阅读说明：本技术 一种高活性钯碳催化剂的制备方法 (Preparation method of high-activity palladium-carbon catalyst ) 是由 肖发新 黄草明 于 2019-10-18 设计创作，主要内容包括：本发明属于催化剂制备技术领域,涉及一种高活性钯碳催化剂的制备方法。该方法为在催化剂制备过程中加入含磷物质预处理活性炭,不改变催化剂制备工艺,操作简便,适合于不同规模的钯碳催化剂制备。本发明制备的钯碳催化剂中负载于活性碳的钯以<3nm的超小尺寸微晶形态存在,Pd微晶平均尺寸小于2nm,负载于活性碳载体上的Pd含量为0.5-10％。(The invention belongs to the technical field of catalyst preparation, and relates to a preparation method of a high-activity palladium-carbon catalyst. The method adds phosphorus-containing substances to pretreat the activated carbon in the preparation process of the catalyst, does not change the preparation process of the catalyst, is simple and convenient to operate, and is suitable for preparing palladium-carbon catalysts with different scales. The palladium loaded on the activated carbon in the palladium-carbon catalyst prepared by the invention exists in a form of ultra-small-size microcrystal with the size less than 3nm, the average size of the Pd microcrystal is less than 2nm, and the content of the Pd loaded on the activated carbon carrier is 0.5-10%.)

1. The preparation method of the high-activity palladium-carbon catalyst is characterized by comprising the following steps of:

(1) adding carrier activated carbon into a phosphorus-containing substance water solution, stirring at 5-100 ℃ for 0.5-24h, cooling, filtering, and washing a filter cake with water until the pH value is neutral to obtain pretreated activated carbon; the molar concentration of the phosphorus-containing substance is 0.05-2M; adding water into the obtained pretreated activated carbon for size mixing to obtain activated carbon size;

(2) adding palladium chloride into a hydrochloric acid solution, and heating and dissolving to obtain a palladium-containing solution; adding the obtained palladium-containing solution into the activated carbon slurry obtained in the step (1), and performing immersion adsorption treatment to obtain a palladium adsorption solution;

(3) adding a reducing agent solution into the palladium adsorption solution obtained in the step (2) to perform a reduction reaction, and controlling the pH value of the solution in the reaction process;

(4) and after the reaction is finished, filtering, washing a filter cake until the pH value is neutral, preparing the Pd/C catalyst, and packaging and storing.

2. The method for preparing Pd/C catalyst with high activity as claimed in claim 1, wherein the specific surface area of the supported activated carbon in step (1) is 200-2000m²The solid powder with more than 300 meshes accounts for more than 60 percent.

3. The method for preparing a high-activity palladium-on-carbon catalyst as claimed in claim 1 or 2, wherein the phosphorus-containing substance in step (1) is selected from the group consisting of phosphorus oxide, phosphorus halide, phosphorus oxyhalide, phosphorus salt and phosphorus oxyacid.

4. The method for preparing a high-activity palladium-carbon catalyst according to claim 1 or 2, wherein the specific process conditions of the impregnation adsorption treatment in the step (2) are as follows: the treatment temperature is 5-40 ℃, and the treatment time is 0.5-6 h.

5. The method for preparing a high-activity palladium-carbon catalyst according to claim 3, wherein the specific process conditions of the impregnation adsorption treatment in the step (2) are as follows: the treatment temperature is 5-40 ℃, and the treatment time is 0.5-6 h.

6. The method for preparing a high-activity palladium-on-carbon catalyst as claimed in claim 1, 2 or 5, wherein the specific process conditions of the reduction reaction in the step (3) are as follows: the reducing agent is one of sodium borohydride, hydrazine hydrate, sodium formate, formic acid or formaldehyde, the reducing temperature is 5-80 ℃, the reducing time is 1-12h, and the pH value of the solution is controlled to be 7-13 in the whole reducing process.

7. The method for preparing high-activity palladium-carbon catalyst according to claim 3, wherein the specific process conditions of the reduction reaction in the step (3) are as follows: the reducing agent is one of sodium borohydride, hydrazine hydrate, sodium formate, formic acid or formaldehyde, the reducing temperature is 5-80 ℃, the reducing time is 1-12h, and the pH value of the solution is controlled to be 7-13 in the whole reducing process.

8. The method for preparing high-activity palladium-carbon catalyst according to claim 4, wherein the specific process conditions of the reduction reaction in the step (3) are as follows: the reducing agent is one of sodium borohydride, hydrazine hydrate, sodium formate, formic acid or formaldehyde, the reducing temperature is 5-80 ℃, the reducing time is 1-12h, and the pH value of the solution is controlled to be 7-13 in the whole reducing process.

Technical Field

The invention belongs to the technical field of catalyst preparation, and relates to a preparation method of a high-activity palladium-carbon catalyst.

Background

The palladium-carbon catalyst is the most commonly used catalyst for catalytic hydrogenation and is widely applied to the fields of double bond, nitro, nitroso, carbonyl hydrogenation and the like. The activated carbon has large surface area, good pore structure, abundant surface groups and good loading performance and reducibility, when palladium is loaded on the activated carbon, on one hand, highly dispersed palladium can be prepared, on the other hand, the activated carbon can be used as a reducing agent to participate in reaction, a reducing environment is provided, the reaction temperature and pressure are reduced, and the activity of the catalyst is improved.

Since 1872 discovered that Pd/C has catalytic action on the nitro-group hydrogenation reduction reaction on benzene ring, Pd/C has advantages of simple process, high conversion rate, high yield, and less three wastes, and is widely used in petrochemical industry, fine chemical industry, and organic synthesis industry. Such as hydrogenation of acetaldehyde, pyridine derivatives and vinyl acetate, hydrocracking, hydrodehalogenation, hydrodedeprotection, reductive amination/alkylation, gas purification, and the like.

The conventional method for preparing the Pd/C catalyst for selective hydrogenation comprises the following steps:

(1) palladium salt solution impregnation method: US2857337 describes a process for preparing palladium by adsorbing and impregnating activated carbon with a water-soluble palladium salt solution such as sodium tetrachloropalladate or palladium chloride solution, and reducing to metallic palladium by a reducing agent such as formaldehyde, glucose, hydrazine, glycerol, etc. Keith et al found that when this solution was immediately dropped onto a carbon support, a shiny metallic palladium film was deposited and the catalyst activity was low. Theoretically, this is due to the fact that palladium salt is directly reduced to metallic palladium by functional groups existing on the surface of activated carbon, such as aldehyde groups or free electrons, thereby causing metal migration and grain growth, so that the catalyst prepared in this way has low dispersity, poor activity ratio and instability.

(2) Palladium compound impregnation method: hydrolysis of water-soluble compounds of Pd to form insoluble compounds Pd (OH) at room temperature₂Or PdO. H₂O, then loaded on activated carbon, and then reduced with a reducing agent such as formaldehyde, sodium formate, glucose, formic acid or hydrogen, thereby preventing Pd migration and grain growth. However, in this preparation method, hydrogen peroxide (US3138560) is often added to hydrolyze the water-soluble compounds of Pd to insoluble compounds. Since hydrogen peroxide is also oxidizing, it can oxidize the surface groups of activated carbon, thereby changing the surface physicochemical properties of the carrier, i.e. changing the surface group structure of the carrier, which has strong uncertain negative effects and can damage other performances of the catalyst, such as the strength of the supported palladium, the service life of the catalyst, the selectivity and the like.

(3) Palladium sol method: patent CN1966144 proposes a method for preparing a supported palladium/carbon catalyst from a colloidal solution, which comprises preparing a nano palladium sol solution with stable surfactant by chemically reducing palladium salt, and then adsorbing the prepared palladium colloidal solution with a proper carrier to obtain highly dispersed nano palladium colloid. Although the method can prepare nano active colloid, the colloid particles are mostly dispersed on the surface of the carrier. It is generally accepted that the greater the surface area of the palladium in contact with the reactants, the better the activity. However, in the actual production process, the catalyst is deactivated by the loss of palladium due to the surface abrasion of the palladium/carbon catalyst in which the eggshell-type active component is distributed, resulting in a short catalyst life.

The Pd carbon catalyst prepared by the traditional method has the advantages that the size of Pd microcrystal is 4-5 nanometers generally, the activity is not high generally, the conversion rate of main reaction is 95-99%, and the reaction is thorough and high in yield generally by high-activity Pd carbon catalysts in refining reaction with high purity requirement, such as the preparation of Cyclohexane Carboxylic Acid (CCA) by the hydrogenation of benzoic acid, the preparation of amino acid by the hydrogenation of amino carboxylic acid and carbonyl compounds, the preparation of benzyl alcohol, dehalogenation coupling reaction and the like.

Research has shown that the surface atomic number ratio of the noble metal nanoparticles with ultra-small size (less than or equal to 2nm) reaches more than about 80%, and atoms are almost completely concentrated on the surface of the particles. As the number of surface atoms of the nanoparticles increases, the coordination number of the surface atoms is insufficient, so that the surface energy and surface tension of the particles are increased, thereby causing changes in the properties of the particles. And the crystal field environment and the bonding energy of the surface atoms are different from those of the internal atoms, and the existence of a large number of unsaturated dangling bonds enables the atoms to be easily bonded with other atoms and tend to be stable, so that the surface activity is high, and the activity of the particles is greatly enhanced. Especially in the field of catalysis, the ultra-small noble metal nano particles with large specific surface area and high surface activity can not only greatly improve the catalytic performance of the catalyst, but also reduce the using amount of the catalyst, reduce the cost of the catalyst and be beneficial to the marketization of the catalyst. Obviously, the improvement of the preparation process and the obtaining of as many ultra-small-sized Pd nano-crystallites as possible in the preparation process are the key points for preparing the high-activity catalyst.

Disclosure of Invention

The invention provides a preparation method of a high-activity palladium-carbon catalyst, aiming at the problems of thick palladium crystal grains and low activity of the traditional preparation method of the palladium-carbon catalyst. The method adds phosphorus-containing substances to pretreat the activated carbon in the preparation process of the catalyst, does not change the preparation process of the catalyst, is simple and convenient to operate, and is suitable for preparing palladium-carbon catalysts with different scales.

In order to achieve the above object, the preparation method of the high-activity palladium-carbon catalyst of the present invention comprises the following steps:

(1) adding carrier active carbon into aqueous solution of phosphorus-containing substance, stirring at 5-100 deg.C for 0.5-24 hr, cooling, filtering, and washing filter cake with water until pH is neutral to obtain pretreated active carbon. The molar concentration of the phosphorus-containing substance is 0.05-2M. Adding water into the obtained pretreated activated carbon for size mixing to obtain activated carbon size.

(2) Adding palladium chloride into a hydrochloric acid solution, and heating and dissolving to obtain a palladium-containing solution. And (3) adding the obtained palladium-containing solution into the activated carbon slurry obtained in the step (1), and performing immersion adsorption treatment to obtain a palladium adsorption solution.

(3) And (3) adding a reducing agent solution into the palladium adsorption solution obtained in the step (2), carrying out reduction reaction for a period of time, and controlling the pH value of the solution in the reaction process.

(4) And after the reaction is finished, filtering, washing a filter cake until the pH value is neutral, preparing the Pd/C catalyst, and packaging and storing.

Further, the specific surface area of the carrier activated carbon in the step (1) is 200-2000m²The solid powder with more than 300 meshes accounts for more than 60 percent.

Further, in the step (1), the phosphorus-containing substance is an oxide of phosphorus, a halide of phosphorus, an oxyhalide of phosphorus, a salt of phosphorus, and an oxyacid of phosphorus.

Further, the specific process conditions of the impregnation and adsorption treatment in the step (2) are as follows: the treatment temperature is 5-40 ℃, and the treatment time is 0.5-6 h.

Further, the specific process conditions of the reduction reaction in the step (3) are as follows: the reducing agent is selected from sodium borohydride, hydrazine hydrate, sodium formate, formic acid or formaldehyde, the reduction temperature is 5-80 ℃, the reduction time is 1-12h, and the pH value of the solution is controlled to be 7-13 in the whole reduction process.

During the pretreatment process, the phosphorus-containing material plays three roles: (1) reacting the phosphorus-containing substance with some surface functional groups on the carrier to remove pore residues in the carrier; (2) the phosphorus-containing substance provides an oxygen-containing functional group which is used as an anchor point of a metal component deposition center, so that the surface activity and the catalytic activity of the catalyst in a catalytic reaction are obviously improved; (3) the phosphorus-containing substance can also play a role in dispersing palladium crystal grains, so that the grain diameter of the prepared palladium crystal grains is finer, and the activity of the catalyst is enhanced.

In the invention, the phosphorus-containing substance is added to pretreat the activated carbon in the preparation process of the catalyst, so that the activity of the catalyst is obviously improved. The palladium loaded on the activated carbon in the palladium-carbon catalyst prepared by the invention exists in a form of ultra-small-size microcrystal with the size less than 3nm, the average size of the Pd microcrystal is less than 2nm, and the content of the Pd loaded on the activated carbon carrier is 0.5-10%.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

In the following scheme, an X-ray diffractometer (XRD) is adopted to measure the particle size of palladium microcrystal, a 500mL hydrogenation high-pressure reaction kettle is adopted to measure the activity of the catalyst, the reaction temperature is 150 ℃, the reaction pressure is 1.6MPa, the dosage of the catalyst is 0.6g (dry basis), the dosage of benzoic acid is 5g, the water amount is 120mL, the reaction time is 2h, the components and the content of a reaction product are analyzed by gas chromatography, and the Pd content of the catalyst is analyzed by ICP-AES.