CN107126973A - A kind of in-situ synthetic method of catalyst of CuFe SAPO 34 and its application - Google Patents

Abstract

The invention discloses an in-situ synthesis method and application of CuFe-SAPO-34 catalyst, belonging to the technical field of catalysis. The method of the present invention comprises the following steps: adding pseudo-boehmite into deionized water for stirring and dissolving, then adding orthophosphoric acid and fumed silicon dioxide, adding copper salt and tetraethylenepentamine after mixing, adding Fe after fully stirring salt and n-propylamine; put the fully stirred gel into a hydrothermal reaction kettle for crystallization, cool to room temperature after the crystallization reaction is completed, separate the solid crystalline product from the mother liquor, wash with deionized water until neutral, dry, and then Roasting in air to obtain CuFe-SAPO-34 small-pore molecular sieve catalyst. The present invention adopts a one-step synthesis method to prepare the CuFe-SAPO-34 catalyst, and the catalytic performance and the low-temperature water resistance performance of the Cu-SAPO-34 catalyst are significantly improved by optimizing the loading amount of Fe.

Description

A kind of in-situ synthesis method and application of CuFe-SAPO-34 catalyst

technical field

The invention relates to an in-situ synthesis method and application of a CuFe-SAPO-34 catalyst, belonging to the technical field of catalysis.

Background technique

NO _x can cause air pollution problems such as smog, acid rain, and photochemical smog. It is an important air pollutant at present, and it is also a key object of air pollution prevention and control in China. Fossil fuel combustion brought about by people's industrial production and living activities is the main source of nitrogen oxides (NOx). Among anthropogenic _NOx emissions, stationary sources such as coal-fired power plant flue gas and mobile sources such as diesel vehicle _exhaust account for about 60% of the emissions. With the improvement of national emission regulations and standards, the combination of in-machine purification technology and post-treatment technology is required to meet the _NOx emission standards of mobile sources. Among them, the improvement of post-processing method is the main way to deal with the rising standards. The selective catalytic reduction technology (SelectiveCatalytic Reduction, SCR) in post-treatment has the advantages of high removal efficiency and low cost, and has received more attention. SCR technology refers to spraying NH ₃ , urea or other reducing agents into the flue gas in the presence of a catalyst to selectively react with NO _x to generate N ₂ instead of non-selective oxidation with O ₂ . Therefore, the purpose of reducing the _NOx reduction temperature and improving the _NOx purification efficiency is achieved. The core of SCR technology is a catalyst with excellent catalytic performance.

At present, the catalyst widely used in China is still V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ . The catalyst has been widely used in the denitrification of fixed-source coal-fired flue gas, and has also been introduced into the field of diesel vehicle exhaust control. However, there are still many problems in the application of the catalyst system in the purification of diesel vehicle exhaust. In order to meet emission standards, in the mobile source exhaust gas treatment system, the SCR treatment system often needs to be used in conjunction with a particulate filter (DPF). In this way, the SCR catalyst is required to be able to withstand the high temperature (higher than 700° C.) and high humidity environment brought about by DPF regeneration, that is, the catalyst needs to have excellent hydrothermal stability. However, the V ₂ O ₅ -WO ₃ (MoO ₃ )/TiO ₂ catalyst will volatilize vanadium and phase change the carrier TiO ₂ above 600°C, so this catalyst is not suitable for the treatment of motor vehicle exhaust at higher temperatures, and cannot meet the future needs. In addition, the biological toxicity of vanadium also limits its use. Other well-researched Cu-based or Fe-based catalysts prepared with ZSM-5, beta, and Y as supports have problems such as narrow temperature operating window, poor hydrothermal stability, and poor resistance to HC poisoning. Therefore, it is very urgent to develop environmentally friendly and efficient NH ₃ -SCR catalysts.

Small-pore molecular sieve catalysts are currently a research hotspot in the field of NH ₃ -SCR. Among them, Cu-SAPO-34 catalyst with a CHA structure is a representative of this type of molecular sieve catalyst. This type of catalyst has high activity, high N ₂ selectivity and excellent Hydrothermal stability. However, this type of catalyst is sensitive to low temperature and water-containing environment, and has poor resistance to sulfur poisoning, which is unfavorable for practical application. Therefore, it is necessary to further improve the catalyst.

Patent No. 2012100717231 discloses that Cu and Fe are loaded onto SAPO-34 carrier by liquid-phase ion exchange method to prepare composite small-pore molecular sieve catalyst for catalytic purification of NOx. However, the steps of this method are cumbersome, multiple loads are required, and the amount of metal loading is not easy to control. The low-temperature water resistance and sulfur poisoning resistance of the obtained catalysts have not been reported.

Contents of the invention

In order to solve the above problems, one of the objects of the present invention is to provide a method for preparing CuFe-SAPO-34 catalyst by in-situ synthesis method. The catalyst is prepared by hydrothermal synthesis method and is a small-pore molecular sieve catalyst. The method of the invention is simple and easy to operate, and the obtained catalyst has excellent NH ₃ -SCR catalytic performance, and can be used in a mobile source NH ₃ -SCR denitrification process. In addition, the prepared catalyst for selective catalytic reduction of nitrogen oxides has a wide operating temperature window, excellent _N2 generation selectivity and hydrothermal stability, and is very suitable for the purification of nitrogen oxides in diesel vehicle exhaust.

The method for preparing the CuFe-SAPO-34 catalyst by the in-situ synthesis method of the present invention is to mix and stir the aluminum source, water, phosphorus source, silicon source, Cu source, tetraethylenepentamine, and iron source evenly, and then add the templating agent, Continue to stir; put the fully stirred gel into a hydrothermal reaction kettle for crystallization, and cool after the crystallization reaction; separate the solid crystallization product from the mother liquor, wash, dry, and roast to obtain CuFe-SAPO-34 small-pore molecular sieve catalyst.

In one embodiment, the aluminum source may be pseudoboehmite AlOOH, aluminum oxide, sodium metaaluminate, and the like.

In one embodiment, the phosphorus source is phosphoric acid.

In one embodiment, the silicon source is silicon dioxide, silica sol, and the like.

In one embodiment, the Cu source is a Cu salt.

In one embodiment, the Cu salt is any one or a combination of two or more of copper sulfate, copper nitrate, copper acetate, copper chloride, copper carbonate, copper oxide, and the like.

In one embodiment, the iron source is an iron salt.

In one embodiment, the iron salt is any one of ferric nitrate, ferric chloride, ferrous sulfate, ferric sulfate, ferrous chloride, ferric citrate, or a combination of two or more.

In one embodiment, the templating agent is any one or a combination of two or more of n-propylamine (C ₃ H ₉ N), diethylamine, triethylamine, tetraethylamine hydroxide, and the like.

In one embodiment, the method specifically includes the following steps:

(1) Pseudo-boehmite is added to deionized water and stirred;

(2) add phosphoric acid again, stir;

(3) add fumed silicon dioxide and stir;

(4) After mixing the above medicines evenly, add Cu salt and tetraethylenepentamine;

(5) After fully mixing, add iron salt and n-propylamine, and continue stirring.

(6) Put the fully stirred gel into a hydrothermal reaction kettle for crystallization, and cool to room temperature after the crystallization reaction is completed. The solid crystalline product is separated from the mother liquor, washed with deionized water until neutral, dried, and then calcined in an air atmosphere to obtain a CuFe-SAPO-34 small-pore molecular sieve catalyst.

In one embodiment, the method controls the molar ratio of aluminum source, phosphorus source, silicon source, water, Cu source, tetraethylenepentamine, iron source, and templating agent to be (0.75-1.25): (0.75-1.25) :(0.4-0.7):(70-80):(0.01-3.5):(0.01-3.5):(0.001-0.1):(0.01-3.5).

In one embodiment, the method controls the molar ratio of aluminum source, phosphorus source, silicon source, water, Cu source, tetraethylenepentamine, iron source, and templating agent to be 1:1:0.57:77.17:0.12:0.12 :(0.019-0.076): 3.38.

In one embodiment, the aluminum source, phosphorus source, silicon source, water, Cu source, tetraethylenepentamine, iron source, template agent are respectively AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine.

In one embodiment, the molar ratio of AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine is 1:1:0.57:77.17:0.12:0.12:0.057 : 3.38.

In one embodiment, the temperature of the crystallization reaction is 150-200°C, such as 150, 155, 160, 165, 170, 175, 180, 185, 190, 195 or 200°C.

In one embodiment, the crystallization reaction time is 24-72 hours, such as 30, 35, 40, 45, 50, 55, 60, 65, 72 hours.

In one embodiment, the crystallization reaction time is 72 hours.

In one embodiment, the washing is to neutral with water.

In one embodiment, the drying temperature is 80-120°C, such as 80°C, 90°C, 100°C, 110°C, 120°C.

In one embodiment, the drying temperature is 100°C.

In one embodiment, the drying time is 3-16 hours, such as 3h, 5h, 6h, 8h, 10h, 12h, 16h.

In one embodiment, the drying time is 12 hours.

In one embodiment, the calcination is calcination in an air atmosphere.

In one embodiment, the calcination temperature is 550-800°C, such as 550°C, 600°C, 650°C, 700°C, 800°C.

In one embodiment, the calcination temperature is 600°C.

In one embodiment, the calcination time is 3-10 hours, such as 3h, 5h, 6h, 8h, 10h.

In one embodiment, the calcination time is 6 hours.

In one embodiment, the heating rate of the calcination is 0.5-5° C./min, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5° C./min.

In one embodiment, the heating rate of the calcination is 1° C./min.

In one embodiment, the method specifically includes the following steps: adding pseudo-boehmite to deionized water for stirring, then adding orthophosphoric acid and fumed silica, and adding copper salt and tetraethylenepenta Amine, after fully stirring, add Fe salt and n-propylamine; put the fully stirred gel into a hydrothermal reaction kettle for crystallization, cool to room temperature after the crystallization reaction is completed, separate the solid crystallization product from the mother liquor, and wash with deionized water until Neutral, dry, and then calcined in air to obtain CuFe-SAPO-34 small-pore molecular sieve catalyst; in which control AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine The molar ratio is 1:1:0.57:77.17:0.12:0.019-0.076:3.38. The catalyst obtained by adopting this scheme has excellent catalytic activity, which has a NOx conversion rate higher than 80% within 300-500° C., and significantly improves the low-temperature water resistance of Cu-SAPO-34.

The second object of the present invention is to provide the CuFe-SAPO-34 small-pore molecular sieve catalyst prepared according to the above method.

The third object of the present invention is to provide the application of the CuFe-SAPO-34 small-pore molecular sieve catalyst.

In one embodiment, the use is for catalyzing nitrogen oxides.

In one embodiment, the application is for NH ₃ -SCR reactions.

In one embodiment, the application is catalytic reduction of nitrogen oxides in diesel vehicle exhaust.

Beneficial effects of the present invention:

(1) This method adopts the in-situ synthesis method to prepare CuFe-SAPO-34 small-pore molecular sieve catalyst, and further controls the loading amount of Fe salt by controlling the input amount of Fe salt to obtain NH ₃ -SCR catalytic activity and water-resistant stability Molecular sieve catalyst with excellent properties; the preparation method of CuFe-SAPO-34 is a one-step synthesis method, which is simpler and more effective than the currently used liquid phase ion exchange method, and does not require multiple ion exchange steps, saving resources.

(2) The catalyst prepared by this method utilizes the synergistic effect between Cu and Fe to widen the temperature window of the catalyst, especially the activity at high temperature is more significantly improved, and is more suitable for diesel vehicle exhaust purification.

(3) The catalyst prepared by this method has improved its low temperature water resistance.

(4) The catalyst prepared by this method has improved resistance to sulfur poisoning.

(5) The catalyst of the present invention is prepared by using non-toxic components, which will not cause harm to human health and ecological environment; the preparation method is simple and easy to operate.

Description of drawings

Fig. 1 is that the catalytic activity of CuFe-SAPO-34 and Cu-SAPO-34 prepared by the present invention and the water intoxication resistance compare;

Fig. 2 is the variation of anti-sulfur poisoning ability of CuFe-SAPO-34 and Cu-SAPO-34 catalysts prepared by the present invention.

specific implementation plan

In the present invention, the evaluation of catalyst takes following method:

Take the CuFe-SAPO-34 molecular sieve catalyst and place it on a fixed-bed reactor for activity evaluation. The simulated waste gas composition is 500ppm NH ₃ , 500ppm NO, 5vol% O ₂ , N ₂ is the balance gas, and the total flow rate is 500mL/min. The speed is 400000h ^-1 .

The following is a detailed description of the present invention.

Example 1

Pseudoboehmite AlOOH is used as aluminum source, silicon dioxide (SiO ₂ ) is used as silicon source, phosphoric acid (H ₃ PO ₄ ) is used as phosphorus source, Cu-TEPA is used as Cu source, Fe(NO ₃ ) ₃ ·9H ₂ O As the iron source, mix the raw materials, then add n-propylamine (C ₃ H ₉ N) as the template agent, stir overnight until the stirring is uniform; then put the solution into the reaction kettle, and put the reaction kettle into an oven at 180°C to crystallize After 3 days; after the reactor is fully cooled, stir and stand still and filter out impurities, then filter with suction, put the filtered sample in an oven at 105°C for 3 hours to dry it; then put the dried sample into a muffle furnace In the process, the temperature was raised to 600°C for 6 hours at a rate of 1°C/min to obtain a CuFe-SAPO-34 catalyst prepared by a one-step synthesis method. Among them, the molar ratio of AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine is controlled to be 1:1:0.57:77.17:0.12::0.12:0.057:3.38.

Control: Cu-SAPO-34 catalyst can be prepared according to the above preparation method without adding Fe salt.

In order to investigate the change of the low-temperature water resistance of the catalyst before and after the addition of Fe salt, the catalyst was aged at 70°C for 16 hours in an air atmosphere containing 10% H ₂ O, and the performance change of the catalyst before and after aging was detected. Figure 1 shows the change in catalyst performance before and after Fe salt addition

It can be seen from Figure 1 that the CuFe-SAPO-34 catalyst has a wide temperature window, and can maintain a NOx conversion rate greater than 70% in the range of 250-550 °C, and the highest activity can reach 90.3%. The control Cu-SAPO-34 has a narrow temperature window, and can only maintain a NOx conversion rate greater than 60% in the range of 250-350°C, and the highest activity can reach 78.6%.

In addition, after CuFe-SAPO-34 was aged at 70°C for 16h, the catalyst could still maintain more than 50% NOx conversion in the range of 300-500°C. However, after the control Cu-SAPO-34 was treated under the same aging conditions, it only maintained a NOx conversion rate greater than 30% in the range of 300-450°C.

From the above data, it can be seen that this method not only improves the activity of the catalyst, but also significantly improves its low-temperature water resistance.

Figure 2 shows the anti-sulfur poisoning ability of the catalyst before and after Fe addition. It can be seen that the CuFe-SAPO-34 catalyst after sulfur poisoning can still retain a conversion rate of more than 60% at 350-500 °C, and the highest NOx conversion rate is 81.5%. But the Cu-SAPO-34 catalyst only retains more than 60% conversion at 400-500°C, and the highest NOx conversion is 62.9%.

Example 2

In this example, the performance of CuFe-SAPO-34 catalysts obtained under different Fe salt additions was investigated.

The preparation method of the catalyst: adjust the dosage of Fe, control the molar ratio of AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine to A (1:1: 0.57:77.17:0.12:0.12:0.0095:3.38), B(1:1:0.57:77.17:0.12:0.12:0.019:3.38), C(1:1:0.57:77.17:0.12:0.12:0.029:3.38) , D(1:1:0.57:77.17:0.12:0.12:0.043:3.38). All the other are identical with embodiment 1.

The catalytic properties of the prepared CuFe-SAPO-34 catalyst at different temperatures are shown in Table 1.

Catalytic properties of catalysts obtained under different Fe additions in table 1

Example 3

In this example, the properties of CuFe-SAPO-34 catalysts obtained at different crystallization temperatures were investigated.

Control the molar ratio of AlOOH, H ₃ PO ₄ , SiO ₂ , H ₂ O, Cu salt, tetraethylenepentamine, Fe salt and n-propylamine to 1:1:0.57:77.17:0.12::0.12:0.057:3.38, crystallization The temperature is respectively 150°C and 200°C, and the rest are the same as in Example 1. The properties of the prepared CuFe-SAPO-34 catalyst are shown in Table 2.

The catalytic performance of the catalyst obtained under the different crystallization temperature of table 2

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore The scope of protection of the present invention should be defined by the claims.

Claims (10)

1. a kind of method that in-situ synthesis prepares CuFe-SAPO-34 catalyst, it is characterised in that methods described be by silicon source, Phosphorus source, silicon source, water, Cu sources, TEPA, and source of iron are mixed evenly, and then add template, continue to stir；It will stir Mix complete gel and be fitted into crystallization in hydrothermal reaction kettle, crystallization is cooled down after terminating；Solid crystallized product is separated with mother liquor, Washing, dry, roasting, that is, obtain CuFe-SAPO-34 small pore molecular sieve catalysts.

2. according to the method described in claim 1, it is characterised in that methods described control silicon source, phosphorus source, silicon source, water, Cu sources, TEPA, source of iron, the mol ratio of template are (0.75-1.25)：(0.75-1.25)：(0.4-0.7)：(70-80)： (0.01-3.5)：(0.01-3.5)：(0.001-0.1)：(0.01-3.5).

3. according to the method described in claim 1, it is characterised in that methods described control silicon source, phosphorus source, silicon source, water, Cu sources, TEPA, source of iron, the mol ratio of template are 1：1：0.57：77.17：0.12：0.12：(0.019-0.076)：3.38.

4. according to the method described in claim 1, it is characterised in that source of aluminium is boehmite AlOOH, alundum (Al2O3) Or sodium metaaluminate.

5. according to the method described in claim 1, it is characterised in that the source of iron is molysite, such as ferric nitrate, iron chloride, sulphur Any one in sour ferrous iron, ferric sulfate, frerrous chloride, ironic citrate or two or more combinations.

6. according to the method described in claim 1, it is characterised in that the Cu sources are Cu salt, such as copper sulphate, copper nitrate, vinegar Any one in sour copper, copper chloride, copper carbonate, cupric oxide or two or more combinations.

7. according to the method described in claim 1, it is characterised in that the temperature of crystallization is 150-200 DEG C.

8. the CuFe-SAPO-34 catalyst prepared according to any methods described of claim 1~7.

9. the application of CuFe-SAPO-34 catalyst described in claim 8.

10. application according to claim 9, it is characterised in that for NH₃- SCR reacts.