CN114177919A

CN114177919A - Method for preparing monolithic metal-based environmental catalyst by metal replacement method

Info

Publication number: CN114177919A
Application number: CN202111457569.7A
Authority: CN
Inventors: 卢晗锋; 周文茜; 李剑宇; 周瑛; 耿俊
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2021-12-02
Filing date: 2021-12-02
Publication date: 2022-03-15

Abstract

The invention discloses a method for preparing an integral metal-based environmental catalyst by a metal replacement method, which comprises the following steps: carrying out acid washing, alkali washing and water washing on the whole metal base material, and then carrying out heat treatment in an air atmosphere for later use; dissolving a noble metal precursor in water, and then adding a surfactant to obtain noble metal precursor replacement liquid; immersing the monolithic metal substrate into a noble metal precursor displacement liquid at 40-95 ℃ to perform metal displacement reaction, taking out and cleaning after complete metal displacement, drying, and roasting at 200-500 ℃ for 3-5 h to obtain the monolithic metal-based catalyst; the invention abandons the whole metal-based catalyst slurry coating technology, and enables metals and alloy materials in any shapes to quickly and firmly load nano noble metal active components on the surface through metal replacement reaction, and the noble metal active components are tightly combined with the metal base material, the shedding rate is almost zero, and the characteristic of catalyzing and oxidizing VOCs is very high.

Description

Method for preparing monolithic metal-based environmental catalyst by metal replacement method

Technical Field

The invention relates to the technical field of preparation of environmental catalysts, in particular to a preparation method of a monolithic metal-based oxidation catalyst for organic waste gases (VOCs).

Background

Currently, various technologies have been developed in the industry for the treatment of VOCs, which mainly include two main categories: one is a recovery method involving adsorption, absorption, membrane separation, condensation, and the like; another class is destruction methods involving catalytic combustion, thermodynamic incineration, biodegradation, photocatalytic decomposition, and plasma oxidation. Due to the principle that the catalyst is applied to reduce the reaction activation energy, the catalytic combustion technology can enable VOCs to be deeply oxidized and completely degraded into harmless CO under mild conditions (generally 200-500℃)₂And H₂O, not only energy saving and environmental protection, but also wide applicability, has been receiving increasing favor and attention in recent years.

Obviously, the most critical part in the catalytic combustion technology is the catalyst, and the performance of the catalyst plays a decisive role in the removal effect of the VOCs and the energy consumption of the catalytic process. With the progress of catalytic preparation technology, the structural form of the catalyst is gradually developed from the traditional powder type to the particle type to the monolithic type widely used nowadays. Compared with the traditional powder type and particle type catalysts, the monolithic catalyst has the following advantages: (1) the heat transfer efficiency is high: the integral catalyst has thin wall and high aperture ratio, and the direct pore channel increases the contact area of the waste gas and the catalyst; (2) the mass transfer efficiency is high: the coating on the load type integral carrier has high specific surface area, the active components can be fully dispersed and distributed on the surface of the coating, the path of the reactant diffusing to the active center is shortened, and the influence of internal diffusion is reduced; (3) bed lamination reduction: the geometrical configuration of the carrier reduces the resistance when the fluid passes through the catalyst bed layer, and the pressure of the gas flow is reduced; (4) the amplification effect is small: the difference between the laboratory and commercial catalysts is the number of channels. The catalytic combustion is mainly a gas-solid phase reaction, and the catalytic effect of the catalytic bed is obviously influenced by the properties of mass transfer, heat transfer and the like of the catalytic bed, so that the monolithic catalyst with the advantages is widely used as a catalytic combustion catalyst.

The carrier of monolithic catalyst is mainly divided into two categories of ceramic carrier and metal carrier according to different base materials, wherein the ceramic carrier mainly comprises cordierite, corundum, magnesium silicate and TiO₂And SiC, etc., and the material generally used for the metal carrier is stainless steel or an alloy. The ceramic carrier is generally prepared into an integral body by mixing and doping different raw material powder and extruding and forming, and the appearance of the ceramic carrier is generally honeycomb-shaped, such as cordierite honeycomb ceramic, silicon carbide honeycomb ceramic and the like; the metal carrier can be prepared into various shapes such as metal wires, metal nets, metal foams and the like due to good ductility, tensile strength and compressive strength. Compared with the defects of slow heat transfer and temperature rise, poor mechanical property and the like of a ceramic carrier, the metal carrier has more excellent properties, mainly comprising the following components: (1) the metal support has a larger geometric surface area; (2) the metal carrier is not controlled by the shape of the metal carrier, and has adjustable and changeable structure; (3) the metal carrier has good conductivity and high mechanical strength; (4) the metal carrier has high heat conductivity, the catalytic combustion speed is high, and the catalyst can play a role quickly. Therefore, monolithic catalysts prepared with metal supports are increasingly being studied and used in the field of catalytic combustion.

The metal monolithic catalyst generally comprises a metal-based carrier and an active component, wherein the carrier is a support place of the catalyst and provides a place for carrying the active component and reacting a circulating material; the active component is the main component of the catalyst to provide combined active sites for the reaction of materials. The prior metal-based VOCs catalyst is generally prepared by coating an oxide coating on the surface of a metal carrier by a slurry coating method, then dipping and adsorbing, and dipping a noble metal active component on a porous carrier in a salt solution form by utilizing capillary action and permeating the noble metal active component to the inner surface. Or a layer of supported noble metal catalyst is directly coated on the surface of the metal, and then the whole catalyst is obtained after high-temperature activation treatment.

Therefore, in order to further improve the preparation efficiency of the metal-supported catalyst and improve the adhesion and dispersion of the noble metal on the surface of the metal-based carrier, it is necessary to develop an innovative preparation method of the monolithic metal-based catalyst, so that the noble metal active component and the metal substrate are tightly combined, and the developed catalyst has better adhesion and stronger metal ductility on the metal surface, thereby breaking through the limitation of the shape of the existing catalyst, and the catalyst can be loaded on the surface of any metal carrier.

Disclosure of Invention

The invention provides a metal replacement preparation technology, which replaces active metal on the surface of a metal-based carrier with highly stable noble metal nano-particles by utilizing different activity of various metals, so that active components of the noble metal nano-particles of a catalyst are embedded into crystal lattices on the surface of an integral metal substrate to form a monodispersed nano active site, the high combination of the metal substrate and the active components is realized, the active components are fully dispersed, and the activity of the catalyst is improved. The method is a brand new preparation method of the metal-based monolithic catalyst.

The technical scheme of the invention is as follows:

a method for preparing a monolithic metal-based catalyst by a metal displacement process, the method comprising the steps of:

(1) carrying out acid washing, alkali washing and water washing on the whole metal base material, and then carrying out heat treatment in an air atmosphere for later use;

the integral metal base material can be stainless steel materials such as 304 and 316, and can also be high-temperature resistant metal materials such as foamed aluminum, foamed nickel or iron-chromium-aluminum, and the shape of the integral metal base material is not limited;

the acid washing and alkali washing can be carried out by using any acid or alkali, such as: sulfuric acid solution, sodium hydroxide solution;

the temperature of the heat treatment is 200-500 ℃, and the treatment time is 2-6 h;

(2) dissolving a noble metal precursor in water, and then adding a surfactant to obtain noble metal precursor replacement liquid;

the noble metal precursor is chloroplatinic acid or chloropalladic acid;

the surfactant is an amphiphilic nonionic surfactant, preferably a polyoxyethylene polyoxypropylene ether block copolymer (trade name F127); the concentration range of the surfactant in the noble metal precursor replacement liquid is 0.1-1.0 wt%;

(3) immersing the integral metal substrate prepared in the step (1) into the noble metal precursor replacement liquid obtained in the step (2) at 40-95 ℃ (preferably 70-80 ℃), carrying out metal replacement reaction, measuring the absorbance of the replacement liquid by using an ultraviolet spectrophotometer in the reaction process until the absorbance is not changed any more and the metal replacement is complete, then taking out, cleaning, drying, and roasting at 200-500 ℃ for 3-5 h to obtain the integral metal-based catalyst;

in the obtained monolithic metal-based catalyst, the amount of substitution of the noble metal is 0.01 to 1.0 wt%, preferably 0.2 wt%, based on the mass of the monolithic metal substrate.

The method provided by the invention can replace the noble metal ions and the base metal on the surface of the metal base material and highly disperse the noble metal ions and the base metal on the surface of the metal base material, thereby forming the alloy catalyst with rich noble metal on the surface.

The monolithic metal-based catalyst prepared by the invention has high activity on catalytic combustion of volatile organic waste gases (VOCs), and can be applied to catalytic combustion for eliminating industrial volatile organic waste gas pollution.

Specifically, the catalytic combustion is carried out on a gas-solid reaction device: placing the catalyst in a reaction tube isothermal zone, feeding raw material gas and air in two paths, leading the raw material gas to pass through a 0 ℃ ice water bath, then converging the raw material gas and the other path of air into the reaction tube, and carrying out catalytic combustion reaction in the reaction tube under the action of the catalyst;

the concentration of the organic waste gas is 1000-10000 mg/m³The catalytic combustion reaction temperature is 150-450 ℃, and the space velocity is GHSV 10000-100000 h^-1。

The invention has the following beneficial effects:

the method abandons the whole metal-based catalyst slurry coating technology, enables metals and alloy materials in any shapes to quickly and firmly load nano noble metal active components on the surface through metal replacement reaction, and the noble metal active components are tightly combined with a metal substrate, the shedding rate is almost zero, and the characteristic of catalyzing and oxidizing VOCs is very high.

Drawings

Fig. 1 shows the metal substitution concentration changes of 304 stainless steel and chloroplatinic acid.

FIG. 2 SEM analysis of Pt/304-W catalyst surface morphology; a.304; b.0.1% Pt/304-W; c.0.2% Pt/304-W; d. 0.4% Pt/304-W.

FIG. 3 is a schematic flow diagram of an apparatus for catalytic combustion of VOCs with a monolithic catalyst; 1-a gas cylinder; 2-mass flow meter; a 3-VOCs generator; 4-constant temperature water bath; 5-gas mixing bottle; 6-a thermocouple; 7-quartz reaction tube; 8-temperature control instrument; 9-alternating current power supply; 10-gas chromatography (mass spectrometry).

Detailed Description

The invention will be further described in the following by means of specific embodiments with reference to the attached drawings, to which, however, the scope of protection of the invention is not limited.

The room temperature is 20-30 ℃.

304, 316, foam nickel, foam iron and the like used in the embodiment of the invention are catalyst carriers and can be cut into any metal integral shape.

The preparation method of the noble metal monolithic catalyst comprises the following steps:

(1) preparation of chloroplatinic acid and chloropalladic acid solutions: weighing H₂PtCl₆·6H₂O or H₂PdCl₄Dissolving the precursor solution into 250ml of water to prepare 2.5-12.5 g/L (based on the mass of noble metal platinum or palladium) of mother solution, preparing chloroplatinic acid or chloropalladite solution with different concentrations from 2.5-12.5 g/L of the mother solution, and weighing 50-200 mg of F127 to dissolve the F127 in the solution to be used as a noble metal precursor solution.

(2) Pretreatment of the metal carrier substrate: firstly, placing a metal material in acetone for ultrasonic oscillation for 30min to remove surface oil stains, taking out the metal material after the ultrasonic oscillation for 30min, washing the metal material with deionized water for three times, and then sequentially placing the metal material in prepared 10-30% NaOH and 10-30% HNO₃Ultrasonic agitation 30 in solutionAnd (3) removing an oxide layer on the surface of the metal net in min, taking out after the completion, washing the metal net clean with deionized water, and treating for 2-6h at 200-500 ℃.

(3) And (2) taking the noble metal precursor solution (weighed according to the load) in the step (1), putting the pretreated metal carrier material in the step (2) into the noble metal precursor solution, performing ion exchange in water bath at 40-95 ℃, measuring the absorbance of the solution by using an ultraviolet spectrophotometer every 1h until the absorbance is not changed, filtering, and treating at 200-500 ℃ for 2-6h to obtain the catalyst with the noble metal load of 0.1-0.5%.

The performance of the catalyst is tested by adopting a VOCs catalytic combustion device, and the concentration of methylbenzene and dimethylbenzene is 1000-10000 mg/m³The catalytic combustion reaction temperature is 150-450 ℃, and the space velocity is GHSV 10000-50000 h^-1。

Example 1

A stainless steel monolithic catalyst was prepared with a loading of 0.1% Pt/304. Mixing 2.5g/L (based on the mass of platinum) of mother liquor 0.4ml and 9.6ml of water, adding 50mg of F127 to prepare a 10ml solution in a test tube, putting 1g of pretreated 304 stainless steel metal net in the test tube, immersing and replacing in a water bath at 90 ℃, measuring the concentration change of the solution by an ultraviolet spectrophotometer every 10min until the concentration of Pt ions becomes 0, filtering, roasting at 300 ℃ for 3h, and marking the obtained catalyst as: 0.1% Pt/304-W.

Example 2

A stainless steel monolithic catalyst was prepared with a loading of 0.2% Pt/304. The conditions were the same as in example 1, taking 0.8ml of 2.5g/L (based on the mass of platinum) of the mother liquor and 9.2ml of water, mixing them, adding 50mg of F127 to prepare a 10ml solution in a test tube, placing 1g of a pretreated 304 stainless steel wire gauze in the test tube, immersing and displacing the solution in a water bath at 90 ℃, measuring the change of the concentration of the solution by an ultraviolet spectrophotometer every 10min until the concentration of Pt ions becomes 0, filtering the solution, and calcining the solution at 300 ℃ for 3 hours, wherein the obtained catalyst was marked as: 0.2% Pt/304-W.

Example 3

A stainless steel monolithic catalyst was prepared with a loading of 0.4% Pt/304. The conditions were the same as in example 1, taking 1.6ml of 2.5g/L (based on the mass of platinum) of the mother liquor and 8.4ml of water, mixing them, adding 50mg of F127 to prepare a 10ml solution in a test tube, placing 1g of a 304 stainless steel wire mesh pretreated in the test tube, immersing and displacing the solution in a water bath at 90 ℃, measuring the change in concentration of the solution with an ultraviolet spectrophotometer every 10min until the concentration of Pt ions became 0, filtering, and calcining at 300 ℃ for 3 hours, wherein the obtained catalyst was marked as: 0.4% Pt/304-W.

Example 4

A0.2% Pd/304 stainless steel monolithic catalyst was prepared. The conditions were the same as in example 1, taking 0.8ml of 2.5g/L (based on the mass of palladium) of the mother liquor and 8.4ml of water, mixing them, adding 50mg of F127 to prepare a 10ml solution in a test tube, placing 1g of a 304 stainless steel wire mesh pretreated in the test tube, immersing and displacing the solution in a water bath at 90 ℃, measuring the change of the concentration of the solution by an ultraviolet spectrophotometer every 10min until the Pt ion concentration becomes 0, filtering the solution, and calcining the solution at 300 ℃ for 3 hours, wherein the obtained catalyst was marked as: 0.2% Pd/304-W.

Example 5

Prepare the stainless steel monolithic catalyst with the loading of 0.2 percent of Pt/316. The conditions were the same as in example 1, 2.5g/L (based on the mass of platinum) of chloropalladic acid mother liquor 0.8ml and 8.4ml of water were mixed, 50mg of F127 was added to prepare a 10ml solution in a test tube, 1g of pretreated 316 stainless steel wire gauze was placed in the test tube, immersion displacement was carried out in a water bath at 90 ℃ and the change in concentration of the solution was measured every 10min with an ultraviolet spectrophotometer until the Pt ion concentration became 0, followed by filtration and calcination at 300 ℃ for 3 hours, and the obtained catalyst was labeled as: 0.2% Pt/316-W.

Example 6

A foamed nickel monolith catalyst was prepared with a loading of 0.2% Pt. The conditions are the same as example 1, 2.5g/L (based on the weight of platinum) of chloropalladate mother liquor 0.8ml and 8.4ml of water are mixed, 50mg of F127 is added to prepare 10ml of solution in a test tube, 1g of pretreated foamed nickel is put into the test tube, the solution is immersed and replaced in a water bath at 90 ℃, the concentration change of the solution is measured by an ultraviolet spectrophotometer every 10min until the concentration of Pt ions becomes 0, then the solution is filtered and roasted at 300 ℃ for 3h, and the obtained catalyst is marked as: 0.2% Pt/Ni-F.

Example 7

A foamed iron monolithic catalyst with a loading of 0.2% Pt was prepared. The conditions are the same as example 1, 2.5g/L (based on the weight of platinum) of chloropalladate mother liquor 0.8ml and 8.4ml of water are mixed, 50mg of F127 is added to prepare 10ml of solution in a test tube, 1g of pretreated foam iron is put into the test tube, the solution is immersed and replaced in a water bath at 90 ℃, the concentration change of the solution is measured by an ultraviolet spectrophotometer every 10min until the concentration of Pt ions becomes 0, then the solution is filtered and roasted at 300 ℃ for 3h, and the obtained catalyst is marked as: 0.2% Pt/Fe-F.

Example 8

FeCrAl screen catalyst with 0.2% Pt loading is prepared. The conditions were the same as in example 1, taking 0.8ml of 2.5g/L (based on the mass of platinum) of the mother liquor and 8.4ml of water, mixing them, adding 50mg of F127 to prepare a 10ml solution in a test tube, placing 1g of the FeCrAl alloy wire mesh pretreated in the test tube, immersing and displacing the mesh in a water bath at 90 ℃, measuring the change of the concentration of the solution by an ultraviolet spectrophotometer every 10min until the concentration of Pt ions becomes 0, filtering, roasting at 300 ℃ for 3 hours, and marking the obtained catalyst as: 0.2% Pt/FeCrAl-W.

Example 9

The Pt ion concentration in the catalyst preparation processes of examples 1-3 was monitored by UV-VIS, and the Pt ion concentration in the noble metal solution was changed with time, as shown in FIG. 1.

The Pt and Pd ion absorption curves are characterized by adopting UV-vis, the instrument model is Shimadzu UV-2600, quantitative analysis is carried out, analysis treatment is carried out at WL 263nm, an absorbance marking line of Pt is made, and the content of Pt in the residual Pt solution is detected; performing analysis treatment at WL 310nm to make an absorbance graticule of Pd, and detecting the content of Pd in the residual Pd solution, wherein the actual load amount of Pt/Pd is calculated according to the following formula: (m represents the mass of the metal carrier, Cx represents the concentration of the Pt/Pd solution before ion exchange, Cy represents the concentration of the residual Pt/Pd solution after the ion exchange reaction, and V represents the volume of the reaction solution).

Example 10

Surface topography analysis of the catalysts of examples 1-3 revealed that after metal exchange, the 304 smooth stainless steel surface was loaded with nano-Pt metal particles, as shown in fig. 2.

The microscopic surface morphology of the catalyst is characterized by SEM, and the instrument models are as follows: zeiss Sigma 300, main technical parameters: 1.0nm @15 kV, 1.6nm @1 kV; acceleration voltage: 0.02-30kV, 10V, probe beam current: 3pA-20 nA.

Example 11

The catalysts prepared in all the examples are subjected to catalytic oxidation performance tests, the activity evaluation of the catalysts is carried out on a normal-pressure continuous flow gas-solid reaction device (as shown in figure 3), the catalyst filling and reaction place is a section of quartz tube, the inner diameter of the quartz tube is 23mm, the constant temperature interval is 10cm long, an integral metal-based catalyst with the weight of 1g is filled, an organic gas generator is placed in an ice water bath or a constant temperature water bath kettle, constant temperature organic steam with the temperature of 0 ℃ or other temperatures is brought out through air and is mixed with other path of air for dilution, the flow of the blown air and the diluted air is regulated through a mass flowmeter, the simulated organic gas with certain concentration and airspeed is obtained through control, and the reaction tail gas is subjected to online detection by a jieming GC1620 spectrometer or a Cirrus 2 mass spectrometer. The results of the activity test are shown in Table 1.

Table 1 performance testing of catalytic oxidation of organic gases by catalysts of each example

Claims

1. a method for preparing a monolithic metal-based catalyst by a metal replacement method, characterized in that the method comprises the steps:

(1) After pickling, alkali washing and water washing, the whole metal base material is heat-treated under air atmosphere for standby use;

The temperature of the heat treatment is 200～500℃, and the treatment time is 2～6h;

(2) dissolving the precious metal precursor in water, and then adding a surfactant to obtain a precious metal precursor replacement liquid;

The precious metal precursor is chloroplatinic acid or chloropalladium acid;

The surfactant is an amphiphilic nonionic surfactant;

(3) at 40-95°C, immerse the monolithic metal substrate prepared in step (1) into the precious metal precursor replacement solution obtained in step (2) to carry out a metal replacement reaction. During the reaction, use an ultraviolet spectrophotometer to measure the replacement liquid absorbance, until the absorbance no longer changes and the metal replacement is complete, then it is taken out for cleaning, dried, and calcined at 200 to 500° C. for 3 to 5 hours to obtain the monolithic metal-based catalyst.

2. the method for preparing monolithic metal-based catalyst by metal replacement method as claimed in claim 1, is characterized in that, in step (1), described monolithic metal base material is 304 stainless steel, 316 stainless steel, foamed aluminum, foamed nickel or iron-chromium aluminum.

3 . The method for preparing a monolithic metal-based catalyst by a metal displacement method according to claim 1 , wherein, in step (2), the surfactant is a polyoxyethylene polyoxypropylene ether block copolymer. 4 .

4 . The method for preparing a monolithic metal-based catalyst by metal replacement according to claim 1 , wherein, in step (2), the concentration of the surfactant in the noble metal precursor replacement liquid ranges from 0.1 to 1.0 wt %. 5 .

5 . The method for preparing a monolithic metal-based catalyst by a metal replacement method according to claim 1 , wherein, in the monolithic metal-based catalyst obtained in step (3), the substitution amount of the precious metal is 0.01-1.0 wt % of the mass of the monolithic metal substrate. 6 . .

6. The monolithic metal-based catalyst prepared by the method of claim 1.

7. The application of the monolithic metal-based catalyst according to claim 6 in catalytic combustion to eliminate industrial volatile organic waste gas pollution.