CN103736479B - A kind of cerium titanium stannum composite oxide catalysts for denitrating flue gas and preparation method thereof - Google Patents

Abstract

The invention discloses a CeO ₂ / _Tix Sn _1-x O ₂ composite oxide denitration catalyst with Ti _x Sn _1-x O ₂ (0<x<1) solid solution as a carrier, which is applied to selective catalytic denitration of ammonia. It is to mix TiCl ₄ ethanol solution and SnCl ₄ aqueous solution with a certain molar ratio of titanium and tin evenly, and under vigorous stirring, add ammonia water to the mixed solution drop by drop until the pH of the solution is 9.0, make it precipitate completely, age overnight, wash Remove Cl ^‑ , dry at 110°C, and then bake at 550°C for 4 hours in an air atmosphere in a muffle furnace to obtain a Ti _x Sn _1‑x O ₂ solid solution. Using Ti _x Sn _1‑x O ₂ solid solution as a carrier, the active component CeO ₂ was loaded by impregnation method, stirred for 3 hours, evaporated to dryness in an oil bath at 100°C, dried at 110°C for 12 hours, and calcined at 500°C or 750°C in an air atmosphere 4h, the CeO ₂ /Ti _x Sn _1‑x O ₂ composite oxide catalyst was obtained. The catalyst prepared by the invention has large specific surface area, good thermal stability, higher NH ₃ -SCR activity compared with a single carrier, excellent water resistance and sulfur resistance, and is an environment-friendly catalyst. At the same time, the preparation method of the catalyst is simple, the equipment is simple, and the raw materials used are cheap and easy to obtain.

Description

A cerium-titanium-tin composite oxide catalyst for flue gas denitrification and its preparation method

Technical field:

The invention relates to a cerium-titanium-tin composite oxide catalyst for the purpose of flue gas denitrification.

Background technique:

Nitrogen oxides (NOx) are the main air pollutants, and it is the chief culprit of photochemical smog and acid rain, which directly threatens the ecological environment. Therefore, countries all over the world pay more and more attention to the issue of NOx emission control and treatment. Ammonia Selective Catalytic Reduction (NH ₃ -SCR) technology is widely used in industrial boilers and power plant units for denitrification treatment due to its high denitrification efficiency and relatively low operating costs. At present, the successfully operating commercial NH ₃ -SCR catalyst is the V ₂ O ₅ -WO ₃ (or MO ₃ )/TiO ₂ catalyst developed in Japan in the 1970s. The catalyst is characterized by a NOx removal efficiency of more than 80% in coal-fired boiler power plants, and has good sulfur resistance performance, and its working temperature is 280-420°C. However, the active component V ₂ O ₅ of the V ₂ O ₅ -WO ₃ (or MO ₃ )/TiO ₂ catalyst is poisonous, and the anatase TiO ₂ carrier in the catalyst is easily transformed into rutile TiO ₂ at high temperature, resulting in The specific surface area decreases, thereby reducing the catalyst activity.

Contents of the invention

China is a country rich in rare earth resources, and the rare earth metal oxide cerium oxide (CeO ₂ ) has been practically used in NOx catalytic elimination, especially in three-way catalysis due to its excellent oxygen storage and release performance and redox performance. At the same time, Ti _x Sn _1-x O ₂ solid solution effectively combines the characteristics of both TiO ₂ and SnO ₂ , and has received extensive attention in the fields of photocatalysis, lithium batteries, and gas sensors. The study found that the Ti _x Sn _1-x O ₂ solid solution prepared by the co-precipitation method has a rutile crystal structure, and has a specific surface area larger than that of single TiO ₂ and SnO ₂ , and the structure remains unchanged after high-temperature calcination. _In addition, we found that the Ti _x Sn _{1-x O 2 solid} solution was used as the _support and _{CeO 2} was the active component _. TiO ₂ and CeO ₂ /SnO ₂ catalysts have more significant advantages. The CeO ₂ /Ti _x Sn _1-x O ₂ catalyst also provides a new solution to the shortcomings of the active component V ₂ O ₅ of the V ₂ O ₅ -WO ₃ (or MO ₃ )/TiO ₂ catalyst, which is toxic and deactivated at high temperature. train of thought.

Through a facile preparation method, we successfully prepared a series of cerium-titanium-tin composite oxide catalysts by combining the advantages of CeO ₂ and Ti _x Sn _1-x O ₂ solid solutions, which exhibited excellent performance in NH ₃ -SCR catalysis Excellent catalytic performance. At the same time, the raw materials used in the catalyst are cheap and easy to obtain, the preparation method is simple and fast, the energy consumption is low, and the environmental pollution is small, so it has potential application prospects in the field of NH ₃ -SCR catalytic denitrification.

The purpose of the present invention is to provide a metal composite oxide catalyst with high activity and high thermal stability and its preparation method, which can be applied in NH ₃ -SCR denitrification catalysis.

The principle of the present invention is as follows: SnO ₂ has a rutile crystal structure, and when Sn ⁴⁺ and Ti ⁴⁺ ions are co-precipitated with NH ₃ ·H ₂ O, SnO ₂ preferentially forms rutile crystal nuclei, and then induces Ti ⁴⁺ ions to form rutile Type Ti-Sn compound seed crystal grows up after crystal aging, and obtains rutile type Ti-Sn solid solution after roasting. Utilizing the interaction between the active component and the support, the active component CeO2 was dispersed _on the surface of the titanium-tin solid solution by the impregnation method to prepare the metal composite oxide catalyst.

The purpose of the present invention is achieved with the following technical solutions:

A method for preparing a CeO ₂ /Tix Sn _{1-x O 2} metal oxide catalyst supported by a Ti _x Sn _1-x O ₂ [0.25≤x≤0.75] solid solution, comprising the following steps:

Step 1. Mix the TiCl ₄ ethanol solution and the SnCl ₄ aqueous solution with a titanium-tin molar ratio of 1:3-3:1, and then add concentrated ammonia water dropwise to the mixed solution under vigorous stirring until the pH of the solution=9.0 , to make the precipitation complete, aging overnight, washing away Cl ^- , drying at 110°C, and then calcining at 550°C for 4h in an air atmosphere in a muffle furnace to obtain a Ti _x Sn _1-x O ₂ solid solution;

Step 2. Use the Ti _x Sn _1-x O ₂ solid solution obtained in step 1 as the carrier, and use 0.1mol L ^-1 Ce(NO ₃ ) ₃ 6H ₂ O solution as the impregnation solution to impregnate the Ti _x Sn _{1-x On} the _O2 carrier, the active component CeO2 accounted for 4.5%-22.5% of the mass fraction of the catalyst, stirred for 3h, evaporated to dryness in an oil bath at 100°C, dried at 110°C for 12h, and calcined at 500°C-750°C for 4h in an air atmosphere , to obtain a ceria-based catalyst supported by Ti _x Sn _1-x O ₂ solid solution.

A CeO ₂ / _Tix Sn _1-x O ₂ metal oxide catalyst supported by a Ti _x Sn _1-x O ₂ (0<x<1) solid solution prepared by the above method.

The present invention has the following advantages:

1. The raw materials used are cheap and easy to obtain, the preparation method is simple, the equipment is simple, and the environment is friendly;

2. The catalyst of the present invention has a large specific surface area rutile structure, and the catalyst has good thermal stability;

3. Compared with a single carrier, the catalyst of the present invention has higher NH ₃ -SCR activity;

4. The catalyst of the present invention has excellent water resistance and sulfur resistance.

Description of drawings

Figure 1 is the XRD patterns of different ratios of titanium-tin solid solution catalysts. Figure 1A is the XRD pattern of pure support, from bottom to top are anatase TiO ₂ , rutile TiO ₂ , Ti _0.75 Sn _0.25 O ₂ , Ti _0.5 Sn _0.5 O ₂ , Ti _0.25 Sn _0.75 O ₂ and SnO ₂ ; Figure 1B is the XRD pattern of supported CeO ₂ catalysts, from bottom to top are 7.5Ce/TiO ₂ (anatase), 7.5Ce/Ti _0.75 Sn _0.25 O ₂ , 7.5Ce/Ti _0.5 Sn _0.5 O ₂ , 7.5 Ce/Ti _0.25 Sn _0.75 O ₂ and 7.5Ce/SnO ₂ .

Fig. 2 is the performance comparison results of NO+NH ₃ +O ₂ reaction of 7.5Ce/TiO ₂ , 7.5Ce/SnO ₂ , 7.5Ce/Tix Sn _{1-x O 2} catalysts and industrial catalysts. Figure 2A is the conversion of NO and Figure 2B is the selectivity of _N2 .

Fig. 3 is the performance comparison results of NO+NH ₃ +O ₂ reaction of catalysts with different contents of CeO ₂ /Ti _0.5 Sn _0.5 O ₂ .

Figure 4 shows the water and sulfur resistance performance results of the 7.5Ce/Ti _0.5 Sn _0.5 O ₂ catalyst at 300°C.

Specific implementation method

Embodiment 1.CeO ₂ /Ti _x Sn _1-x O ₂ preparation of catalyst

Mix TiCl ₄ (x mol·L ^-1 ) ethanol solution and SnCl ₄ (1-x mol·L ^-1 )[0.25≤x≤0.75] aqueous solution in equal volumes, and add ammonia water drop by drop under vigorous stirring solution until the pH of the solution is 9.0, make it precipitate completely, age overnight, wash away Cl ^- , dry at 110°C, and then bake in a muffle furnace at 550°C for 4h in an air atmosphere to obtain Ti _x Sn _{1-x O2} solid solution. Prepare a 0.1mol L ^-1 Ce(NO ₃ ) ₃ 6H ₂ O solution, then impregnate the above solution on a Ti _x Sn _1-x O ₂ support so that the mass fraction of CeO ₂ accounts for 7.5% of the total mass of the catalyst, and stir 3h, evaporated to dryness in oil bath at 100°C, dried at 110°C for 12h, calcined at 500°C in air atmosphere for 4h, the sample is marked as 7.5Ce/TixSn _{1-x ,} the catalyst with TiO ₂ or SnO ₂ as the carrier is marked as 7.5Ce /Ti and 7.5Ce/Sn. With other conditions unchanged, the calcination temperature of the 7.5Ce/Ti _0.5 Sn _0.5 catalyst was changed to 750°C, which was marked as 7.5Ce/Ti _0.5 Sn _0.5 -750. The XRD and specific surface area comparisons of different supports and catalysts are shown in Figure 1 and Table 1.

Table 1

Example 2. NH ₃ -SCR Performance Evaluation of Catalyst

Applying the catalyst prepared in Example 1 to NH ₃ -SCR reaction, 7.5Ce/Tix Sn _{1-x showed} better catalytic activity than single-component support. Under the condition of no SO ₂ and H ₂ O, titanium The activity window of the catalyst prepared after optimizing the tin component is wider than that of the industrial catalyst, and the results are shown in Figure 2. At the same time, the performance of 7.5Ce/Ti _0.5 Sn _0.5 catalyst aged at high temperature (750oC) is better than that of Ce/Ti catalyst without high temperature aging, which confirms the excellent thermal stability of Ce/TiSn catalyst. The reaction is carried out on a micro-reaction catalytic device, the reaction gas composition is 500ppm NH ₃ , 500ppm NO, 5%O ₂ , the residual gas is N ₂ , the space velocity is 100,000h ^-1 , the catalyst dosage is 0.1 _g , and the catalytic reaction temperature is 150–450 °C, the NO conversion of the reaction as well as the N selectivity _were detected using infrared methods.

Example 3 Evaluation of NH ₃ -SCR Performance of CeO ₂ /Ti _0.5 Sn _0.5 O ₂ Catalysts with Different Contents

Catalysts with different contents of CeO ₂ /Ti _0.5 Sn _0.5 O ₂ were prepared according to the method in Example 1. The loading amount of CeO ₂ was x (x=4.5%-22.5%) of the total mass of the catalyst, and the samples were marked as xCe/TiSn. Meanwhile, the NH ₃ -SCR performance of the catalyst was evaluated according to the method in Example 2, and the results are shown in FIG. 3 . It can be found that within the selected loading range of CeO2, the Ce/TiSn catalysts _both exhibit excellent NO conversion and _N2 selectivity.

Anti-SO of embodiment 4 catalyst ₂ and anti-H ₂ O performance evaluation

The 7.5Ce/Ti _0.5 Sn _0.5 catalyst prepared in Example 1 was used to perform anti-SO ₂ and anti-H ₂ O performance tests, and the results are shown in FIG. 4 . The reaction gas composition is 500ppm NH ₃ , 500ppm NO, 5%O ₂ , 100ppm SO ₂ (used in sulfur resistance test), 3.5%H ₂ O _(g) (used in water resistance test), residual gas is N ₂ , air The rate is 100,000 h ^-1 , the amount of catalyst is 0.1 g, and the reaction temperature is 300°C.

Claims (3)

1. one kind with Ti_xSn_1-xO₂[0.25≤x≤0.75] solid solution is the CeO of carrier₂/Ti_xSn_1-xO₂Metal oxide oxidation catalyst The preparation method of agent, is characterized in that it comprises the steps:

Titanium stannum mol ratio is the TiCl of 1:3-3:1 by step 1.₄Ethanol solution and SnCl₄Aqueous solution is uniform, then With vigorous stirring, strong aqua ammonia is added dropwise in mixed solution, until the pH=9.0 of solution so that it is precipitation is complete, Age overnight, eccysis Cl^-, 110 DEG C of drying, 550 DEG C of roasting 4h, obtain Ti the most in air atmosphere_xSn_1-xO₂ Solid solution；

The Ti that step 2. obtains with step 1_xSn_1-xO₂Solid solution is carrier, uses 0.1mol L^-1Ce(NO₃)₃·6H₂O is molten Liquid is impregnation liquid, is impregnated into Ti_xSn_1-xO₂On carrier, active component CeO₂The mass fraction accounting for catalyst is 4.5%-22.5%, stirs 3h, 100 DEG C of evaporating water of oil bath, is dried 12h, lower 500 DEG C of air atmosphere at 110 DEG C -750 DEG C of roasting 4h, obtain described catalyst.

2. the catalyst prepared by method described in claim 1.

3. the application in smoke catalytic denitration of the catalyst described in claim 2.