, Includes the following steps: S1) Preparation of V-based catalysts with different oxide supports 1) Five V source solutions were prepared using oxalic acid dihydrate C2H2O4・2H2O and ammonium metavanadate NH4VO3 as raw materials and deionized water as solvent; 2) Take TiO2, γ-Al2O3, SiO2, CeO2, and ZrO2 and disperse them separately in the five V source solutions obtained in step 1). Heat and stir until a viscous solution is formed, dry, and calcine to obtain five catalysts with 2.0% V-TiO2, 2.0% V-γ-Al2O3, 2.0% V-SiO2, 2.0% V-CeO2, and 2.0% V-ZrO2. S2) Preparation of V-based catalysts with different loadings Using TiO2 oxide as a support, and following step S1), TiO2 catalysts with different V loadings were prepared by employing different ratios of oxalic acid dihydrate C2H2O4・2H2O to ammonium metavanadate NH4VO3.

2. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of NH4VO3 to C2H2O4・2H2O is 1:1 to 1:3, the content of V is 2.0 wt%, and the amount of deionized water used is no more than 100 mL.

3. The preparation method according to claim 1, characterized in that: The molar ratio of NH4VO3 to C2H2O4・2H2O mentioned in step S2) is 1:1 to 1:

3.

4. The preparation method according to claim 1, characterized in that: When heating and stirring in step 2), the heating temperature should be controlled to not exceed 100 °C; the drying time should be 10~24 h; when calcining, the temperature should be controlled to 400~600 °C and the time should be 1~4 h.

5. The preparation method according to claim 1, characterized in that: In step S2), the V loading in the TiO2 catalyst with different V loadings is 0.5% to 10.0%.

6. The application of the oligomeric vanadium (V)-based catalyst prepared by the method according to any one of claims 1-5 in the selective oxidation of ethyl acetate to acetic acid, characterized in that: In the selective oxidation of ethyl acetate to acetic acid using oligomeric vanadium (V)-based catalysts, the molar ratio of ethyl acetate to O2 is 1:0 to 1:3, the concentration of ethyl acetate is 3.0 vol% to 10.0 vol%, and N2 is used as the equilibrium gas; the reaction temperature is 200 to 240 °C; and the gas hourly space velocity (GHSV) is 5000 to 20000 mL g. -1 h -1 .

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