CN111167474A

CN111167474A - Preparation of supported catalyst and application thereof in catalytic oxidation of benzene

Info

Publication number: CN111167474A
Application number: CN201811334466.XA
Authority: CN
Inventors: 黄家辉; 王丽丽; 谢妍
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-11-09
Filing date: 2018-11-09
Publication date: 2020-05-19

Abstract

The invention belongs to the field of environmental catalysis, and particularly relates to a preparation method of a supported catalyst, which is applied to catalytic oxidation to remove volatile organic benzene. The method is a mode combining an impregnation method and a sedimentation method, the noble metal is firstly supported on the alumina, the synthesis method has universality, is simple to operate, has no obvious metal loss, reduces the preparation cost of the catalyst by reducing the amount of the noble metal, and is easy to amplify and synthesize. The prepared catalyst has the advantages of wide temperature range for catalytic oxidation of volatile organic compounds, good stability at high temperature, difficult inactivation and the like.

Description

Preparation of supported catalyst and application thereof in catalytic oxidation of benzene

Technical Field

The invention belongs to the technical field of volatile organic compound treatment, and particularly relates to a preparation method of a supported catalyst and application of the supported catalyst in catalytic oxidation reaction of benzene.

Background

In China, Volatile Organic Compounds (VOCs) refer to organic compounds with saturated vapor pressure of more than 133.32Pa at normal temperature and boiling point of 50-260 ℃ below at normal pressure, or any organic solid or liquid capable of volatilizing at normal temperature and normal pressure. VOCs can be further classified into: alkanes, aromatic hydrocarbons, esters, aldehydes, and others. More than 300 have been identified so far. The most common of the pollutants are benzene, toluene, xylene, styrene, trichloroethylene, trichloromethane, trichloroethane, diisocyanate (TDI), diisocyanatophenyl ester and the like, which are important components of atmospheric gaseous pollutants and have serious harm to the ecological environment and human health. Benzene is a common volatile organic compound, and in indoor building materials such as paint and coating, the benzene can cause great damage to blood after being contacted for a long time, so that chronic poisoning is caused, and neurasthenia syndrome and the like are caused. Benzene can damage bone marrow, reduce the number of red blood cells, white blood cells, platelets, and distort chromosomes, resulting in leukemia and even aplastic anemia. Benzene can also cause excessive bleeding, thereby inhibiting the function of the immune system and making the disease more productive. The latency of benzene in vivo can be as long as 12-15 years as reported by studies. In 2007, benzene has been identified as a carcinogen in our country. Therefore, the removal of benzene in the air is of great significance to human health and improvement of air quality.

At present, the detection of trace benzene in the air can be carried out by absorbing with volatile organic solvent such as methyl silicone oil or low molecular weight polymer, and then analyzing by chromatography; or analyzing by a colorimetric method; alternatively, benzene-containing air may be deep-frozen, the benzene may be frozen, and ferric sulfate and hydrogen peroxide solution may be added to obtain a yellow-brown or black precipitate, which is then dissolved in nitric acid and analyzed by colorimetry. Or directly using nitric acid to absorb benzene in the air, nitrifying the benzene into m-dinitrobenzene, and then using titanium dichloride solution to titrate, or using methyl ethyl ketone alkali solution prepared by m-xylene to carry out colorimetric quantification.

Benzene elimination techniques can be divided into two categories: recovery techniques and destruction techniques. To pairAnd collecting benzene with high concentration by adopting a recovery technology, and then utilizing the benzene. Common recovery techniques include adsorption, membrane separation, condensation, and the like; for medium and low benzene with concentration, the medium and low benzene is not easy to collect, secondary pollution is avoided, and a destroying technology is preferably adopted. Common destruction technologies include biodegradation, plasma technology, direct combustion, catalytic oxidation, and the like. The catalytic oxidation method is superior to the benzene treatment under the direct combustion condition, has the advantages of green and pollution-free products, recyclable catalyst and the like, and is one of the most effective methods for treating benzene commercially. Therefore, new highly efficient catalytic materials were developed. In the Catalysis Science Technology 8(2018)806-816, metal Pd (PdCl) is reacted with PVA as a protective agent (Pd: PVA: 1:1.2 mass ratio) and sodium borohydride as a reducing agent₂Is a precursor metal salt of Pd) is loaded on the mesoporous CoO, and the catalyst is roasted for 1 hour at 320 ℃ in a nitrogen atmosphere to obtain the loaded catalyst 1 percent Pd/CoO, the catalyst has better catalytic activity on the catalytic oxidation of o-xylene in VOCs, and the conversion rate of the o-xylene is 90 percent at 173 ℃.

Disclosure of Invention

This patent then adopts noble metal and non-noble metal to form the alloy mode and obtains bimetal or the multi-metal and carry type catalyst, greatly reduced noble metal's use amount, though noble metal's loading volume reduces but still better to benzene catalytic oxidation's activity, and catalytic reaction under the high temperature, the catalyst is still stable. Noble metal and noble metal alloy catalysts are highly valued for their good catalytic activity, stability and selectivity. Because the noble metal alloy can be loaded on a carrier with high specific surface area and can be highly dispersed, from the practical application perspective, the supported noble metal alloy catalyst with low noble metal loading and good catalytic activity is prepared.

The invention provides a preparation method of a supported catalyst and application thereof in benzene catalytic oxidation reaction, and the supported catalyst has the advantages of simple operation, short synthesis time, no obvious metal loss and easy amplification synthesis.

The invention provides a preparation method of a supported catalyst, which comprises the following steps:

(1) dissolving an alloy precursor in water, adding a proper amount of a protective agent, stirring and dissolving, adding a metal oxide carrier after the protective agent is completely dissolved, and stirring for 20-120min to obtain a solution A;

(2) dissolving a reducing agent sodium borohydride in ice water to obtain a solution B;

(3) adding the solution B into the solution A, stirring for 30-40min, washing with deionized water, and drying in an oven at 50-150 ℃ for 4-24h to obtain solid powder A.

(4) Placing the solid powder A in a muffle furnace at 400-700 ℃ for roasting, keeping the solid powder A at the initial temperature of 20-30 ℃ for 2-4 hours at the temperature rising rate of 2-5 ℃/min when the solid powder A reaches the roasting temperature, and naturally cooling after roasting to obtain the supported catalyst; the mass ratio of the metal precursor to the protective agent to the reducing agent to the carrier is 1-5: 5-50: 100-200.

Based on the technical scheme, preferably, the noble metal precursor is one or a mixture of more than two of chloride, nitrate, acetate and carbonate of noble metal; the noble metal is platinum, palladium and gold; the transition metal precursor is one or a mixture of more than two of chloride, nitrate, acetate and carbonate of transition metal; the transition metal is nickel, iron, copper, zinc or cobalt; the molar ratio of the noble metal to the transition metal in the alloy precursor is 1:1-1: 5.

Based on the technical scheme, preferably, the metal oxide carrier is Al₂O₃、TiO₂、ZrO₂、 Fe₃O₄、SiO₂、Co₃O₄、CeO₂、ZnO、Fe₂O₃、La₂O₃、MnO₂At least one of them.

Based on the above technical scheme, preferably, the protective agent is PVA (Polyvinyl alcohol), PVP (Polyvinyl pyrrolidone), Silica sol (Silica sol), P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide), or Poloxamer (polyoxyethylene polyoxypropylene ether block copolymer, Poloxamer).

Based on the technical scheme, the roasting temperature is preferably 450 ℃, 550 ℃, 650 ℃ and 700 ℃.

In another aspect, the present invention provides a supported catalyst prepared by the above method, wherein the supporting amount of the alloy on the metal oxide is 0.1 wt% to 1 wt%.

The invention further provides an application of the supported catalyst in the catalytic oxidation reaction of benzene.

Based on the above technical solution, preferably, the application is: introducing a mixed gas composed of benzene and background gas filled with inert gas into a fixed bed reactor filled with the supported catalyst at 50-300 deg.C and 8000-100,000mL/g_catalystCarrying out catalytic oxidation benzene reaction at an hourly space velocity; the concentration of the benzene is 100-1000 ppm.

Based on the technical scheme, preferably, the background gas is a mixed gas of oxygen and inert gas, and the volume percentage of the oxygen in the mixed gas is 10-80%, preferably 10-50%.

Based on the technical scheme, preferably, the inert gas is nitrogen, argon or helium, and the concentration of the benzene is 100-500 ppm.

Based on the technical scheme, preferably, the space velocity is 20,000-60,000mL/g_catalyst·h。

The method comprises the steps of mixing and stirring noble metal salt and non-noble metal salt precursor aqueous solution, adding a protective agent PVP and carrier alumina, reducing by sodium borohydride, washing and drying to obtain a sample A. And placing the sample A in a muffle furnace to be roasted to prepare a supported catalyst B. The supported catalyst A is directly roasted, and the noble metal mainly exists in an oxidation state; the supported catalyst A is roasted in a muffle furnace to remove the protective agent PVP, so that the metal is better exposed on the surface of the carrier. The obtained supported catalyst is placed in a fixed reactor filled with mixed gas consisting of benzene and background gas, and the catalytic oxidation reaction of the benzene is detected at a temperature of between 100 and 300 ℃ and a certain space velocity.

Advantageous effects

Compared with the prior art, the invention has the following advantages: the preparation method of the supported catalyst is simple, avoids loss of the noble metal precursor, is suitable for large-scale synthesis, and has wide development space and market application value; reducing agents, stabilizing agents and surface active agents which are not friendly to the environment are not used in the preparation process; no byproducts except water and carbon dioxide are generated in the benzene oxidation process, the method is green and environment-friendly, and completely meets the requirements of sustainable development of China at present.

The documents Microporous and Mesoporous Materials 224(2016)311-322

Cr will be used in the reference₂O₃As carrier, PVA as protecting agent and aqueous solution of sodium borohydride are reduced, in which Au (HAuCl)₄) And Pd (PdCl)₂) The molar ratio, mass ratio of metal to PVA (1:1.5), molar ratio of metal to sodium borohydride (1.5:1) gave a supported catalyst of 0.90 wt% Au/Cr₂O₃,1.00wt％ Pd/Cr₂O₃,and xAu₁Pd₂/Cr₂O₃(x ═ 0.50 to 1.95 wt%), with the best catalyst performance being 1.95 wt% Au₁Pd₂/Cr₂O₃The conversion rate of benzene can reach 90 percent at the space velocity of 20,000mL/(g h) and the reaction temperature of 165 ℃, and the catalyst is more than that of Au and Pd which are loaded on Cr independently₂O₃The catalytic activity of the catalyst is excellent because the catalytic activity of the catalyst is greatly improved due to the interaction between the metals.

Drawings

Placing the prepared supported catalyst in a fixed reaction bed reactor, introducing benzene and background gas with certain concentration, slowly raising the temperature for reaction, drawing a temperature-conversion rate curve and reading data.

FIG. 1 is an activity test chart of example 12.

FIG. 2 is an activity test chart of example 13.

FIG. 3 is an activity test chart of example 14.

Detailed Description

Example 1

1) 2.5mg of K₂PtCl₄And 2.62mg Ni (NO)₃)₂·6H₂Dissolving O metal salt in 10mL water, placing in 50mL beaker, adding 7.5mg PVP, stirring at 400-1000rpm for dissolving, and adding 500mg Al₂O₃Stirring the carrier for 20min, dissolving 3mg of sodium borohydride in ice water, quickly adding the sodium borohydride into a beaker, stirring for 30min, washing with deionized water, placing the mixture into a vacuum drying oven, and drying for 12h to obtain solid powder A; n is_Pt:n_Ni＝1:1.5。

2) The powder A was calcined in a muffle furnace at 550 ℃ to produce 0.3 wt% Pt-Ni/Al₂O₃A catalyst.

Examples 2 to 5

Preparation of Pt-X/Al₂O₃(X＝Fe、Co、Zn、Cu，n_Pt:n_X＝1:1.5)

A catalyst was prepared by the method of example 1 except that transition metal precursor salts were changed to ferric chloride, cobalt nitrate, zinc chloride and copper nitrate, and other steps were separately prepared by referring to example 1 to obtain Pt-Fe/Al₂O₃、Pt-Co/Al₂O₃、Pt-Zn/Al₂O₃、Pt-Cu/Al₂O₃A catalyst.

Examples 6 to 8

The catalyst prepared by the method of example 1 was used to prepare Pt-Ni/Al by changing the calcination temperatures of 450 deg.C, 650 deg.C, and 700 deg.C, respectively₂O₃-450℃、Pt-Ni/Al₂O₃-650℃、Pt-Ni/Al₂O₃Catalyst at-700 ℃ in a molar ratio of the metals of 1: 1.5.

Examples 9 to 11

A catalyst was prepared by the method of example 1, changing the molar ratios of platinum to nickel in the metal alloy to 1:1, 1:2, 1:3, respectively, to prepare Pt-Ni/Al₂O₃-550℃(1:1.1)、Pt-Ni/Al₂O₃-550℃(1:1.2)、 Pt-Ni/Al₂O₃Catalyst at 550 deg.C (1: 1.3).

Example 12

In a fixed reaction bedThe catalyst prepared in examples 1 to 5 was placed in a reactor, benzene and background gas were fed in, and the space velocity was 60,000mL/g_catalystAnd h, slowly raising the temperature to carry out the reaction.

The catalysts prepared in examples 1-5 all achieved 90% conversion at 180 deg.C, with example 1 preparing Pt-Ni/Al₂O₃The performance is most excellent at 550 ℃ below zero, and the conversion rate of benzene can reach 90% at 167 ℃.

Example 13

A catalytic oxidation experiment of benzene was conducted in the same manner as in example 12 except that in example 1 and

experiments were conducted with catalysts prepared in examples 6-8 at different temperatures. The data obtained are shown in FIG. 2, and the catalysts at different temperatures all show excellent catalytic performance, among which Pt₁Ni_1.5/Al₂O₃The catalyst activity is best at-650 ℃ and 90% conversion of benzene is achieved at 163 ℃.

Example 14

A catalytic oxidation experiment of benzene was conducted in the same manner as in example 11 except that example 1 and example 1 were mixed

The catalysts prepared in examples 9-11 in different proportions were tested and the data obtained are shown in FIG. 3, where n represents excellent performance for the catalysts in different proportions_Pt:n_Ni1:1.5 and n_Pt:n_NiThe performance is better than 1:2, and at 164 ℃, 90% conversion of benzene can be achieved.

Example 15

1) 2.212mg of Pd (NO)₃)₂And 3.35mg Co (NO)₃)₂·6H₂Dissolving O metal salt in 10mL water, placing in 50mL beaker, adding 7.5mg PVA, stirring at 400rpm to dissolve, adding 500mg CeO₂Stirring the carrier for 40min, dissolving 3mg of sodium borohydride in ice water, quickly adding the sodium borohydride into a beaker, stirring for 30min, washing with deionized water, putting the beaker into a vacuum drying oven, and drying for 24h to obtain solid powder A; n is_Pt:n_Co＝1:1.2。

2) Placing powder A in a muffle furnace at 550 deg.CTo be roasted to prepare Pd-Co/Al₂O₃A catalyst.

Example 16

1) 1.589mg of Pd (NO)₃)₂And 2.995mg Ce (NO)₃)₃·6H₂Dissolving O metal salt in 10mL water, placing in 50mL beaker, adding 7.5mg PVA, stirring at 400rpm to dissolve, and adding 500mg TiO₂Stirring the carrier for 40min, dissolving 3mg of sodium borohydride in ice water, quickly adding the sodium borohydride into a beaker, stirring for 30min, washing with deionized water, putting the beaker into a vacuum drying oven, and drying for 24h to obtain solid powder A; n is_Pt:n_Co＝1:1。

2) Roasting the powder A at 550 ℃ in a muffle furnace to prepare Pd-Ce/TiO₂A catalyst.

Example 17

1) 2.5mg of K₂PtCl₄And 2.62mg Ni (NO)₃)₂·6H₂Dissolving O metal salt in 10mL water, placing in a 50mL beaker, adding 7.5mg PVP, stirring at 400rpm for dissolving, and adding 500mg ZrO₂Stirring the carrier for 20min, dissolving 3mg of sodium borohydride in ice water, quickly adding the sodium borohydride into a beaker, stirring for 30min, washing with deionized water, putting the beaker into a vacuum drying oven, and drying for 12h to obtain solid powder A; n is_Pt:n_Ni＝1:1.5。

2) Roasting the powder A at 550 ℃ in a muffle furnace to prepare 0.1-1 wt% of Pt-Ni/ZrO₂A catalyst.

The method adopted by the invention is a mode combining an impregnation method and a sedimentation method, precious metal is firstly loaded on alumina, then the catalytic activity of the catalyst is improved by adjusting the metal proportion, the roasting temperature and modulating the second metal, PVP is adopted as a protective agent to avoid the oversize of metal particles, and in addition, the doping of the second metal can further improve the catalytic activity. The post-treatment of the invention is to directly roast in the air atmosphere at a certain temperature, so that the noble metal mainly exists in an oxidation state by the direct roasting, and the instability existing in a metal state is avoided. Whether the active site for catalytic oxidation is an oxidized noble metal or a reduced noble metal or a mixture thereof remains a controversial issue. Different after-treatments can produce large differences in catalyst activity.

Claims

1. A method of preparing a supported catalyst comprising the steps of:

(1) dissolving an alloy precursor in water, adding a proper amount of a protective agent, stirring and dissolving, adding a metal oxide carrier, and stirring for 20-120min to obtain a solution A;

(3) adding the solution B into the solution A, stirring for 20-120min, washing with deionized water, and drying in an oven at 50-150 ℃ for 4-24h to obtain solid powder A;

(4) placing the solid powder A in a muffle furnace at 400-700 ℃ for roasting, keeping the solid powder A at the initial temperature of 20-30 ℃ for 2-4 hours at the temperature rising rate of 2-5 ℃/min when the solid powder A reaches the roasting temperature, and naturally cooling after roasting to obtain the supported catalyst;

the mass ratio of the metal precursor to the protective agent to the reducing agent to the carrier is 1-5: 5-50: 100-200.

2. The method according to claim 1, wherein the alloy precursor is a mixture of a noble metal precursor and a transition metal precursor, and the noble metal precursor is one or a mixture of more than two of chloride, nitrate, acetate and carbonate of noble metal; the noble metal is platinum, palladium and gold; the transition metal precursor is one or a mixture of more than two of chloride, nitrate, acetate and carbonate of transition metal; the transition metal is nickel, iron, copper, zinc or cobalt; the molar ratio of the noble metal to the transition metal in the alloy precursor is 1:1-1: 5.

3. The method of claim 1, wherein the metal oxide support is Al₂O₃、TiO₂、ZrO₂、Fe₃O₄、SiO₂、Co₃O₄、CeO₂、ZnO、Fe₂O₃、La₂O₃、MnO₂At least one of (1).

4. The method of claim 1, wherein the protective agent is PVA (Polyvinyl alcohol), PVP (polyvinylpyrrolidone), Silica sol (Silica sol), P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide), or Poloxamer (polyoxyethylene polyoxypropylene ether block copolymer, Poloxamer).

5. The method of claim 1, wherein the firing temperature is 450 ℃, 550 ℃, 650 ℃, 700 ℃.

6. A supported catalyst prepared by the process of any of claims 1-5, wherein the alloy is supported on the metal oxide support at a level of from 0.1 to 1 wt%.

7. Use of the supported catalyst of claim 6 in the catalytic oxidation of benzene.

8. Use according to claim 7, characterized in that: introducing a mixed gas composed of benzene and background gas filled with inert gas into a fixed bed reactor filled with the supported catalyst at 50-300 deg.C and 8000-100000mL/g_catalystBenzene catalytic oxidation reaction is carried out at an hourly space velocity; the concentration of benzene in the mixed gas is 100-1000 ppm.

9. Use according to claim 8, characterized in that: the background gas is a mixed gas of oxygen and inert gas, and the content of oxygen in the background gas is 10-80%, preferably 10-50%.

10. The use according to claim 8 or 9, wherein the inert gas is one or a mixture of two or more of argon, nitrogen or helium.