阅读说明：本技术 一种高活性脱硝分子筛的金属负载方法及应用 (Metal loading method and application of high-activity denitration molecular sieve ) 是由 胡晓倩 程士敏 王闯 孙洪平 李盛鹏 罗金玲 袁龙 于 2019-09-20 设计创作，主要内容包括：本发明公开了一种高活性脱硝分子筛的金属负载方法,将一定浓度的有机金属溶液和H型分子筛混合,搅拌均匀后,放入微波反应器中,搅拌并在微波加热下,金属有机化合物分子进入分子筛孔道,进行金属负载；完成后,将分子筛固体与溶剂分离,并经洗涤、干燥、焙烧后制得金属负载的分子筛。与传统离子交换方法相比,本发明具有条件温和、能耗低、方法简便、交换速率快、交换度高的优点,通过微波加热使得金属有机化合物分子以较高的运动速率快速进入分子筛中较难交换的孔道中并均匀分布,形成较多的孤立态活性中心,使得制得的过渡金属分子筛在氨选择性催化还原反应中具有较高的催化活性,尤其制备适用于作为高活性的柴油车尾气脱硝分子筛。(The invention discloses a metal loading method of a high-activity denitration molecular sieve, which comprises the steps of mixing an organic metal solution with a certain concentration with an H-type molecular sieve, uniformly stirring, putting into a microwave reactor, stirring, and allowing metal organic compound molecules to enter a molecular sieve pore channel under microwave heating to carry out metal loading; and after the completion, separating the molecular sieve solid from the solvent, and washing, drying and roasting to obtain the metal-loaded molecular sieve. Compared with the traditional ion exchange method, the method has the advantages of mild conditions, low energy consumption, simple and convenient method, high exchange rate and high exchange degree, and the metal organic compound molecules rapidly enter pore channels which are difficult to exchange in the molecular sieve at a high movement rate and are uniformly distributed through microwave heating to form more isolated active centers, so that the prepared transition metal molecular sieve has high catalytic activity in the ammonia selective catalytic reduction reaction, and is particularly suitable for preparing the high-activity diesel vehicle tail gas denitration molecular sieve.)

1. A metal loading method of a high-activity denitration molecular sieve is characterized by comprising the following steps:

(a) mixing an organic metal solution with a certain concentration and an H-type molecular sieve, and uniformly stirring;

(b) putting the mixture into a microwave reactor, stirring, and under microwave heating, allowing metal organic compound molecules to enter a molecular sieve pore channel for metal loading;

(c) and after the loading is finished, separating the molecular sieve solid from the solvent, and washing, drying and roasting to obtain the metal-loaded molecular sieve.

2. The method of claim 1, wherein the organic metal in the step (a) comprises iron acetylacetonate, ferrocene, iron naphthenate, and copper naphthenate;

the organic metal solution solvent comprises benzene, toluene, methanol, dichloromethane and trichloromethane;

the concentration of the organometallic solution was 0.001 ~ 1 mol/L.

3. The method of claim 1, wherein the molecular sieve in step (a) is free of a template agent and comprises H/beta, H/ZSM-5 or H/SSZ-13 molecular sieve, and Si/Al is 5 ~ 20.

4. The method as claimed in claim 1, wherein the volume of the organometallic solution in step (a) is 100-1000ml, and the mass of the molecular sieve is 5 ~ 100 g.

5. The method of claim 1, wherein the microwave reactor in the step (b) is lined with PEEK.

6. The method as claimed in claim 1, wherein the stirring speed in step (b) is 100 ~ 600r/min, the microwave heating power is 100-2000W, the temperature is 30-90 ℃, and the time is 0.1 ~ 10 h.

7. The method of claim 1, wherein the washing agent used in the washing in the step (c) is a polar organic solvent.

8. The method of claim 1, wherein the drying in the step (c) is performed at 90 ~ 140 ℃ for 1 ~ 8 hours.

9. The method as claimed in claim 1, wherein the calcination in step (c) is carried out at 400-650 ℃ for 3 ~ 10 hours.

10. Use of a molecular sieve prepared by a metal-loading method according to any one of claims 1 to 9, characterized in that it is applied to ammonia selective catalytic reduction for removal of nitrogen oxides.

Technical Field

The invention relates to a metal loading method of a molecular sieve, in particular to a metal loading method of a high-activity denitration molecular sieve and application thereof.

Background

The tail gas of motor vehicles contains a large amount of pollutants, which is one of the important reasons for damaging the air quality and harming human health, wherein the harm of nitrogen oxides (NOx) is the largest, and the nitrogen oxides discharged by diesel vehicles account for more than 60 percent of the total discharge of the motor vehicles. With the stricter and stricter automobile emission regulations, the emission control of nitrogen oxides of diesel vehicles has important significance.

Ammonia selective catalytic reduction technology (NH)₃-SCR) refers to the selective reduction of nitrogen oxides to nitrogen using ammonia as a reducing agent under oxygen-rich conditions for the purpose of removing nitrogen oxides. The ammonia selective catalytic reduction technology has high nitrogen oxide removal efficiency and nitrogen selectivity, and has wide application prospect in the field of mobile source nitrogen oxide emission control.

The catalyst is the core and key of ammonia selective catalytic reduction technology, and in recent years, transition metal molecular sieves are widely concerned due to good SCR reaction activity and nitrogen selectivity, wherein ZSM-5 molecular sieves, Beta and CHA type molecular sieves are most commonly used, and generally, copper-based molecular sieves have good medium and high temperature SCR reaction activity while iron-based molecular sieves have better high temperature activity. The common methods for loading transition metals include ion exchange and equal volume impregnation, and metal salts can also be added in the hydrothermal synthesis process.

Ion exchange is generally carried out under heating conditions by using an aqueous solution of a metal inorganic salt as an exchange liquid, and factors influencing the metal loading result include exchange time, exchange temperature, exchange times, inorganic salt types, stirring rotation speed, pH value of the solution, concentration and volume of the solution and the like. The pore diameter of the molecular sieve is small, a large driving force is needed for metal hydrated ions to enter the pore channel, and metal species are easily distributed on the outer layer of the crystal grain of the molecular sieve, so that the pore channel in the crystal grain cannot be effectively utilized. The traditional ion exchange method has the problems of long exchange time, low utilization rate of exchange liquid and uneven distribution. The ion exchange is carried out under the action of microwave, the movement rate of water molecules and metal ions is much faster than that of a common heating mode, metal hydrated ions can enter a pore passage which is difficult to exchange, the metal hydrated ions are uniformly distributed, and the molecular sieve has higher catalytic activity compared with the molecular sieve prepared by the traditional ion exchange method. The microwave-assisted ion exchange has the advantages of mild conditions, low energy consumption, simple and convenient method, high exchange rate, high exchange degree and the like.

The silicon-aluminum molecular sieve is in skeleton electronegativity due to the replacement of silicon by aluminum, proton hydrogen balances the skeleton charge to form a B acid center, and metal ions replace H⁺By loading in the channels of the molecular sieve with multiply charged cations replacing a plurality of adjacent H' s⁺Formation of catalytically active centers (e.g. isolated Cu)²⁺Isolated form of Fe³⁺) Metal ions that do not occupy the exchange sites form metal oxides during firing.

In a conventional ion exchange process carried out in an aqueous solution of a metal inorganic salt, metal cations enter the pores of the molecular sieve in the form of hydrated ions and exchange with protons. The metal cations lose part of bound water under the drying condition, have small volume, and migrate and are stabilized on ion exchange positions of the molecular sieve in the roasting process. When the metal ions in the pore channels of the molecular sieve are distributed unevenly and concentrated in a local area, the metal ions are easy to form metal oxide due to insufficient exchange sites in the roasting process. The isolated metal ions are usually the active centers of ammonia selective catalytic reduction reactions, while the metal oxides are the active centers of side reactions of ammonia oxidation to nitrogen oxides.

The invention takes organic metal solution as exchange liquid, the adopted metal organic compound exists in molecular state in organic solvent, the volume is moderate, the metal organic compound can enter molecular sieve pore channels under microwave-assisted heating, the metal organic compound can not be decomposed under drying condition, and the metal is loaded on the exchange sites in the roasting process, and meanwhile, proton hydrogen and organic groups are combined and oxidized, decomposed and removed. The space structure of the metal organic compound enables metal atoms to have larger distance, which is beneficial to improving the dispersion degree of the metal on the molecular sieve, thereby forming more isolated active centers.

CN104276582A discloses a method for exchanging Na-type molecular sieve into NH under microwave heating₄ ⁺Process for forming molecular sieves, but NH₄ ⁺Is much smaller than the metal hydrate ion, and thus easily enters the molecular sieve pore canal and is uniformly distributed, NH₄ ⁺The conditions of the exchange are not suitable for metal ion exchange. Tanshiya et al (chemical research and application, 1997, vol. 9, phase 4) studied the metal cation La by microwave heating³⁺、Co²⁺、Cu²⁺、Zn²⁺The aqueous solution of (2) and the NaX molecular sieve have ion exchange behaviors, but the ion exchange rate and the exchange degree are mainly concerned, and the application effect in the reaction field is not involved.

In conclusion, the ion exchange technology of the medium and small-aperture denitration molecular sieve still has the problems of long exchange time, low utilization rate of exchange liquid, uneven distribution and the like, increases the preparation cost of the molecular sieve and influences the catalytic activity.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a metal loading method and application of a high-activity denitration molecular sieve, which are convenient and rapid to use and have high exchange degree.

In order to achieve the above object, the present invention adopts the following technical solutions:

a metal loading method of a high-activity denitration molecular sieve comprises the following steps:

(a) mixing an organic metal solution with a certain concentration and an H-type molecular sieve, and uniformly stirring;

(b) putting the mixture into a microwave reactor, stirring, and under microwave heating, allowing metal organic compound molecules to enter a molecular sieve pore channel for metal loading;

(c) and after the loading is finished, separating the molecular sieve solid from the solvent, and washing, drying and roasting to obtain the metal-loaded molecular sieve.

The organic metal in the step (a) comprises ferric acetylacetonate, ferrocene, ferric naphthenate and copper naphthenate; or other metal organic compounds that are soluble in organic solvents and have moderate molecular structure and volume.

The organic metal solution solvent comprises benzene, toluene, methanol, dichloromethane and trichloromethane;

the concentration of the organometallic solution is 0.001 ~ 1mol/L, and preferably, the concentration of the organometallic solution is 0.005 ~ 0.5.5 mol/L.

The molecular sieve in the step (a) does not contain a template agent, and comprises H/beta, H/ZSM-5 or H/SSZ-13 molecular sieve, and Si/Al is 5 ~ 20.

The volume of the organic metal solution in the step (a) is 100-1000ml, and the mass of the molecular sieve is 5 ~ 100g, preferably, the volume of the organic metal solution is 100 ~ 500ml, and the mass of the molecular sieve is 10 ~ 50 g.

The microwave reactor in step (b) above is lined with PEEK.

The stirring speed in the step (b) is 100 ~ r/min, the microwave heating power is 100-.

In the washing in the step (c), the washing agent used is a polar organic solvent.

The drying in the above step (c) was carried out at 90 ~ 140 ℃ for 1 ~ 8 hours.

The calcination in the step (c) is carried out at the temperature of 400 ℃ and 650 ℃ for 3 ~ 10 hours.

The molecular sieve prepared by the metal loading method is applied to ammonia selective catalytic reduction reaction to remove nitrogen oxides, and is particularly used as a diesel vehicle tail gas denitration catalyst.

The invention has the advantages that:

the invention relates to a metal loading method of a high-activity denitration molecular sieve, which takes an organic metal solution as a switching liquid, and metal organic compounds enter a molecular sieve pore channel under the microwave-assisted heating condition and are uniformly distributed on an ion exchange position in the roasting process, so that the metal loading of the molecular sieve is quickly realized.

Compared with metal hydrated ions, the molecular structure of the metal organic compound enables metal atoms to have larger distance, which is beneficial to improving the dispersion degree of metal on the molecular sieve, but the aperture of the molecular sieve is smaller, and a larger driving force is needed for metal species to enter a pore channel; under the action of microwaves, solvent molecules and metal species have higher movement rate compared with a common heating mode; the metal species rapidly enter the pore canal which is difficult to exchange and are uniformly distributed, so that the prepared transition metal molecular sieve has higher catalytic activity in the ammonia selective catalytic reduction reaction.

Different kinds of metal inorganic salts exist in the form of hydrated ions in an aqueous solution, and the metal hydrated ions entering the pore channels of the molecular sieve lose part of bound water under the dry condition, so that the volume is reduced, the distance is shortened, and the dispersion of metal species is not facilitated. The metal organic compound adopted by the invention has moderate volume, can enter the molecular sieve pore canal, can not be decomposed in the drying process, and the metal atoms are positioned in the space structure among a plurality of organic groups to ensure that each group isThe metal atoms have larger spacing, which is beneficial to improving the dispersion degree and improving the distribution of metal species. In addition, low temperature (<100^oC) The sewage has a destructive effect on the structure of the molecular sieve, and the molecular sieve is firstly subjected to NH₄ ⁺Exchange prevents the structure from collapsing, and the H-type molecular sieve can be directly used for metal loading in the organic solution, thereby saving NH₄ ⁺And (5) exchanging.

Compared with the traditional ion exchange method, the method has the advantages of mild conditions, low energy consumption, simple and convenient method, high exchange rate and high exchange degree, metal organic compound molecules can enter exchange positions which are difficult to enter by the conventional method and are uniformly distributed to form more isolated active centers, and the method is particularly suitable for preparing the high-activity diesel vehicle tail gas denitration molecular sieve.

Drawings

FIG. 1 is an X-ray diffraction pattern of examples 1, 2 of the present invention and comparative example 1;

FIG. 2 is a graph showing the results of SCR evaluation of examples 1, 3 and 9 of the present invention and comparative example 3;

FIG. 3 is a graph showing the results of SCR evaluation of examples 2, 4, 5, 10 of the present invention and comparative example 1;

fig. 4 is a graph showing the SCR evaluation results of examples 6, 7, 8 of the present invention and comparative example 2.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

The detection instrument used by the invention comprises:

fourier transform Infrared Analyzer, MKS MultiGas 6030

The specific method for applying the metal-loaded molecular sieve in the following embodiment to the ammonia selective catalytic reduction reaction comprises the steps of roasting the molecular sieve at the temperature of 400-650 ℃ for 3 ~ 10 hours, tabletting, crushing and sieving, collecting particles with the size of 40 ~ 60 meshes as a molecular sieve catalyst, filling the catalyst particles into a fixed bed reactor, and introducing 500ppm NO and 500ppm NH₃，5%O₂，8%CO₂，3.5%H₂O，N₂Equilibrium, volume space velocity 480000h^-1。

The ammonia selective catalytic reduction reaction is carried out at 100 ~ 600 ℃ and the products are detected and quantitatively analyzed on line by using a Fourier transform infrared analyzer.