CN108993586B - Preparation method of Beta type molecular sieve for resisting propylene poisoning - Google Patents

Abstract

The invention discloses a preparation method of an anti-propylene poisoning Beta type molecular sieve, which is characterized in that the diameter of a pore channel for loading Fe is 6.3-6.8

The Beta type molecular sieve is taken as a substrate; adding an oxide auxiliary agent into the molecular sieve substrate, uniformly stirring, and grinding for 40-90 min; mechanically mixing and grinding the sample, and roasting the sample in air at 500 ℃ for 4 hours at the heating rate of 2-5 ℃/min; wherein the oxide promoter is selected from MnO_x，CeO₂Or MnO_x/CeO₂Said MnO being_x/CeO₂In MnO of_xThe loading of (b) was 50%. The prepared catalyst is applied to NH containing propylene in atmosphere₃In SCR reaction, the catalyst has the characteristics of high activity and high sulfur poisoning resistance, and makes up the defect that the conventional catalyst has poor propylene poisoning resistance or poor sulfur poisoning resistance.

Description

A kind of preparation method of Beta type molecular sieve resistant to propylene poisoning

technical field

The invention belongs to the technical field of nitrogen oxide control in environmental protection, and particularly relates to the synthesis and performance research of a composite catalyst based on molecular sieve and oxide.

Background technique

_NOx emission sources include stationary sources (the combustion of fossil fuels such as coal and petroleum in production, domestic use, and exhaust gas from factories that use nitric acid) and mobile sources (vehicle exhaust). In recent years, people's voices for environmental protection are getting louder and louder. Industrial developed countries such as the United States, Japan, South Korea and Europe have successively formulated and implemented new emission standards in recent years, and the emission restrictions on NO have become increasingly strict. Therefore, how to control nitrogen oxides has become a research hotspot at home and abroad. _NH3 -selective catalytic reduction of _NOx ( _NH3 -SCR) is currently the most effective method for purifying _NOx , which utilizes the reducing agent _NH3 to reduce _NOx to harmless _N2 and _H2O on a catalyst. The core of SCR technology is a catalyst with high activity and stability. Noble metals, metal oxides, etc. have all been proved to be effective SCR catalysts. Among these catalysts, vanadium-based catalysts supported by _TiO2 have good activity and water resistance. Sulfur resistance. Vanadium-based catalysts with V ₂ O ₅ as the active component have been industrially produced abroad in the 1970s and 1980s. Due to their good activity and water and sulfur resistance, these catalysts can be used in stationary sources to burn soot. It has been widely used in gas denitrification. In terms of NO _x purification of diesel vehicle exhaust, relevant research has also been carried out in Europe in the past few years, and it has been applied to the exhaust purification of NO _x in heavy-duty diesel vehicles (Appl. Catal. B 18 (1998) 1 36.). However, the catalyst still has shortcomings in the control of vehicle exhaust gas. First, the active component V ₂ O ₅ is toxic, which will cause harm to the atmospheric environment after volatilization at high temperature. Second, the SO ₂ in the exhaust gas on the catalyst is easily oxidized to SO ₃ . Further emissions of sulfate particulate matter. What is more serious is that on diesel vehicles equipped with particulate matter traps, when the trap is regenerated, the temperature often exceeds 700 °C, which causes the catalyst carrier TiO ₂ to undergo a phase change, resulting in a significant decrease in catalyst activity. Molecular sieve catalysts have high catalytic activity for the selective reduction of _NOx , and the activity temperature window is relatively wide, so they have attracted much attention in the technology of selective catalytic reduction of _NOx . The use of molecular sieve as a catalyst is based on its special microporous structure, and its type, silicon-aluminum ratio, exchanged ion species, reaction conditions, exchange degree, etc. will affect its activity. Molecular sieves used for SCR catalyst carriers mainly include ZSM series, Y type, Mordenite (MOR), BEA type, etc., while metal elements used for ion exchange mainly include Fe, Cu, Mn, Ce, Co and Ni. In recent years, many studies have been carried out on Fe/ZSM-5, and good results have been obtained in the reduction of _{NOx by} NH ₃ (J. Catal., 207 (2002): 224 231; Appl. Catal. B, 60(2005): 1322.). For the purification of NO _x in vehicle exhaust gas, catalysts with Cu and Fe as active components and H-ZSM-5 and Beta as carriers are currently favored by the industry. However, in practical applications, it is found that the inevitable hydrocarbon emission in the exhaust gas will cause different degrees of carbon deposition and deactivation of the catalyst. At present, domestic research on molecular sieve catalysts to purify NO _x in vehicle exhaust has just started. The thermal stability of catalysts and the poisoning of catalysts by HC compounds are the key issues that need to be solved in practical applications of such catalysts.

SUMMARY OF THE INVENTION

The purpose of this invention is to provide a kind of preparation method of Beta type molecular sieve resistant to propylene poisoning. The prepared catalyst is applied to the NH ₃ -SCR reaction containing propylene in the atmosphere, and has the characteristics of high activity and high anti-sulfur poisoning performance, which makes up for the deficiency of the existing catalysts that have poor anti-propylene poisoning performance or poor anti-sulfur poisoning performance.

The present invention is achieved through the following technical solutions:

的Beta型分子筛为基底；向分子筛基底中加入氧化物助剂，搅拌均匀，研磨40～90min；经过机械混合研磨后的样品，以2～5℃/min的升温速率，在500℃空气中焙烧4小时；所述氧化物助剂选自MnO_x，CeO₂或MnO_x/CeO₂。所述MnO_x/CeO₂中，MnO_x的负载量为50wt％。A preparation method of Beta-type molecular sieve resistant to propylene poisoning, wherein the Fe-loaded pore diameter is about

The Beta molecular sieve is the base; add oxide additives to the base of the molecular sieve, stir evenly, and grind for 40-90 minutes; the samples after mechanical mixing and grinding are calcined in air at 500°C at a heating rate of 2-5°C/min 4 hours; the oxide auxiliary agent is selected from MnO _x , CeO ₂ or MnO _x /CeO ₂ . In the MnO _x /CeO ₂ , the loading amount of MnO _x is 50wt%.

Further, in the above technical solution, when the oxide auxiliary agent is added, the mass ratio of the molecular sieve substrate and the oxide auxiliary agent is 0.5-3.5:1.

Further, in the above technical solution, an agate mortar is used for the grinding. Place the accurately weighed two components in a mortar, stir evenly, and then fully grind with an agate pestle for 40-90 minutes until the color of the sample is uniform and the particles are uniform.

The present invention provides the application of the above catalyst in the NH ₃ -SCR reaction containing propylene in the atmosphere.

Further, in above-mentioned technical scheme, the preparation of Fe-Beta is:

A series of Fe-Beta catalysts were prepared by equal volume impregnation method with ferrocene toluene solution using template-free synthesized Beta molecular sieve (Si/Al≈9) as support. First, the Na-Beta molecular sieve was placed in a 0.5 mol/L ammonium nitrate solution, vigorously stirred at 80 °C for 4 hours, then filtered, washed, and dried at 120 °C for 8 to 12 hours. The obtained sample was again treated with the same concentration of ammonium nitrate solution After the exchange, the NH ₄ -Beta molecular sieve is obtained; then, the toluene saturation adsorption capacity of the NH ₄ -Beta molecular sieve is accurately measured, and the calculated amount of ferrocene is added to the corresponding toluene to prepare a solution, and then the ferrocene toluene solution is added. Slowly add it dropwise into NH ₄ -Beta molecular sieve, stir evenly, and let it stand at room temperature for more than 50 hours; finally, the obtained sample is calcined in static air, raised to 500 °C at a heating rate of 2-5 °C/min and kept for 4 hours to obtain Fe -Beta catalyst.

Further, in above-mentioned technical scheme, the preparation of oxide auxiliary agent is:

_CeO2 was purchased from Tianjin Huahong New Materials Co., Ltd. MnO _x is loaded onto the surface of the carrier by means of deposition and precipitation: first, an appropriate amount of manganese nitrate solution is mixed with the carrier, and then the Na ₂ CO ₃ solution is added dropwise to the corresponding suspension under stirring until the pH reaches 8.5-9.0. After stirring and aging at room temperature for 1 h, it was filtered and washed with suction. The obtained solid powder was dried in an oven at 110° C. for 6 hours, and further calcined in a muffle furnace at 400° C. for 4 hours to obtain a MnO _x /CeO ₂ catalyst with a MnO _x loading of 50%. For MnO _x catalyst, an appropriate amount of manganese nitrate solution was added to deionized water, and then Na ₂ CO ₃ solution was added dropwise under stirring until pH reached 8.5-9.0. After stirring and aging at room temperature for 1 h, it was filtered and washed with suction. The obtained solid powder was dried in an oven at 110° C. for 6 hours, and further calcined in a muffle furnace at 400° C. for 4 hours to obtain a MnO _x catalyst.

Invention Beneficial Effects

1. The molecular sieve catalyst is combined with the auxiliary agent by the method of mechanical grinding, and a high-activity composite catalyst with anti-propylene poisoning performance in the NH ₃ -SCR reaction is successfully prepared. For example, MnO _x /CeO ₂ is used as the auxiliary agent. After being mixed with Fe-Beta at 1:3, the activity is 38% higher than that of pure Fe-Beta at 150°C.

2. Different active effects can be obtained by adjusting the types and proportions of auxiliary agents. For example, when MnO _x is used as the auxiliary agent, it is easier to obtain excellent low-temperature activity, and the conversion rate can reach more than 90% in the temperature range of 200-350 °C; when CeO ₂ is used as the auxiliary agent, the activity is better in the middle and high temperature section. , the conversion rate of more than 90% can be obtained in the temperature range of 300 to 450 °C; while the catalyst with MnO _x /CeO ₂ as an auxiliary agent can obtain a wider reaction temperature window, and the conversion rate in the range of 200 to 400 ° C. above 90%.

3. By changing the type of additives, the anti-sulfur poisoning performance of the composite catalyst can be significantly improved. For example: when the auxiliary agent is MnO _x , the activity can only reach 37% after 8 hours of reaction at 250 °C with SO ₂ , but after the auxiliary agent is changed to MnO _x /CeO ₂ , the activity can be reached after 8 hours of reaction under the same conditions. remains at 68%.

Description of drawings

5 of the accompanying drawings of the present invention,

Fig. 1 is the activity comparison diagram of the NH ₃ -SCR reaction containing propylene in the atmosphere prepared by Fe-Beta prepared in Example 1-3 and samples mechanically mixed with different additives;

Fig. 2 is the activity comparison diagram of the NH ₃ -SCR reaction containing propylene in the atmosphere prepared by Fe-Beta and MnO _x /CeO ₂ mechanically mixed in different ratios prepared in Examples 3-5 and Comparative Example 1;

Figure 3 is a graph showing the activity comparison of the anti-sulfur poisoning performance of Fe-Beta prepared in Examples 1-3 and samples mechanically mixed with different additives at 250°C;

Figure 4 is a comparison chart of the activity of HBEA molecular sieve modified by CeO ₂ in order to improve the anti-propylene poisoning performance in the literature [1];

Figure 5 is a comparison chart of the activity of synthesizing the core-shell structure in the outer layer of the molecular sieve in order to improve the anti-propylene poisoning performance in the literature [2].

[1] Y. Shi, X. Wang, Y. Xia, C. Sun, C. Zhao, S. Li, W. Li, Molecular Catalysis 433 (2017) 265-273.

[2] T. Zhang, F. Qiu, J. Li, Applied Catalysis B: Environmental 195 (2016) 48-58.

Detailed ways

The following non-limiting examples may enable those of ordinary skill in the art to more fully understand the present invention, but do not limit the present invention in any way.

Example 1 Preparation and activity evaluation of Fe-Beta+MnO _x (FM)

1) The preparation of Fe-Beta:

A series of Fe-Beta catalysts were prepared by equal volume impregnation method with ferrocene toluene solution using template-free synthesized Beta molecular sieve (Si/Al≈9) as support. The specific steps are: firstly put Na-Beta molecular sieve in 0.5mol/L ammonium nitrate solution, stir vigorously at 80°C for 4h, then suction filter, wash, and dry at 120°C for 8-12h, the obtained sample is again treated with the same After the concentration of ammonium nitrate solution is exchanged, NH ₄ -Beta molecular sieve is obtained; then, the toluene saturation adsorption capacity of NH ₄ -Beta molecular sieve is accurately measured, and the amount of ferrocene required for calculation is added to the corresponding toluene to prepare a solution, and then the 2 The ferrocene toluene solution was slowly added dropwise to the NH ₄ -Beta molecular sieve, stirred evenly, and allowed to stand at room temperature for more than 50 hours; finally, the obtained sample was calcined in static air, raised to 500°C at a heating rate of 2-5°C/min, and then heated to 500°C. Keep for 4h to get Fe-Beta catalyst.

2) Preparation of MnO _x :

An appropriate amount of manganese nitrate solution was added to deionized water, and Na ₂ CO ₃ solution was added dropwise with stirring until pH reached 8.5-9.0. After stirring and aging at room temperature for 1 h, it was filtered and washed with suction. The obtained solid powder was dried in an oven at 110° C. for 6 hours, and further calcined in a muffle furnace at 400° C. for 4 hours to obtain a MnO _x catalyst.

3) Preparation of Fe-Beta+MnO _x (FM):

Mix Fe-Beta and MnO _x at a mass ratio of 3:1, use an agate mortar to fully grind the two components for 40-90 min, and raise the temperature to 500 °C at a heating rate of 2 to 5 °C/min. Roasting is carried out.

The FM catalyst has good activity in the NH ₃ -SCR reaction containing propylene in the atmosphere, it can reach 73% at 150°C, and the conversion rate can reach more than 90% in the temperature range of 200-350°C. Compared with Fe-Beta, the activity of FM catalyst increased by 53% at 150 °C, indicating that the addition of _MnOx as a promoter can effectively improve the low-temperature activity of the catalyst. As the temperature increases further, the catalyst activity decreases further. Therefore, if the practical application focuses more on low-temperature activity, MnO _x can be used as a co-agent to modify the catalyst.

Example 2 Preparation and activity evaluation of Fe-Beta+CeO ₂ (FC)

The steps and process conditions of this example are the same as those of Example 1, except that CeO ₂ (Tianjin Huahong New Materials Co., Ltd.) is used to replace MnO _x to prepare Fe-Beta+CeO ₂ (FC) catalyst.

The activity of catalyst FC with CeO ₂ as co-agent increased slightly between 200 and 300 ℃, but the magnitude was not obvious. However, the catalyst has good activity at high temperature, and the activity between 300 and 450°C is above 90%.

Comparative Example 1 Preparation and Activity Evaluation of MnO _x /CeO ₂

Preparation of _MnOx /CeO2 _:

_CeO2 was purchased from Tianjin Huahong New Materials Co., Ltd.; the loading of _MnOx was set at 50%, and was loaded onto the surface of the carrier by means of deposition and precipitation: first, an appropriate amount of manganese nitrate solution was mixed with the carrier, and then under stirring conditions, the The Na ₂ CO ₃ solution was added dropwise to the corresponding suspension until the pH reached 8.5-9.0; after stirring and aging at room temperature for 1 h, it was filtered and washed with suction; the obtained solid powder was dried in an oven at 110 °C for 6 h, and further dried in air at 400 °C After calcination at ℃ for 4h, MnO _x /CeO ₂ catalyst was obtained.

From the activity, it can be seen that the _MnOx / _CeO2 catalyst has poor activity in the entire temperature window, and the conversion rate can only reach below 70%. And with the increase of temperature, the activity decreased rapidly, and the conversion rate was 0 at 450 °C.

Example 3 Preparation and activity evaluation of Fe-Beta+MnO _x /CeO ₂ (FMC3)

The steps and process conditions of this example are the same as those of Example 1, except that MnO _x /CeO ₂ is replaced with MnO _x (wherein, the preparation method of MnO _x /CeO ₂ is the same as that of Comparative Example 1), thereby preparing Fe-Beta +MnO _x /CeO ₂ (FMC3) catalyst.

When MnO _x /CeO ₂ is used as a promoter, the activity of the catalyst at 150°C is increased from 19% to 35%, and the conversion rate of more than 90% can be maintained between 200 and 400°C, which is comparable to pure Fe-Beta or MnO _x The activity of /CeO ₂ is much higher than that of the catalyst, which indicates that the catalyst prepared by the mechanical mixing method can obtain ideal results and effectively improve the activity of the molecular sieve in the NH ₃ -SCR reaction containing propylene in the atmosphere.

Example 4 Preparation and activity evaluation of Fe-Beta+MnO _x /CeO ₂ (FMC2)

The steps and process conditions of the present embodiment are the same as those in Example 3, except that the mass ratio of molecular sieve and MnO _x /CeO ₂ is changed to 2:1, thereby preparing Fe-Beta+MnO _x /CeO ₂ (FMC 2 ) catalyst.

By changing the ratio of MnO _x /CeO ₂ to molecular sieve and increasing the content of oxide additives, the low-temperature activity of the catalyst will be further improved, and the conversion rate of 41% can be achieved at 150°C.

Example 5 Preparation and activity evaluation of Fe-Beta+MnO _x /CeO ₂ (FMC1)

The steps and process conditions of this example are the same as those of Example 3, except that the mass ratio of molecular sieve and MnO _x /CeO ₂ is changed to 1:1, thereby preparing Fe-Beta+MnO _x /CeO ₂ (FMC1) catalyst.

Further increase the amount of oxide additives, the low temperature activity will continue to improve. Compared with FMC2 and FMC3 samples, FMC1 sample has the best low temperature activity. The _NOx conversion rate of 59% can be obtained at 150°C. At the same time, the high-temperature activity of the sample can also be maintained at a high level, and the conversion rate of more than 80% can still be maintained at 450°C. The anti-sulfur poisoning performance is also an important index to evaluate the NH ₃ -SCR catalyst. The FMC1 catalyst with MnO _x /CeO ₂ as co-agent not only has high reactivity, but also can maintain a conversion rate of about 70% after 8 hours of reaction under the condition of SO ₂ in the atmosphere. Compared with the results of literature (MolecularCatalysis 433(2017) 265-273, AppliedCatalysis B: Environmental 195(2016) 48-58), the FMC1 catalyst in this patent has more excellent conversion rate and anti-sulfur poisoning performance in the full temperature window , which provides an effective method for the industrial application of molecular sieve catalysts.

Claims (2)

1. a preparation method of the Beta type molecular sieve of anti-propylene poisoning is characterized in that, with the pore diameter of the Fe-loaded

The Beta molecular sieve is the base; add oxide additives to the base of the molecular sieve, stir evenly, and grind for 40-90 minutes; the samples after mechanical mixing and grinding are calcined in air at 500°C at a heating rate of 2-5°C/min 4 hours; wherein, the oxide auxiliary agent is selected from MnO _x /CeO ₂ , and in the MnO _x /CeO ₂ , the loading amount of MnO _x is 50%; the mass ratio of the molecular sieve substrate to the oxide auxiliary agent is 0.5～ 3.5:1; The oxide auxiliary agent MnO _x /CeO ₂ is prepared by the following method: mixing manganese nitrate solution with cerium oxide carrier, then adding Na ₂ CO ₃ solution dropwise under stirring condition, stirring and aging at room temperature, filtering with suction , washing, drying and roasting to obtain MnO _x /CeO ₂ oxide auxiliary agent. 2. The catalyst obtained by the preparation method of claim 1 is used in the NH ₃ -SCR reaction containing propylene in the atmosphere.

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