CN115920876A - A kind of preparation method and application of Nb-Ce-Zr denitration catalyst for SCR degradation - Google Patents

Abstract

The invention discloses a method for preparing NH ₃ Nb-Ce-Zr/TiO for degrading NO by SCR ₂ A catalyst and application thereof, belonging to the fields of atmospheric pollution treatment and environmental protection catalysis. The catalyst is TiO ₂ The catalyst is used as a carrier, nb is used as a main active component, and metals Ce and Zr are used as auxiliary agents, and the catalyst is prepared by adopting an impregnation method. Firstly, weighing C in a metering ratio ₁₀ H ₅ NbO ₂₀ ·xH ₂ O、Zr(NO ₃ ) ₄ ·5H ₂ O and Ce (NO) ₃ ) ₃ ·6H ₂ Dissolving O in deionized water, magnetically stirring to dissolve, and adding TiO as carrier into the solution ₂ And magnetically stirring in 70 ℃ water bath until the water is completely evaporated. Then the prepared powder is put in a drying oven to be dried overnight, roasted for 5 hours at 500 ℃, and naturally cooled to obtain the N for degrading NO by SCRb‑Ce‑Zr/TiO ₂ A catalyst. Nb-Ce-Zr/TiO of the invention ₂ The catalyst has high capability of degrading NO by SCR. Meanwhile, the auxiliary agents Ce and Zr and the active component Nb can play a good role in concerted catalysis, so that the medium-low temperature activity of the catalyst is improved, and the operation temperature window of the catalyst is widened.

Description

A kind of preparation method and application of Nb-Ce-Zr denitration catalyst for SCR degradation

technical field

The invention relates to a preparation method and application of an NH ₃ -SCR Nb-Ce-Zr catalyst for degrading NO. Specifically, it is a catalyst for effectively degrading gas pollutants, and belongs to the field of air pollution control and environmental protection and catalytic environment.

Background technique

Nitrogen oxides NO _X (NO, NO ₂ and N ₂ O) are one of the main pollutants in the atmosphere and also one of the main factors that produce smog, of which NO accounts for more than 90%. NO _X not only endangers human health, but also produces secondary pollution such as photochemical smog and acid rain. Therefore, reducing NOx emissions and improving NOx removal efficiency has become one of the hot research directions in the field of environmental catalysis.

SCR technology is currently a denitrification technology in commercial use. The core of this technology lies in the development of an efficient NO degradation catalyst. Under the action of the catalyst, an external reducing agent (NH ₃ ) is added to selectively reduce NO _X to N ₂ , making the _NOx is degraded. Therefore, the development of catalysts for SCR degradation of NO _X is imperative.

Commercial V ₂ O ₅ -WO ₃ /TiO ₂ catalysts at home and abroad have poor low-temperature activity and a narrow operating temperature window (350-400°C) (A remarkable catalyst combination to widen the operating temperature window of the selective catalytic reduction of NO by NH ₃ .Chem Cat Chem,2014,6:2263-2269.), and V ₂ O ₅ is a highly toxic substance, while molecular sieve catalysts have poor resistance to water and sulfur, and the preparation cost of noble metal catalysts is high, and they are prone to sulfur poisoning. It is easy to sinter and deactivate, and cannot remove NO _x economically and greenly, so it cannot meet the increasingly stringent emission standards of coal-fired power plants. Therefore, it is urgent to develop an SCR catalyst with high catalytic activity and wide operating temperature window.

The design idea of this patent is to screen out metal active components with good NO removal effect and low cost and low toxicity. Adding additives can not only promote the high dispersion of active components, but also strengthen the additives, active components and carriers. The interaction between them improves the low-temperature denitrification activity and stability of the catalyst. Therefore, according to the classification and structural characteristics of metals, we found that Nb element has similar properties to V because it is in the same group as V, and its toxicity is weaker than that of V. As a solid acid catalyst, niobium-based materials can significantly improve the acidity of the catalyst. So we explored the content of active component Nb and found that 10% active component Nb has certain high-temperature activity, but low-temperature activity is poor. According to literature reports, Cu, La, Fe, Co and In additives are introduced to improve the low-temperature activity of catalysts, but the low-temperature catalytic effects of Fe, Cu, La, Co, and In additives are not satisfactory. It was thought that the metal composite oxide structure of Cu, La, Fe, Co and In additives has the ability to store and release oxygen, and should have the ability to improve low-temperature activity and stability, but it failed to show.

Contents of the invention

The purpose of the present invention is to provide a preparation method and application of a Nb-Ce-Zr catalyst for degrading NO by SCR. The method has the advantages of simple process, easy operation and low cost. The Nb-Ce-Zr catalyst prepared by this method obviously improves the denitrification activity of the catalyst and widens the operating temperature window. In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A kind of Nb-Ce-Zr catalyst preparation method of SCR degradation NO comprises the following steps:

(a) Dissolve measured amounts of C ₁₀ H ₅ NbO ₂₀ .xH ₂ O, Zr(NO ₃ ) ₄ .5H ₂ O and Ce(NO ₃ ) ₃ .6H ₂ O in deionized water, and stir to dissolve;

(b) Add the measured _TiO2 carrier into the solution of (a), heat it in a magnetic stirrer at a constant temperature of 70°C, and dry it in a water bath;

(c) Place the sample in step (b) in an oven at 110°C and dry for 12 hours;

(d) Place the sample in step (c) in a muffle furnace at 500°C and calcinate for 5 hours to obtain the Nb-Ce-Zr/TiO ₂ catalyst.

According to the above scheme, the active component Nb is added in an amount of 3% to 15%, taking the mass of the carrier as 100%.

According to the above scheme, the additive Ce is added in an amount of 1% to 9% based on the weight of the carrier as 100%.

According to the above scheme, the addition amount of the auxiliary agent Zr is 0.5% to 3% based on the weight of the carrier as 100%.

The present invention also provides the application of the Nb-Ce-Zr catalyst for SCR prepared by the preparation method described in any one of the above technical solutions in the NO reaction of flue gas SCR degradation.

Compared with prior art, the present invention has following advantage:

(1) The Nb-Ce-Zr catalyst used for the SCR degradation NO reaction provided by the present invention has higher catalytic activity and a wider operating temperature window, and the NO conversion rate at 200 ° C is 80%, the highest NO conversion The reaction temperature with a rate of 100% is T _top =250-450°C, and the operating temperature window T ₈₀ is 210-500°C.

(2) The preparation method has simple process, easy control of preparation conditions, and is suitable for industrial production.

Description of drawings

Fig. 1 is the catalytic activity test figure of the catalyst prepared in embodiment 1, example 2, example 3, example 4 and example 5.

Fig. 2 is the catalytic activity test chart of the catalyst prepared in Example 1, Example 5, Example 6, Example 7, Example 8, Example 9 and Example 10.

Fig. 3 is the catalytic activity test chart of the catalyst prepared in Example 1, Example 11, Example 12, Example 13, Example 14 and Example 15.

Fig. 4 is the catalytic activity test diagram of the catalyst prepared in Example 1, Example 9 and Example 12.

Fig. 5 is the XRD spectrogram of the catalyst prepared in Example 1, Example 9 and Example 12.

Detailed ways

A kind of Nb-Ce-Zr catalyst preparation method of SCR degradation NO comprises the following steps:

(a) Dissolve measured amounts of C ₁₀ H ₅ NbO ₂₀ .xH ₂ O, Ce(NO ₃ ) ₃ .6H ₂ O and Zr(NO ₃ ) ₄ .5H ₂ O in deionized water, and stir to dissolve;

(b) Add the measured _TiO2 carrier into the solution of (a), heat it in a magnetic stirrer at a constant temperature of 70°C, and dry it in a water bath;

(c) Place the sample in step (b) in an oven at 110°C and dry for 12 hours;

(d) Place the sample in step (c) in a muffle furnace at 500°C, bake it for 5 hours, and cool it down to room temperature naturally to obtain the Nb-Ce-Zr/TiO ₂ catalyst.

According to the above scheme, the active component Nb is added in an amount of 3% to 15%, taking the mass of the carrier as 100%.

According to the above scheme, the additive Ce is added in an amount of 1% to 9% based on the weight of the carrier as 100%.

According to the above scheme, the addition amount of the auxiliary agent Zr is 0.5% to 3% based on the weight of the carrier as 100%.

The specific implementation of the present invention will be further described below in conjunction with some examples, but the present invention is not limited to the scope of the examples.

Embodiment 1 10%Nb/TiO ₂ synthesis of catalyst

Weigh 0.810g of C ₁₀ H ₅ NbO ₂₀ .xH ₂ O and dissolve it in 30ml of deionized water, mix and stir until dissolved; add 2g of TiO ₂ ; then heat and dry in a water bath in a magnetic stirrer at a constant temperature of 70°C; The sample was dried in a drying oven at 110°C for 12 hours; finally, it was roasted in a muffle furnace at 550°C for 5 hours; the calcined powder was crushed to 20-40 meshes with a tablet machine under a pressure of 10Mpa, and it was prepared 10% Nb/ _TiO2 catalyst.

Catalyst evaluation

The activity evaluation of the catalyst was carried out in a self-made continuous flow fixed-bed reactor. The reaction tube is a quartz tube with an inner diameter of 6 mm and a length of 33 cm. The reaction temperature is measured by a thermocouple placed in the middle of the reaction tube, and the reaction temperature is controlled by a temperature programming controller. The gas flow rate is controlled by a mass flow meter. The reaction raw material gas: 400ppm NH ₃ , 400ppm NO, 3% O ₂ and balance gas Ar. In the experiment, the catalyst dosage is 0.2g, the reaction temperature is 150-500°C, and samples are taken every 50°C. The flue gas analyzer (MRU, VARIO PLUS) was used for detection to calculate the conversion rate of NO. Figures 1, 2, 3, and 4 show the NO conversion curves of the catalyst at different temperature points, and see Table 1 for the NO conversion rate and operating temperature window at 200°C and the optimum activation temperature.

Embodiment 2-5

Compared with Example 1, only the Nb content of the catalyst active component is different, and the other processes are the same as in Example 1, that is, Nb/TiO ₂ catalysts with different Nb contents are prepared. The catalyst compositions of Examples 2 to 5 are shown in Table 1.

Catalyst evaluation

According to the evaluation method of Example 1, the NO conversion curves of the catalyst at different temperature points are shown in FIG. 1 . Table 2 shows the NO conversion rate and operating temperature window at 200°C and the optimum activation temperature.

Example 6-10

The difference from Example 1 is that the auxiliary agent Ce is added, and the content of the auxiliary agent Ce is different. Other processes are the same as in Example 1, specifically as follows: Weigh 0.810g C ₁₀ H ₅ NbO ₂₀ .xH ₂ O, 0.025g～ 0.454g Ce(NO ₃ ) ₂ ·6H ₂ O, 30ml deionized water, mix and stir until dissolved; add 2g TiO2; then heat and dry in a water bath in a magnetic stirrer at a constant temperature of 70°C; then place the dried sample in Dry in a drying oven at 110°C for 12 hours; finally bake in a muffle furnace at 550°C for 5 hours; crush the calcined powder to 20-40 meshes with a tablet machine under a pressure of 10Mpa, and obtain different Ce additives content of Nb-Ce/TiO ₂ catalyst. The catalyst compositions of Examples 6 to 11 are shown in Table 1.

Catalyst evaluation

According to the evaluation method of Example 1, the NO conversion curves of the catalyst at different temperature points are shown in FIG. 1 . Table 2 shows the NO conversion rate and operating temperature window at 200°C and the optimum activation temperature.

Examples 11-15

The difference from Example 10 is that the auxiliary agent Zr is added, and the content of the auxiliary agent Zr is different. Other processes are the same as in Example 1, specifically as follows: Weigh 0.810g C ₁₀ H ₅ NbO ₂₀ .xH ₂ O, 0.353g Ce (NO ₃ ) ₂ 6H ₂ O, 0.035g～0.209g Zr(NO ₃ ) ₄ .5H ₂ O 30ml deionized water, mix and stir until dissolved; add 2g TiO ₂ ; then heat in a magnetic stirrer at a constant temperature of 70°C Dry in a water bath; then place the dried sample in a drying oven at 110°C for 12 hours; finally bake it in a muffle furnace at 550°C for 5 hours; crush the calcined powder with a tablet machine under a pressure of 10Mpa The Nb-Ce-Zr/TiO ₂ catalysts with different Ce additive contents are obtained to 20-40 meshes. The catalyst composition of embodiment 12 to embodiment 16 is as shown in table 1

Catalyst evaluation

According to the evaluation method of Example 1, the NO conversion curves of the catalyst at different temperature points are shown in FIG. 1 . Table 2 shows the NO conversion rate and operating temperature window at 200°C and the optimum activation temperature.

Embodiment Molecular sieve catalyst composition table:

The specific embodiment catalyst composition is as shown in table 1:

Activity evaluation results:

The specific activity evaluation results are shown in Table 2:

XRD characterization

In Figure 5, the three catalysts all have the characteristic diffraction peaks of anatase and rutile phase TiO ₂ , and the anatase TiO ₂ crystal structure is the main one, and the three catalysts cannot detect Nb ₂ O ₅ , ZrO _{2 ,} etc. The characteristic diffraction peaks of metal oxides indicate that these substances may exist in amorphous or poor crystalline phases, or are highly dispersed on the catalyst surface, and it is also possible that the size of these crystallites may be lower than the detection limit of XRD; in addition, 10% Nb-7%Ce/TiO ₂ and 10%Nb-7%Ce-0.7%Zr/TiO ₂ catalysts showed weak characteristic diffraction peaks of cubic CeO ₂ crystal form, and the intensity of TiO ₂ characteristic diffraction peaks decreased, indicating that The addition of additives is beneficial to reduce the crystallinity of the catalyst. The grain size of anatase phase TiO ₂ (101) was calculated by using the Scherrer formula. The grain size of the catalyst was almost unchanged after the introduction of additive Ce, but after the introduction of additive Zr, 10% Nb-7% Ce/ _TiO The catalyst grain size decreased from 15.8 nm to 15.6 nm. This may be due to the enhancement of the interaction between the active component Nb, the coagent and the carrier TiO ₂ after the introduction of the promoter Zr into the catalyst, which promotes the reduction of the crystallite size to varying degrees.

Claims (7)

1. For NH ₃ The preparation method of the Nb-Ce-Zr denitration catalyst degraded by SCR is characterized by comprising the following steps:

(1) Weighing active component C in a metering ratio ₁₀ H ₅ NbO ₂₀ .xH ₂ O, auxiliary Zr (NO) ₃ ) ₄ .5H ₂ O and an auxiliary Ce (NO) ₃ ) ₃ ·6H ₂ Adding 30ml of deionized water into one or two or three of O, and stirring until the mixture is completely dissolved to obtain a transparent solution;

(2) Metered amount of TiO ₂ Adding a carrier into the transparent solution obtained in the step (1) to obtain mixed slurry;

(3) Adding a magnetic stirrer into the mixed slurry obtained in the step (2), heating the magnetic stirrer at a constant temperature of 70 ℃, and drying in a water bath;

(4) Putting the sample obtained in the step (3) in an oven, and drying overnight;

(5) And (4) grinding the sample obtained in the step (4) into fine powder, placing the fine powder in a muffle furnace, roasting, and naturally cooling to room temperature to obtain the SCR degradation NO catalyst.

2. The method according to claim 1, wherein the amount of Nb added is 3-15% based on 100% by mass of the carrier.

3. The preparation method of the catalyst for SCR degradation of NO as recited in any one of claims 1 to 2, wherein the mass percentage of the auxiliary Ce is 0.5-9% based on 100% of the mass of the carrier.

4. The method according to any one of claims 1 to 3, wherein the mass percent of Zr as an auxiliary agent is 0.5-3% based on 100% of the mass of the carrier.

5. Method for the preparation of a catalyst for the SCR degradation of NO according to any one of claims 1 to 4, wherein the support is TiO ₂ 。

6. The method according to any one of claims 1 to 5, wherein the stirring temperature is 70 ℃;

the drying temperature is 110 ℃;

the drying time is 12h;

the roasting temperature is 500 ℃;

the roasting time is 5 hours.

7. Use of a catalyst according to any one of claims 1-6 for SCR degradation of NO in denitration of exhaust gases.

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