WO2020151577A1

WO2020151577A1 - Cerium oxide catalyst modified by phosphoric acid, and preparation method and application of cerium oxide catalyst

Info

Publication number: WO2020151577A1
Application number: PCT/CN2020/072585
Authority: WO
Inventors: 吴忠标; 翁小乐; 戴晓霞; 刘越; 王海强
Original assignee: 浙江大学
Priority date: 2019-01-23
Filing date: 2020-01-17
Publication date: 2020-07-30
Also published as: CN109603869B; CN109603869A

Abstract

The present invention relates to the technical field of air pollution control. Disclosed are a cerium oxide catalyst modified by phosphoric acid, and a preparation method and application of the cerium oxide catalyst. The preparation method comprises the following steps: (1) soaking cerium oxide in a phosphoric acid solution, then filtering out the cerium oxide, washing the cerium oxide to be neutral, and drying same; (2) calcining the dried cerium oxide at the temperature of 100-400 °C for 1-4 hours to obtain the cerium oxide catalyst modified by the phosphoric acid. The catalyst prepared by means of the preparation method of the present invention can be used for catalytic oxidation degradation of chlorine-containing volatile organic compounds, has high catalytic activity, strong chlorine poisoning resistance, sulfur poisoning resistance and water resistance, and long catalytic service life, cannot easily generate toxic by-products when the chlorine-containing volatile organic compounds are catalytically oxidized, and has no secondary pollution.

Description

Phosphoric acid modified cerium oxide catalyst and preparation method and application thereof

Technical field

The invention relates to the technical field of air pollution control, in particular to a phosphoric acid modified cerium oxide catalyst and a preparation method and application thereof.

Background technique

Chlorine-containing volatile organic compounds are a type of organic matter, such as chlorobenzene, dichlorobenzene, trichloroethylene, etc., which are commonly used reagents in industrial production processes and are discharged into the environment in the form of waste water or exhaust gas. Most of the chlorinated volatile organic compounds are environmentally persistent and highly toxic. They can exist for a long time in the atmosphere or water environment, and accumulate in organisms through the food chain, causing "carcinogenic, teratogenic, and mutagenic" effects. Chlorine-containing organic compounds are generally toxic. The U.S. Environmental Protection Agency screened out 65 categories and 129 priority control "blacklists" from more than 70,000 compounds based on the toxicity of the compounds, the possibility of natural degradation, and the probability of occurrence in water. , Of which there are 7 kinds of PCBs and related compounds. On the "blacklist", the most serious pollutants to my country's environment include one type of polychlorinated biphenyls, four types of chlorinated benzenes, and ten types of halogenated hydrocarbons. It can be seen that the pollution of organic chlorides is quite common and serious, so the treatment of organic chlorides is currently an important part of environmental protection.

Chlorine-containing volatile organic compounds can be roughly divided into two categories: one is low molecular weight organic chlorides, mainly including chloroform, carbon tetrachloride, dichloroethane, trichloroethylene, trichloroethane, and tetrachloride Ethylene, chlorobenzene, etc.; the second is polychlorinated compounds, including polychlorinated biphenyl furans and dioxins. Most of these compounds come from organic solvents in industrial applications, fire extinguishing agents, thermal conductive fluids, intermediates of chemical products, and by-products of the power industry. Their concentration in industrial waste gas or incineration plants varies greatly. The former is typically between 200 and 2000 ppm, while the latter is usually less than 1 ng/m ³ . Organized emission of chlorine-containing volatile organic compounds can generally be collected and processed to effectively reduce the content in the exhaust gas. As the last line of defense, the development and application of high-efficiency terminal processing technology is the focus of current research work. In recent years, low-temperature plasma technology and membrane separation technology have gradually emerged in the treatment of low-concentration organic waste gas, and photocatalytic technology has also been further developed. At present, the commonly used control technologies mainly include thermal combustion, catalytic combustion, adsorption, absorption, condensation, etc. The removal efficiency is usually related to the inlet concentration. On the basis of ensuring removal efficiency, combined with investment costs, applicable working conditions and operational safety, the current technology has its own advantages and disadvantages. Catalytic combustion technology has become one of the most promising technologies due to its high processing efficiency, low energy consumption, heat recovery and no secondary pollution.

The key problem to be solved in the development of catalysts in the catalytic combustion of chlorinated volatile organic pollutants is to increase the service life of the catalyst. Although some transition metal oxides such as manganese oxide and cerium oxide show good activity in the catalytic combustion of chlorine-containing organic substances, these transition metal oxides can even achieve the same catalytic activity as noble metals, but they cannot avoid catalyst chlorination. The problem of poisoning. The chlorine adsorbed on the surface of the catalyst can form oxychloride or chloride with metal ions, thereby reducing the number of active centers of the catalyst or affecting the redox performance of the active centers, and inhibiting the activity of the catalyst. In addition, this process also increases the environmental risk of producing highly toxic polychlorinated by-products, especially dioxins.

The Chinese patent document with the publication number CN108295852A discloses a Ce-Zr catalyst for the catalytic oxidation of chlorine-containing volatile organic compounds, especially a Ru/CeZrO _x type catalyst, which can maintain a relatively high temperature at a lower temperature. Good activity and conversion rate. Due to the use of Ru, the catalyst cost is higher.

The Chinese patent document with publication number CN103962134A discloses a method for the combustion and elimination of chlorinated aromatic hydrocarbons, using cerium oxide nanorods, nanocubes and nano-octahedrons as carriers to support precious metal (Ru) ruthenium as a catalyst, and the reaction is absorbed by dilute alkali solution exhaust. The method has high catalytic activity and no secondary pollutants are generated in the reaction. Also, due to the use of Ru, the catalyst cost is relatively high.

The Chinese patent document with publication number CN10389425A discloses a catalyst for the combustion of polychlorinated aromatic hydrocarbons, which is Fe, Ni, Cr, Bi or Mn doped with cobalt tetroxide. The catalyst has high catalytic activity and strong resistance to chlorine poisoning, but its structure is fragile and cannot be suitable for exhaust gas treatment at high airspeed.

The Chinese patent document with the publication number CN103962127A discloses a catalyst for the combustion of chlorinated aromatic hydrocarbons, which is Sr, Ce, Mg, Al, Fe, Co, Ni, Cu doped perovskite structure LaMnO ₃ . The catalyst has the advantages of simple preparation, low cost, good thermal stability, but low catalytic activity and easy low-temperature chlorine poisoning.

In addition, the existing catalysts for catalytic oxidation of chlorine-containing volatile organic compounds have poor water resistance and sulfur resistance, and have higher requirements for the moisture content and sulfur content of the flue gas of chlorine-containing volatile organic compounds. Before the catalytic oxidation degradation, The flue gas needs to be dehydrated and desulfurized first.

Summary of the invention

The invention provides a phosphoric acid-modified cerium oxide catalyst and a preparation method thereof. The prepared catalyst can be used for the catalytic oxidation and degradation of chlorine-containing volatile organic compounds. The catalyst has high catalytic activity, and has strong resistance to chlorine poisoning, sulfur poisoning and water resistance. , Catalytic life is long, and it is not easy to produce toxic by-products during the catalytic oxidation of chlorine-containing volatile organic compounds, and there is no secondary pollution.

The specific technical solutions are as follows:

A preparation method of phosphoric acid modified cerium oxide catalyst includes the following steps:

(1) Soak the cerium oxide in a phosphoric acid solution, then filter out the cerium oxide, wash it to neutrality, and dry;

(2) Calcining the dried cerium oxide at 100-400° C. for 1 to 4 hours to obtain a phosphoric acid modified cerium oxide catalyst.

In the preparation method of the present invention, cerium oxide is immersed in a phosphoric acid solution to introduce characteristic phosphoric acid groups on the surface of the catalyst (it will be converted into trihydroxyphosphate in the presence of water vapor), which can be effectively used in the presence of oxygen and water The chlorine-containing volatile organic compounds are dechlorinated to promote the desorption of chlorine on the catalyst surface and prevent chlorine poisoning of the catalyst. At the same time, the water in the flue gas promotes the catalytic oxidation process. The experimental data shows that the catalyst also has good resistance. Sulfur performance.

The loading of phosphorus in the catalyst has an important effect on the catalytic activity of the catalyst. When the loading of phosphorus is low, it has little effect on the chlorine resistance, sulfur resistance and water resistance of the catalyst, and the increase in catalytic activity is not obvious. A higher loading will reduce the catalytic activity of the catalyst, so the phosphorus loading needs to be controlled.

Preferably, based on the mass percentage of the phosphorus element, the phosphorus loading in the cerium oxide catalyst is 0.1-5%.

Further preferably, based on the mass percentage of the phosphorus element, the phosphorus loading in the cerium oxide catalyst is 0.3 to 1%.

When the phosphorus loading is controlled at 0.3 to 1%, the catalyst not only has higher catalytic activity, but also has excellent resistance to chlorine, sulfur and water.

Preferably, in step (1), the concentration of the phosphoric acid solution is 10 to 200 g/L, and the molar ratio of cerium oxide to phosphoric acid is 1:0.05 to 1. More preferably, the molar ratio of cerium oxide to phosphoric acid is 1. ：0.05～0.2.

Preferably, in step (1), the soaking temperature of cerium oxide is 10 to 80°C, and the soaking time is 0.5 to 3h; more preferably, in step (1), the soaking temperature of cerium oxide is 10 to 40°C, and the soaking time For 0.5～1h.

Step (1) After soaking, cooling, filtering and washing, a light yellow precipitate is obtained.

In step (2), calcination can be performed under nitrogen or air atmosphere.

The calcination temperature of the catalyst is too high to obtain a form with good catalytic performance and the catalytic efficiency is reduced; the calcination temperature is too low to obtain a catalyst of the target composition.

Preferably, in step (2), the calcination temperature is 200-300°C.

The catalyst calcination time is not easy to be too long, and the calcination time is too long, which causes the catalyst lattice to collapse and the specific surface area decreases.

Preferably, in step (2), the calcination time is 1 to 2 hours.

The present invention also provides the application of the phosphoric acid-modified cerium oxide catalyst in the catalytic oxidation and degradation of chlorine-containing volatile organic substances, including:

Reacting the flue gas containing chlorine-containing volatile organic compounds and water vapor under the action of the cerium oxide catalyst;

The volume fraction of water vapor in the flue gas is 0.1 to 5%;

The reaction temperature is 100 to 300°C.

Preferably, the mass fraction of water vapor in the flue gas is 0.5-2%.

Appropriately increasing the content of water vapor in the flue gas, the catalyst's catalytic oxidation efficiency of chlorinated volatile organic compounds is improved. When the content of water vapor is 0.5-2%, the catalyst shows the best removal efficiency of chlorobenzene, increasing water When the steam content is increased to 5%, the catalyst still exhibits better catalytic activity.

Preferably, the reaction temperature is 200-300°C.

The cerium oxide catalyst has better oxidation efficiency for chlorine-containing volatile organic compounds in the medium and low temperature zone of 100-300°C, and the catalytic efficiency is the best when the temperature zone is 200-300°C.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention has simple preparation process, low cost, and is suitable for large-scale production;

(2) The CeO ₂ catalyst treated by phosphoric acid of the present invention makes full use of CeO ₂ due to the reversible conversion of Ce ⁴⁺ /Ce ³⁺ , which has good oxygen storage and release performance and oxygen fluidity, and the effect of phosphate on the water of chlorine-containing organic matter The dechlorination ability enables the catalyst of the present invention to stably convert chlorine-containing volatile organic pollutants into H ₂ O, CO ₂ and HCl for a long time in the environment of industrial waste gas and flue gas. Better chlorine performance;

(3) Experimental data shows that the catalyst of the present invention has better sulfur resistance;

(4) The catalyst of the present invention uses cheap cerium oxide as the active material and uses phosphoric acid treatment, which greatly increases the life of the catalyst, inhibits the generation of toxic by-products during the catalytic reaction, and avoids secondary pollution.

Description of the drawings

Figure 1 is the SS NMR characterization result diagram of the catalyst prepared in Example 1;

Fig. 2 is a graph showing the in-situ infrared characterization results of the catalyst prepared in Example 1.

detailed description

Example 1

Catalyst preparation:

(1) Mixing cerium oxide powder and phosphoric acid (concentration of phosphoric acid solution: 1mol/L) at a molar ratio of 1:0.05, reacting at 30°C for 0.5h, cooling, standing, and washing the resulting mixture to obtain yellow cerium oxide precipitation.

(2) Wash the obtained mixture to neutrality, and after drying, calcinate at 200° C. for 1 hour in an air atmosphere to obtain a catalyst.

The phosphorus loading of the prepared catalyst is 0.7%.

As shown in Figure 1, the SS NMR characterization proved the existence of phosphate groups on the surface of cerium oxide. The subsequent in-situ infrared characterization is shown in Figure 2, which also proves the presence of P-O and P=O on the cerium oxide surface after phosphoric acid treatment. After experimental characterization, the main form of phosphoric acid on the surface of the catalyst after phosphoric acid treatment is dihydroxyphosphate.

Example 2

Catalyst preparation:

(1) Mixing cerium oxide powder and phosphoric acid at a molar ratio of 1:0.05, reacting at 80° C. for 0.5 h, cooling, standing, and washing the resulting mixture to obtain yellow cerium oxide precipitation.

The phosphorus loading of the prepared catalyst is 0.4%.

Example 3

Catalyst preparation:

(1) Mixing cerium oxide powder and phosphoric acid at a molar ratio of 1:0.05, reacting at 30° C. for 0.5 h, cooling, standing, and washing the resulting mixture to obtain yellow cerium oxide precipitation.

(2) Wash the obtained mixture to neutrality, and after drying, calcinate at 300° C. for 2 hours in an air atmosphere to obtain a catalyst.

The phosphorus loading of the prepared catalyst is 0.7%.

Example 4

Catalyst preparation:

(1) The cerium oxide powder and phosphoric acid were mixed at a molar ratio of 1:0.2, and reacted at 30° C. for 1 h, and the resulting mixture was cooled, stood still, and washed to obtain a yellow cerium oxide precipitate.

The phosphorus loading of the prepared catalyst is 1.2%.

Example 5

Catalyst preparation:

The phosphorus loading of the prepared catalyst is 1.2%.

Comparative example 1

The cerium oxide powder was directly calcined at 300° C. for 2 hours in an air atmosphere to obtain a catalyst.

Application example 1

Catalytic oxidation of chlorobenzene with the catalyst prepared in the above 5 examples is as follows:

The activity experiment was carried out on a fixed bed reactor, the catalyst loading was 1.0g, and the particle size was 40-60 mesh. The initial gas concentration is: chlorobenzene=1000ppm, [O ₂ ]=10%, [H ₂ O]=0.2%, N ₂ is the carrier gas, and GHSV (gas space velocity)=10000h ^-1 . The test reaction temperature is 100°C, 150°C, 200°C, 225°C, 250°C, 300°C, and the test data for 1 hour reaction is shown in Table 1.

Table 1 Catalytic oxidation efficiency of catalyst to chlorobenzene/%

It can be seen from the experimental results in Table 1 that the catalyst prepared by the method of the present invention has better oxidation efficiency for chlorobenzene in the medium and low temperature zone of 150-300°C, especially the catalysts prepared in Examples 1 and 3 The catalytic efficiency of 300℃ temperature zone is above 90%. It can be seen that the catalyst of the present invention is very suitable for the catalytic oxidation of chlorobenzene in flue gas at medium and low temperature.

Application example 2

The following experiments were carried out on a fixed bed reactor with a catalyst loading of 1g and a particle size of 40-60 mesh. The initial gas concentration is: chlorobenzene=1000 ppm, [O ₂ ]=10%, [H ₂ O]=0.5%, N ₂ is the carrier gas, and GHSV (gas space velocity)=10000h ^-1 . The test reaction temperature is 100°C, 150°C, 200°C, 225°C, 250°C, 300°C, and the test data for 1 hour reaction is shown in Table 2.

Table ₂ The influence of H ₂ O (0.5%) on the catalytic oxidation efficiency of chlorobenzene/%

Application example 3

The following experiments were carried out on a fixed bed reactor with a catalyst loading of 1g and a particle size of 40-60 mesh. The initial gas concentration is: chlorobenzene=1000ppm, [O ₂ ]=10%, [H ₂ O]=2%, N ₂ is the carrier gas, GHSV (gas space velocity)=10000h ^-1 . The specific test reaction temperature is 100°C, 150°C, 200°C, 225°C, 250°C, 300°C, and the test data for 1 hour reaction is shown in Table 3.

Table 3 The effect of H ₂ O (2%) on the catalytic oxidation efficiency of chlorobenzene/%

Application example 4

The following experiments were carried out on a fixed bed reactor with a catalyst loading of 1g and a particle size of 40-60 mesh. The initial gas concentration is: chlorobenzene=1000ppm, [O ₂ ]=10%, [H ₂ O]=5%, N ₂ is the carrier gas, GHSV (gas space velocity)=10000h ^-1 . The test reaction temperature is 100°C, 150°C, 200°C, 225°C, 250°C, 300°C, and the test data for 1 hour reaction is shown in Table 4.

Table 4 The influence of H ₂ O (5%) on the catalytic oxidation efficiency of chlorobenzene/%

It can be seen from the experimental results in Tables 1 to 4 that if the content of H ₂ O in the flue gas is appropriately increased, the catalytic oxidation efficiency of the catalyst of the present invention on chlorobenzene is still improved. When the water flow is 0.2 to 2%, the performance is best The removal efficiency of chlorobenzene. When the water content is increased to 5%, the catalyst of the present invention still shows better activity, and the catalytic efficiency is above 85% at 300°C. It can be seen that the catalyst can make full use of H ₂ O in the flue gas and greatly promote the catalytic oxidation of chlorobenzene.

In Comparative Example 1, the catalytic oxidation efficiency of chlorobenzene on the catalyst without phosphoric acid modification at 200～300℃ and low moisture content in the flue gas is relatively good, but as the moisture content in the flue gas increases, The catalytic oxidation efficiency of benzene drops rapidly, indicating that the water resistance of the cerium oxide catalyst without phosphoric acid modification is poor.

Application example 5

Stability test of catalyst for catalytic oxidation of chlorobenzene

The following experiments were carried out on a fixed bed reactor with a catalyst loading of 1g and a particle size of 40-60 mesh. The initial gas concentration is: chlorobenzene=1000 ppm, [O ₂ ]=10%, [H ₂ O]=0.5%, N ₂ is the carrier gas, and GHSV (gas space velocity)=10000h ^-1 . The test reaction temperature is specifically set at 300°C, N ₂ is the carrier gas, and the test data is shown in Table 5.

Table 5 Stability of catalyst/% (test temperature is 300℃)

It can be seen from Table 5 that the chlorobenzene oxidation activity of the catalyst of the present invention is almost unaffected after the catalyst is treated with chlorobenzene for several hours (contains a certain amount of water vapor). The catalyst of the present invention has good chlorine poisoning resistance and can grow Time stable operation.

However, the catalyst of Comparative Example 1 without phosphoric acid modification has poor stability and is prone to chlorine poisoning and loses catalytic activity.

Application example 6

Test of sulfur resistance of catalyst for catalytic oxidation of chlorobenzene

The following experiments were carried out on a fixed bed reactor with a catalyst loading of 1g and a particle size of 40-60 mesh. The initial gas concentration is: chlorobenzene=1000ppm, [O ₂ ]=10%, [H ₂ O]=0.5%, [SO ₂ ]=50ppm, N ₂ is carrier gas, GHSV (gas space velocity)=10000h ^-1 . The test reaction temperature is specifically 300°C, N ₂ is the carrier gas, and the test data is shown in Table 6.

Table 6 Anti-sulfur activity of the catalyst/% (test temperature is 300℃)

It can be seen from Table 6 that the chlorobenzene oxidation activity of the catalyst of the present invention is almost unaffected after SO _{2 is} treated on the catalyst for several hours. The catalyst of the present invention is highly adaptable to flue gas components and is suitable for various compositions. Used in flue gas.

On the other hand, the stability of the catalyst without phosphoric acid modification in Comparative Example 1 was poor, and it was prone to chlorine and sulfur poisoning to lose its catalytic activity.

The above-mentioned embodiments describe the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Anything within the principle scope of the present invention Any modifications, additions, and equivalent replacements made should all be included in the protection scope of the present invention.

Claims

A method for preparing a phosphoric acid modified cerium oxide catalyst is characterized in that it comprises the following steps:

(1) Soak the cerium oxide in a phosphoric acid solution, then filter out the cerium oxide, wash it to neutrality, and dry;

(2) Calcining the dried cerium oxide at 100-400° C. for 1 to 4 hours to obtain a phosphoric acid modified cerium oxide catalyst.
The method for preparing a phosphoric acid-modified cerium oxide catalyst according to claim 1, wherein the phosphorus loading in the cerium oxide catalyst is 0.1 to 5% based on the mass percentage of phosphorus element.
The method for preparing a phosphoric acid modified cerium oxide catalyst according to claim 1, wherein in step (1), the concentration of the phosphoric acid solution is 10 to 200 g/L, and the molar ratio of cerium oxide to phosphoric acid is 1. : 0.05～1.
The method for preparing a phosphoric acid-modified cerium oxide catalyst according to claim 1 or 3, wherein in step (1), the soaking temperature of the cerium oxide is 10 to 80° C., and the soaking time is 0.5 to 3 hours.
The method for preparing a phosphoric acid-modified cerium oxide catalyst according to claim 1, wherein in step (2), the calcination temperature is 200-300°C.
The method for preparing a phosphoric acid modified cerium oxide catalyst according to claim 5, wherein in step (2), the calcination time is 1 to 2 hours.
A phosphoric acid modified cerium oxide catalyst, characterized in that it is prepared according to the preparation method of any one of claims 1 to 6.
An application of the phosphoric acid-modified cerium oxide catalyst according to claim 7 in the catalytic oxidative degradation of chlorine-containing volatile organic compounds, characterized in that it comprises:

Reacting the flue gas containing chlorine-containing volatile organic compounds and water vapor under the action of the cerium oxide catalyst;

The volume fraction of water vapor in the flue gas is 0.1 to 5%;

The reaction temperature is 100 to 300°C.
The application according to claim 8, wherein the mass fraction of water vapor in the flue gas is 0.5-2%.
The application according to claim 8, characterized in that the reaction temperature is 200-300°C.