CN1140341C - A kind of method for electroless plating preparation supported silver catalyst - Google Patents

Abstract

A method for preparing a loaded silver catalyst by electroless plating. In the prior art, there is no preparation method of this type of catalyst with simple process, low cost, and stable combination of silver and carrier. The loaded silver of the present invention is prepared by electroless plating, that is, the silver and one or several kinds of insoluble solid particles are evenly loaded on the porous catalyst carrier by the electroless plating method. The supported silver catalyst prepared by this method has uniform distribution of silver metal, strong combination of silver and carrier, and good catalyst stability. During the preparation, particles that can promote catalyst performance can be uniformly added to form a stable structure with silver, which can significantly improve the performance of the catalyst. active.

Description

A kind of method for electroless plating preparation supported silver catalyst

technical field

The invention relates to a method for preparing a supported silver catalyst by electroless plating. The catalyst can be used for the oxidation of alcohol to produce corresponding aldehydes and ketones, such as the synthesis of formaldehyde by gas-phase oxidation of methanol, the synthesis of glyoxal by gas-phase oxidation of glyoxal, and the synthesis of ethyl lactate by gas-phase oxidation. Ethyl pyruvate, phenylethanol gas-phase oxidation synthesis of phenylacetaldehyde and so on.

Background technique

Supported silver has been used for many years as a catalyst for the oxidation of ethylene to ethylene oxide and alcohol oxidation to the corresponding aldehydes and ketones. Supported silver is made by distributing silver on the surface of an inert material, that is, a carrier. Usually, the carrier is porous , Insoluble spherical, ring or flake, supported silver catalysts are used in many chemical reactions, such as hydrogenation, cracking, dehydrogenation, epoxidation and production of aldehydes and ketones from primary and secondary alcohols. Silver is a precious metal. In order to reduce the amount of silver used, many methods for loading silver on a carrier have been developed. U.S. Patent No. 1,067,665 immerses the carrier in silver nitrate solution, then dries and roasts to obtain loaded silver containing 35% to 50% silver. The loaded silver produced by this method has a small specific surface area, uneven distribution, and unsatisfactory activity. U.S. Patent US 3,702,259, US3,956,184 and US 4,126,582 adopt the impregnation solution of silver amine complex ion and cyanide complex ion, add reducing agent to make loaded silver, but after adding reducing agent, silver will be precipitated on the surface of the container and in the solution, and some Accelerators that improve catalyst performance cannot be uniformly added during preparation. U.S. Patent No. 2,805,229 uses silver ammine ions to load on a porous tubular carrier, and obtains a loaded silver catalyst after thermal decomposition. U.S. Patent No. 4,330,437 wets the carrier with a volatile liquid before impregnating the silver salt, then impregnates, dries, and roasts to obtain a loaded silver catalyst. U.S. Patent No. 6,184,175B1 uses hydrocarbon as a solvent to load silver salt on a porous carrier, and obtains a loaded silver catalyst after thermal decomposition. At present, there is no preparation method of this type of catalyst with simple process, low cost, and stable combination of silver and carrier.

Contents of the invention

The purpose of the present invention is to provide a preparation method of a supported silver catalyst with excellent performance.

The embodiment of the present invention relates to adopting electroless plating to prepare supported silver as a catalyst, aliphatic alcohol or aromatic alcohol is oxidized by air in one step to generate corresponding aldehyde or ketone, and the oxidation reaction is carried out in a fixed-bed adiabatic reactor.

The loaded silver catalyst of the present invention is prepared by an electroless plating method, and the electroless plating is a plating method in which redox occurs in the same solution by means of a reducing agent when no current passes through, so that metal ions are reduced and deposited on the surface of the carrier. Previous supported silver catalysts were prepared by homogeneous chemical reduction, and the deposition process of silver would occur on all objects in contact with the plating solution without distinction, while the composition of the electroless plating solution and its corresponding working conditions made the reaction only limited. The reaction is carried out on the surface of the porous carrier with catalytic effect, but the reaction does not proceed spontaneously in the solution body and on the container wall. The invention reduces and deposits silver ions on the porous catalyst carrier, thereby preparing a silver catalyst with stable combination of silver and the carrier.

The present invention adopts electroless plating to prepare the loaded silver catalyst, and the carrier can be any porous solid that does not dissolve in the plating solution, such as pumice, molecular sieve, silicon oxide, aluminum oxide, ceramics and the like.

The above-mentioned carrier can be pumice, molecular sieve, etc. in various shapes such as spherical, columnar, or annular. The plating solution is generally composed of silver ammonium ions, ammonia water and reducing agent. The speed of electroless silver plating increases with the content of silver ions, but the concentration of silver ions is high and the solution is unstable. Generally, the medium and low concentration of 0.05-0.5mol/L is used. Ammonia in the plating solution is beneficial to the stability of silver ammonium ions, increasing the concentration of ammonia water will increase the stability of silver ammonium ions, but if it is too high, it will slow down the silver plating speed. Generally, the molar ratio of free ammonia to silver ammonium ions is 1 to 10 .

Reducing agents generally include formaldehyde, glucose, tartrate or hydrazine sulfate, and the reduction rate is formaldehyde>glucose>tartrate>hydrazine sulfate. For the same reducing agent, the concentration is low, and the electroless plating speed is slow. Cause the plating solution to self-decompose, and metal silver is precipitated in the plating solution phase, generally the molar ratio of the reducing agent to the silver ammonium ion is 1-10.

Sodium hydroxide is a speed regulator. With the increase of alkalinity, the reduction speed will be accelerated. If it is too high, it will lead to self-decomposition of the plating solution. Generally, the concentration of sodium hydroxide is 0-0.5mol/L.

In addition, when using electroless plating to prepare loaded silver, one or several solid particles with different properties can be conveniently embedded in metallic silver. Liquid solids, such as ceramics, phosphides, halides, TiO ₂ , ZrO ₂ , La ₂ O ₃ , etc., are added in an amount of 10-200g/L.

The invention adds nanometer-level solid particles into the plating solution, which can be uniformly distributed in the plating metal and improves the activity of the catalyst.

The loaded silver prepared by electroless plating is washed, dried, and then calcined at 400-700°C for 1-6 hours to obtain the loaded silver catalyst.

The preparation method of the present invention is further illustrated as follows: (1) silver nitrate is dissolved in distilled water, after being completely dissolved, ammoniacal liquor is slowly added while stirring, and brown silver hydroxide precipitation and pitchy silver oxide precipitation are formed first, and excessive ammoniacal liquor is added After forming colorless transparent silver-ammonia complex solution; (2) reducing agent is added in distilled water, sodium hydroxide can be added when needed, stirring and dissolving; (3) the above two solutions are mixed to obtain electroless plating solution, which can be added when needed adding solid particles; (4) putting the carrier into an electroless plating solution for electroless plating; (5) filtering and drying at 400-700° C. for 1-6 hours to obtain a loaded silver catalyst.

The supported silver catalyst prepared by the present invention can be used for alcohol oxidation to produce corresponding aldehydes and ketones, such as the synthesis of formaldehyde by gas-phase oxidation of methanol, the synthesis of glyoxal by gas-phase oxidation of ethylene glycol, the synthesis of ethyl pyruvate by gas-phase oxidation of ethyl lactate, and the synthesis of ethyl pyruvate by gas-phase oxidation of phenylethanol. Oxidation synthesis of phenylacetaldehyde and so on.

When the supported silver catalyst prepared by the present invention is used for the gas-phase oxidation of alcohol to produce corresponding aldehydes or ketones, the reaction materials are gas-phase compounds composed of alcohol, water vapor, oxygen and nitrogen, and the molar ratio of oxygen and alcohol in the air during feeding is 0.6-2.0 , the reaction has the best activity. The water content is 10-30% (wt%). If the water distribution is too high, the product concentration will be too low to be directly made into a commercial product. If the water distribution is too low, the catalyst activity will be affected. The liquid hourly space velocity of feed is 6-60hr ^-1 (liquid hourly space velocity is the liquid volume number of the raw material alcohol that passes through per hour on the unit volume catalyst), the liquid hourly space velocity is too small and can affect the selectivity of product aldehyde or ketone, liquid hourly space velocity If the speed is too high, the conversion rate of alcohol will be affected. The reaction is carried out continuously at 400-750°C. After the product is quenched, it is sprayed and absorbed, and the commercial aldehyde can be obtained by adjusting the water replenishment amount of the spray. The conversion rate of alcohol in the invention can reach 100%, and the selectivity of aldehyde or ketone can reach 80%.

The metal silver of the loaded silver catalyst prepared by the method of the present invention is evenly distributed, and the bonding force between the coating and the carrier is strong. If nano or micron particles are added in the preparation process, the particles can be very uniformly distributed in the coating metal, and the physical properties of the metal can be adjusted. and chemical properties to further improve the activity of the catalyst. The invention has simple process, low cost and good effect.

Detailed ways

1. Dissolve silver nitrate in distilled water to make a solution of 0.05mol/L, then slowly add ammonia water while stirring, first, brown silver hydroxide precipitate and dark brown silver oxide precipitate are formed, and colorless transparent silver is formed after adding excess ammonia water Ammonia complex solution, the molar ratio of excess ammonia to silver ammine ions is 1. Add reducing agent formaldehyde in another distilled aqueous solution, the molar ratio of formaldehyde and silver ammine ion is 2, adjust alkalinity with NaOH, make NaOH concentration be 0.4mol/L. After the above two solutions are mixed evenly, the electroless plating solution is obtained. Put the NaY type molecular sieve as carrier into the electroless plating solution for electroless plating, after plating, filter, dry and bake at 450°C for 5 hours to obtain the supported silver catalyst.

Put 5 grams of catalyst into a stainless steel reactor with a diameter of 14mm, inject the 1,2-propanediol aqueous solution into the gasifier with a metering pump, mix with the preheated air, and then enter the catalytic bed for reaction after being heated. The liquid hourly space velocity of 1,2-propanediol is 30hr ^-1 , the air feed flow rate is 0.055M ³ /h, the reaction temperature is 450°C, the product is quenched and absorbed by spraying, and the supplementary water quantity of spraying is controlled to obtain 40% of methylglyoxal The conversion rate of the product, 1,2-propanediol is 100%, the selectivity of methylglyoxal is 80.6%, and the service life of the catalyst is 60 days.

2. Dissolve silver nitrate in distilled water to prepare a solution of 0.05mol/L, then slowly add ammonia water while stirring, firstly brown silver hydroxide precipitate and dark brown silver oxide precipitate are formed, and colorless transparent silver is formed after adding excess ammonia water Ammonia complex solution, the molar ratio of excess ammonia to silver ammine ions is 1. Add reducing agent tartrate in another distilled aqueous solution, its molar ratio to silver ammonium complex ion is 2, adjust alkalinity with NaOH, make NaOH concentration be 0.4mol/L. After the above two solutions are mixed evenly, an electroless plating solution is obtained. 100 g/L high-temperature ceramic particles with a particle size of 20-30 μm are added to the plating solution, and stirred by compressed air. Put silicon oxide as a carrier into the electroless plating solution for electroless plating, filter after plating, dry and bake at 450°C for 5 hours to obtain the supported silver catalyst.

Put 5 grams of catalyst into a stainless steel reactor with a diameter of 14mm, inject the 1,2-propanediol aqueous solution into the gasifier with a metering pump, mix with the preheated air, and then enter the catalytic bed for reaction after being heated. The liquid hourly space velocity of 1,2-propanediol is 30hr ^-1 , the air feed flow rate is 0.055M ³ /h, the reaction temperature is 580°C, the product is quenched and absorbed by spraying, and the supplementary water quantity of spraying is controlled to obtain 40% methylglyoxal The conversion rate of the product, 1,2-propanediol is 100%, the selectivity of methylglyoxal is 79.5%, and the service life of the catalyst is 90 days.

3. Dissolve silver nitrate in distilled water to prepare a solution of 0.5mol/L, then slowly add ammonia water while stirring, and first form brown silver hydroxide precipitate and dark brown silver oxide precipitate, and form colorless transparent silver after adding excess ammonia water Ammonia complex solution, the molar ratio of excess ammonia to silver ammine ions is 10. Add reducing agent glucose to the above solution, the molar ratio of glucose to silver ammine ions is 9, and mix well to obtain the electroless plating solution. Add 10g/L silver phosphide and 200g/L La ₂ O ₃ nanoparticles to the chemical plating solution, use ultrasonic waves to stir the solution, put aluminum oxide as a carrier into the chemical plating solution for chemical plating, filter after plating, After drying, it was calcined at 500°C for 4 hours to obtain a supported silver catalyst.

Put 5 grams of catalyst into a stainless steel reactor with a diameter of 14mm, inject ethylene glycol into the gasifier with a metering pump, mix with preheated air and water vapor, and then enter the catalytic bed for reaction. The liquid hourly space velocity is 50hr ^-1 , the air feed flow rate is 0.055M ³ /h, the reaction temperature is 620°C, the conversion rate of ethylene glycol is 100%, the selectivity of glyoxal is 81.5%, and the service life of the catalyst is 100 days.

4. Dissolve silver nitrate in distilled water to prepare a 0.3mol/L solution, and then slowly add ammonia water while stirring, first forming brown silver hydroxide precipitate and dark brown silver oxide precipitate, and forming colorless transparent silver after adding excess ammonia water Ammonia complex solution, the molar ratio of excess ammonia to silver ammine ions is 5. Add reducing agent hydrazine sulfate to the above solution, its molar ratio to silver ammine ions is 5, and mix well to obtain electroless plating solution. Add 10g/L silver bromide, 50g/L TiO ₂ and 100g/L ZrO ₂ particles into the electroless plating solution, the particle size is 1-10μm, use ultrasonic waves to stir the solution, put pumice as a carrier into the chemical plating solution Perform electroless plating, filter after plating, dry and bake at 500° C. for 3 hours to obtain a supported silver catalyst.

5 grams of catalyst are packed into a stainless steel reactor with a diameter of 14mm, and phenylethyl alcohol is injected into the gasifier with a metering pump, mixed with preheated air and water vapor, and enters the catalytic bed for reaction. The liquid space-time of phenylethyl alcohol The speed is 10hr ^-1 , the air feed flow rate is 0.015M ³ /h, the reaction temperature is 420°C, the conversion rate of phenylethanol is 98.2%, the selectivity of phenylacetaldehyde is 74.3%, and the service life of the catalyst is 80 days.

5. the silver catalyst that 5 grams of examples 4 are made is packed into a diameter and is in the stainless steel reactor of 14mm, and ethyl lactate aqueous solution is squeezed into vaporizer with metering pump, mixes with the air after preheating, and after heating Enter the catalytic bed to react, the liquid hourly space velocity of ethyl lactate is 45hr ^-1 , the air feed flow rate is 0.070M ³ /h, the reaction temperature is 600°C, the conversion rate of ethyl lactate is 100%, and the selectivity of ethyl lactate is 81.9%. The service life of the catalyst is 85 days.

Claims (6)

1. A method for electroless plating to prepare loaded silver catalyst, characterized in that loaded silver is prepared by electroless plating, that is, by the method of electroless plating, silver is loaded onto a porous catalyst carrier, and the specific conditions are: the plating solution of electroless plating It is composed of silver ammonium ions, ammonia water and reducing agent; the content of silver ions in electroless plating is 0.05-0.5mol/L, the molar ratio of free ammonia to silver ammonium ions is 1-10, and the molar ratio of reducing agent to silver ammonium ions 1-10; the loaded silver prepared in the plating solution is washed, dried, and fired at 400-700° C. for 1-6 hours. 2. the method for preparing supported silver catalyst by electroless plating according to claim 1 is characterized in that the solid carrier is spherical or columnar or annular. 3. electroless plating according to claim 1 prepares the method for supported silver catalyst, is characterized in that reducing agent is formaldehyde or glucose or tartrate or hydrazine sulfate. 4. the method for preparing supported silver catalyst by electroless plating according to claim 1 is characterized in that sodium hydroxide is added as a speed regulator in the electroless plating solution, and its concentration is 0～0.5mol/L. 5. The method for preparing a supported silver catalyst by electroless plating according to claim 1, characterized in that solid particles of 1.0 nm to 40 μm are added in the plating solution, and the addition is 10 to 200 g/L. 6. the method for preparing supported silver catalyst by electroless plating according to claim 5 is characterized in that adding nanoscale solid particles in the plating solution.