CN102716737B - Preparation of Catalyst Supported by Cerium-Zirconium Solid Solution and Its Application in NOx Removal - Google Patents

Abstract

The invention relates to a preparation method of transition metal chromium loaded on a cerium-zirconium solid solution as a carrier and its application in the selective catalytic oxidation of NO in flue gas. The preparation method of the catalyst comprises the following steps: 1. Dissolving cerium and zirconium oxychloride in deionized water and stirring, fully reacting, drying and calcining to obtain a cerium-zirconium solid solution carrier; 2. dissolving chromium nitrate and cerium-zirconium solid solution carrier in water and stirring, drying and calcining after reaction to obtain Catalyst Cr/ _{CexZr1 -xO2 .} The catalyst prepared by the present invention adds superoxide free radicals on the carrier for catalytic oxidation of NO, which is beneficial to the migration and diffusion of bulk oxygen, and promotes the probability of NO being oxidized on the surface of the carrier, thereby showing a good catalytic oxidation of NO by the catalyst. ability.

Description

Preparation of Catalyst Supported by Cerium-Zirconium Solid Solution and Its Application in NOx Removal

technical field

The invention relates to a catalyst preparation method and its application, in particular to a preparation method of transition metal chromium supported by cerium-zirconium solid solution and its application in selective catalytic oxidation of NO in flue gas, which belongs to inorganic chemical field.

Background technique

At present, China's energy consumption is increasing rapidly, the number of motor vehicles is increasing year by year, and the emission of NO _x is constantly increasing. The type of acid rain has changed from sulfuric acid to sulfuric acid and nitric acid. With the maturity of SO ₂ removal technology, NO _x removal has become a research focus.

Various methods applied to _NOx removal so far include: Selective Catalytic Reduction (SCR), Continuous Regeneration Replenishment (CRT), _NOx Storage and Reduction (NSR) and wet denitrification, etc. The common point of these methods is that NO ₂ has a higher activity than NO for NO _x removal. Moreover, according to literature reports, NO is basically insoluble in water, so it is not easy to be absorbed, but it can oxidize part of NO in flue gas to NO ₂ , so that the oxidation degree of NO _x (NO ₂ /NO _x ) reaches 50%~60%, At this time, it is equivalent to absorbing equal molecules of NO and NO ₂ (that is, equivalent to absorbing N ₂ O ₃ , N ₂ O ₃ has a relatively large solubility in water), so the absorption rate of NO _x is the highest. Therefore, if NO can be selectively catalyzed into NO ₂ , it will be an important contribution to similar denitrification methods.

At present, there are different ways of oxidation-absorption, mainly including liquid phase oxidation absorption method, gas phase oxidation absorption method and catalytic oxidation absorption method.

In the patent CN1658951A (2005), the gas phase oxidation-liquid phase absorption method is used, and the oxidant _ClO is used to oxidize a part of the low-oxide NOx in the waste gas stream into a high-valent oxide, and then absorb it with alkaline solution, absorb it with a reducing solution, wash it with water, and ammonia Injection and catalytic oxidation, etc.

Patent CN101791550A (2010) uses plasma technology to prepare nano-scale catalysts, which efficiently catalyzes and oxidizes NO at 50-150°C. After NO oxidation, it is absorbed by lye, and the conversion rate of NO can reach 80-96%.

The patent CN101773780A (2010) adopts plasma cooperative low-temperature catalytic oxidation of NO to remove NOx technology, and quantitatively oxidizes NO in the activated mixed gas to NO ₂ under the condition of 50~150°C.

In comparison, the catalytic oxidation method is superior to the gas-phase and liquid-phase oxidation methods, but the role of the carrier is not highlighted. In recent years, cerium-zirconium solid solution (Ce-Zr-O) has attracted much attention due to its high oxygen storage/release capacity. F. Ocampo et al. (F. Ocampo, B Louis, A Kiennemann, et al. CO ₂ methanolation over Ni-Ceria-Zirconia catalysts: effect of preparation and operating conditions [J]. Materials Science and Engineering, 2011, 19: 1- 11) The methanation of CO ₂ was studied using cerium-zirconium solid solution as a carrier, and the preparation method of cerium-zirconium solid solution was complicated by the pseudo-sol-gel method. Zhong Wang et al. (Zhong Wang, Zhenping Qu, Xie Quan, et al. Selective catalytic oxidation of ammonia to nitrogen over ceria-zirconia mixed oxides [J]. Applied Catalysis A: General, 2012, 411-412: 131-138) to The catalytic oxidation of ammonia (NH ₃ ) was studied using cerium-zirconium solid solution as a carrier, but cetyltrimethylammonium bromide (CTAB) was used as a dispersant in the preparation of the carrier, and the method was a bit complicated. B. Caglar et al. (B. Caglar, D. Uner. NO oxidation and NO _x storage over Ce-Zr mixed oxide supported catalysts [J]. Catalysis Communications, 2011, 12: 450-453) used cerium-zirconium solid solution for NO storage and reduction (NSR), but the preparation method of its carrier is more complicated, and the complexing agent citric acid and ethylene glycol are used. Moreover, in the current research on cerium-zirconium solid solution, it has not been applied to the catalytic oxidation of NO, so the present invention takes this as an innovative point, and uses it as a carrier to support transition metal chromium for catalytic oxidation of NO, and has achieved good results. Effect.

Contents of the invention

The purpose of the present invention is to provide a preparation method of a catalyst that uses cerium-zirconium solid solution as a carrier to support transition metal chromium, and applies the catalyst to _NOx removal.

The object of the present invention is achieved through the following technical solutions: a catalyst with cerium-zirconium solid solution as a carrier, the catalyst is a transition metal chromium (Cr/Ce _x Zr _1-x O ₂ ) supported by a cerium-zirconium solid solution as a carrier , its preparation method comprises the following steps:

Step 1: dissolving cerium nitrate and zirconium oxychloride in deionized water and stirring, drying and calcining after fully reacting to obtain a cerium-zirconium solid solution carrier;

Step 2: Dissolving chromium nitrate and cerium-zirconium solid solution carrier in water and stirring, drying and calcining after reaction to obtain catalyst Cr/ _Cex Zr _1-x O ₂ .

The Ce/Zr of cerium nitrate and zirconium oxychloride described in step 1 is 0.25:1～4:1 (mass ratio), described stirring time is 2～3 hours, and described reaction time is 4～6 hours. hours, the reaction temperature is 60-80°C, the calcination temperature is 400-600°C, and the calcination time is 4-6 hours.

The ratio of chromium nitrate and cerium-zirconium solid solution carrier described in step 2 is 3-10% (mass fraction), the described stirring time is 2-3 hours, the described reaction time is 4-6 hours, and the described The reaction temperature is 60-80°C, the calcination temperature is 300-600°C, and the calcination time is 4-6 hours.

The above-prepared catalyst Cr/ _Cex Zr _1-x O ₂ is applied to NO _x removal to catalyze the oxidation of NO to NO ₂ .

The reaction conditions for catalytic oxidation are: NO concentration 390 ppm, O ₂ 8v%, N ₂ as carrier gas, gas flow rate 100 mL/min, and reaction temperature 150-400°C.

Compared with the prior art, the present invention has the following remarkable points: (1) The present invention prepares cerium-zirconium solid solution with high oxygen storage/release capacity as a carrier through an easy-to-operate hydration method, and increases the catalytic oxidation of NO on the carrier Superoxide free radicals are beneficial to the migration and diffusion of bulk oxygen, and promote the probability of NO being oxidized on the surface of the carrier, thereby showing a good ability of the catalyst to catalyze the oxidation of NO; (2) The present invention simplifies the The preparation conditions are greatly simplified, and the preparation steps of the carrier are greatly simplified; (3) At the same time, in view of the excellent oxygen storage/release capacity of the cerium-zirconium solid solution, it is applied to the catalytic oxidation of NO and has achieved good catalytic effect.

In the present invention, the cerium-zirconium solid solution with high oxygen storage/release capacity is prepared by using water method as a carrier, and superoxide radicals are added to the carrier for catalytic oxidation of NO, which is beneficial to the migration and diffusion of bulk oxygen, and promotes the NO on the surface of the carrier. The probability of being oxidized shows that the catalyst has a good ability to catalyze the oxidation of NO.

The specific structure of the present invention is given by the following examples.

Description of drawings

Figure 1 is the XRD spectrum of the 7%Cr/Ce _0.14 Zr _0.86 O ₂ catalyst prepared in Example 1 of the present invention.

Fig. 2 is the Cr/Ce _x Zr _1-x O ₂ catalysts prepared by each embodiment of the present invention The catalytic oxidation effect figure (a: embodiment 1; b: embodiment 2; c: embodiment 3; d: : embodiment 4).

Detailed ways

Below in conjunction with embodiment, the present invention is described in further detail.

Embodiment one:

The catalyst for catalytic oxidation of NO prepared according to the present invention, wherein the Ce/Zr mass ratio of the cerium-zirconium solid solution carrier is 0.25:1, and the loading amount of the main active component chromium is 7% (mass fraction).

(1) Preparation of cerium-zirconium solid solution carrier by hydration method:

Dissolve cerium nitrate and zirconium oxychloride (according to the above ratio) in deionized water, stir for 2 hours, reflux in a water bath at 60°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 6 Hour;

(2) Loading active component chromium to cerium-zirconium solid solution carrier by impregnation method:

Dissolve chromium nitrate and cerium-zirconium solid solution carrier in deionized water according to the above ratio, stir for 2 hours, reflux in a water bath at 60°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 400°C in air for 6 hours. After the loading is completed, the catalyst 7%Cr/Ce _0.14 Zr _0.86 O ₂ is obtained. Its XRD spectrum is shown in Figure 1, and several peaks appearing in it completely conform to the characteristics of Ce _0.14 Zr _0.86 O ₂ (card number: 38-1437). peak, and the Cr element could not detect its characteristic peak due to the small amount of loading. The above results show that the catalyst prepared by this method conforms to the characteristics of cerium-zirconium solid solution.

Embodiment two:

The catalyst for catalytic oxidation of NO produced according to the present invention, wherein the Ce/Zr of the cerium-zirconium solid solution carrier is 4:1 (mass ratio), and the loading amount of the main active component chromium is 10% (mass fraction).

(1) Preparation of cerium-zirconium solid solution carrier by hydration method:

Dissolve cerium nitrate and zirconium oxychloride (according to the above ratio) in deionized water, stir for 2 hours, reflux in a water bath at 60°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 6 Hour;

(2) Loading active component chromium to cerium-zirconium solid solution carrier by impregnation method:

Dissolve chromium nitrate and cerium-zirconium solid solution carrier in deionized water according to the above ratio, stir for 2 hours, reflux in a water bath at 60°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 6 hours. After the loading is completed, the catalyst 10%Cr/Ce _0.72 Zr _0.18 O ₂ is obtained.

Embodiment three:

The catalyst for catalytic oxidation of NO prepared according to the present invention, wherein the Ce/Zr of the cerium-zirconium solid solution carrier is 1:1 (mass ratio), and the loading amount of the main active component chromium is 10% (mass fraction).

(1) Preparation of cerium-zirconium solid solution carrier by hydration method:

Dissolve cerium nitrate and zirconium oxychloride (according to the above ratio) in deionized water, stir for 2 hours, reflux in a water bath at 80°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 6 Hour;

(2) Loading active component chromium to cerium-zirconium solid solution carrier by impregnation method:

Dissolve chromium nitrate and cerium-zirconium solid solution carrier in deionized water according to the above ratio, stir for 2 hours, reflux in a water bath at 60°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 4 hours. After the loading is completed, the catalyst 10%Cr/Ce _0.5 Zr _0.5 O ₂ is obtained.

Embodiment four:

The catalyst for catalytic oxidation of NO produced according to the present invention, wherein the Ce/Zr of the cerium-zirconium solid solution carrier is 0.25:1 (mass ratio), and the loading amount of the main active component chromium is 7% (mass fraction).

(1) Preparation of cerium-zirconium solid solution carrier by hydration method:

Dissolve cerium nitrate and zirconium oxychloride (according to the above ratio) in deionized water, stir for 2 hours, reflux in a water bath at 80°C for 4 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 500°C in air for 6 Hour;

(2) Loading active component chromium to cerium-zirconium solid solution carrier by impregnation method:

Dissolve chromium nitrate and cerium-zirconium solid solution carrier in deionized water according to the above ratio, stir for 2 hours, reflux in a water bath at 80°C for 6 hours, dry in an oven at 120°C for 12 hours, and finally calcinate at 600°C in air for 5 hours. The loading was completed, and the catalyst 7%Cr/Ce _0.14 Zr _0.86 O ₂ was obtained.

Embodiment five:

The catalyst 7%Cr/Ce _0.14 Zr _0.86 O ₂ prepared in the above example 1 was simulated on a fixed bed for catalytic oxidation.

The reaction conditions for catalytic oxidation are: NO concentration 390 ppm, O ₂ 8v%, N ₂ as carrier gas, gas flow rate 100 mL/min, and reaction temperature 150-400°C.

The effect of catalytic oxidation is shown in Figure 2. It can be seen from Figure 2 that at 250 °C, the NO conversion rate is 44.32%, and at 300 °C, the NO conversion rate reaches 62.33%, and the catalytic effect is remarkable.

Embodiment six:

The catalyst 10%Cr/Ce _0.72 Zr _0.18 O ₂ prepared in the above-mentioned Example 2 was simulated for catalytic oxidation on a fixed bed.

The reaction conditions for catalytic oxidation are: NO concentration 390 ppm, O ₂ 8v%, N ₂ as carrier gas, gas flow rate 100 mL/min, and reaction temperature 150-400°C.

The effect of catalytic oxidation is shown in Fig. 2.

Embodiment seven:

The catalyst 10%Cr/Ce _0.5 Zr _0.5 O ₂ prepared in the above-mentioned Example 3 was simulated for catalytic oxidation on a fixed bed.

The reaction conditions for catalytic oxidation are: NO concentration 390 ppm, O ₂ 8v%, N ₂ as carrier gas, gas flow rate 100 mL/min, and reaction temperature 150-400°C.

The effect of catalytic oxidation is shown in Fig. 2.

Embodiment eight:

The catalyst 7%Cr/Ce _0.14 Zr _0.86 O ₂ prepared in the above-mentioned Example 4 was simulated for catalytic oxidation on a fixed bed.

The reaction conditions for catalytic oxidation are: NO concentration 390 ppm, O ₂ 8v%, N ₂ as carrier gas, gas flow rate 100 mL/min, and reaction temperature 150-400°C.

The effect of catalytic oxidation is shown in Fig. 2.

Claims (3)

1. method for preparing catalyst take cerium zirconium sosoloid as carrier is characterized in that described catalyst for take cerium zirconium sosoloid as carrier loaded transition metal chromium, and its preparation method may further comprise the steps:

Step 1: be dissolved in cerous nitrate and zirconium oxychloride in the deionized water and stirred 2～3 hours, dry and 400～600 ℃ of lower calcinings of temperature 4～6 hours after 4～6 hours in the lower reaction of 60～80 ℃ of temperature, get the cerium zirconium sosoloid carrier, wherein the mass ratio of the Ce/Zr of cerous nitrate and zirconium oxychloride is 0.25:1～4:1;

Step 2: chromic nitrate and cerium zirconium sosoloid carrier is soluble in water and stirred 2～3 hours, dry and 300～600 ℃ of lower calcinings of temperature 4～6 hours after 4～6 hours in 60～80 ℃ of lower reactions of temperature, get catalyst Cr/Ce _xZr _1-xO ₂, wherein the proportioning of chromic nitrate and cerium zirconium sosoloid carrier is 3～10wt%.

2. the catalyst take cerium zirconium sosoloid as carrier is at NO _xThe application that removes is characterized in that catalyst Cr/Ce claimed in claim 1 _xZr _1-xO ₂Be applied to NO _xRemoving, is NO with the catalytic oxidation of NO ₂

3. the catalyst take cerium zirconium sosoloid as carrier according to claim 4 is at NO _xThe application that removes is characterized in that the reaction condition of catalytic oxidation is: NO concentration 390ppm, O ₂8v%, N ₂Do carrier gas, gas flow is 100mL/min, and reaction temperature is 150～400 ℃.

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