CN110508290B - High-dispersion palladium/cobalt hydroxide catalyst and preparation method and application thereof - Google Patents

Abstract

The present invention provides a highly dispersed Pd/Co(OH) ₂ catalyst and its preparation method and application. The present invention firstly prepares a Co(OH) ₂ carrier with a higher specific surface area by a simple method, and then calcinations etc. The operation makes the surface of the carrier have more defect sites, and then the palladium impregnation solution is supported on the Co(OH) ₂ carrier to prepare a highly dispersed Pd/Co(OH) 2 catalyst with better performance; the highly dispersed Pd/Co(OH) ₂ catalyst of the present invention The preparation of Pd/Co(OH) ₂ catalyst is used in the selective hydrogenation of acetylene, which not only has high catalytic activity and high ethylene selectivity, but also has the advantages of excellent stability and high atom utilization.

Description

Highly dispersed palladium/cobalt hydroxide catalyst, preparation method and application thereof

(1) Technical field

The invention relates to a highly dispersed Pd/Co(OH) ₂ catalyst, a preparation method thereof, and an application in the selective hydrogenation of acetylene.

(2) Background technology

Ethylene is one of the most important chemical products in the world and is widely used in various fields such as synthetic plastics, rubber, fibers, medicines, pesticides and dyes. Industrial ethylene is mainly produced by the cracking of raw materials such as naphtha and diesel, but in the process of preparing ethylene gas, about 0.3%-3% acetylene is often generated; these trace amounts of acetylene will poison the Ziegler-Natta of the downstream polyethylene process The catalyst will not only reduce the activity and service life of the catalyst, but also seriously affect the product quality of the polyethylene process. Therefore, the removal of trace acetylene in feed gas has important industrial significance.

The commonly used method for removing acetylene in industry is selective hydrogenation, which has the advantages of no pollution, low energy consumption and simple process and is widely used. However, although the palladium-based catalysts traditionally used in the industry have better catalytic activity, they have poor ethylene selectivity, which may cause excessive hydrogenation to generate ethane or oligomerization to generate green oil, which affects the catalyst performance. service life. Therefore, the ethylene selectivity of palladium-based catalysts in acetylene hydrogenation is very important to the ethylene industry. Therefore, it is necessary to modify the catalyst to prevent excessive hydrogenation of ethylene to ethane, thereby further improving the selectivity of ethylene. .

The surface of the synthesized carrier has more abundant defect sites, which can be combined with metal higher. The abundant -OH functional groups on the surface can effectively anchor the metal atoms, so that the metal atoms are highly dispersed on the surface of the carrier. Compared with the common alumina, the synthesized support has weaker acidity at the defect site, which further improves the selectivity and stability of the catalyst.

Based on the above background, the present invention proposes the preparation of a highly dispersed Pd/Co(OH) ₂ catalyst to improve the selectivity of the palladium-based catalyst in the acetylene hydrogenation reaction.

(3) Contents of the invention

The invention provides a highly dispersed Pd/Co(OH) ₂ catalyst, a preparation method thereof, and an application in the selective hydrogenation of acetylene. The preparation method of the invention is simple in process, and the prepared catalyst can greatly improve the ethylene selectivity in the selective hydrogenation reaction of acetylene.

The technical scheme of the present invention is as follows:

A highly dispersed Pd/Co(OH) ₂ catalyst is prepared as follows:

(1) prepare palladium dipping solution: palladium compound is dissolved in solvent to obtain palladium dipping solution;

In the palladium dipping solution, the concentration of the palladium compound in terms of palladium is 0.001-0.01 g/mL;

The palladium compound is palladium acetate, palladium acetylacetonate, dichlorodiamine palladium, ammonium tetrachloropalladate, sodium chloropalladate or tetraammine palladium nitrate, preferably palladium acetate;

The solvent is determined according to the type of the palladium compound, and can be water, hydrochloric acid, ethanol, acetone, etc., and the present invention has no special requirements for this;

(2) Synthesis of Co(OH) ₂ carrier: dissolve cobalt chloride hexahydrate and precipitant in deionized water, stir for 0.5 h, then add propylene oxide, and stir at room temperature (20-30 ° C) for 0.5-5 h, Precipitation was precipitated, and then dried at 80 °C for 12 h. The solid product was washed with methanol and deionized water, dried at 110 °C for 8 to 12 h, and finally placed in a muffle furnace, and calcined at 350 to 700 °C for 2-6 h. Obtain Co(OH) ₂ carrier;

The material ratio of the cobalt chloride hexahydrate, the precipitating agent and the propylene oxide is 1:1-5:1-10, preferably 1:2:10;

The precipitating agent is sodium lauryl sulfate, hexamethylenetetramine, ammonium nitrate, ammonium fluoride or ammonium chloride, preferably ammonium chloride;

(3) Preparation of highly dispersed Pd/Co(OH) ₂ catalyst: The Co(OH) ₂ carrier was immersed in a palladium impregnation solution, dispersed uniformly, immersed at room temperature for 9-12 h, and then dried at 110-130 °C for 9- 12h, then put into a tube furnace, and calcined at 300-700°C for 6-10h to obtain a highly dispersed Pd/Co(OH) ₂ catalyst;

In the present invention, after the cobalt hydroxide in step (3) is immersed in the palladium dipping solution for 9-12 hours, the system can be placed in a microwave reactor, and microwaved at 110-130° C. for 20-80 minutes, which can further promote the metal The components are dispersed on the carrier, and then the sample is placed in an oven at 110-130°C for 9-12 hours, and then calcined to obtain the final catalyst.

In the catalyst obtained in the present invention, based on the mass of the carrier, the loading amount of the palladium compound calculated as palladium is 0.01-0.5wt%, preferably 0.01-0.1wt%, more preferably 0.01-0.03wt%.

In the preparation method of the catalyst of the present invention, the palladium compound can be considered as all supported, and those skilled in the art can select the added amount of the palladium compound and the carrier according to the required loading.

The highly dispersed Pd/Co(OH) ₂ catalyst of the present invention can be applied to the hydrogenation reaction of acetylene. Specifically, the application method is:

Before the selective hydrogenation of acetylene, the catalyst needs to be reduced with hydrogen, the reduction temperature is 130-230 ° C, and the time is 1-4 h; then the reduced catalyst is used for the selective hydrogenation of acetylene, the reaction The conditions are: temperature 60-210°C (preferably 60-150°C), pressure 0.1-1MPa (preferably 0.1-0.3MPa, more preferably normal pressure), space velocity 1000-10000h ^-1 (preferably 4000-8000h ^-1 );

In the selective hydrogenation reaction of acetylene, the initial gas composition of the reaction is (volume fraction): 0.33% C ₂ H ₂ , 0.66% H ₂ , 33.3% C ₂ H ₄ , and the balance N ₂ .

Compared with the prior art, the beneficial effects of the present invention are:

(1) The preparation of the highly dispersed Pd/Co(OH) ₂ catalyst of the present invention firstly prepares a carrier of Co(OH) ₂ with a higher specific surface area by a simple method, and then makes the surface of the carrier with more defect sites. Then, the palladium impregnation solution was supported on the Co(OH) ₂ carrier to prepare a highly dispersed Pd/Co(OH) ₂ catalyst with better performance. On the one hand, palladium obtains a higher degree of dispersion on the support, which is favorable for acetylene hydrogenation; on the other hand, the acidity of the surface of this support is lower than that of alumina, which means that the surface of this support is almost There is no medium-strong acid site, and less green oil will be generated in the acetylene hydrogenation reaction, so that the prepared highly dispersed Pd/Co(OH) ₂ catalyst has higher stability; finally, the highly dispersed Pd/Co The surface of the (OH) ₂ catalyst contains a large number of hydroxyl groups, which can better stably anchor the presence of palladium, so that palladium is further dispersed on the catalyst. In addition, the anchor between the hydroxyl group and palladium exists in a chemical form, and the hydroxyl group can provide electron transfer to the palladium active site, so that the palladium active center exhibits an electron-rich state, thereby obtaining high ethylene selectivity.

(2) The preparation method of the highly dispersed Pd/Co(OH) ₂ catalyst of the present invention is simple in process.

(3) The preparation of the highly dispersed Pd/Co(OH) ₂ catalyst of the present invention is applied to the selective hydrogenation of acetylene, which not only has high catalytic activity and high ethylene selectivity, but also has excellent stability and atomic Advantages of high utilization.

(4) Specific implementations

The present invention will be further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

In the following examples, the Co(OH ₎ carrier was synthesized as follows:

Put 0.01mol of cobalt chloride hexahydrate and 0.02mol of precipitant ammonium chloride in a small beaker, add a certain amount of deionized water to dissolve, stir for 0.5h, then add 0.1mol of propylene oxide, and stir at room temperature for 5h , precipitated out, and then dried at 80 °C for 12 h. The solid product was washed with methanol and deionized water for 3-5 times, dried at 110 °C overnight, and finally placed in a muffle furnace and calcined at 600 °C for 6 h to obtain Co(OH) ₂ carrier.

Examples 1-5

A certain amount of palladium acetate was weighed and dissolved in concentrated hydrochloric acid, transferred to a volumetric flask, and a certain amount of deionized water was added to the corresponding scale to obtain a chloropalladium acid solution with a mass concentration of 0.001 g/mL of palladium. According to the load amount listed in Table 2 and its proportioning, the metered chloropalladium acid solution is mixed with a certain amount of deionized water, and after stirring, the highly dispersed Co(OH ₎ carrier (the specific surface area is about 150 -250m ² /g) was poured into the immersion solution and sonicated to make it evenly dispersed. The wetted Co(OH) ₂ carrier was impregnated at room temperature for 12 h, and dried at 110 °C for 12 h. After taking out the sample, the sample was calcined at 350 to 700 °C for 6 h to obtain highly dispersed Pd/ A catalyst for Co(OH) ₂ .

The comparison of texture properties of Co(OH) ₂ carrier before and after loading Pd in Example 4 is shown in Table 1:

Table 1 Comparison of carrier texture properties before and after Pd loading

Example 6

Referring to the operation of Example 5, the difference is only that the carrier is replaced with alumina with a specific surface area of 60 m ² /g, and a simple Pd/Al ₂ O ₃ catalyst is prepared.

Example 7

Referring to the operation of Example 5, the only difference is that the carrier is replaced with alumina with a specific surface area of 420 m ² /g, and a simple Pd/Al ₂ O ₃ catalyst is prepared.

Example 8

The highly dispersed Pd/Co(OH) ₂ catalyst prepared in Example 2 was reacted in a microwave reactor at 100° C. for 80 min to obtain a finished catalyst.

Example 9

The highly dispersed Pd/Co(OH) ₂ catalyst prepared in Example 5 was reacted in a microwave reactor at 120° C. for 60 min to obtain a finished catalyst.

The obtained catalyst was evaluated for catalyst activity and selectivity according to the following methods:

0.3 g of the catalyst was placed in a small quartz tube reactor, and the quartz tube was placed in a temperature-controlled heating mantle. Before the evaluation of the acetylene selective hydrogenation reaction, the catalyst needed to be reduced in a pure H atmosphere at 180 °C for ₁ h. The reducing gas flow rate was 10 mL/min; after reduction, the reaction was carried out at the temperature shown in Table 2. The composition of the reaction gas is (volume fraction): 0.33% acetylene, 33.3% ethylene, 0.66% hydrogen, the remainder nitrogen, the flow rate of the reaction gas is 50 mL/min, and the reaction pressure is normal pressure. The reaction gas outlet is connected to gas chromatography online detection, and the evaluation results of the catalyst are shown in Table 2 below.

Table ₂ Evaluation results of selective hydrogenation of acetylene over highly dispersed Pd/Co(OH) catalysts

Examples 10-15

With reference to the preparation methods of the catalysts of Examples 1-5, the loading of the palladium impregnation solution is shown in Table 3, and a highly dispersed Pd/Co(OH) ₂ catalyst was prepared.

The evaluation method of catalyst activity and selectivity is the same as above, and the calcination temperature for preparing the catalyst and the reaction temperature in the acetylene hydrogenation reaction are changed at the same time. The evaluation results of the catalyst are shown in Table 3 below.

Table 3 Evaluation results of selective hydrogenation of acetylene over highly dispersed Pd/Co(OH) ₂ catalysts

Claims (3)

1. the application of a highly dispersed Pd/Co(OH) catalyst in the selective _{hydrogenation} of acetylene, is characterized in that, the method for described application is: Before the selective hydrogenation of acetylene, the catalyst was first reduced with hydrogen, the reduction temperature was 130-230 °C, and the reduction time was 1-4 h; then the reduced catalyst was used for the selective hydrogenation of acetylene, The reaction conditions are: temperature 60-210 ℃, pressure 0.1-1 MPa, space velocity 1000-10000 h ^-1 ; in the selective hydrogenation reaction of acetylene, the initial gas volume fraction composition of the reaction is: 0.33% C ₂ H ₂ , 0.66% H ₂ , 33.3% C ₂ H ₄ , balance N ₂ ; The preparation method of the catalyst is: (1) Preparation of palladium dipping solution: dissolving the palladium compound in a solvent to obtain a palladium dipping solution; The palladium compound is palladium acetate, palladium acetylacetonate, dichlorodiamine palladium, ammonium tetrachloropalladate, sodium chloropalladate or tetraammine palladium nitrate; (2) Synthesis of Co(OH) ₂ carrier: Dissolve cobalt chloride hexahydrate and precipitant in deionized water, stir for 0.5h, then add propylene oxide, stir at room temperature for 0.5~5h, precipitate out, and then place in After drying at 80°C for 12h, the solid product was washed with methanol and deionized water, dried at 110°C for 8~12h, and finally placed in a muffle furnace, and calcined at 350~700°C for 2-6h to obtain Co(OH) ₂ carrier; The ratio of the amount of cobalt chloride hexahydrate, precipitant and propylene oxide is 1:(1~5):(1~10); The precipitating agent is sodium lauryl sulfate, hexamethylenetetramine, ammonium nitrate, ammonium fluoride or ammonium chloride; (3) Preparation of highly dispersed Pd/Co(OH) ₂ catalyst: The Co(OH) ₂ carrier was immersed in a palladium impregnation solution, dispersed uniformly, immersed at room temperature for 9-12 h, and the system was placed in a microwave reactor, Microwave at 110-130 °C for 20-80 min, then dry at 110-130 °C for 9-12 h, then put in a tube furnace, and calcined at 300-700 °C for 6-10 h to obtain highly dispersed Pd/Co ( OH) ₂ catalyst; In the catalyst, based on the mass of the carrier, the loading amount of the palladium compound in terms of palladium is 0.01-0.5 wt %. 2 . The application according to claim 1 , wherein, in step (1) of the preparation method of the catalyst, the concentration of the palladium compound in the palladium impregnation solution in terms of palladium is 0.001-0.01 g/mL. 3 . 3. The application according to claim 1, characterized in that, in the preparation method step (2) of the catalyst, the ratio of the amount of the cobalt chloride hexahydrate, the precipitant and the propylene oxide is 1: 2:10.