A V2O5 / AC catalyst and its preparation method and application

Abstract

The present invention discloses a V2O5 / AC catalyst, a preparation method, and an application thereof. The V2O5 / AC catalyst is prepared by loading V2O5 onto a commonly used activated coke catalyst and optimizing the catalyst through a pre-oxidation process. The optimized catalyst has strong acidity and redox properties, exhibits good catalytic reduction denitration capabilities, and has the advantages of high catalytic efficiency and low activation temperature. This solves technical problems such as low denitration performance of activated coke and is suitable for selective catalytic denitration treatment of stationary source flue gas, such as flue gas generated in the steel industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of SCR catalysts, and in particular relates to a V2O5 / AC catalyst and a preparation method and application thereof. Background Art

[0002] With rapidly increasing energy consumption and the number of motor vehicles growing annually, NOx emissions are steadily rising. With the increasing maturity of SO2 removal technology, NOx removal has become a research hotspot. Flue gas denitrification is a widely adopted method for reducing NOx emissions in developed countries, offering high NOx removal efficiency. There are various flue gas denitrification technologies, the main ones being selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR). SNCR uses ammonia or urea as a reducing agent to react with NOx in the absence of a catalyst to produce N2 and H2O. The reaction temperature ranges from 900 to 1000°C, achieving a denitrification rate of 30-50%. Selective catalytic reduction (SCR) of nitrogen oxides (NOx) using ammonia as a reducing agent is an effective technology for reducing NOx in stationary flue gas. For the steel industry, the most mature and widely used denitrification technology is activated coke as a catalyst, offering high denitrification rates and meeting current emission regulations and standards. Catalysts are the core of the technology. Activated coke, due to its high specific surface area and strong resistance to toxicity, has been widely used in flue gas denitrification in the steel industry. However, the selective catalytic reduction reaction rate on the activated coke surface is relatively slow. While loading the activated coke with V2O5 improves the efficiency of the activated coke catalyst to a certain extent, it still only reaches approximately 70%. Therefore, improving the denitrification activity of SCR catalysts is currently the most important challenge facing activated coke denitrification catalysts. Furthermore, the operating temperature of current activated coke catalysts is relatively high, resulting in high catalyst costs. Therefore, the development of SCR catalysts with low activation temperatures and a wide activity temperature window is of great significance to the development of flue gas denitrification. Summary of the Invention

[0003] In response to the above technical problems, the present invention aims to provide a V2O5 / AC catalyst, a preparation method and an application thereof. The V2O5 / AC catalyst has the advantages of high catalytic efficiency and low activation temperature, and is suitable for catalytic denitrification of fixed source flue gas.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for preparing a V2O5 / AC catalyst comprises the following steps:

[0006] S1, adding activated coke and ammonium metavanadate measured at a loading amount of 5 wt% into a deionized water solution to obtain a mixed solution;

[0007] S2, stirring the mixed solution, heating in a water bath, drying, and calcining to obtain a V2O5 / AC catalyst to be treated;

[0008] S3, pre-oxidizing the V2O5 / AC catalyst to be treated in air for 4 hours to obtain a V2O5 / AC catalyst with a loading of 5%.

[0009] Furthermore, in step S1, the particle size of the activated coke is 40-80 mesh.

[0010] Furthermore, the step S2 is specifically stirring at room temperature for 1 hour, heating in a water bath at 80°C for 2 hours, then thermally drying at 120°C for 5 hours, and finally calcining at 350°C to 450°C in an inert atmosphere for 4 hours.

[0011] Furthermore, the inert atmosphere is N2.

[0012] Furthermore, in step S3, the pre-oxidation temperature is 250°C.

[0013] The present invention also claims protection for a V2O5 / AC catalyst prepared by the above preparation method.

[0014] The present invention also claims the use of the above-mentioned V2O5 / AC catalyst in flue gas denitrification.

[0015] The present invention loads V2O5 on an activated coke carrier and further optimizes the catalyst through a pre-oxidation process. Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The pre-oxidized V2O5 / AC catalyst has strong acidity and redox properties, which can effectively improve the adsorption and activation of NH3 and NO on the support, thereby broadening the active temperature window of the V2O5 / AC catalyst, regulating the proportion of reduced vanadium species and the oxidation of NO, and showing good low-temperature selective catalytic reduction of NOx ability;

[0017] (2) Through pre-oxidation treatment, the activation temperature of the catalyst is lowered, thereby reducing the cost of the catalyst, making it suitable for factory flue gas denitrification;

[0018] (3) The pre-oxidized V2O5 / AC catalyst has good sulfur resistance, which improves the denitrification efficiency of the catalyst to a certain extent.

[0019] Figures in the specification

[0020] Figure 1The figure is a comparison chart of the catalytic efficiency of the catalysts prepared in Example 1 and Comparative Examples 1 to 4.

[0021] Figure 2 This is the sulfur resistance performance diagram of V / AC-4 catalyst.

[0022] Figure 3 This is a graph showing the water resistance of V / AC-4 catalyst.

[0023] Figure 4 This is a test chart of the denitrification activity stability after 60 hours of catalytic reaction using V / AC-4 catalyst.

[0024] Figure 5 The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1 to 4 are shown. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the embodiments. It should be noted that, unless otherwise specified, the embodiments and features of the embodiments of the present invention may be combined with each other. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0026] Example 1 Preparation of V2O5 / AC Catalyst Pre-oxidized for 4h

[0027] A V2O5 / AC catalyst was prepared by an impregnation method. Stoichiometrically, appropriate amounts of activated coke and ammonium metavanadate were used, resulting in a 5 wt% loading. The activated coke was sieved through a 40-80 mesh screen. The 40-80 mesh activated coke and NH4VO3 were added to 100 mL of deionized water. After stirring at room temperature for 1 hour, the resulting solution was heated in an 80°C water bath to evaporate the solvent. The resulting solution was then dried in a 120°C oven for 5 hours. The dried sample was calcined at 400°C under a N2 atmosphere for 5 hours and finally pre-oxidized in a muffle furnace at 250°C for 4 hours to obtain the V2O5 / AC catalyst. The V2O5 loading was 5%, and the catalyst sample was designated V / AC-4.

[0028] Comparative Example 1 Preparation of AC Catalyst

[0029] The specific preparation method of the AC catalyst of this comparative example is to sieve the activated coke through 40-80 mesh, and the obtained catalyst sample is recorded as AC.

[0030] Comparative Example 2 Preparation of V2O5 / AC Catalyst without Pre-oxidation

[0031] This comparative example is compared with Example 1, the only difference being that no pre-oxidation is performed after calcination. The remaining steps are the same as those in Example 1, and the obtained catalyst sample is recorded as V / AC-0.

[0032] Comparative Example 3 Preparation of V2O5 / AC Catalyst Pre-oxidized for 3h

[0033] This comparative example is compared with Example 1, with the only difference being that the pre-oxidation time after calcination is 3 h. The remaining steps are the same as those in Example 1, and the obtained catalyst sample is designated as V / AC-3.

[0034] Comparative Example 4 Preparation of V2O5 / AC Catalyst Pre-oxidized for 5h

[0035] This comparative example is compared with Example 1, with the only difference being that the pre-oxidation time after calcination is 5 h. The remaining steps are the same as those in Example 1, and the obtained catalyst sample is recorded as V / AC-5.

[0036] Example 2 Catalytic Performance Test

[0037] The catalytic performance of the catalysts prepared in Example 1 and Comparative Examples 1-4 was tested, and XRD and BET analyses were performed.

[0038] 2.1 NO conversion rate

[0039] The catalytic performance test conditions are as follows: the activity measurement was carried out in a fixed bed quartz reactor using 0.7 g of catalyst. The inner diameter of the fixed bed was 5 mm. The feed gas mixture contained 500 ppm NO, 550 ppm NH3, and 5% O2 and N2 as the balance gas. The total flow rate of the feed gas was 200 cm 3 •min -1 , which is equivalent to 12000 h -1 The NO removal rate of each catalyst was evaluated under the conditions of GHSV (Gross High Temperature Saturation Value) and activity data were collected when the catalytic reaction actually reached steady state at each temperature. The composition of the inlet and outlet gases was continuously monitored using an infrared flue gas analyzer. The NO conversion value can be calculated as follows:

[0040] NO X Conversion(%)=([NO X ] in - [NO X ] out ) / [NO X ] in ×100%.

[0041] The results are as follows Figure 1As shown in the figure, (1) the NO conversion rate of catalyst AC is much lower than that of the V2O5 loaded catalyst, indicating that V2O5 loading can effectively improve the performance of activated coke catalyst in low-temperature selective catalytic reduction of NOx. (2) Preoxidation treatment can reduce the activation temperature of V2O5 loaded catalyst, and the preoxidation time can affect the catalytic performance of the catalyst. When the temperature is 240℃, the NO conversion rate of the unpreoxidized V / AC-0 catalyst is only 76%, while the NO conversion rates of the preoxidized V / AC-3, V / AC-4, and V / AC-5 exceed 80%, among which the conversion rate of the V / AC-4 catalyst can reach 94%. Therefore, the optimal preoxidation time for the V2O5 / AC catalyst is 4h.

[0042] 2.2 Sulfur and water resistance of V / AC-4 catalyst

[0043] In order to study the effect of SO2 and H2O on the catalyst activity, the V / AC-4 catalyst with the best catalytic performance was selected, and 300ppm SO2 and 5% H2O were introduced into the reaction gas mixture for catalytic reaction. The other conditions were the same as above. The results are shown in Figure 2. Figure 2 、 Figure 3 .

[0044] Depend on Figure 2 It can be seen that after adding SO2 into the reaction atmosphere, the catalytic activity of the catalyst not only did not decrease, but increased; it is worth noting that when the introduction of SO2 was stopped, the activity of the catalyst still maintained a slightly increasing trend, so the V / AC-4 catalyst has good sulfur resistance.

[0045] Depend on Figure 3 It can be seen that after adding 5% H2O to the reaction atmosphere, the catalytic activity of the catalyst not only did not decrease, but actually increased; it is worth noting that when the addition of H2O was stopped, the activity of the catalyst still maintained a slightly increasing trend, so the V / AC-4 catalyst has good water resistance.

[0046] 2.3 Denitrification activity stability of V / AC-4 catalyst

[0047] Select the V / AC-4 catalyst with the best catalytic performance, set the catalytic time to 0-60h, and monitor the catalytic activity in real time during the time period. The monitoring results are shown in Figure 4 As can be seen from the figure, during the 60h reaction process, the catalytic activity of the catalyst not only did not decrease, but slightly increased, which shows that the V / AC-4 catalyst has good stability.

[0048] 2.4 XRD analysis

[0049] The XRD analysis results are shown in Figure 5 , indicating that V2O5 is evenly distributed on the surface of activated coke.

[0050] 2.5 BET Analysis

[0051] BET analysis results are shown in Table 1. As shown, AC has a specific surface area of ​​214 m² / g, a pore volume of 0.025 cm³ / g, and an average pore diameter of 4.44 nm. Compared to AC, the specific surface area, pore volume, and average pore diameter of V / AC-0 decreased. With increasing preoxidation time, the specific surface area, pore volume, and average pore diameter of V / AC-3 and V / AC-4 increased, while the specific surface area, pore volume, and average pore diameter of V / AC-5 decreased significantly compared to V / AC-4. This is due to structural changes during the preoxidation process. While the specific surface area of ​​V / AC-4 is similar to those of V / AC-3 and V / AC-0, V / AC-4 exhibits the largest pore volume and average pore diameter, resulting in the best NH3-SCR performance. This indicates the formation of a new pore structure that is favorable for the NH3-SCR reaction.

[0052] Table 1 BET analysis results

[0053] Sample name <![CDATA[Specific surface area (m² / g -1 )]]> <![CDATA[Pore volume (cm³g -1 )]]> Pore ​​diameter (nm) AC 214 0.025 4.44 V / AC-0 186 0.018 4.07 V / AC-3 197 0.028 4.86 V / AC-4 196 0.030 5.08 V / AC-5 166 0.018 3.93

[0054] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art shall fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a V2O5 / AC catalyst, characterized in that: The following steps are involved: S1, adding activated coke and ammonium metavanadate measured at a loading amount of 5 wt% into a deionized water solution to obtain a mixed solution; S2, stirring the mixed solution, heating in a water bath, drying, and calcining under an inert atmosphere to obtain a V2O5 / AC catalyst to be treated; S3, pre-oxidizing the V2O5 / AC catalyst to be treated in air for 4 hours to obtain a V2O5 / AC catalyst with a loading of 5%; the pre-oxidation temperature is 250°C.

2. The preparation method according to claim 1, characterized in that The particle size of the activated coke in step S1 is 40-80 mesh.

3. The preparation method according to claim 1, characterized in that The stirring temperature in step S2 is room temperature, and the stirring time is 1 h.

4. The preparation method according to claim 1, characterized in that In step S2, the water bath heating temperature is 80° C. and the water bath heating is performed for 2 h.

5. The preparation method according to claim 1, characterized in that In step S2, the drying temperature is 120° C. and the drying time is 5 h.

6. The preparation method according to claim 1, characterized in that In step S2, the calcination temperature is 350° C. to 450° C., and the calcination time is 4 hours.

7. The preparation method according to claim 1, characterized in that The inert atmosphere is N2.

8. A V2O5 / AC catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the V2O5 / AC catalyst according to claim 8 in flue gas denitrification.

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