阅读说明：本技术 高分散的单原子Pd/介孔氧化铝催化剂及其制备方法与应用 (high-dispersion monatomic Pd/mesoporous alumina catalyst and preparation method and application thereof ) 是由 张群峰 黄伟民 周静 马磊 卢春山 丰枫 李小年 于 2019-08-30 设计创作，主要内容包括：本发明提供了一种高分散的单原子Pd/介孔Al<Sub>2</Sub>O<Sub>3</Sub>催化剂及其制备方法与应用,本发明中原位合成表面缺陷更多的介孔Al<Sub>2</Sub>O<Sub>3</Sub>,并以原子层积技术将钯原子稳定的负载于缺陷位点更多的介孔Al<Sub>2</Sub>O<Sub>3</Sub>上,能够有效的实现钯原子与介孔中的不饱和五配位Al<Sup>3+</Sup>的最大数目的锚定,从而制备出分散程度更高的单原子Pd催化剂,不仅可以有效地提高原子效率,最大限度地利用贵金属,降低催化剂的成本,而且该高分散的单原子Pd/介孔Al<Sub>2</Sub>O<Sub>3</Sub>催化剂在乙炔选择性加氢工艺中能够保持较高的乙炔转化率,同时也大大提高了乙烯的选择性。(The invention provides a high-dispersion monatomic Pd/mesoporous Al 2 O 3 The catalyst, the preparation method and the application thereof, in the invention, mesoporous Al with more surface defects is synthesized in situ 2 O 3 And stably loading palladium atoms on more mesoporous Al with more defect sites by using atomic lamination technology 2 O 3 in addition, unsaturated pentacoordinate Al in palladium atoms and mesopores can be effectively realized 3+ The maximum number of anchoring can be realized, so that the monatomic Pd catalyst with higher dispersion degree can be prepared, the atomic efficiency can be effectively improved, the noble metal can be utilized to the maximum degree, the cost of the catalyst can be reduced, and the monatomic Pd/mesoporous Al with high dispersion degree 2 O 3 The catalyst can keep higher acetylene conversion rate in the acetylene selective hydrogenation process, and simultaneouslyThe selectivity of ethylene is greatly improved.)

1. High-dispersion monatomic Pd/Hmesoporous Al₂O₃The catalyst is characterized by being prepared by the following method:

(1) Preparing a palladium impregnation solution: dissolving a palladium compound in a solvent to obtain a palladium impregnation solution;

The palladium compound is chloropalladic acid, palladium nitrate, palladium acetate, palladium acetylacetonate, dichlorodiammine palladium, ammonium tetrachloropalladate, sodium chloropalladate or tetraamminepalladium nitrate;

(2) Mesoporous Al₂O₃The preparation of (1): dissolving P123 in absolute ethyl alcohol, adding acid and aluminum isopropoxide, stirring until the solution is completely dissolved, drying at 50-80 ℃ to obtain a white solid sample, placing the sample in a muffle furnace, and roasting at 300-700 ℃ for 4-9 hours to obtain mesoporous Al₂O₃；

The acid is: the mass ratio of 37 wt% hydrochloric acid to citric acid is 3.5-4: 1, 67 wt% of nitric acid or 37 wt% of hydrochloric acid and salicylic acid in a mass ratio of 3.5-4: 1;

The volume consumption of the acid is 0.375-1.6 mL/g calculated by the mass of the aluminum isopropoxide;

The amount ratio of the P123 to the aluminum isopropoxide is 0.01 to 0.03: 1;

(3) High-dispersion monatomic Pd/mesoporous Al₂O₃Preparation of the catalyst: immersing the palladium immersion liquid in the mesoporous Al₂O₃Then, putting the sample into atomic layer deposition equipment, and carrying out atomic layer deposition for 1-6 h; and then, carrying out ultrasonic treatment on the sample for 30min, dipping the sample for 12h at room temperature, drying the sample for 12h at 110 ℃, and calcining the sample for 4-6 h at 300-1000 ℃ in a tubular furnace to obtain a finished product.

2. The highly dispersed monatomic Pd/mesoporous Al according to claim 1₂O₃The catalyst is characterized in that in the step (1), the concentration of the palladium compound in palladium in the palladium impregnation liquid is 0.001-0.01 g/mL.

3. the highly dispersed monatomic Pd/mesoporous Al according to claim 1₂O₃A catalyst, characterized in that, in the step (3), the obtained catalyst is placedAnd (3) performing microwave treatment in a microwave reactor at 100-120 ℃ for 20-80 min.

4. The highly dispersed monatomic Pd/mesoporous Al according to claim 1₂O₃The catalyst is characterized in that the loading amount of palladium in the catalyst is 0.01-0.5 wt% based on the mass of a carrier.

5. The highly dispersed monatomic Pd/mesoporous Al according to claim 1₂O₃The application of the catalyst in selective hydrogenation reaction of acetylene.

6. The application of claim 5, wherein the method of applying is:

Before the selective hydrogenation reaction of acetylene, reducing the catalyst by using hydrogen at the temperature of 120-230 ℃ for 1-3 h; and then the reduced catalyst is used for acetylene selective hydrogenation reaction, and the reaction conditions are as follows: the temperature is 70-180 ℃, the pressure is 0.1-1 MPa, and the space velocity is 4000-10000 h^-1；

In the acetylene selective hydrogenation reaction, the initial reaction gas composition is as follows: 0.33% C₂H₂、0.66％H₂、33.3％C₂H₄The balance of N₂。

(I) technical field

The invention relates to a high-dispersion monatomic Pd/mesoporous Al₂O₃a catalyst and a preparation method thereof, and application in acetylene hydrogenation reaction.

(II) background of the invention

Ethylene is one of the most important chemical products in the world, and is widely applied to various fields such as synthetic plastics, rubber, fibers, medicines, pesticides and dyes. Industrial ethylene is mainly produced by cracking naphtha, diesel oil and other raw materials, but about 0.3 to 3 percent of acetylene is often generated in the process of preparing ethylene gas; these traces of acetylene poison the Ziegler-Natta catalysts of downstream polyethylene processes, not only reducing the activity and lifetime of the catalyst, but also severely affecting the product quality of the polyethylene process. Therefore, the method has important industrial significance for removing trace acetylene in the raw material gas.

The method for removing acetylene commonly used in industry is a selective hydrogenation method, which has the advantages of no pollution, low energy consumption, simple process and the like and is widely applied. However, the palladium-based catalyst conventionally used in industry has a poor ethylene selectivity although it has a good catalytic activity, and may be excessively hydrogenated to ethane or oligomerized to green oil, thereby affecting the service life of the catalyst. Thus, the ethylene selectivity of palladium-based catalysts in acetylene hydrogenation is of great importance to the ethylene industry, and therefore, it is necessary to modify the catalysts to prevent the excessive hydrogenation of ethylene to ethane, thereby further improving the ethylene selectivity.

Carrier Al₂O₃Al with eight, five and tetrahedral ligands in it³⁺Ions of which five coordinate Al³⁺Ion (Al)³⁺ _penta) Can better generate electricity with metalThe molecules interact, thereby allowing better binding of the metal to the support. Thus, penta-coordinated Al can be utilized³⁺ _pentaSo as to anchor the metal on the carrier better and further prepare the monoatomic palladium catalyst. Therefore, the utilization rate of palladium atoms can be improved, and the preparation cost of the catalyst is reduced; the adsorption mode of ethylene on palladium can be changed from sigma bond with stronger binding capacity to pi bond with weaker binding capacity, and the selectivity of ethylene is greatly improved.

Based on the background, the invention provides a high-dispersion monatomic Pd/mesoporous Al₂O₃The catalyst is used for improving the selectivity of ethylene in the acetylene hydrogenation reaction.

Disclosure of the invention

The invention aims to provide high-dispersion monatomic Pd/mesoporous Al₂O₃A catalyst and a preparation method thereof, and application in acetylene hydrogenation reaction. The invention anchors active center palladium on Al to a great extent by Atomic Layer Deposition (ALD)₂O₃Therefore, single palladium atoms are highly dispersed on the surface of the carrier, the ethylene selectivity in the acetylene selective hydrogenation reaction is greatly improved, and the atom utilization rate can be improved.

the technical scheme of the invention is as follows:

high-dispersion monatomic Pd/mesoporous Al₂O₃the catalyst is prepared by the following method:

(1) Preparing a palladium impregnation solution: dissolving a palladium compound in a solvent to obtain a palladium impregnation solution;

In the palladium impregnation liquid, the concentration of a palladium compound in terms of palladium is 0.001-0.01 g/mL;

The palladium compound is chloropalladic acid, palladium nitrate, palladium acetate, palladium acetylacetonate, dichlorodiammine palladium, ammonium tetrachloropalladate, sodium chloropalladate or tetraamminepalladium nitrate, preferably chloropalladate;

The solvent can be deionized water, ethanol, acetone and the like, and the invention has no special requirement for the solvent;

(2) Mesoporous Al₂O₃The preparation of (1): dissolving P123 in absolute ethanol, and thenAdding acid and aluminum isopropoxide, stirring until the solution is completely dissolved, drying at 50-80 ℃ (2-4 days) to obtain a white solid sample, placing the sample into a muffle furnace, and roasting at 300-700 ℃ for 4-9 hours to obtain mesoporous Al₂O₃；

The acid is: the mass ratio of 37 wt% hydrochloric acid to citric acid is 3.5-4: 1, 67 wt% of nitric acid or 37 wt% of hydrochloric acid and salicylic acid in a mass ratio of 3.5-4: 1;

the volume consumption of the acid is 0.375-1.6 mL/g calculated by the mass of the aluminum isopropoxide;

The amount ratio of the P123 to the aluminum isopropoxide is 0.01 to 0.03: 1;

(3) High-dispersion monatomic Pd/mesoporous Al₂O₃Preparation of the catalyst: immersing the palladium immersion liquid in the mesoporous Al₂O₃Then, putting the sample into an atomic layer deposition device, and calculating the volume of the gas required corresponding to different time of atomic layer deposition, wherein the gas is generally nitrogen, and the time for carrying out atomic layer deposition is 1-6h (preferably 1-2 h, most preferably 2 h); and then, carrying out ultrasonic treatment on the sample for 30min, dipping the sample for 12h at room temperature (20-30 ℃), drying the sample for 12h at 110 ℃, and calcining the sample for 4-6 h in a tubular furnace at 300-1000 ℃ (preferably 400-800 ℃) to obtain a finished product.

preferably, the obtained catalyst is placed in a microwave reactor, and microwave is carried out for 20-80 min at the temperature of 100-120 ℃, so that the dispersion of the metal components can be further promoted fully.

The high-dispersion monatomic Pd/mesoporous Al prepared by the invention₂O₃In the catalyst, the supported amount of palladium is 0.01 to 0.5 wt%, preferably 0.01 to 0.2 wt%, based on the mass of the carrier.

In the preparation method of the catalyst of the invention, palladium can be regarded as being completely supported, and a person skilled in the art can select the adding amount of the palladium impregnation liquid according to the required supporting amount.

the high-dispersion monatomic Pd/mesoporous Al prepared by the invention₂O₃The catalyst can be applied to acetylene selective hydrogenation reaction. Specifically, the application method comprises the following steps:

Before the selective hydrogenation of acetyleneReducing the catalyst by using hydrogen at the temperature of 120-230 ℃ for 1-3 h; and then the reduced catalyst is used for acetylene selective hydrogenation reaction, and the reaction conditions are as follows: the temperature is 70-180 ℃ (preferably 70-140 ℃), the pressure is 0.1-1 MPa (preferably 0.1-0.3 MPa, more preferably normal pressure), and the space velocity is 4000-10000 h^-1(4000～8000h^-1)；

In the acetylene selective hydrogenation reaction, the gas composition at the initial reaction is as follows (volume fraction): 0.33% C₂H₂、0.66％H₂、33.3％C₂H₄the balance of N₂。

compared with the prior art, the invention has the beneficial effects that:

Preparing a high-dispersion monatomic Pd/mesoporous Al₂O₃The catalyst is applied to acetylene selective hydrogenation reaction. Compared with the traditional supported catalyst, the monatomic catalyst can be uniformly dispersed on the surface of the catalyst in a monatomic form, and can perform acetylene selective hydrogenation reaction by using an isolated single palladium atom, so that the monatomic catalyst has higher ethylene selectivity, high atom utilization rate and higher catalytic activity. In-situ synthesis of mesoporous Al with more surface defects in the invention₂O₃And stably loading palladium atoms on mesoporous Al with more defect sites by Atomic Layer Deposition (ALD)₂O₃In addition, unsaturated pentacoordinate Al in palladium atoms and mesopores can be effectively realized³⁺Thereby preparing a more highly dispersed monatomic Pd catalyst.

Not only can effectively improve the atomic efficiency, maximally utilize noble metal and reduce the cost of the catalyst, but also the high-dispersion monatomic Pd/mesoporous Al₂O₃The catalyst can keep higher acetylene conversion rate in the acetylene selective hydrogenation process, and simultaneously greatly improves the selectivity of ethylene.

(IV) detailed description of the preferred embodiments

the present invention is further illustrated by the following specific examples, but the scope of the invention is not limited thereto.