RU2771045C1 - Sorption-catalytic material for neutralization of emissions of vocal organic compounds - Google Patents

Abstract

FIELD: air purification.

SUBSTANCE: invention relates to purification of air from volatile organic compounds, in particular, purification of indoor air, waste gases of chemical and other enterprises, exhaust gases of internal combustion engines, including during cold start of the engine. The sorption-catalytic material used in the reaction of deep oxidation of toluene to CO₂ and water is mesoporous silicon oxide with the SBA-15 structure, with silver or silver and cerium oxide nanoparticles stabilized on its surface. Silver nanoparticles or silver and cerium oxide nanoparticles have a size of less than 8 nm. The material contains 10 wt.% silver and has a specific surface S_sp 570 m²/g or the material contains 10 wt.% silver and 20 wt.% cerium oxide and has a specific surface area S_sp of 470 m²/g.

EFFECT: material has a high sorption capacity with respect to toluene and catalytic activity in the oxidation of toluene.

1 cl, 1 dwg, 1 tbl, 3 ex

Description

SUBSTANCE: invention relates to purification of air from volatile organic compounds, in particular, purification of indoor air, waste gases of chemical and other enterprises, exhaust gases of internal combustion engines, including during cold start of the engine.

Air pollution with volatile organic compounds, which include methanol, formaldehyde, toluene, benzene and other compounds, causes great harm to the environment and poses a great danger to human health. The main sources of volatile organic compounds are various industrial processes, transportation, tobacco smoke, solvents, insulation materials, furniture, etc. A significant amount of volatile organic compounds is released when starting internal combustion engines, since at this moment the catalyst intended for their combustion is at ambient temperature and does not provide the necessary conversion of unburned fuel fragments to CO ₂ and water.

The main methods for neutralizing volatile organic compounds are sorption, plasma-chemical, catalytic, photocatalytic, biological and other methods.

Biological methods for neutralizing volatile organic compounds are based on the use of special strains of bacteria that can process pollutant molecules (Malhautier L. et al. Kinetic characterization of toluene biodegradation by Rhodococcus erythropolis: Towards a rationale for microflora enhancement in bioreactors dedicated to air treatment //Chemical Engineering Journal 2014. V. 247. P. 199-204.). The main disadvantages of biological methods are the limited scope of their application due to structural difficulties, the limited stability of bacteria, and the relatively low rate of pollutant processing.

The disadvantages of plasma-chemical methods are the relatively high costs required to obtain plasma, as well as the possible formation of side compounds.

Photocatalytic methods for the neutralization of volatile organic compounds are known (Vikrant K., Park C.M., Kim K.-H., Kumar S., Jeon E.-C. Recent advancements in photocatalyst-based platforms for the destruction of gaseous benzene: Performance evaluation of different modes of photocatalytic operations and against adsorption techniques // Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2019. V. 41, 100316). The disadvantages of photocatalytic neutralization methods are the complexity of organizing a photocatalytic reactor that provides effective contact of pollutants with the surface of a heterogeneous photocatalyst while simultaneously irradiating this surface with a lamp.

The most widespread are adsorption and catalytic methods of combating volatile organic compounds.

An adsorbent is known for removing hydrocarbons from vehicle exhaust gases, which is an organometallic frame structure of the MOF-5 type, containing terephthalic acid or biphenyldicarboxylic acid residues as a linker (RF patent 2406558, B01D 53/04, B01J 23/00, F01N 3/00, publ. 20.12.2010) and characterized by a high sorption capacity for toluene 0.9 g/g. However, the main disadvantages of organometallic frameworks are their high cost, complexity of production and relatively low thermal stability (200-350°C), which significantly limits the possibility of their use, especially in the vehicle exhaust gas aftertreatment system, the temperature in which can significantly exceed 350°C. .

Known sorbent for trapping volatile organic compounds, in particular toluene, based on hydrophobic silicon oxide with the structure SBA-15 (patent CN 108101066, B01J 20/22, B01J 20/28, C01B33/12, publ. 06/01/2018). The essence of the invention consists in obtaining silicon oxide with the SBA-15 structure, additionally containing hydrophobic functional organic groups on its surface. However, the toluene sorption capacity of such materials is not very high and reaches 105 mg/g.

Catalytic approaches to the neutralization of volatile organic compounds based on their deep oxidation to CO ₂ and water at temperatures of 100-500°C, depending on the type and concentration of volatile organic compounds, are very effective. The most effective are catalysts based on noble metals, in particular Pt, Pd, Au. Known catalyst based on the composition of Pt-MnO _x deposited on mesoporous cerium oxide, providing 90% conversion of toluene at a concentration of 1000 ppm at a temperature of 171°C (patent CN 110639519, B01J 23/656, C01B 32/50, C01B 5/00, published on 01/03/2020). Known catalyst based on Au-Cu ₂ O-MnO ₂ (patent CN 110314685, B01D 53/72, B01D 53/86, B01J 23/68, B01J 35/02, publ. 10/11/2019), on which complete conversion toluene is observed at 230°C. However, in addition to the high cost of Pt, Pd, and Au metals, a disadvantage of the catalytic approach to neutralize volatile organic compounds is the need for constant heating of the catalyst bed to maintain a temperature of 170-350°C, sufficient for the conversion of pollutants. In this connection, catalytic approaches are quite energy-consuming, and also do not allow solving the problem of the emission of volatile organic compounds at room or low temperature, for example, when starting a car.

The solution to this problem can be a combined sorption-catalytic approach, in which a functional porous material is simultaneously a sorbent for a volatile organic compound at ambient temperature and a catalyst for its oxidation when the temperature rises above 100-150°C.

The result is achieved by using highly porous silicon oxide with the SBA-15 structure as the primary carrier, which has a high sorption capacity with respect to volatile organic compounds due to high values of the specific surface area (more than 600 m ² /g) and pore volume (more than 0 .8 cm ³ /g), as well as the introduction of active components into its structure, not from among the expensive Pt, Pd, Au, but providing strong adsorption of volatile organic compounds and their subsequent oxidation to CO ₂ and water.

The closest solution is a silver-containing bimetallic catalyst based on SBA-15 (CN patent 101992105, B01D 53/72, B01D 53/86, B01J 23/68, B01J 23/89, B01J 37/02, published on 03/30/2011) . The catalyst based on silver and copper supported on SBA-15 provides 99% conversion of toluene at a concentration of 400-1200 ppm at 290-310°C. The sorption characteristics of the material with respect to toluene are not indicated. The specific surface area of the material is 449.5 m ² /g.

The objective of the present invention is to obtain a material that has a high sorption capacity for volatile organic compounds, including toluene, at ambient temperature, and also has catalytic activity in the reaction of deep oxidation of toluene to CO2 and water, which will make it possible to use such a material for trapping toluene vapor with their subsequent oxidation on the surface of the material during heating.

In the present invention, the result, expressed in the presence of both sorption and catalytic characteristics of the material, is achieved by using mesoporous silicon oxide with the SBA-15 structure as a support, synthesized by the classical template method using the Pluronic P125 triblock copolymer as a template. The highly porous carrier SBA-15 is characterized by high specific surface area (Table 1) and pore volume, which provides a high sorption capacity for volatile organic compounds, in particular toluene. Silver and cerium oxide are introduced into the structure of the SBA-15 support by impregnation according to moisture capacity, which provide a more strongly bound state of toluene during its adsorption and subsequent catalytic oxidation when heated above 150°C. A feature of the materials is also that silver and cerium oxide are stabilized in the form of nanoparticles with a size of predominantly less than 5 nm.

Examples illustrating the invention:

Example 1

Sorption-catalytic material, which is mesoporous silicon oxide SBA-15, with cerium oxide nanoparticles less than 8 nm in size stabilized in its structure in an amount of 20% wt, and having a high sorption capacity for toluene and catalytic activity in the reaction of deep oxidation of toluene to CO2 and water.

Example 2. Sorption-catalytic material according to claim 1, characterized in that it contains not cerium oxide nanoparticles, but silver nanoparticles in an amount of 10% wt., having a size of less than 8 nm.

Example 3. Sorption-catalytic material according to claim 1, characterized in that it contains both cerium oxide nanoparticles in an amount of 20% wt., and silver nanoparticles in an amount of 10% wt., having a size of less than 8 nm.

Table 1 presents the sorption and catalytic properties of the examples given, the starting material SBA-15 used to obtain sorption-catalytic materials, as well as the prototype sample of the bimetallic Ag-Cu/SBA-15 catalyst.

Table 1

Sample Compound S _ud ,
m ² /g V _then , cm ³ /g Toluene capacity, g/g Т of the beginning of toluene oxidation, °С Т _98% oxidation of toluene, °С SBA-15 SBA-15 (SiO ₂ ) 759 1.087 0.82 - - Example 1 CeO ₂ , SBA-15 554 0.692 0.61 230 490 Example 2 Ag, SBA-15 570 0.844 0.62 215 270 Example 3 Ag, CeO ₂ , SBA-15 470 0.604 0.49 140 233 Prototype Ag, Cu, SBA-15 449.5 0.6784 not specified ~ 200 290

Figure 1 shows TEM and STEM images for the catalyst according to claim 3 and the corresponding particle size distribution, constructed from the given STEM image. As can be seen from the particle size distribution, the particle size of silver and cerium oxide is predominantly 1-4 nm, the average particle size is 2.84 nm.

It can be seen from the presented data that the SBA-15 material itself has a high sorption capacity for toluene, but does not show catalytic activity in its oxidation.

Material SeO ₂ /SBA-15 (example 1) has a sorption capacity for toluene of 0.61 g/g, but is not characterized by high activity in the oxidation of toluene.

Sorption-catalytic materials according to examples 2 and 3 are characterized by high sorption capacity for toluene, and high catalytic activity in the oxidation of toluene. When the concentration of toluene in the mixture of 2000 ppm 98% conversion is achieved at 270 and 233°C, which is superior to the catalytic activity of the prototype.

The higher activity of the sorption-catalytic materials according to examples 2 and 3 compared with the prototype is determined by the higher values of the specific surface area and the stabilization of silver and cerium oxide in the form of nanoparticles with a size of predominantly less than 5 nm.

Claims (1)

Sorption-catalytic material used in the reaction of deep oxidation of toluene to CO ₂ and water, which is a mesoporous silicon oxide with the SBA-15 structure, with silver or silver and cerium oxide nanoparticles stabilized on its surface, characterized in that silver nanoparticles or silver nanoparticles and cerium oxide have a size of less than 8 nm, while the material contains 10% wt. silver and has a specific surface area S _sp 570 m ² /g or the material contains 10% wt. silver and 20% wt. cerium oxide and has a specific surface area S _sp 470 m ² /g.

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