CN113275034A

CN113275034A - Hierarchical pore molecular sieve catalyst for eliminating VOCs and preparation method thereof

Info

Publication number: CN113275034A
Application number: CN202110756892.8A
Authority: CN
Inventors: 边超群; 万晓燕; 颜研; 郑璐; 雷鹏辉; 曾敏芳
Original assignee: Jinhua Oulun Catalytic Technology Co ltd; Jinhua Polytechnic
Current assignee: Jinhua Oulun Catalytic Technology Co ltd; Jinhua Vocational And Technical University
Priority date: 2020-10-29
Filing date: 2021-07-05
Publication date: 2021-08-20
Anticipated expiration: 2041-07-05
Also published as: CN112452353A; CN113275034B

Abstract

The invention discloses a multi-level porous molecular sieve catalyst for eliminating VOCs and a preparation method thereof. The preparation of the catalyst includes the following steps: (1) mixing silicon source, aluminum source, alkali source and water together, stirring evenly, removing alcohol organic matter generated by decomposition, and obtaining gel; (2) transferring the gel to The reaction kettle is sealed and crystallized to obtain a white powdery solid, which is the ZSM-5 molecular sieve carrier; (3) the ZSM-5 molecular sieve carrier is immersed in an aqueous solution containing precious metal soluble salt, and subjected to ultrasonication, stirring, standing, drying, and roasting. , to obtain a hierarchical porous molecular sieve catalyst loaded with precious metals. The multi-level porous molecular sieve catalyst prepared by the invention has low cost, simple application, can be directly used for purifying VOCs in the environment without reduction treatment, has stable performance, and has high catalytic performance and high performance for the catalytic elimination of VOCs under different conditions. Lower catalytic elimination temperature.

Description

Hierarchical pore molecular sieve catalyst for eliminating VOCs and preparation method thereof

Technical Field

The invention relates to the field of environmental catalysis, in particular to a hierarchical pore molecular sieve catalyst for eliminating VOCs and a preparation method thereof.

Background

Volatile Organic Compounds (VOCs) are a class of chemical substances with high toxicity and serious pollution, and are also one of the important precursors for aggravating atmospheric combined pollution. The currently widely used pollution control technologies for VOCs are basically divided into two main categories: one is physical recovery, in which VOCs are enriched by physical methods and then recovered by post-treatment, and the methods comprise porous material adsorption technology, solution absorption technology and the like. Although the method is simple to operate, the method has the problems of secondary pollution and the like. The other is the oxidative degradation of VOCs into non-toxic or low-toxicity inorganic substances such as carbon dioxide and water by using chemical or biological technology, and comprises direct combustion technology, photocatalysis technology, plasma technology, catalytic combustion technology and the like. Compared with other methods, the catalytic combustion method can treat the low-concentration VOCs waste gas at a temperature far lower than the direct oxidation temperature, has the characteristics of high purification efficiency, no secondary pollution, low energy consumption, wide application range and the like, and is one of the most effective methods in the actual VOCs treatment application at present.

The catalyst for eliminating VOCs waste gas by catalytic oxidation process mainly includes non-noble metal oxide and its compound (MnO)_x,CuO_x,ZrO_xEtc.), perovskite catalysts (LaMnO)₃,SrFeO₃Etc.) and supported noble metal catalysts (Pt/ZrO)₂,Pt/TiO₂,Au/CeO_xEtc.) three major classes. The stability and catalytic activity of non-noble metal oxides, their compounds and perovskite catalysts need to be further improved after years of research. The supported noble metal catalyst has lower VOCs eliminating reaction temperature, relatively higher selectivity and stability, and arouses the interest of researchers. The zeolite molecular sieve gradually becomes one of the research hotspots of the catalytic oxidation of the VOCs by virtue of the advantages of large specific surface area, regular pore channels, high hydrothermal stability, adjustable framework silicon-aluminum ratio and the like.

In a preparation method of a solid-phase-like VOCs degradable high-silicon ZSM-5 molecular sieve disclosed in patent CN110496595A, a silicon source, an alkali source, a template agent, a ZSM-5 molecular sieve seed crystal and water are mixed to form gel; (2) placing the gel obtained in the step (1) in a reaction kettle for hydrothermal treatment, and after the reaction is finished, carrying out solid-liquid separation, washing, drying and roasting to obtain molecular sieve raw powder; (3) and (3) putting the molecular sieve raw powder obtained in the step (2) into an ammonium salt solution for ion exchange to obtain an ammonium type ZSM-5 molecular sieve, and then roasting to obtain HZSM-5. The molecular sieve catalyst prepared according to the patent has the advantages of small particle size, large specific surface area, good hydrophobicity, strong VOC adsorption performance and the like. However, in the technical scheme of the patent, the synthesis of the ZSM-5 molecular sieve uses tetraethylammonium hydroxide, tetrapropylammonium hydroxide and the like as a template agent in addition to a conventional silicon source, an aluminum source, an alkali source and water, and has high synthesis cost.

In patent CN111085218A, a manganese cobalt composite oxide catalyst for removing VOCs and a preparation method and an application thereof, a water-soluble salt of manganese and a water-soluble salt of cobalt are respectively dissolved in deionized water to obtain corresponding manganese solution and cobalt solution, the manganese solution and the cobalt solution are mixed and stirred, urea is added, the mixture is placed into a reactor for heating and stirring, and then the mixture is allowed to stand, filtered, washed, dried and roasted to obtain the manganese cobalt composite oxide catalyst. The catalyst prepared according to the patent has the advantages of good stability, no secondary pollution and the like. However, the elimination temperature of the catalyst for toluene is between 307 ℃ and 350 ℃, and the problem of high catalytic temperature exists.

In a catalyst for eliminating volatile organic compounds and a preparation method thereof disclosed in patent CN110898834A, Nb is adopted₂O₅-Al₂O₃/CeVO₄As a carrier, MoO₃The catalyst is a catalyst auxiliary agent, and Pt is an active component, and provides a catalyst for completely oxidizing VOCs (volatile organic compounds) with low Pt content of noble metal and high catalytic performance and a preparation method thereof. The catalyst can be used for purifying volatile organic waste gas at a lower temperature range, and has high reaction activity on benzene, toluene, ethyl acetate, acetone, n-hexanol and diethyl ether. However, the catalyst of the patent has the problem of higher catalytic temperature when the elimination temperature of toluene is between 210 ℃ and 240 ℃.

Disclosure of Invention

Based on the above-mentioned deficiencies in the prior art, the present invention provides a hierarchical pore molecular sieve catalyst for the elimination of VOCs and a method for preparing the same.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a hierarchical pore molecular sieve catalyst for eliminating VOCs comprises the following steps:

(1) mixing a silicon source, an aluminum source, an alkali source and water together, uniformly stirring, and removing alcohol organic matters generated by decomposition to obtain gel;

(2) transferring the gel into a reaction kettle, sealing and crystallizing to obtain white powdery solid, namely the ZSM-5 molecular sieve carrier;

(3) the molecular sieve carrier is immersed in an aqueous solution containing soluble salts of noble metals, and the hierarchical pore molecular sieve catalyst loaded with noble metals is obtained through ultrasound, stirring, standing, drying and roasting.

Preferably, the silicon source is tetraethyl silicate.

Preferably, the aluminum source is sodium metaaluminate or aluminum sulfate.

Preferably, the alkali source is potassium hydroxide or sodium hydroxide.

Preferably, the alcohol organic substance is ethanol.

Preferably, the obtained gel ratio is SiO₂:Al₂O₃:K₂O:H₂O is (30-50): 1, (2-6): 1500.

Preferably, the crystallization reaction conditions are as follows: the reaction temperature is 180 ℃, and the reaction time is 5 days.

Preferably, the aqueous solution of the soluble salt of the noble metal is one of platinum chloride, chloroplatinic acid, potassium chloroplatinate, palladium nitrate and chloroauric acid.

Preferably, the time of the ultrasonic treatment is 30 min; the stirring time is 4 hours; the standing time is 12 hours; the drying time is 2 hours, the drying temperature is 80 ℃, and stirring is needed during drying; the roasting time is 4 hours, and the roasting condition is a muffle furnace at 550 ℃.

The invention also provides a hierarchical pore molecular sieve catalyst, which adopts the preparation method, the weight percentage of the active components of the hierarchical pore molecular sieve catalyst is 1-20%, and the ZSM-5 molecular sieve is a K-type molecular sieve.

Compared with the prior art, the invention has the following beneficial effects:

1. the hierarchical pore molecular sieve catalyst is simple to prepare, does not use organic matters as template agents, and is all inorganic matters as raw materials, so that the production cost of the catalyst is reduced, and the obtained catalyst has a large number of hierarchical pores while having lower cost.

2. The ZSM-5 synthesized by the method is a K-type molecular sieve, and no additional ion exchange is needed after synthesis, so that the synthesis steps are simplified.

3. The hierarchical pore molecular sieve catalyst can be directly used for purifying VOCs in the environment without reduction treatment when in use, thereby simplifying the application steps.

4. The catalyst has stable performance, and has higher catalytic performance and lower catalytic elimination temperature for the catalytic elimination of VOCs under different conditions.

Drawings

FIG. 1 is an XRD pattern of the hierarchical pore ZSM-5 molecular sieve synthesized in example 3.

FIG. 2 is an SEM image of the multi-stage pore ZSM-5 molecular sieve synthesized in example 3.

Figure 3 is a plot of toluene elimination performance for different noble metal supported catalysts.

Detailed Description

In order to better illustrate the present invention and to facilitate the understanding of the technical solutions thereof, a typical but non-limiting implementation of the present invention is as follows:

preparation of catalyst carrier:

the molecular sieve used in the invention is an aluminum-rich ZSM-5 molecular sieve with multi-level pores, and is obtained by a hydrothermal synthesis method, tetraethyl silicate, sodium metaaluminate, sodium hydroxide and water are mixed together and stirred for a proper time to remove ethanol decomposed from tetraethyl silicate, and finally the solution is made to be in proportion to SiO₂:Al₂O₃:K₂O:H₂O is (30-50): 1, (2-6): 1500, and the mixed solution is put into a polytetrafluoroethylene kettle scale and crystallized for 5 days at 180 ℃ after being sealed. The white powdery solid obtained after crystallization is the hierarchical porous aluminum-rich ZSM-5 molecular sieve which is required to be prepared. The specific surface area of 300-500 m can be obtained by adjusting the proportion of the ZSM-5 molecular sieve with the multilevel pores²/g。

Compared with the conventional synthesis method, the preparation method of the application does not use template agents such as tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide and the like, simplifies the preparation process and reduces the synthesis cost.

Example 1

Preparation of the catalyst:

selecting a synthesized hierarchical pore ZSM-5 molecular sieve as a carrier, soaking the carrier in an aqueous solution containing platinum chloride, wherein the ratio of the carrier to the solution is 10g: 2-40 mL, performing ultrasonic treatment for 30min, stirring for 4h, standing for 12h, then stirring and mixing at 80 ℃, evaporating the water in the mixed solution to dryness, and uniformly loading an active component on the carrier. Roasting the obtained dried noble metal-loaded molecular sieve at 550 ℃ for 4 hours to obtain the hierarchical pore molecular sieve catalyst with the VOCs eliminated, wherein the mass content of the active component platinum is 1%.

Example 2

The balance was the same as in example 1, except that the platinum content was 2% by mass.

Embodiment 3

The balance was the same as in example 1, and the platinum content was 5% by mass. FIG. 1 is an XRD diagram and FIG. 2 is an SEM diagram.

Example 4

The balance was the same as in example 1, and the platinum content was 10% by mass.

Example 5

The balance was the same as in example 1, and the platinum content was 20% by mass.

Example 6

The same procedure as in example 3 was repeated except that a chloroplatinic acid solution was used for the impregnation.

Example 7

The same procedure as in example 3 was repeated except that a potassium chloroplatinate solution was used for the impregnation.

Example 8

The rest is the same as the embodiment 3, and a palladium nitrate solution is adopted during the impregnation, so that the catalyst with palladium as an active component is obtained.

Example 9

The rest is the same as the embodiment 3, and a chloroauric acid solution is adopted during the impregnation, so that the catalyst with gold as an active component is obtained.

Embodiment 10

Evaluation of catalytic performance:

0.1g of the catalyst of the embodiment 1-5 is taken, and the catalyst is respectively tableted, granulated and sieved to obtain 40-60 mesh catalyst particles. The catalyst is loaded into a quartz reaction tube with the inner diameter of 6mm, two ends of the quartz reaction tube are fixed by quartz wool, and then the reaction tube is placed in an open tubular furnace, wherein the position of the catalyst is positioned in the middle of the reaction furnace. Toluene was selected as a model compound for VOCs, and standard air (21)％N₂+79％O₂) The total flow of each path of gas is controlled to be 100mL/min and the space velocity is controlled to be 30000 mL/(g.h) by respectively serving as a carrier gas and a diluent gas. The catalytic performance of the catalyst was evaluated as shown in Table 1.

The temperature at which the toluene conversion is 50% is recorded as T₅₀And the temperature at 95% conversion is denoted as T₉₅In units of ℃. The high or low conversion temperature can show the reactivity of the catalyst in the catalytic reaction.

TABLE 1 EXAMPLES 1-5 evaluation of catalyst Performance

As can be seen from Table 1, the hierarchical pore molecular sieve catalyst prepared by the method has a catalytic temperature of 173-211 ℃, has a lower catalytic temperature compared with that of CN110898834A (the catalytic temperature is 210-240 ℃) and CN111085218A (the catalytic temperature is 307-350 ℃), and still has a very good catalytic effect.

Example 11

Evaluation of catalytic performance at high humidity: 0.1g of the catalyst of example 7 was taken, and the remaining test conditions were the same as in example 10, and standard air as a carrier gas was bubbled through a reagent bottle containing water to carry water vapor of a certain concentration, and mixed with the remaining reaction gas. The relative humidity is measured by a humidity detector.

Table 2 example 7 catalytic performance at different humidities

Example 12

And (3) evaluating catalytic performance at different space velocities: 0.1g of the catalyst of example 4 was used, and the performance test was carried out under the same test conditions as in example 10 and at space velocities of 60000 and 120000 mL/(g.h), respectively.

TABLE 3 catalytic Performance of example 4 at different space velocities

Example 13

Evaluation of catalytic performance of the catalyst under different noble metal loads: 0.1g of the catalysts of examples 8 to 10 was taken, and the remaining test conditions were the same as in example 10.

TABLE 4 evaluation of the Performance of different noble Metal catalysts

The applicant claims that the present invention specifies the composition of the catalyst, but the present invention is not limited to the above detailed composition, i.e. it does not mean that the present invention must rely on the above detailed composition to be carried out. It should be apparent to those skilled in the art that any modifications to the present invention are within the scope and disclosure of the present invention.

Claims

1. a preparation method for the multi-level porous molecular sieve catalyst that VOCs eliminates, is characterized in that, comprises the following steps:

(1) mix silicon source, aluminium source, alkali source and water together, stir, remove the alcohol organic matter that decomposition produces, obtain gel;

(2) the gel is transferred to the reactor for sealing and crystallization, and the obtained white powdery solid is the ZSM-5 molecular sieve carrier;

(3) The ZSM-5 molecular sieve carrier is immersed in an aqueous solution containing precious metal soluble salt, and subjected to ultrasonication, stirring, standing, drying and roasting to obtain a precious metal-loaded hierarchical porous molecular sieve catalyst.

2. The preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, wherein the silicon source is tetraethyl silicate.

3. The preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, wherein the aluminum source is sodium metaaluminate or aluminum sulfate.

4. the preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, is characterized in that, described alkali source is potassium hydroxide or sodium hydroxide.

5. the preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, is characterized in that, described alcohol organic matter is ethanol.

6. the preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, is characterized in that, described obtained gel SiO ₂ :Al ₂ O ₃ :K ₂ O:H ₂ O ratio is ( 30～50):1:(2～6):1500.

7 . The preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1 , wherein the crystallization reaction conditions are: a reaction temperature of 180° C. and a reaction time of 5 days. 8 .

8. the preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, is characterized in that, the aqueous solution of described noble metal soluble salt is platinum chloride, chloroplatinic acid, potassium chloroplatinate, palladium nitrate, A kind of chloroauric acid;

The ratio of the aqueous solution of the ZSM-5 molecular sieve carrier to the precious metal soluble salt is 10 g: 2-40 mL.

9. the preparation method of the hierarchical porous molecular sieve catalyst for VOCs elimination according to claim 1, is characterized in that, the time of described ultrasonic is 30min; The time of described stirring is 4h; The time of described standing is 12h The drying time is 2h, the drying temperature is 80°C, and stirring is required during drying; the roasting time is 4h, and the roasting condition is a muffle furnace at 550°C.

10. The hierarchically porous molecular sieve catalyst obtained by the preparation method according to any one of claims 1-9, wherein the obtained hierarchically porous molecular sieve catalyst has an active component weight percentage of 1%-20%;

The ZSM-5 molecular sieve is a K-type molecular sieve.