TWI488690B - The method of preparation of cerium oxide-manganese oxide supported nano-palladium catalysts and its application in destruction of volatile organic compounds in air - Google Patents

Description

Nano palladium supported on cerium oxide-manganese oxide catalyst and its application in removing organic waste gas from air

The invention discloses a method for preparing a palladium catalyst supported on a cerium oxide-manganese oxide mixed carrier, and a method for reacting organic waste gas with oxygen in air under the catalyst of nano palladium supported by cerium oxide-manganese oxide. The method for removing organic waste gas; the present invention uses a palladium/yttria-manganese oxide catalyst in an organic waste gas in the air, using a packed bed reactor to remove organic waste gas.

In recent years, due to the rapid development of industrial development, the economic growth has also caused environmental pollution. In particular, the semiconductor industry is likely to cause a large amount of volatile organic compounds (VOCs) to escape in the air during the manufacturing process. The accompanying pollution is the industry. Unavoidable topics. VOCs refer to non-methane hydrocarbons containing carbon (C2~C6), such as benzene, toluene, nitrogen-containing amines, etc. Under normal conditions, the boiling point is below 250 °C. Most of the VOCs are harmful air pollutants. The human body is exposed to the environment of VOCs for a long time, and even at low concentrations, it may cause poisoning or carcinogenic tumors. In addition, VOCs in the atmosphere are highly photochemically active, and generate high-oxidation pollutants such as ozone, PAN (peroxy acethyl nitrate) and PBN (peroxy benzene nitrate) by ultraviolet light irradiation, which is very irritating and harmful to the human body. Therefore, how to reduce the harm of these pollutants to the environment and the human body is the goal that researchers must strive for.

The treatment methods of VOCs can be roughly divided into the following two types: one is destruction, which includes high temperature and catalytic oxidation or reduction, and biological filter bed method, in which organic pollutants are converted into carbon dioxide and water; One is recovery, and the pollutants are transferred or recovered from the exhaust gas by means of absorption, adsorption condensation and membrane separation to make it a clean gas. In the early days, most VOCs were treated by high-temperature combustion, and when sufficient oxygen, temperature and reaction time were sufficient, any hydrocarbon could be oxidized into carbon dioxide and water through the combustion process, and the malodorous gas could be burned to become tasteless and harmless. Gas is emitted into the atmosphere, but there are many kinds of organic volatile gases, and various gases have different ignition points. Therefore, the temperature of the furnace to be obtained by the organic volatile gas in the combustion mode is different. If a plurality of organic volatile gases are mixed, The operating temperature and conditions are more complicated. Generally, the operating temperature of the direct-fired furnace needs to reach 700 to 9.8 degrees Celsius or higher to remove most of the VOCs, but heating also consumes a lot of energy (electricity, diesel). Causes an increase in processing costs. Therefore, most of the industrial use of catalyst combustion method to remove VOCs, the advantages of catalytic combustion method than direct combustion method are: (1) low temperature treatment of organic pollutants (2) high energy efficiency (3) product no pollution to the environment (product For carbon dioxide and water).

Catalysts for treating organic pollutants are mainly classified into (1) low-activity but inexpensive metal oxides (CuO, Cr2O3, MnOx, V2O5) and (2) noble metals with high activity but high valence (Pt, Rh, Pd, Ag, Au), Palladium catalyst was chosen in this report because palladium catalyst has (1) lower price (2) better oxidation activity than other precious metals (Pt, Ag, Au, Rh) (3) ) High temperature durability. Palladium is a precious metal, atomic order 46, on the periodic table and platinum, nickel is the same family, and is the same as strontium and silver. Palladium is a transition metal, grayish white, excellent in ductility, easy to process, and its properties are like platinum but more than platinum metal. Other elements are more susceptible to acid corrosion. Palladium has a melting point of 1828K and is resistant to high temperatures. Industrially, palladium is generally produced as a by-product of the selection of copper and nickel ore. In addition, it can absorb 900 times its own volume of hydrogen. The study of the support catalyst is an extremely important subject in the catalytic reaction of the catalyst. The support of the support can increase the surface area of the active component of the catalyst, change the properties of the catalyst, increase the activity and selectivity of the reaction, and greatly reduce the precious metals. The cost of preparation of the catalyst.

Toluene is a clear, colorless liquid with a distinct taste. It is an aromatic hydrocarbon with benzene. It is often used in today's practical applications to replace the relatively toxic benzene as an organic solvent. Many of its properties are similar to benzene. However, unlike the oxidation reaction of benzene, the oxidation reaction of toluene does not occur on the benzene ring but on the methyl group. Therefore, only a very small amount of a by-product (a carcinogenic epoxide) which is often present in the oxidation reaction of benzene is contained in the oxidation product of toluene. Wu [Catal. Today, Vol. 63 (2000), pp. 419-426] et al. found that platinum catalyst with activated carbon as a support can completely oxidize toluene below 200 ° C, where activated carbon can be flowed in nitrogen. Heat to 400 ° C or 800 ° C and wash with hydrofluoric acid to remove surface impurities or minerals. Luo [Appl. Catal. B: Environ. Vol. 69 (2007) pp. 213-218] et al. prepared a palladium catalyst using CeO2-Y2O3 co-oxide as a support, and the catalyst was washed and coated with water. On honeycomb ceramics, the catalyst calcined at 500 ° C was found to completely oxidize toluene at 210 ° C. The durability of the catalyst in addition to its activity is also an important factor. The researchers will measure the catalyst at 200 to 240. The temperature was repeatedly raised and lowered between °C and 10 °C for 8 times. During this 30 hours, no significant change in the activity of the catalyst was observed, indicating its repeatability and stability. Hosseini [Catalysis Today, Vol. 122 (2007), pp. 391-396] and others used a sedimentation method and an impregnation method to support gold and palladium on a high surface area titanium dioxide support having a porous structure. The activity is 0.5% by weight Pd-1%Au/TiO2>1.5% Pd/TiO2>0.5% Pd/TiO2>1% Au-0.5% Pd/TiO2>1% Au/TiO2>TiO2, the best activity 0.5% Pd-1% Au/TiO2 can completely oxidize toluene at 230 °C. Zheng et al. [Catalysis Communications, Vol. 9 (2008), pp. 990-994] used stainless steel as a support, prepared by anodizing procedures, and calcined at 1000 ° C to obtain the best active catalyst. The complete conversion temperature to p-toluene was 210 °C. Qingbao et al. [Chinese Journal of Catalysis, Vol. 29 (2008), pp. 373-378] uses ZrO2 to easily exchange the tetragonal phase of oxygen atoms and its characteristics of wear resistance, high temperature resistance and corrosion resistance, and it is made with CeO2. The combination of the appropriate ratios showed that the Pd/Ce0.8Zr0.2O2/substrate monolithic catalyst had a calcination temperature of 400 ° C and a reaction temperature of 210 ° C to obtain 97% toluene conversion. Tidahy et al. [Catalysis Today, Vol. 119 (2007), pp. 317-320) supported nanopalladium on Faujasite zeolite at a calcination temperature of 400 ° C and an activity of 0.5 by weight. %Pd/CsFAU>0.5% Pd/NaFAU>0.5% Pd/HFAU, the most active 0.5% Pd/NaFAU can completely oxidize toluene at 220 °C. Giraudon et al. [Applied Catalysis B: Environmental, Vol. 75, pp. 157-166) used a good oxygen transport capacity and redox capacity of 镧-type perovskite to prepare a palladium catalyst with good effect. The Pd/LaFeO3 catalyst can completely oxidize toluene at 220 °C. Li et al. [Reaction Kinetics, Mechanisms and Catalysis, Vol. 103 (2011), pp. 419-429] utilizes cerium oxide and cerium oxide co-oxide as a mixed support and is then coated on a honeycomb structure. On the material, calcined at 400 ° C, it was found that Pd / Ce0.8La0.2O2 / substrate catalyst can completely oxidize toluene at 210 ° C.

The existing domestic patents, most of the palladium catalyst patents are used in hydrogenation and hydrogenation, and there is no organic waste gas oxidation reaction in the air environment, and no reaction is carried out using cerium oxide-manganese oxide as a support; The patents on palladium catalyst applications are listed in Table 1. The foreign patents on palladium catalyst applications are listed in Table 2. From the published patent, there is no method for carrying out organic waste gas removal by using a nanopalladium catalyst supported on a cerium oxide-manganese oxide as disclosed in the present invention.

The invention discloses a method for preparing a palladium catalyst supported on a cerium oxide-manganese oxide mixed support, and a method for reacting organic waste gas with oxygen in air under the catalyst of nano palladium supported by cerium oxide-manganese oxide. To remove organic waste gas. The present invention uses a palladium/yttria-manganese oxide catalyst in an organic waste gas in the air, using a packed bed reactor to remove organic waste gas.

[Embodiment 1]

First, take an appropriate amount of cerium nitrate (Ce(NO ₃ ) ₃ ‧6H ₂ O) and manganese nitrate (Mn(NO ₃ ) ₂ ‧4H ₂ O) in an appropriate amount to remove the water and stir evenly, then add ammonia to precipitate it, and Stirring is continued for 8 to 16 hours, and the precipitate is washed with water, dried at any temperature between 70 and 110 ° C for 4 to 12 hours, and calcined at any temperature between 300 and 600 ° C for 4 to 16 hours. Then, a cerium oxide-manganese oxide support can be obtained.

Take an appropriate amount of yttrium oxide-manganese oxide support to test the pore volume, slowly drop the deionized water into the support and stir it to ensure that the deionized water can be filled in the pores. When the support reaches a slightly wet, deionized water The volume of the volume is the pore volume of the support; after testing the initial moisture content of the catalyst, an appropriate amount of Pd(NO ₃ ) ₂ ‧2H ₂ O is dissolved in the measured amount of water, and the metal salt solution is slowly dropped. Into the cerium oxide-manganese oxide support, the solution can be completely sucked into the pores; dried at any temperature between 70 and 100 ° C for 2 to 10 hours, and calcined at any temperature between 300 and 600 ° C. 4 Pd/CeO ₂ -MnO _x catalyst can be obtained up to 16 hours.

Example 1 Preparation of 0.5 wt. % Pd/CeO ₂ -MnO _x (Ce: Mn atomic ratio = 1:9)

1. Take 3.13 Ce(NO ₃ ) ₃ ‧6H ₂ O, 16.35 g Mn(NO ₃ ) ₂ ‧4H ₂ O dissolved in 400 ml of deionized water and mix well, add 25wt.% by weight at a rate of 10 ml/min 400 ml of ammonia water to cause precipitation and stirring for 12 hours;

2. The solution containing the precipitate is washed with water to a pH of 8 or less, dried at 110 ° C for 12 hours, heated to 500 ° C at a rate of 10 ° C / minute, and calcined at 500 ° C for 6 hours to obtain 6.0 g. CeO ₂ -MnO _x (1:9) support;

3. Test the initial moisture content of CeO ₂ -MnO _x (1:9), then dissolve 0.0256g of Pd(NO ₃ ) ₂ ‧2H ₂ O into the measured amount of water, and slowly drop the metal salt solution into 2 grams. CeO ₂ -MnO _x (Ce: Mn atomic ratio = 1:9) in the carrier, allowing the solution to be completely absorbed into the pores;

4. Dry at 80 ° C for 2 hours, then increase the temperature to 350 ° C at 10 ° C / min, and then calcine at 350 ° C for 8 hours to obtain 0.5 wt.% Pd / CeO2-MnOx (1:9) catalyst. ;

[Embodiment 2]

The catalyst Pd/CeO ₂ -MnO _{x is} placed in a packed reaction bed reactor to carry out a reaction of completely oxidizing toluene in air, and the experiment is carried out in a continuous catalyst packed bed reactor; the flow rate is controlled, and at a fixed temperature, Carry out the reaction.

Example 2

1. The weight percentage of 0.5wt.% Pd/CeO2-MnOx (1:9) catalyst is placed in a U-type catalyst packed reaction bed to carry out the reaction of oxidizing toluene in air to form a continuous catalyst packed bed reaction. Carry out experiments;

2. The control flow rate is 40 ml per minute, the space flow rate is controlled at 10000/hour, and it is introduced into the reactor at room temperature. The inner and outer diameters of the tube are 0.9 cm and 1.3 cm, the length is 21 cm, and the melted quartz is 0.5 cm in the middle. Sand to support the catalyst of the reaction;

3. The weight of the catalyst is 0.2 gram into the U-shaped quartz tube. The temperature of the toluene saturator is controlled at 30 °C. The temperature of the catalyst is raised from room temperature to 250 °C, and the temperature is raised at 4 °C/min. After 5 minutes, when the reaction temperature was reached, the temperature was controlled, and the reaction test was carried out 10 minutes later;

4. The feed flow rate is controlled by the flow controller. The feed steam is taken out with a small amount of air through a conical flask containing the feed toluene, and then the feed concentration is adjusted by another air dilution to pass the U-type catalyst. The reaction bed is filled, and the reacted gas flows through a gas chromatograph and is analyzed by a flame free detector. The reaction results are as follows;

The toluene conversion rate is defined as follows:

Toluene conversion = (imported toluene concentration - outlet toluene concentration) ÷ imported toluene concentration.

From these results, it was confirmed that the catalyst of the present invention can completely remove toluene in the air at 190 ° C or higher.

Claims (2)

A method for producing a palladium catalyst supported on cerium oxide-manganese oxide, the weight percentage of palladium is 0.5-2 wt.%, and the molar ratio of cerium oxide: manganese oxide is 1:9 to 9:1, which is characterized by cerium nitrate and nitric acid. Manganese is dissolved in deionized water and then added with aqueous ammonia solution and stirred for 4-12 hours to prepare a cerium oxide-manganese oxide support, followed by drying at 50-200 ° C, heating to 400-500 ° C, and maintaining calcination at the final temperature 2-10 In an hour, the aqueous palladium nitrate solution is impregnated with cerium oxide-manganese oxide, followed by drying at 50-200 ° C for 2 to 10 hours, and after raising the temperature to 200-400 ° C, and maintaining at the final temperature for 2 to 10 hours. A method for removing organic waste gas in air, which is obtained by a method for producing a palladium catalyst supported on ruthenium oxide-manganese oxide according to the first aspect of the patent application, in air at 50-250 ° C The reaction is carried out at any temperature to completely oxidize the organic exhaust gas in the air.