阅读说明：本技术 一种反向制备整体式催化剂的方法 (Method for reversely preparing monolithic catalyst ) 是由 左海珍 于 2019-11-24 设计创作，主要内容包括：本发明提供了一种反向制备整体式催化剂的方法,所述反向为先负载金属活性组分,后构建金属载体,催化剂载体机械强度高、导热性好,所述催化剂为整体式具有通过电化学沉积的三维网状金属载体,有利于气体的传质,更有利于高空速气固相催化反应。(The invention provides a method for reversely preparing an integral catalyst, wherein the reverse direction is to load a metal active component and construct a metal carrier, the mechanical strength of the catalyst carrier is high, the thermal conductivity is good, the catalyst is an integral three-dimensional reticular metal carrier which is deposited by electrochemistry, and the catalyst is favorable for mass transfer of gas and is more favorable for high space velocity gas-solid phase catalytic reaction.)

1. A method for reversely preparing an integral catalyst is characterized in that the reverse direction is to load a metal active component and then construct a metal carrier, and specifically comprises the following steps:

(a) preparing or purchasing macroporous polymer foam with uniform pore channels;

(b) preparing a metal active component aqueous solution;

(c) filling active components to the surfaces of the polymer foam pore channels through vacuum filling;

(d) immersing the polymer foam filled in the step (c) as a cathode in electroplating solution for electrochemical deposition treatment;

(e) placing the polymer foam obtained by electrochemical deposition in the step (d) in inert gas, performing temperature programming treatment, and removing the macroporous polymer foam in the step (a) to obtain a three-dimensional reticular metal plating carrier, wherein the surface of the carrier is loaded with active components;

(f) and (e) carrying out high-temperature reduction treatment on the product obtained in the step (e) to obtain the monolithic catalyst.

2. The process for reverse production of a monolithic catalyst as set forth in claim 1, wherein the macroporous polymeric foam is polystyrene or polyurethane foam.

3. The process for reverse preparation of a monolithic catalyst as claimed in claim 1, wherein the aqueous solution of active components contains graphite flakes or graphene, and the activity is one or more of chloroplatinic acid, chloroauric acid, ruthenium nitrosyl nitrate, cobalt nitrate, copper nitrate.

4. The method for reversely preparing the monolithic catalyst according to claim 1, wherein the vacuum filling is performed by using a vacuum pump until no air bubbles are blown out from the surface of the polymer foam immersed in the aqueous solution of the metal active component, and then the polymer foam is dried in the oven, and the filling and the drying are repeated for 3 to 5 times.

5. The method for reverse preparation of monolithic catalyst according to claim 1, wherein the electroplating solution is a nickel electroplating solution, the nickel electroplating solution is composed of 180-230 g/L nickel sulfate, 30-50 g/L nickel chloride, 20-30 g/L boric acid, 40-50g/L potassium sulfate, 3-5g/L sodium fluoride, 0.01-0.02 g/L sodium octyl sulfate, and has a pH of 3-6, and the electroplating process is pulse electroplating: the pulse frequency is 10-20Hz, the pulse duty ratio is 50-65%, and the temperature is 20-40%^oC, current density of 2-3A/dm²And (5) stirring for 0.5-2 h of electroplating time.

6. The process for reverse preparation of a monolithic catalyst as claimed in claim 1, wherein the inert gas is nitrogen or argon and the temperature-programmed process is: by 5^oThe temperature is raised to 100 ℃ at the rate of C/min^oC, keeping the temperature for 0.5h, and then 3^oThe temperature rises to 600 ℃ at a rate of C/min^oAnd C, keeping the temperature for 12-24 hours.

7. The process for reverse production of a monolithic catalyst according to claim 1, wherein the high temperature reduction treatment is: 5wt.% H₂Hydrogen and nitrogen mixed gas of 300 deg.C^oC, after reducing for 2 hours at constant temperature, stopping heating, continuously ventilating,and (4) cooling to room temperature.

8. The process for reverse production of a monolithic catalyst as in claim 1, wherein the macroporous polymeric foam has a pore size of 10 to 50 μm.

9. The catalyst obtained by the reverse preparation method of monolithic catalyst according to any one of claims 1 to 8, wherein the compressive strength of the catalyst is 0.5 to 3.5MPa, and the thermal conductivity is 30 to 50W m^-1K^-1。

10. The application of the method for reversely preparing the monolithic catalyst as claimed in any one of claims 1 to 9, which is characterized in that the method is used for preferential oxidation of carbon monoxide in hydrogen-rich gas, hydrogen production by ethanol steam reforming or methane catalytic combustion reaction.

Technical Field

The invention relates to a method for reversely preparing an integral catalyst through electrochemical deposition, belongs to the field of electrochemical preparation of catalysts, and particularly relates to gas-solid phase catalytic reaction.

Technical Field

The gas-solid reaction is a reaction process of gas-phase components under the action of a solid catalyst, and is a reaction process with the widest application and the largest scale in the chemical industry. According to statistics, about 90% of the catalytic reaction process is a gas-solid phase catalytic reaction process. The gas-solid phase catalytic reaction process generally comprises the following steps: (1) the reaction gas diffuses to the inner surface of the solid catalyst particles through the intra-particle micropores. (2) The reaction gas is adsorbed by the active centers on the surface of the catalyst. (3) Gas-solid phase reaction is carried out on the surface active center. (4) The reaction product is desorbed from the surface active sites. (5) The reaction products diffuse from the outer surface of the catalyst particles back into the bulk of the gas stream.

The catalysts for gas-solid phase catalytic reaction mainly comprise granular catalysts and monolithic catalysts. For the particle type catalyst, for example, CN103263918A adopts a wet chemical method, and the tetragonal perovskite PbTiO synthesized by a hydrothermal method₃Nanoparticle, chloroplatinic acid hexahydrate (H)₂PtCl₆ ^。6H₂O), sodium borohydride (NaBH)₄) Anddeionized water is used as a reaction material, and Pt is reduced to PbTiO by utilizing the reducibility of sodium borohydride₃The surface of the nano-particles forms unstable Pt nano-particles which are then completely crystallized in the subsequent drying process, so that the Pt-PbTiO3 nano-particle catalyst for CO catalytic oxidation is obtained, however, for the particle type catalyst, especially for gas-solid phase catalytic reaction, as shown in figure 1, the catalyst has the following disadvantages that (1) the loading and unloading are troublesome; (2) is not easy to form and the mechanical strength can not meet the requirement; (3) mass and heat transfer are greatly hindered, and the treatment efficiency is reduced; (4) the pressure drop difference between the front and the back of the catalyst bed is large, and the energy consumption is increased. The monolithic catalyst integrates active components of the catalyst, a structured carrier and a reactor, has the advantages of large geometric surface area of a bed layer in unit volume, mass transfer, high heat transfer efficiency, reduced bed lamination, high catalytic efficiency and the like, is beneficial to adsorption of reactants on the surface of the catalyst, desorption and release of products, removal of heat, and strengthening of a chemical reaction process, is easy to assemble, maintain and disassemble, and is considered to be one of the development directions with the most prospects in the current heterogeneous catalysis field, for example, Chinese patent (CN105289653.A) treats cordierite through an acid aqueous solution, coats a composite metal oxide coating, finally impregnates a precious metal active component to prepare the monolithic catalyst, and can realize effective CO removal under the conditions of low temperature, low CO concentration, high airspeed, high water vapor and sulfur. However, the honeycomb ceramic substrate has the defects of low mass transfer and heat transfer efficiency, low mechanical strength, poor structural adjustability and the like.

In addition, in the current catalyst preparation process, besides the problem that the catalyst needs to be prepared as a monolithic body, the preparation process of the catalyst should also attract attention, and the prior art generally prepares the carrier first, and then loads the active component on the surface of the carrier, i.e. the active component is directly adsorbed on the surface of the catalyst, as shown in fig. 2, in other words, the part with the strongest adsorption force of the active component is directly adsorbed-fixed on the surface of the catalyst carrier, when the reactants a and B are catalyzed through the diffusion-chemisorption-product desorption process, i.e. the part with the strongest adsorption force of the active component is always in close contact with the carrier substrate in the whole process, there is no chance of catalytic reaction, and the part with the weaker adsorption force is in contact with the gas, there is an opportunity of catalytic reaction, and chemisorption known in the art is the most important step, the chemical adsorption activates the reactant molecules, which is the key of the catalysis, so that the improvement of the adsorption process in the prior art is very necessary, and therefore, the invention provides a process for reversely preparing the catalyst, namely, the active component is loaded on the carrier a (the part with strong adsorption of the active component is contacted with the carrier a), then the carrier B is prepared on the carrier a, finally the carrier a is removed through heat treatment, and finally the part with the strongest adsorption of the active component is exposed to the reactants A and B, so that the chemical adsorption process is improved, the chemical adsorption process is accelerated, and the catalytic efficiency is improved.

As a method for producing a porous metal, conventionally, a high-strength porous metal body obtained by applying a coating material containing fine reinforcing particles of an oxide, a carbide, a nitride or the like of an element belonging to groups II to VI of the periodic table to the surface of a skeleton of a three-dimensional network resin having interconnected pores, further forming a metal plating layer of a Ni alloy or a Cu alloy on the coating film of the coating material, and then dispersing the fine particles in the metal plating layer by heat treatment has been proposed as JPH 07150270A. WO2013099532 proposes a method for producing a porous body, in which, when the surface of a resin-formed body having a three-dimensional network structure is subjected to a conductive treatment, a metal powder is mixed in a carbon coating material to be coated, and then a desired metal is plated and subjected to a heat treatment to obtain a homogeneous alloy porous body. US2018030607 discloses a method for manufacturing a nickel alloy porous body, comprising: a step of applying a coating material containing nickel having a volume average particle diameter of 10 [ mu ] m or less and a metal-added nickel alloy powder onto a surface of a skeleton of a resin-formed body having a three-dimensional network structure; a step of plating nickel on the surface of the skeleton of the resin-formed body to which the coating material is applied; a step of removing the resin formed body; and a step of diffusing the additive metal into nickel by heat treatment.

Although the porous metal body described in the above prior art has a possibility as a catalyst carrier, there is no clear disclosure that the porous metal body can be used in a gas-solid phase catalytic reaction, and further, the above patent document uses a metal powder having a volume average particle diameter of 10 μm or less, such as a nickel alloy powder, for conducting treatment of the skeleton surface of a resin formed body, the metal powder particles are in the micron order, obviously far out of the size range of the catalytically active component, and have no catalytic activity (generally, the size of the metal active component of the catalyst should be in the nanometer order to have catalytic activity), although the above document describes that a smaller size nickel powder can be prepared using an atomization method, it is difficult to achieve the nanometer nickel powder, and the nanometer nickel powder cannot be uniformly supported on a three-dimensional resin template surface, and the preparation method of the document has many places to be improved, such as the coating method, the strength of the porous metal body.

Disclosure of Invention

Based on the problems in the prior art, the invention provides a method for reversely preparing an integral catalyst, wherein the catalyst is an integral three-dimensional meshed catalyst, has high compressive strength and good thermal conductivity, is very suitable for gas-solid phase catalytic reaction, and specifically comprises the following steps:

(a) preparing or purchasing macroporous polymer foam with uniform pore channels;

(b) preparing a metal active component aqueous solution;

(c) filling active components to the surfaces of the polymer foam pore channels through vacuum filling;

(d) immersing the polymer foam filled in the step (c) as a cathode in electroplating solution for electrochemical deposition treatment;

(e) placing the polymer foam obtained by electrochemical deposition in the step (d) in inert gas, performing temperature programming treatment, and removing the macroporous polymer foam in the step (a) to obtain a three-dimensional reticular metal plating carrier, wherein the surface of the carrier is loaded with active components;

(f) and (e) carrying out high-temperature reduction treatment on the product obtained in the step (e) to obtain the monolithic catalyst.

Further, the macroporous polymer foam is polystyrene or polyurethane foam.

Further, the active component aqueous solution contains graphite flakes or graphene, and the activity is one or more of chloroplatinic acid, chloroauric acid, ruthenium nitrosyl nitrate, cobalt nitrate and copper nitrate.

Further, the vacuum filling is performed by using a vacuum pump until no bubbles emerge from the surface of the polymer foam immersed in the metal active component aqueous solution, and then the polymer foam is dried in an oven, and the filling and drying are repeated for 3-5 times.

Further, the electroplating solution is a nickel electroplating solution, the nickel electroplating solution is composed of 180-230 g/L of nickel sulfate, 30-50 g/L of nickel chloride, 20-30 g/L of boric acid, 40-50g/L of potassium sulfate, 3-5g/L of sodium fluoride and 0.01-0.02 g/L of sodium octyl sulfate, the pH value is 3-6, and the electroplating process adopts pulse electroplating: the pulse frequency is 10-20Hz, the pulse duty ratio is 50-65%, and the temperature is 20-40%^oC, current density of 2-3A/dm²And (5) stirring for 0.5-2 h of electroplating time.

Further, the inert gas is nitrogen or argon, and the programmed temperature rise process is as follows: by 5^oThe temperature is raised to 100 ℃ at the rate of C/min^oC, keeping the temperature for 0.5h, and then 3^oThe temperature rises to 600 ℃ at a rate of C/min^oAnd C, keeping the temperature for 12-24 hours.

Further, the high-temperature reduction treatment comprises the following steps: 5wt.% H₂Hydrogen and nitrogen mixed gas of 300 deg.C^oAnd C, reducing at constant temperature for 2 hours, stopping heating, and continuously ventilating to room temperature.

Further, the pore size of the macroporous polymer foam is 10-50 μm.

Furthermore, the compressive strength of the catalyst is 0.5-3.5 MPa, and the heat conductivity coefficient is 30-50W m^-1K^-1。

Further, the method is used for preferential oxidation of carbon monoxide in hydrogen-rich gas, hydrogen production by ethanol steam reforming or methane catalytic combustion reaction.

In the plating solution of the present invention, the main salt is selected from nickel sulfate, and the concentration of the main salt is generally 180-230 g/L, and the main salt is used as a main salt for generating nickel ions; the invention selects nickel chloride as the activator, the activator can provide nickel ion and chloride ion, and other metal ions are not added, so the invention is an ideal activator; the conductive salt can be sodium sulfate, potassium sulfate and ammonium sulfate from the conductivity; a buffering agent, wherein boric acid is usually added as the buffering agent to prevent the acidity of the plating solution from changing sharply in production, the pH = 3-6 is controlled, and the boric acid has a buffering effect and can improve the cathode polarization and the conductivity of the plating solution so as to improve the density of the scorching current; the pinhole preventing agent can be made of oxidants such as hydrogen peroxide, sodium perborate and the like in common nickel plating, and the amount of hydrogen precipitated on a cathode is reduced or eliminated, so that pinholes are eliminated; the surfactant can reduce the interfacial tension between the electrode and the plating solution, so that the formed hydrogen is difficult to stay on the surface of the electrode to prevent pinholes and pockmarks; acidity (pH value) is in a range of pH 3-6, when the pH value is low, a large amount of hydrogen is separated out from a cathode, the current efficiency is reduced, when the pH value is lower than 3, the hydrogen is violently discharged, even the current efficiency is 0, but when the pH value exceeds 6 or is close to neutral, nickel hydroxide precipitate is generated, the nickel hydroxide precipitate is mixed in a nickel layer to enable a plating layer to be peeled off, embrittled, difficult to deposit in deep holes and the like, when the pH value is high, the sulfuric acid solution is used for adjustment, and when the pH value is low, 3% of sodium hydroxide can be added for adjustment; when sodium hydroxide is added, precipitate is easy to generate, the sodium hydroxide is slowly added under continuous stirring, and the effect of replacing the sodium hydroxide by the nickel carbonate is better; the temperature has great influence on the internal stress of the plating layer, when the temperature is increased from 10 ℃ to 35 ℃, the internal stress of the nickel layer is rapidly reduced, and the internal stress is slowly reduced when the temperature is increased from 35 ℃ to 60 ℃. When the temperature is further increased, the internal stress hardly changes. The heating can also increase the solubility of each component in the electroplating solution, and further, concentrated nickel plating solution can be adopted; meanwhile, the temperature is increased, the conductivity of the plating solution is increased, and the current efficiency is improved.

Compared with common electroplating, the pulse electroplating technology has the obvious advantages that the mass transfer process in the electroplating process can be controlled, and the peak value higher than the average current can be generatedThe current, thus influencing the instantaneous current magnitude and reaction speed in the electroplating process and the nucleation and growth of crystal grains in the electroplating process, for example, when the current density is less than 2A/dm2, the surface appearance of the coating is better, and the coating is more uniform and fine. When the current density is 2-3A/dm²In time, the appearance of the plating layer is rough, the crystal grains are large, and the crystal grains become large along with the increase of the current; the scorch phenomenon occurs when the current density exceeds 1.6A/dm2, and in the present invention, the roughness of the carrier is favorable for the smooth proceeding of the catalytic reaction, so the current density is selected to be 2-3A/dm²The duty ratio is 50-65%, the filling property is good, and a small amount of pitting and pinholes can be generated; for the frequency, the accompanying frequency is large, the growth rate of the carrier coating becomes fast, so that the thickness of the carrier increases in the same time.

The graphene and the graphite flake in the active component mainly play a role in electric conduction and are used for preparing a polymer for an electrodeposition cathode, wherein the graphene is preferred, and the graphene is used as a novel nano material (such as a pure graphene material, the surface area can reach 2000-4000 m2/g) which is the thinnest, the maximum strength and electric conduction performance and the strongest optical performance and is found at present, so that the graphene is a very promising catalyst carrier, and is beneficial to heat transfer-heat conduction of the invention and reduction of a catalytic hot spot.

The scheme of the invention has the following beneficial effects:

(1) the catalyst carrier is a three-dimensional reticular metal coating, which is beneficial to mass transfer of gas and high-airspeed gas-solid phase catalytic reaction;

(2) the catalyst carrier is a three-dimensional reticular metal coating, so that the problem of hot spots of a catalyst bed layer caused by heat release in the catalytic reaction process can be effectively reduced, the inactivation of the catalyst is avoided, and the stability of the catalyst is facilitated;

(3) the catalyst is an integral catalyst, and has the advantages of pressure reduction, high mechanical strength, adjustable structure and strong applicability;

(4) the active component can be highly dispersed on the surface of the catalyst carrier, has uniform size and good catalytic performance for gas-solid phase reaction.

Drawings

FIG. 1 is a schematic view of a state of the art particulate catalyst and monolith catalyst in a CO preferential oxidation unit;

FIG. 2 is a schematic diagram showing different states of active components and a gas phase adsorption catalysis process in the prior gas-solid phase reaction technology.

Detailed Description