CN108404930A - A kind of low-temperature denitration catalyst and preparation method thereof with nucleocapsid - Google Patents

Abstract

The invention provides a low-temperature denitration catalyst with a core-shell structure, which uses iron oxide and manganese oxide as active components, and the core-shell structure is composed of iron oxide and manganese oxide, the manganese oxide is the core, and the oxide Iron is the shell part, and the molar ratio of manganese to iron is 8:5. The present invention also provides a method for preparing a low-temperature denitrification catalyst with a core-shell structure. Add manganese nitrate samples to ethylene glycol solution, stir at room temperature, pour the solution into a polyvinyl chloride reactor for hydrothermal treatment, and cool to room temperature. Weigh the ferric nitrate sample and add it, stir and ultrasonically vibrate, then pour it into a polyvinyl chloride reactor for hydrothermal treatment, then cool, and centrifuge to obtain a precipitate; finally, dry and calcinate the precipitate to obtain the required sample. The catalyst of the invention can significantly improve the low-temperature destocking activity, nitrogen selectivity and sulfur dioxide resistance.

Description

A low-temperature denitration catalyst with core-shell structure and preparation method thereof

technical field

The invention belongs to the field of chemical industry and relates to a catalyst, in particular to a low-temperature denitrification catalyst with a core-shell structure and a preparation method thereof.

Background technique

Atmospheric pollutants have a great impact on human life, and nitrogen oxides are one of the main pollutants. How to effectively reduce the emission of nitrogen oxides in the atmosphere has become an urgent problem. Selective catalytic denitrification (SCR) technology has become the most effective method for flue gas denitrification because of its high efficiency and mature technology. The research on the performance of denitrification catalysts has always been the focus of SCR research.

Catalyst is the core product of flue gas denitrification, and its quality directly determines the efficiency of flue gas denitrification. In catalytic denitrification technology, catalyst is very important, and most of the cost of denitrification process also comes from the aging of catalyst and reducing agent. consumption. The investment cost of denitrification catalysts usually accounts for 40% to 60% of the entire denitrification investment. During the "Twelfth Five-Year Plan" period, flue gas denitrification will bring a new market of nearly 20 billion yuan for denitrification catalysts. At present, the domestic production of titanium dioxide for catalysts The production technology is monopolized by a few foreign companies. Therefore, the research and development of SCR denitrification catalysts with independent intellectual property rights is of great significance to the development of flue gas denitrification in my country.

In recent years, Mn and Fe-based metal oxides have attracted much attention in the direction of SCR denitration catalysts due to their high activity. Due to its special structure and size, nano core-shell materials have great advantages in surface effect, small size effect and quantum effect. Therefore, the research on core-shell structure catalysts has become a hot direction in the field of scientific research. The catalyst with the core-shell structure prepared by the composite oxide not only makes up for the deficiency of the catalytic reaction of a single material, but also greatly improves the anti-poisoning of the special structure. The patent of this invention will prepare and synthesize the catalyst with the core-shell structure MnOx@FeOx catalyst is also used in SCR denitration reaction to improve its catalytic efficiency and anti-SO ₂ poisoning performance.

Contents of the invention

Aiming at the above-mentioned technical problems in the prior art, the present invention provides a low-temperature denitration catalyst with a core-shell structure and a preparation method thereof. The low-temperature denitration catalyst with a core-shell structure and a preparation method thereof must solve the existing In the technology, the catalyst used for low-temperature flue gas denitrification has low activity and poor ability to resist sulfur dioxide poisoning.

The invention provides a low-temperature denitration catalyst with a core-shell structure, which uses iron oxide and manganese oxide as active components, and the core-shell structure is composed of iron oxide and manganese oxide, the manganese oxide is the core, and the oxide Iron is the shell part, and the molar ratio of manganese to iron is 8:5.

The present invention also provides a method for preparing the above-mentioned low-temperature denitration catalyst with a core-shell structure, comprising the following steps:

1) take iron nitrate and manganese nitrate according to the molar ratio of manganese element and iron element being 8:5;

2) dissolving manganese nitrate in ethylene glycol solution;

3) the solution of step 2) is transferred to a polyvinyl chloride reactor for hydrothermal treatment;

4) cooling and shaking the suspension after the reaction in step 3) and adding ferric nitrate to stir;

5) transfer the mixed suspension of step 4) into a polyvinyl chloride reactor for hydrothermal treatment;

6) Centrifuge and wash the reacted precipitate, then take it out and dry it, and then roast it at 450-500° C. for 3-4 hours to obtain a low-temperature denitration catalyst with a core-shell structure.

Further, step 3) hydrothermal reaction at 180° C. for 9 hours to promote the formation of manganese oxide nanoparticles.

Further, step 4) stirring at room temperature and ultrasonically oscillating for 1 h.

Further, step 5) hydrothermally reacting in a polyvinyl chloride reactor at 190° C. for 8 hours, so that the iron oxide is uniformly coated on the nano-manganese oxide particles to form a core-shell structure.

Further, step 6) repeated centrifugation and alcohol washing for 3 times.

Further, step 6) drying is carried out at 100-110° C. for 12-15 hours.

In the present invention, manganese oxide and iron oxide are used as bimetallic oxides as active components, and a MnOx@FeOx catalyst with a core-shell structure is synthesized by a two-step hydrothermal method.

The XPS characterization results show that the iron element in the catalyst mainly exists as ferric iron, and the catalyst with the best activity contains a lot of ferric hydroxy iron, which is conducive to the increase of NH4 ⁺ -Bronsted acid sites. At the same time, the proportion of tetravalent manganese is also enhanced, which indicates that the catalyst has enhanced adsorption of NH ₃ and has stronger redox ability. The H ₂ -TPR characterization shows that the catalyst with the core-shell structure has a stronger redox ability, which is mutually corroborated by the XPS characterization.

In addition, from the XPS of S element, it can be seen that the peak intensity of the catalyst with the core-shell structure is much smaller than that of the ordinary structure catalyst, indicating that there is less sulfate on its surface, thus improving its anti- _SO2 poisoning effect.

The results of in-situ infrared characterization show that the LH mechanism and ER mechanism of the catalyst coexist. In the LH mechanism at low temperature, the increase of hydroxyl iron is conducive to the chemical adsorption of ammonia on the surface of the catalyst, and the adsorption of easily reactive nitrous acid groups , gradually less nitrates with strong thermal stability. At the same time, the adsorption of NH ₃ and NO by MnOx@FeOx with core-shell structure is much stronger than that of the catalyst with ordinary structure after sulfidation. This characterization indicates that the catalyst with core-shell structure has stronger adsorption and anti-SO ₂ effect.

The catalyst of the invention can treat nitrogen oxides in waste gas discharged from gas turbines for power generation and coal-fired boilers, etc., and can obviously improve low-temperature destocking activity and sulfur dioxide resistance.

Compared with the prior art, the technical progress of the present invention is remarkable. The catalyst provided by the invention has high catalytic reduction activity of NO at low temperature, that is, when the denitrification temperature is 250° C., the conversion rate of NO reaches more than 93%. The catalyst preparation process is simple, environmentally friendly and non-polluting. The catalyst using double metal oxide components and uniform nanoparticles with a core-shell structure overcomes the problem that ordinary catalysts are easily affected by _SO2 due to a single active component, and has a strong industrial potential. Value. The catalyst prepared by the present invention is at 150-450°C, especially below 300°C. Compared with the reference catalyst, the activity and water resistance and _SO2 resistance are greatly improved, which is more conducive to the arrangement of the SCR denitrification device in the tail flue of the thermal power plant , in order to reduce waste heat loss and improve the operating economy of thermal power plants.

Description of drawings

Fig. 1 is the catalytic efficiency of flue gas denitrification of the catalyst of the present invention and common catalyst under the same conditions.

Figure 2A is a TEM electron micrograph of a common structure MnFeOx catalyst, Figure 2B is a TEM electron micrograph of a core-shell structure MnOx@FeOx catalyst, and Figure 2C is a high-resolution HRTEM image of a core-shell structure MnOx@FeOx catalyst.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited.

The catalytic reactor used in the embodiment of the present invention adopts the 4100 type fixed bed micro-reaction evaluation device with an outer diameter of 16 mm and a length of 480 mm purchased from Zhejiang Fantai Instrument Co., Ltd. The raw material gas enters the reactor through preheating, and the reaction temperature is at 100- 400°C, flow rate 1000ml/min, space velocity 108000h ^-1 .

Simulated flue gas composition: NO 600ppm, NH ₃ 600ppm and O ₂ 5%, the remaining gas Ar was used as a balance gas, and the gas flow rate was controlled by a CS200 mass flow meter purchased from Beijing Qixing Huachuang Electronics Co., Ltd.

The molar concentration used in the present invention is 1% NO, NH ₃ , the balance gas is Ar, purchased from Shanghai Veichuang Standard Gas Co., Ltd., and O ₂ and Ar with a purity of 99.99% are purchased from Jiangnan Mixed Gas Co., Ltd.; used Ferric nitrate, manganese nitrate, and ethylene glycol with a drug purity of 99.9% are purchased from Aladdin, and the following are specific examples:

Example 1

According to the catalyst for catalytic reduction of NO with a core-shell structure prepared according to the present invention, the molar ratio of active components is: Mn:Fe=8:5. Concrete preparation steps are as follows:

The MnOx@FeOx catalyst with core-shell structure was prepared by a two-step hydrothermal method. Add 200 mL of ethylene glycol solution to the weighed manganese nitrate sample, and stir at room temperature for 15 minutes; then pour the solution into a polyvinyl chloride reactor at 180°C for 9 hours, cool to room temperature, and obtain suspension A. Weigh the ferric nitrate sample, add it into the suspension A, and keep stirring, and record it as the suspension B. Pour the solution B into a polyvinyl chloride reactor at 190°C to react for 8 hours, cool down, wash with deionized water and alcohol and centrifuge, and dry the obtained precipitate at 100°C for 24 hours. Finally, the solid powder was calcined in a muffle furnace at 450°C for 4 hours to obtain the MnOx@FeOx catalyst, which was ground and screened for later use.

Figure 2A is a TEM electron micrograph of a common structure MnFeOx catalyst, Figure 2B is a TEM electron micrograph of a core-shell structure MnOx@FeOx catalyst, and Figure 2C is a high-resolution HRTEM image of a core-shell structure MnOx@FeOx catalyst.

The TEM characterization results in Figure 2 show that regular-shaped spherical particles with a core-shell structure and a radius of 200 nm were synthesized by a two-step hydrothermal method, and the lattice fringes of the shell correspond to the (3 1 1) crystal plane of Fe ₃ O ₄ . It shows that the shell part is mainly iron oxide, and the core part is mainly manganese oxide.

Example 2

The catalyst for catalytic reduction of NO with a common structure prepared according to the present invention, wherein the molar ratio of active components is: Mn:Fe=8:5. Specific steps are as follows:

MnFeOx catalysts were prepared by co-precipitation method. Weigh the manganese nitrate sample and ferric nitrate sample respectively, add 200mL deionized water, stir continuously at room temperature, add ammonia water to adjust the pH to 8, at this time the solution appears precipitation, after stirring continuously for 30 minutes, the deionized water is fresh to neutral. Afterwards, filter, dry at 100°C for 24 hours, and finally, calcinate the solid powder in a muffle furnace at 450°C for 4 hours to obtain a MnFeOx catalyst, which is ground and screened for future use.

The simulated gas (flue gas flow rate 1000ml/min, gas concentration: NO is 600ppm, _NH3 is 600ppm and _O2 is 5%, the rest of the gas is Ar) is mixed in the gas mixing box, and then sent to the fixed bed micro-reactor evaluation device Under the action of anti-potassium poisoning denitrification catalyst and common catalyst, NH ₃ reduces NO to N ₂ , and the reacted mixed gas absorbs unreacted NH ₃ through phosphoric acid solution, and then discharges into the atmosphere through the exhaust pipe. The concentration is detected by the model60i flue gas analyzer in the United States, and the denitrification results are shown in the table below:

Table 1 Data table of activity evaluation results of different catalysts

Among them, the calculation formula of denitrification efficiency in Table 1 is as follows:

Table 2 The denitrification efficiency calculation formula is as follows:

It can be seen from Table 1 that the catalyst with a core-shell structure prepared by the present invention and the ordinary catalyst perform flue gas denitrification under the same conditions, and the denitration efficiency is higher than that of the ordinary catalyst. When the denitration temperature in the low temperature section is 100-300 ° C The denitrification efficiency of MnOx@FeOx catalyst with core-shell structure is about 15% higher than that of MnFeOx catalyst. And it is also higher than the MnFeOx catalyst with ordinary structure in the high temperature section.

The catalysts prepared above were respectively placed under 100ppm SO ₂ for anti-SO ₂ poisoning experiments, and the experimental results are shown in Figure 1. The results show that the anti-SO ₂ experiment of the catalyst prepared by the present invention and the ordinary catalyst is carried out under the same conditions, and the anti-poisoning performance of the MnOx@FeOx catalyst with the core-shell structure is better than that of the MnFeOx catalyst with the ordinary structure.

In summary, the catalyst prepared by the present invention has greatly improved activity and anti- _SO2 ability compared with ordinary catalysts at 150-450°C, especially below 300°C, which is more conducive to deploying SCR denitrification devices in thermal power plants Tail flue to reduce waste heat loss and improve the operating economy of thermal power plants.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention belongs to the scope of protection of the present invention.

Claims (7)

1. a kind of low-temperature denitration catalyst with nucleocapsid, it is characterised in that：Using iron oxide and manganese oxide as active component, Nucleocapsid is formed by iron oxide and manganese oxide, the manganese oxide is core portion, and the iron oxide is shell portion, manganese element and iron The molar ratio of element is 8：5.

2. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid described in claim 1, it is characterised in that packet Include following steps：

1）It is 8 according to the molar ratio of manganese element and ferro element：5 weigh ferric nitrate and manganese nitrate；

2）Manganese nitrate is dissolved in ethylene glycol solution；

3）By step 2）Solution be transferred to hydro-thermal process in pvc response kettle；

4）By step 3）Suspension after reaction is cooling, shake and ferric nitrate stirring is added；

5）By step 4）Mixing suspension be transferred to hydro-thermal process in pvc response kettle；

6）By sediment centrifugation, the cleaning after reaction, then takes out and dry, roasted at 450-500 DEG C again later, roasted Row 3-4h is burnt into, the low-temperature denitration catalyst with nucleocapsid is obtained.

3. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid according to claim 2, feature exist In：Step 3）Hydro-thermal reaction 9 hours at 180 DEG C.

4. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid according to claim 2, feature exist In：Step 4）It is stirred under room temperature, ultrasonic vibration 1h.

5. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid according to claim 2, feature exist In：Step 5）In pvc response kettle at 190 DEG C hydro-thermal reaction 8h.

6. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid according to claim 2, feature exist In：Step 6）It is centrifuged repeatedly, alcohol washes 3 times.

7. a kind of preparation method of low-temperature denitration catalyst with nucleocapsid according to claim 2, feature exist In：Step 6）Drying carries out 12-15h at 100-110 DEG C.