CN108889304A - A kind of high stability cladded type copper-based catalysts and preparation method and application - Google Patents

Abstract

A high-stability coated copper-based catalyst is composed of CuO 36-59%, ZnO 24-40%, and SiO ₂ 1-40% in mass percentage. The invention has the advantages of low cost, simple production process, high stability and high dispersibility.

Description

A high-stability coated copper-based catalyst, its preparation method and application

technical field

The invention belongs to the field of catalyst preparation, in particular to a preparation method and application of a high-stability coated copper-based catalyst.

Background technique

Copper-based catalysts have been widely used in many industrial reactions due to their high reactivity, such as synthesis gas to methanol, synthesis gas to ethanol, methanol gasification and reforming, CO oxidation or hydrogenation reaction, water gas shift reaction, ethanol removal, etc. Hydrogen reaction, etc. Therefore, the research on copper-based catalysts continues to receive extensive attention and has become a research hotspot, and many high-performance copper-based catalysts have emerged as the times require.

However, due to the characteristics of copper itself, the stability of such catalysts is relatively poor, and deactivation is very easy to occur during the reaction process. For example, CuZnO/Al ₂ O ₃ has been widely used in industrial methanol synthesis reactions. However, within 1000 hours, nearly 1/3 of the catalyst will be deactivated. The main reason is that the number of active sites decreases due to the growth of copper species particles during the reaction process, which leads to a decrease in catalyst activity. At present, for the particle growth phenomenon in copper-based catalysts, scholars at home and abroad have proposed two mechanisms. The first is the migration and agglomeration mechanism, which means that the heating process will cause the metal centroids to shift and approach each other, in which the active metals with smaller distances will touch each other and aggregate and grow. The second mechanism is due to the aging mechanism. According to this mechanism, the growth of metal particles has nothing to do with the distance between particles, and the growth is mainly due to the uneven size of metal particles in the catalyst. Because metal particles with different particle sizes have different surface metal concentrations, it is generally believed that the smaller the metal particle size, the greater the surface metal concentration. Therefore, a metal concentration gradient will form on the surface of metals with different particle sizes, resulting in larger particles at the expense of disappearance of small particles. For the above two particle growth mechanisms, scholars have proposed several solutions. For example, adding a carrier to promote the dispersion of active metals and using the confinement of carrier channels to prevent metal growth; organic modification of the supported catalyst to hinder metal migration and contact to prevent metal growth, etc.

Chinese patent CN 106064239 A discloses a method for preparing hollow anti-rattle/silica core-shell nanoparticles with high dispersion. However, the preparation steps of this method are relatively cumbersome, and an organic metal salt is used as a metal source in the preparation process, and the cost is high and it is difficult to realize mass production.

Chinese patent CN 105576207 A discloses a preparation method and application of a hollow copper-tin alloy@silica core-shell nanocomposite material. Although this method only uses ethanol as an organic solvent in the preparation process, it is relatively environmentally friendly. However, due to the need to prepare the "core" in advance, the coating is not uniform.

Chinese patent CN 105170995 A discloses a method for coating gold-silver alloy nanoparticles with silicon dioxide. However, in this method, tetraethyl orthosilicate is used as the silicon source, and the cost is relatively high, and a gold-silver alloy with relatively good stability is used as the nucleus to achieve a more uniform coating during the preparation process.

Contents of the invention

The object of the present invention is to provide a coated copper-based catalyst with low cost, simple production process, high stability and high dispersibility, its preparation method and application.

The high-stability coated copper-based catalyst of the present invention is composed of 36-59% CuO, 24-40% ZnO and 1-40% _SiO2 in terms of mass percentage.

The preparation method of catalyst of the present invention comprises the steps:

Step 1, adding copper nitrate and zinc nitrate to distilled water to prepare a mixed aqueous solution of metal salts with a concentration of 1-2M, ultrasonically dissolving until clear and transparent, and obtaining solution A;

Step 2, mixing Na ₂ CO ₃ and Na ₂ SiO ₃ to prepare an aqueous solution with anion concentration of 1-2 M as precipitant B, wherein the molar ratio of Na ₂ CO ₃ to Na ₂ SiO ₃ is 0.5-100, and Prepare a Na ₂ CO ₃ aqueous solution with a concentration of 1-2 M as the precipitant C;

Step 3: At 60-80°C, add solution A dropwise to water at a rate of 60-80r/min, and at the same time add precipitant B dropwise, when precipitant solution B is added dropwise, quickly add precipitant solution C, The whole dropping process is controlled at a pH between 7-9. After the dropping is completed, continue to age for 1-3 hours, filter, wash, dry, and then calcined at a temperature of 350-450° C. to obtain a copper-based catalyst.

The catalyst of the present invention is suitable for the hydrogenation of _CO2 in a fixed-bed reactor to synthesize methanol, and the catalyst is loaded into a continuous fixed-bed reactor, first at 240-280°C, at normal pressure, and the volume percentage of the reducing gas is 5-10% _H2 In the mixed gas of 90-95% N ₂ , pre-reduction is carried out for 4-6 hours, and the air velocity of the mixed gas is 9000-12000 mL/(g h); after that, the gas consisting of CO _{2 ,} H ₂ and an inert atmosphere is introduced The mixed gas reacts, the reaction temperature is 240-280°C, the reaction pressure is 3.0-5.0MPa, the space velocity is 9000-12000mL/(g h), the volume percentage of each component of the raw material is: H ₂ 72-78%, CO ₂ 13-24%, inert atmosphere 4-10%.

The inert atmosphere as mentioned above is _N2 or Ar.

The invention discloses a method for preparing a coated copper-based catalyst, and the catalyst is used in the reaction of _CO hydrogenation to prepare methanol. The beneficial effects of the invention are as follows:

(1) The present invention adopts the method of hydrolysis and precipitation to prepare the coated copper-based catalyst. Compared with the traditional catalyst prepared by using silica as a carrier, the catalyst prepared by this method is more uniform, and the uniform mixing of active metal and _SiO2 is realized in the preparation process, and the dispersion of active metal is promoted.

(2) Compared with the catalyst prepared by the traditional co-precipitation method, the catalyst prepared by the hydrolysis precipitation method in the present invention has more uniform distribution of active components and a more uniform size. At the same time, the active metal is coated in the silica shell, and the growth is limited limit, thus improving stability.

(3) Compared with other coated catalysts, the catalyst prepared by the hydrolysis precipitation method in the present invention can coat the active metal in the _SiO2 shell in one step. The operation is simple and convenient, the production process has low energy consumption, low cost and Green and environmental protection, so the market application prospect is broad.

The preparation method disclosed in this patent is further described below through specific examples, but the present invention is not limited by the following examples.

Example 1

Put 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salt with a concentration of 2M, and dissolve it by ultrasonic for 1 hour to obtain a blue clear and transparent solution A. Weigh 0.5g of silicon nonahydrate Na 2 CO 3 precipitant solution C with an anion concentration of 2 M and 200 mL of Na ₂ CO ₃ precipitant solution C with an anion concentration of 2 M were prepared with sodium carbonate and 15 g of sodium carbonate. Under the condition of water bath at 60°C, drop solution A and solution B into 400mL of water together, in which the drop speed of metal salt solution A is 80r/min, when the mixed precipitant solution B is added dropwise, quickly add precipitant solution C , keep the pH of the whole process control solution at 9±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 1 hour, filter and wash. After drying at 80°C for 12 hours, it was calcined at 350°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 59%; ZnO 40%; SiO ₂ 1%.

See attached table 1 for the reduction conditions, activity evaluation conditions and evaluation results of the catalyst in _CO Hydrogenation to prepare methanol, and the specific steps are as follows:

First, sieve the prepared catalyst pellets into 20-40 meshes to be evaluated. Then 0.5 g of the sieved catalyst was placed in a fixed-bed reactor, and 30 mesh quartz sands were installed at both ends of the reactor. At normal pressure, at a certain temperature, with a certain volume percentage of the reducing mixture, the reduction is performed at a certain space velocity for 4-6 hours. After the reduction is completed, the temperature of the reactor is naturally lowered to below 100°C (to prevent premature reaction), and the reducing gas is switched to the raw material gas. The methanolylation reaction ends after a period of time.

Example 2

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salts with a concentration of 1M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 5.3g of sodium silicate nonahydrate and 13.2g of _sodium carbonate to prepare precipitant solution B with anion concentration of 1M, and prepare 200mL of _{Na2CO3precipitant} solution C with concentration of 2M for later use. Under the condition of water bath at 65°C, drop solution A and solution B into 400mL water together, in which the drop speed of metal salt solution A is 60 r/min. C, keep the pH of the control solution throughout the process at 7.5±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 1.5h, filter and wash. After drying at 80°C for 12 hours, it was calcined at 350°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 53%; ZnO 37%; SiO ₂ 10%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

Example 3

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salt with a concentration of 1.5M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 11.8g of sodium silicate nonahydrate and 10.8g of sodium carbonate to prepare precipitant solution B with anion concentration of 1.5 M, and prepare ₂₀₀ mL of _Na2CO3 precipitant solution C with a concentration of 2M for later use. Under the condition of water bath at 80°C, add solution A and solution B to 400mL of water dropwise, in which the drop speed of metal salt solution A is 75 r/min. C, keep the pH of the control solution throughout the process at 7±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 3h, filter and wash. After drying at 80°C for 12 hours, it was calcined at 400°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 47%; ZnO 33%; SiO ₂ 20%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

Example 4

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salts with a concentration of 2M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 20.3g of sodium silicate nonahydrate and 7.6g of _sodium carbonate to prepare precipitant solution B with anion concentration of 2M, and prepare 200mL of _{Na2CO3precipitant} solution C with concentration of 2M for later use. Under the condition of water bath at 75°C, drop solution A and solution B into 400mL water together, in which the metal salt solution A drop speed is 70 r/min, after the mixed precipitant solution B is added dropwise, quickly add the precipitant solution C, keep the pH of the control solution throughout the process at 8±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 3h, filter and wash. After drying at 80°C for 12 hours, it was calcined at 450°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 41%; ZnO 29%; SiO ₂ 30%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

Example 5

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salts with a concentration of 1.2M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 31.6g of sodium silicate nonahydrate and 7.6g of anhydrous sodium carbonate to prepare precipitant solution B with anion concentration of ₂ M, and prepare 200 mL of _Na2CO3 precipitant solution C with concentration of 1.2M for later use. Under the condition of water bath at 70°C, drop solution A and solution B into 400mL water together, in which the drop speed of metal salt solution A is 65 r/min. C, keep the pH of the whole process control solution at 8.5±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 3h, filter and wash. After drying at 80°C for 12 hours, it was calcined at 450°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 36%; ZnO 24%; SiO ₂ 40%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

Comparative example 1

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salts with a concentration of 1M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 18.2 g of anhydrous sodium carbonate to prepare precipitant solution B with anion concentration of 1 M. Under the condition of water bath at 70°C, solution A and solution B were added dropwise to 400mL of water, in which the drop rate of metal salt solution A was 65 r/min, and the drop rate of precipitant solution B was controlled to make the solution pH during the whole dropping process Keep it at 7.5±0.1, and keep stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 1 hour, filter and wash. After drying at 80°C for 12 hours, it was calcined at 400°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 65%; ZnO 35%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

Comparative example 2

Weigh 22.5g of copper nitrate and 14.9g of zinc nitrate into a beaker, add a certain amount of distilled water to make a mixed solution of metal salts with a concentration of 1M, and ultrasonically dissolve for 1 hour to obtain blue clear and transparent solution A. Weigh 18.2 g of anhydrous sodium carbonate to prepare precipitant solution B with anion concentration of 1 M. Weigh 2.5g of fumed silica and add it to 400mL of 70°C water and stir evenly, then add solution A and solution B to 400mL of water side by side, in which the droplet velocity of metal salt solution A is 65 r/min, and control the precipitant solution B The dropping speed keeps the pH of the solution at 7.5±0.1 during the whole dropping process, and keeps stirring. After solution A is added dropwise, stop dropping the precipitating agent immediately and continue to age for 1 hour, filter and wash. After drying at 80°C for 12 hours, it was calcined at 400°C for 4 hours to prepare the catalyst. The mass fraction percentage composition of the catalyst is: CuO 47%; ZnO 33%; SiO ₂ 20%.

The reduction conditions, activity evaluation conditions and evaluation results of the catalyst for preparing methanol by hydrogenation of _CO2 are shown in Attached Table 1, and the specific steps are shown in Example 1.

From the evaluation result data of Examples 1 to 5 in Table 1, it can be seen that the activity of the catalyst prepared by this method shows a trend of first increasing and then decreasing. The reason is that the dispersion of active species can be promoted when a small amount of silicon is added. , Most of the active metals are covered in the silica shell, unable to contact the reaction gas, so the reactivity decreases.

From the evaluation result data of Examples 1 to 5 in Table 1 and the evaluation result data of Comparative Example 1, it can be known that the stability of the catalyst prepared by this method is stronger than that of the common co-precipitation method, and this is because the enhancement of silicon oxide promotes the activity. The interaction force between species and the silica shell inhibit the growth of active metal particles, which in turn promotes the improvement of catalyst stability.

From the evaluation result data of Example 3 in Table 1 and the evaluation result data of Comparative Example 2, it can be seen that although the activity of the catalyst prepared by the hydrolysis precipitation method is slightly lower than that of the catalyst of Comparative Example 2, the stability has been greatly improved. This is because the catalyst prepared by the co-precipitation method, the active metal mainly exists on the outer surface of the carrier, so the catalyst activity is high, but it is easy to agglomerate and grow, which induces catalyst deactivation. For the catalyst prepared by the encapsulation method, although the active metal is wrapped in the silicon shell, resulting in a slight decrease in activity, the presence of the silicon shell can greatly inhibit the agglomeration and growth of the active metal and improve the stability of the catalyst.

The above description is only the preferred mode of the embodiment of the present invention, and the present invention is not limited to the above embodiment. For those skilled in the art, the present invention can have transformation and replacement, for example, using this method to prepare and adopt other silicon sources to prepare package Coated catalysts, etc. Therefore, any modification, equivalent replacement, improvement, etc. made under the principle and spirit of the embodiments described in the method of the present invention belong to the protection scope of the present invention.

Table 1

Note: The ratio of activity decrease is relative to the initial activity. After 60 hours of activity evaluation, the activity decreased by 6-19%. The smaller the activity decrease ratio, the better the stability.

Claims (4)

1. a high-stability coated copper-based catalyst, characterized in that the high-stability coated copper-based catalyst of the present invention, by mass percentage, consists of CuO 36-59%, ZnO 24-40%, SiO ₂ 1-40%. 2. the preparation method of a kind of high stability coated copper-based catalyst as claimed in claim 1, is characterized in that comprising the steps: Step 1, adding copper nitrate and zinc nitrate to distilled water to make a mixed aqueous solution of metal salts with a concentration of 1-2M, ultrasonically dissolving until clear and transparent, and obtaining solution A; Step 2, Na ₂ CO ₃ and Na ₂ SiO ₃ are mixed to form an aqueous solution with anion concentration of 1-2 M as precipitant B, wherein the molar ratio of Na ₂ CO ₃ to Na ₂ SiO ₃ is 0.5-100, and Prepare Na ₂ CO ₃ aqueous solution with a concentration of 1-2 M as precipitant C; Step 3, at 60-80°C, drop solution A into water at a rate of 60-80r/min, and add precipitant B dropwise at the same time, and quickly add precipitant solution C dropwise after the addition of precipitant solution B is completed, The whole dropping process is controlled at a pH between 7-9. After the dropping is completed, continue to age for 1-3 hours, filter, wash, dry, and then calcined at 350-450° C. to obtain a copper-based catalyst. 3. the application of a kind of high-stability coated copper-based catalyst as claimed in claim 1, is characterized in that comprising the steps: The catalyst is suitable for _CO2 hydrogenation into methanol in a fixed-bed reactor, the catalyst is loaded into a continuous fixed-bed reactor, firstly at 240-280°C, normal pressure, the volume percentage of reducing gas is 5-10% _H2 and 90- In the mixed gas of 95% N ₂ , carry out pre-reduction for 4-6 hours, and the space velocity of the mixed gas is 9000-12000 mL/(g h); after that, CO ₂ and H ₂ are introduced, where H ₂ : CO ₂ The volume ratio is 3-6:1, the reaction temperature is 240-280°C, the reaction pressure is 3.0-5.0MPa, the space velocity is 9000-12000mL/(g h), and the volume percentage of each component of the raw material is: H ₂ 72 -78%, CO ₂ 13-24%, inert atmosphere 4-10%. 4. the application of a kind of high-stability coated copper-based catalyst as claimed in claim 3, is characterized in that described inert atmosphere is N ₂ or Ar.