CN118437344A - A modified iron vanadate catalyst and its preparation method and application - Google Patents

Abstract

The invention provides a modified ferric vanadate catalyst and a preparation method and application thereof, wherein the modified ferric vanadate catalyst comprises FeVO ₄ and a carrier, and the carrier comprises Nb _xTi_1‑xO_y, wherein x is more than 0 and less than or equal to 0.5, and y is more than 2 and less than or equal to 2.25. According to the modified ferric vanadate catalyst, the niobium-titanium composite oxide carrier is introduced, so that the modified ferric vanadate catalyst has excellent catalytic activity in NH ₃ -SCR denitration reaction, the temperature window of the catalyst is wide, the preparation method is simple, and the modified ferric vanadate catalyst can be applied to fixed source flue gas denitration under complex working conditions.

Description

A modified iron vanadate catalyst and its preparation method and application

Technical Field

The invention belongs to the technical field of catalysts and relates to a modified iron vanadate catalyst and a preparation method and application thereof.

Background technique

_NOx (nitrogen oxides) emissions can cause environmental problems such as acid rain, photochemical smog and global warming, and are also seriously harmful to human health. Therefore, controlling the emission of nitrogen oxides is crucial to environmental protection. _NH3 -SCR (ammonia selective catalytic reduction) is a highly efficient technology for removing nitrogen oxides. In view of the complex characteristics of fixed source emission conditions, it is necessary to design catalysts with high catalytic activity.

At present, many catalysts have been developed for the selective catalytic reduction of nitrogen oxides by ammonia, such as molecular sieve catalysts, metal oxide catalysts, etc. Among them, the most typical NH ₃ -SCR catalyst is V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ catalyst, but it has problems such as V ₂ O ₅ being easy to sublimate at high temperatures and having a narrow active temperature window. Therefore, many researchers are working hard to improve vanadium-based catalysts.

In recent years, FeVO ₄ has attracted extensive attention as a transition metal vanadate. It has the characteristics of low cost, high thermal stability, rich surface defects, etc., and has shown great potential in the field of NH ₃ -SCR. For example, CN 108465467A discloses a high-efficiency NH ₃ -SCR denitration catalyst for medium and low temperature flue gas, a preparation method and its application. The NH ₃ -SCR denitration catalyst comprises or consists of the following components: (a). α-Fe ₂ O ₃ ; (b). FeVO ₄ , which can be widely used in the selective catalytic reduction removal of nitrogen oxides in medium and low temperature flue gas. However, the FeVO ₄ catalyst has the problems of narrow temperature window and low N ₂ selectivity at high temperature, which limits its further application. In order to optimize the catalytic denitration performance of the FeVO ₄ catalyst, it needs to be modified.

Based on the above research, it is necessary to provide a modified iron vanadate catalyst, which has a wide temperature window and can be applied to fixed source flue gas denitrification with complex working conditions.

Summary of the invention

The purpose of the present invention is to provide a modified iron vanadate catalyst and a preparation method and application thereof. The modified iron vanadate catalyst exhibits excellent catalytic activity in NH ₃ -SCR denitration reaction by introducing a niobium-titanium composite oxide carrier, and the catalyst has a wide temperature window and a simple preparation method, and can be applied to fixed source flue gas denitration with complex working conditions.

In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a modified iron vanadate catalyst, the modified iron vanadate catalyst comprising FeVO ₄ and a carrier, the carrier comprising Nb _x Ti _1-x O _y , wherein 0＜x≤0.5, 2＜y≤2.25.

The present invention obtains an iron-vanadium-niobium-titanium catalyst by introducing a niobium-titanium composite oxide carrier on the basis of a FeVO ₄ catalyst, wherein Nb _x Ti _1-x O _y as a carrier can provide a large specific surface area and abundant acid sites for FeVO ₄ ; at the same time, due to the high dispersion of FeVO ₄ on the Nb _x Ti _1-x O _y carrier, the iron-vanadium-niobium-titanium catalyst exhibits stronger redox performance than FeVO _4. In addition, there is an interaction between FeVO ₄ and the Nb _x Ti _1-x O _y carrier, which increases the proportion of low-valent Fe and V species, thereby promoting the formation of surface adsorbed oxygen, and more surface adsorbed oxygen can promote the "fast SCR" reaction, which is beneficial to the improvement of low-temperature catalytic activity. Moreover, the NH ₃ -SCR reaction on FeVO ₄ only follows the ER mechanism. After the introduction of the Nb _x Ti _1-x O _y carrier, the iron vanadium niobium titanium catalyst can adsorb NO _x and promote the reaction, so that the catalyst can exhibit excellent catalytic activity in the NH ₃ -SCR denitrification reaction. At the same time, in the Nb _x Ti _1-x O _y carrier used in the present invention, the molar ratio of Nb and Ti should be matched with each other. If the x value is too large, that is, the amount of Nb is too much, the activity window of the catalyst will become narrower.

The carrier includes Nb _x Ti _1-x O _y , wherein 0＜x≤0.5, for example, 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5, 2＜y≤2.25, but not limited to the listed values, other values not listed in the numerical range are also applicable, preferably 0.1≤x≤0.5.

In the present invention, x is preferably 0.1-0.5, so as to promote the synergistic effect of Nb and Ti and further improve the performance of the catalyst.

The carrier includes Nb _x Ti _1-x O _y , wherein 2<y≤2.25, for example, 2.05, 2.1, 2.15, 2.2 or 2.25, but not limited to the listed values, and other values not listed within the numerical range are also applicable.

The Nb _x Ti _1-x O _y of the present invention satisfies chemical balancing, therefore, x and y correspond to each other, and after the x value is confirmed, the y value is confirmed accordingly.

Preferably, in the modified iron vanadate catalyst, the content of _FeVO4 is 3-20wt%, for example, it can be 3wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable, preferably 6-9wt%, and more preferably 9wt%.

In the modified iron vanadate catalyst of the present invention, the content of _FeVO4 will affect the catalytic performance. If the content of _FeVO4 is too little, the catalyst activity window will become narrower. If the content of _FeVO4 is too much, the catalyst activity window will become narrower. In the modified iron vanadate catalyst of the present invention, the low-temperature performance is better when the content of _FeVO4 is 9wt%.

In a second aspect, the present invention provides a method for preparing the modified iron vanadate catalyst as described in the first aspect, the preparation method comprising the following steps:

The iron source, the vanadium source and the solvent are mixed according to the formula amount, and then the carrier is added to the mixed solution to continue mixing, and then the solvent is removed and calcined to obtain the modified iron vanadate catalyst.

The modified iron vanadate catalyst of the present invention is prepared by an impregnation method, and the preparation method is simple and low in cost.

Preferably, oxalic acid is added when the iron source, vanadium source and solvent are mixed.

Preferably, the iron source comprises ferric nitrate nonahydrate, the vanadium source comprises NH ₄ VO ₃ (ammonium metavanadate), and the solvent comprises deionized water.

In the present invention, the iron source and the vanadium source are first dissolved in water, and oxalic acid (H ₂ C ₂ O ₄ ·2H ₂ O) needs to be added to the deionized water in advance to promote the dissolution of NH ₄ VO ₃ .

Preferably, the method of removing the solvent comprises rotary evaporation and drying in sequence.

Preferably, the calcination temperature is 500-600°C, such as 500°C, 550°C or 600°C, and the calcination time is 3-6h, such as 3h, 4h, 5h or 6h, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

Preferably, the calcining atmosphere is an air atmosphere.

Preferably, the method for preparing the carrier comprises the following steps:

According to the formula, the niobium source, the titanium source and the solvent are mixed, and then a precipitant is added to react. After the reaction is completed, solid-liquid separation, washing, drying and sintering are performed to obtain the carrier.

Preferably, the niobium source includes niobium oxalate (C ₁₀ H ₅ NbO ₂₀ ), the titanium source includes titanium sulfate, and the solvent includes deionized water.

Preferably, after the precipitant is added, the pH of the reaction system is 7-14, for example, 7, 8, 9, 10, 11, 12, 13 or 14, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

Preferably, the precipitant comprises any one of ammonia water, sodium hydroxide or potassium hydroxide, or a combination of at least two thereof.

Preferably, the reaction time is 10-15 h, for example, 10 h, 12 h, 14 h or 15 h, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

Preferably, the sintering temperature is 500-700°C, such as 500°C, 600°C or 700°C, and the sintering time is 5-7h, such as 5h, 6h or 7h, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

Preferably, the sintering atmosphere is an air atmosphere.

As a preferred technical solution of the preparation method of the present invention, the preparation method comprises the following steps:

(1) Mixing a niobium source, a titanium source and a solvent according to the formula, then adding a precipitant, reacting for 10-15 hours, performing solid-liquid separation, washing and drying, and then heating to 500-700° C. for sintering for 5-7 hours to obtain a carrier;

(2) According to the formula, the iron source, vanadium source, oxalic acid and solvent are mixed, and then the carrier described in step (1) is added to the mixed solution to continue mixing, and then rotary evaporation and drying are performed in sequence, and then the temperature is raised to 500-600° C. and calcined for 3-6 hours to obtain the modified iron vanadate catalyst.

In a third aspect, the present invention provides an application of the modified iron vanadate catalyst as described in the first aspect, wherein the application includes use for selective catalytic reduction of ammonia.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention introduces a niobium-titanium composite oxide carrier on the basis of the FeVO ₄ catalyst to obtain an iron-vanadium-niobium-titanium catalyst, so that the modified iron vanadate catalyst exhibits excellent catalytic activity in the NH ₃ -SCR denitration reaction. The modified iron vanadate catalyst has a wide temperature window and a simple preparation method, and can be applied to fixed-source flue gas denitration with complex working conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a test graph of _NOx conversion rates of the catalysts described in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 of the present invention;

FIG2 is a graph showing the _N2 selectivity test of the catalysts described in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention;

FIG3 is a test diagram of NO _x conversion rates of the catalysts described in Examples 1, 4 and 5 of the present invention;

FIG. 4 is a graph showing the N ₂ selectivity test of the catalysts described in Examples 1, 4, and 5 of the present invention.

Detailed ways

The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

Example 1

This embodiment provides a modified iron vanadate catalyst, the modified iron vanadate catalyst comprises FeVO ₄ and a carrier, the carrier is Nb _0.2 Ti _0.8 O _2.1 , and the content of FeVO ₄ in the modified iron vanadate catalyst is 9wt%;

The preparation method of the modified iron vanadate catalyst comprises the following steps:

(1) Dissolving niobium oxalate in deionized water according to the formula amount, then mixing, adding ammonia water to make the system pH = 10, reacting for 10 hours, filtering and washing after the reaction to pH = 7, drying at 120° C. for 12 hours, and then heating to 500° C. at a heating rate of 5° C./min in an air atmosphere for sintering for 5 hours to obtain a carrier;

(2) According to the formula, ferric nitrate nonahydrate, ammonium metavanadate, oxalic acid and deionized water are mixed for 1 hour, and then the carrier described in step (1) is added to the mixed solution and the mixture is mixed for 1.5 hours, followed by rotary evaporation and drying at 120°C for 12 hours, and then the temperature is increased to 500°C in an air atmosphere at a heating rate of 5°C/min and sintered for 3 hours to obtain the modified iron vanadate catalyst; wherein the amount of oxalic acid added is 15wt% of the mass of ammonium metavanadate.

Example 2

This embodiment provides a modified iron vanadate catalyst, which is the same as that of embodiment 1 except that the content of FeVO ₄ is 6wt%;

The preparation method of the modified iron vanadate catalyst is the same as that of Example 1 except that the formula amount is adaptively changed.

Example 3

This embodiment provides a modified iron vanadate catalyst, which is the same as that of embodiment 1 except that the content of FeVO ₄ is 15wt%;

The preparation method of the modified iron vanadate catalyst is the same as that of Example 1 except that the formula amount is adaptively changed.

Example 4

This embodiment provides a modified iron vanadate catalyst, which is the same as that of Embodiment 1 except that the carrier is Nb _0.1 Ti _0.9 O _2.05 ;

The preparation method of the modified iron vanadate catalyst is the same as that of Example 1 except that the formula amount is adaptively changed.

Example 5

This embodiment provides a modified iron vanadate catalyst, which is the same as that of Embodiment 1 except that the carrier is Nb _0.5 Ti _0.5 O _2.25 ;

The preparation method of the modified iron vanadate catalyst is the same as that of Example 1 except that the formula amount is adaptively changed.

Comparative Example 1

This comparative example provides a catalyst, wherein the catalyst is FeVO ₄ ;

The method for preparing the catalyst is the same as that of Example 1 except that step (1) is not performed and a carrier is not added in step (2).

Comparative Example 2

This comparative example provides a catalyst, wherein the catalyst is Nb _0.2 Ti _0.8 O _2.1 ;

The preparation method of the catalyst is the same as that of Example 1 except that step (2) is not performed.

The catalysts obtained in the above examples and comparative examples were pressed into tablets and sieved to 40-60 mesh (passing through a 40 mesh sieve but not through a 60 mesh sieve), and the particles were placed in a catalyst activity evaluation device, and the activity evaluation was carried out in a fixed bed reactor. The test conditions were: [NO] = [NH ₃ ] = 500ppm, [O ₂ ] = 5%, [H ₂ O] = 5%, N ₂ as a balance gas, a total gas flow rate of 500mL/min, a reaction space velocity of 100000h ^-1 , and a reaction temperature of 160-490°C. The gas concentrations in the inlet and outlet gas streams were measured using an FTIR spectrometer (Thermo Fisher IGS) to test the NO _x conversion rate and N ₂ selectivity; the NO _x conversion rate test graphs of the catalysts described in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 are shown in FIG1 , and the N ₂ selectivity of the catalysts described in Example 1, Example 2, Example 3 and Comparative Example 1 are shown in FIG2 . The NO _x conversion test graph of the catalysts described in Example 1, Example 4 and Example 5 is shown in FIG. 3 , and the N ₂ selectivity of the catalysts described in Example 1, Example 4 and Example 5 is shown in FIG. 4 .

The test results are shown in Table 1:

Table 1

From Table 1 we can see that:

The catalyst obtained by the present invention has a wider temperature window; from Example 1 and Comparative Examples 1-2, combined with Figures 1 and 2, it can be seen that the introduction of niobium-titanium composite oxide into _FeVO4 in the present invention can improve the temperature window of the catalyst; from Example 1 and Examples 2-5, it can be seen that the content of iron vanadate in the catalyst of the present invention and the molar ratio of Nb and Ti in the carrier will affect the catalyst performance.

In summary, the present invention provides a modified iron vanadate catalyst and a preparation method and application thereof. The modified iron vanadate catalyst exhibits excellent catalytic activity in NH ₃ -SCR denitration reaction by introducing a niobium-titanium composite oxide carrier, and the catalyst has a wide temperature window and a simple preparation method, and can be applied to fixed-source flue gas denitration with complex working conditions.

The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims (10)

1. The modified ferric vanadate catalyst is characterized by comprising FeVO ₄ and a carrier, wherein the carrier comprises Nb _xTi_1-xO_y, x is more than 0 and less than or equal to 0.5, and y is more than 2 and less than or equal to 2.25.

2. The modified iron vanadate catalyst according to claim 1, wherein x is 0.1.ltoreq.0.5;

preferably, the content of FeVO ₄ in the modified ferric vanadate catalyst is 3-20wt%.

3. A method for preparing the modified iron vanadate catalyst according to claim 1 or 2, comprising the steps of:

Mixing an iron source, a vanadium source and a solvent according to the formula amount, adding a carrier into the mixed solution obtained by mixing, continuously mixing, removing the solvent and roasting to obtain the modified ferric vanadate catalyst.

4. The method according to claim 3, wherein oxalic acid is further added when the iron source, the vanadium source and the solvent are mixed.

5. The method according to claim 3 or 4, wherein the solvent removal means comprises rotary evaporation and drying performed sequentially;

preferably, the roasting temperature is 500-600 ℃ and the time is 3-6h.

6. The method of any one of claims 3 to 5, wherein the method of preparing the carrier comprises the steps of:

Mixing a niobium source, a titanium source and a solvent according to the formula amount, adding a precipitant for reaction, and carrying out solid-liquid separation, washing, drying and sintering after the reaction is finished to obtain the carrier.

7. The process according to claim 6, wherein the pH of the reaction system is 7 to 14 after the addition of the precipitating agent;

Preferably, the precipitant comprises any one or a combination of at least two of ammonia water, sodium hydroxide or potassium hydroxide.

8. The method according to claim 6 or 7, wherein the reaction time is 10 to 15 hours;

Preferably, the sintering temperature is 500-700 ℃ and the sintering time is 5-7h.

9. The preparation method according to any one of claims 3 to 8, characterized in that the preparation method comprises the steps of:

(1) Mixing a niobium source, a titanium source and a solvent according to the formula amount, adding a precipitator, reacting for 10-15 hours, performing solid-liquid separation, washing and drying, and then heating to 500-700 ℃ for sintering for 5-7 hours to obtain a carrier;

(2) Mixing an iron source, a vanadium source, oxalic acid and a solvent according to the formula amount, adding the carrier obtained in the step (1) into the mixed solution obtained by mixing, continuously mixing, sequentially performing rotary evaporation and drying, and heating to 500-600 ℃ for roasting for 3-6 hours to obtain the modified ferric vanadate catalyst.

10. Use of the modified iron vanadate catalyst according to claim 1 or 2, wherein the use comprises for ammonia selective catalytic reduction.