CN116809111A - A catalyst and catalytic converter for zero emission of N2O in gasoline engines - Google Patents

Abstract

The application discloses a gasoline engine N ₂ O zero-emission catalyst and catalyst, wherein Rh is used as main catalyst and CeO is used as main catalyst ₂ The catalyst is a cocatalyst, and graphene/molecular sieve modified by graphene is used as a coating with a multi-layer structure and honeycomb cordierite ceramic is used as a carrier. The catalyst is formed by catalyst encapsulation design. Through multilayer staggered structure design of graphene/molecular sieve, N is prolonged ₂ Adsorption and diffusion time of O, increase N ₂ The adsorption quantity of O ensures that the catalyst has sufficient ignition time. By modifying the molecular sieve with graphene, enterThe thermal stability and the hydrothermal stability of the molecular sieve are guaranteed in one step, and the working condition requirement of the gasoline engine is met. Thereby realizing N pairs of ₂ O is adsorbed and catalyzed in a shape-selective way to reach N ₂ Zero emission target of O.

Description

A catalyst and catalytic converter for zero emission of N2O in gasoline engines

Technical field

This application relates to the technical field of gasoline engine exhaust gas treatment, and in particular to a catalyst and catalytic converter for zero emission of N ₂ O in gasoline engines.

Background technique

N ₂ O is a colorless, sweet gas that has anesthetic effects. N ₂ O is a trace gas, and its contribution to the greenhouse effect is 21 times that of CH _4. The global warming potential (GWP) of N ₂ O is 310 times that of CO ₂ . Every doubling of the atmospheric concentration of N ₂ O will cause global warming to rise by 0.3°C. N ₂ O is very stable and has a residence time of up to 120 years. Therefore, the damage to the atmospheric environment caused by N ₂ O emissions is very serious.

N ₂ O in the atmosphere mainly comes from agriculture, industry, fossil fuel combustion, biomass burning, wastewater and urban garbage, among which agricultural N ₂ O emissions account for more than 2/3 of global N ₂ O emissions. Global transport emissions account for 3±1% of current estimates of total anthropogenic emissions. Research on greenhouse gas emissions from domestic motor vehicles also shows that light passenger vehicles and gasoline vehicles are the main sources of N ₂ O emissions from motor vehicles.

Since N ₂ O is not highly active, it is difficult to react with most known gases in the atmosphere, making the treatment of N ₂ O very difficult. The activation, activation and splitting of N ₂ O is a research and engineering application. challenging work. At present, N ₂ O in gasoline engine exhaust has not been effectively treated

Contents of the invention

In view of the problem in the prior art that the three-way catalytic converter for automobile gasoline engines cannot achieve zero emission of N ₂ O, the present invention proposes a catalyst and catalytic converter for zero emission of N ₂ O in gasoline engines, which can reduce the N 2 O emission after the three-way catalytic converter of the gasoline engine. Achieve zero emission goals.

The invention provides a catalyst for zero emission of N ₂ O in gasoline engines. The catalyst uses Rh as the main catalyst, CeO ₂ as the cocatalyst, and graphene/molecular sieve modified by graphene as a multi-layered structure coating. , honeycomb cordierite ceramic as carrier.

Preferably, the coating sequence on the cordierite carrier is a multi-level structure of graphene/molecular sieve/graphene, and the channel surface layer is graphene.

Preferably, the coating sequence on the cordierite carrier is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve.

Preferably, the cordierite carrier is divided into two parts, front and rear, along the channel direction. The coating sequence of the first half is a multi-level structure of graphene/molecular sieve/graphene, etc., and the channel surface layer is graphene; the coating of the second half is The sequence is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve.

Preferably, the cordierite carrier is divided into two parts, front and rear, along the channel direction. The coating sequence of the first half is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve; the coating sequence of the second half is sequentially. It is a multi-level structure of graphene/molecular sieve/graphene, etc., and the channel surface layer is graphene.

Further, the Rh catalyst and CeO ₂ cocatalyst are directly coated on the graphene or molecular sieve channel surface.

Preferably, the Rh catalyst and CeO ₂ cocatalyst are also coated on the surface of graphene or molecular sieve inside the structure.

The invention also provides a preparation method for the above catalyst, which includes the following steps:

The method for modifying molecular sieves with graphene is as follows:

1) Using the in-situ hydrothermal synthesis method, the honeycomb cordierite ceramic carrier is placed in the configured molecular sieve precursor solution, and in-situ crystallization is performed, so that the molecular sieve is directly "grown" on the carrier to obtain a molecular sieve coating.

2) Directly add hydrazine hydrate to the graphene oxide aqueous solution, and then reduce it by hydrothermal method to prepare the graphene solution, and obtain a graphene solution that is evenly and stably dispersed in water;

3) Place the honeycomb cordierite ceramic carrier with molecular sieve coating in the graphene solution, and use the ultrasonic impregnation method to highly disperse the graphene into the surface and pores of the molecular sieve to complete the modification of the surface and pores of the molecular sieve to obtain Graphene/molecular sieve coating after graphene modification of molecular sieve.

4) Further, repeat the above steps to obtain a multi-layered coating.

The invention also provides a gasoline engine N ₂ O zero-emission catalytic converter, which is packaged by the above-mentioned catalyst.

Compared with the existing technology, the technical solution of the present invention has the following advantages:

(1) The multi-level staggered structure of graphene/molecular sieve significantly increases the contact area between the catalyst and N2O, which can increase the adsorption amount of _N2O .

(2) The multi-level staggered structure of graphene/molecular sieve significantly increases the internal nanopore structure space of the catalyst, which can increase the molecular diffusion path of N ₂ O in the nanopores and prolong the adsorption and diffusion time of N ₂ O.

(3) The multi-level staggered structure of graphene/molecular sieve can improve the thermal conductivity and thermal diffusion performance of the catalytic converter, quickly increase the internal temperature of the N ₂ O catalytic converter under low-temperature starting conditions of the engine, and allow the catalytic converter to have sufficient ignition time. .

(4) The small pore structure molecular sieve has a crystal structure, which can ensure the thermal stability and structural stability of the molecular sieve. The modification of molecular sieves by graphene can further ensure the thermal and hydrothermal stability of the molecular sieves and meet the working conditions of gasoline engines.

(5) According to the structure and polarity of N ₂ O, graphene can regulate the pore structure and adsorption performance of molecular sieves to achieve shape-selective adsorption and catalysis of N ₂ O and achieve the goal of zero emission of N ₂ O.

Description of the drawings

In order to explain the embodiments of the present application or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic structural diagram of the N ₂ O zero emission catalyst of the gasoline engine in the present invention;

Figure 2 is a schematic structural diagram of different multi-layer coatings in the N ₂ O zero emission catalyst of the gasoline engine of the present invention;

Among them, (a) represents the coating sequence on the cordierite carrier, which is a multi-level structure of graphene/molecular sieve/graphene, etc., and the channel surface layer is graphene; (b) represents the coating sequence on the cordierite carrier. The order is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve; (c) indicates that the cordierite carrier is divided into front and rear parts along the channel direction, and the coating order of the first half is graphene/molecular sieve/ The multi-level structure of graphene, etc., the channel surface layer is graphene; the coating sequence of the second half is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., the channel surface layer is molecular sieve; (d) represents the cordierite carrier It is divided into two parts along the channel direction. The coating order of the first half is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the surface layer of the channel is molecular sieve. The coating order of the second half is graphene/molecular sieve/graphite. It has a multi-level structure such as graphene, and the channel surface layer is graphene.

Figure 3 is a schematic structural diagram of different catalyst coating positions in the N ₂ O zero emission catalyst of the gasoline engine of the present invention;

Among them, (a) indicates that the Rh catalyst and CeO ₂ cocatalyst are directly coated on the surface of graphene or molecular sieve channels; (b) indicates that the Rh catalyst and CeO ₂ cocatalyst are modified according to the multi-level staggered structure of molecular sieve/graphene, respectively. Coated on molecular sieve/graphene surface

Figure 4 is a schematic diagram of the polarity of some molecules in gasoline engine exhaust;

Figure 5 is a schematic diagram of N ₂ O shape-selective adsorption and catalysis by graphene/molecular sieve in the N ₂ O zero emission catalyst of the present invention;

Figure 6 is a schematic structural diagram of the gasoline engine N ₂ O zero emission catalytic converter in the gasoline engine exhaust after-treatment system in the present invention;

Figure 7 is a schematic structural diagram of the N ₂ O catalytic converter of the gasoline engine in the present invention;

Among them, (a) represents the N ₂ O catalytic converter; (b) represents the radial sectional view of the honeycomb structure inside the catalytic converter; (c) represents the sectional view of the partial axial channel in the middle; (d) represents the sectional view of the partial axial channel at the boundary; ( e) represents the local surface structure diagram of the channel;

Figure 8 is a schematic diagram of the physical and chemical adsorption process of N ₂ O in the N ₂ O zero-emission catalyst of a gasoline engine;

Among them, (a) represents physical adsorption, (b) represents chemical adsorption

Detailed ways

In order to make the above objects, features and advantages of the present application more obvious and easy to understand, the specific implementation modes of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described here. Those skilled in the art can make similar improvements without violating the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

A catalyst for zero emission of N ₂ O in gasoline engines, as shown in Figure 1. The catalyst uses Rh as the main catalyst, CeO ₂ as the cocatalyst, and uses graphene/molecular sieve modified by graphene as a multi-level structure. Coating, honeycomb cordierite ceramic as carrier. The multi-layer structure is shown in Figure 2-3.

In a preferred embodiment, as shown in Figure 2(a), the coating sequence on the cordierite carrier is a multi-level structure of graphene/molecular sieve/graphene, and the channel surface layer is graphene.

In a preferred embodiment, as shown in Figure 2(b), the coating sequence on the cordierite carrier is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve.

In a more preferred embodiment, as shown in Figure 2(c), the cordierite carrier is divided into two parts, the front and back parts along the channel direction, and the coating sequence of the first half is multi-layered graphene/molecular sieve/graphene, etc. Structure, the channel surface layer is graphene; the coating sequence of the second half is a multi-level structure of molecular sieve/graphene/molecular sieve, etc., and the channel surface layer is molecular sieve.

In a preferred embodiment, as shown in Figure 2(d), the cordierite carrier is divided into front and rear parts along the channel direction, and the coating sequence of the first half is a multi-level structure of molecular sieve/graphene/molecular sieve, etc. , the channel surface layer is molecular sieve; the coating sequence of the second half is a multi-level structure of graphene/molecular sieve/graphene, etc., and the channel surface layer is graphene.

On the basis of the above structure, a multi-level staggered structure scheme of Rh catalyst, CeO ₂ cocatalyst or similar scheme is proposed. Single-layer coating on the channel surface can be adopted, that is, Rh catalyst and CeO ₂ cocatalyst are directly coated on the graphene or molecular sieve channel surface. As shown in Figure 3(a), the Rh catalyst and CeO ₂ cocatalyst are directly coated on the surface of graphene or molecular sieve channels.

As shown in Figure 3(b), the Rh catalyst and CeO ₂ co-catalyst are coated in multiple layers inside the structure and on the surface of the channel, that is, the Rh catalyst and CeO ₂ co-catalyst are also coated on the graphene or molecular sieve inside the structure. surface. The single-layer coating on the channel surface is similar to the structure of the existing three-way catalytic converter, while the multi-level staggered coating inside the structure and on the channel surface can further improve the oxygen storage and release capacity of the adsorber, which is beneficial to the control of oxygen molecules. The structure of the multi-layer coated Rh main catalyst and CeO ₂ cocatalyst can increase the contact area between the catalyst and N ₂ O and the spatial diffusion area of the structure in the pores, prolong the adsorption time of N ₂ O, and improve the performance of the engine under low temperature starting conditions. N ₂ O catalyst internal temperature.

As shown in Figure 4, among the exhaust components, N ₂ O is a linear polar molecule; CO ₂ is a linear non-polar molecule; the molecular structure of H ₂ O is a V-shaped polar molecule; NH ₃ The spatial structure is a triangular pyramidal polar molecule. According to the structure and polarity of N ₂ O molecules, the pore structure of graphene can be adjusted to adjust the pore structure of the molecular sieve, changing its structure and specific surface area, so that the size and polarity of the pores are suitable for the adsorption of N ₂ O molecules. and diffusion. The modified graphene/molecular sieve has shape-selective adsorption and catalysis of N ₂ O while reducing the influence of H ₂ O and NH ₃ , as shown in Figure 5.

In a more preferred embodiment, the preparation method of the above catalyst includes the following steps:

The method for modifying molecular sieves with graphene is as follows:

1) Using the in-situ hydrothermal synthesis method, the honeycomb cordierite ceramic carrier is placed in the prepared molecular sieve precursor solution, and in-situ crystallization is performed at a certain temperature, so that the molecular sieve can be directly "grown" on the carrier to obtain the molecular sieve. coating.

2) Add hydrazine hydrate directly to the graphene oxide aqueous solution, and then reduce it by hydrothermal method to prepare the graphene solution. A uniform and stably dispersed graphene solution in water is obtained, which avoids the need for surfactants and organic solvents in the conventional preparation of stable graphene aqueous solutions. Addition of solvent or superacid.

3) Place the honeycomb cordierite ceramic carrier with molecular sieve coating in the graphene solution, and use the ultrasonic impregnation method to highly disperse the graphene into the surface and pores of the molecular sieve to complete the modification of the surface and pores of the molecular sieve to obtain Graphene/molecular sieve coating.

4) Further, repeat the above steps to obtain a multi-layered coating.

A catalytic converter for N ₂ O zero emission of a gasoline engine, which is packaged by the above-mentioned catalyst. The catalytic converter is placed after the three-way catalytic converter of the gasoline engine, and its layout in the exhaust after-treatment system of the gasoline engine is shown in Figure 6.

The structural schematic diagram of the N ₂ O catalytic converter of a gasoline engine is shown in Figure 7. In the figure (a) is the N ₂ O catalytic converter; (b) shows the radial cross-sectional view of the honeycomb structure inside the catalytic converter; (c) shows the partial axial direction in the middle. Channel cross-section; (d) represents the boundary partial axial channel cross-section; (e) represents the local surface structure diagram of the channel.

The technical principle is as follows:

(1) Thermal performance

The thermal conductivity λ ₁ and thermal diffusion coefficient a ₁ of graphene are much larger than the thermal conductivity λ ₂ and thermal diffusion coefficient a ₂ of molecular sieve. The specific heat capacity c ₁ of graphene is smaller than the specific heat capacity c ₂ of molecular sieve. After graphene has modified the molecular sieve, the thermal conductivity λ ₃ , thermal diffusion coefficient a ₃ , and specific heat capacity c ₃ of the graphene/molecular sieve material should be between those of graphene and molecular sieve, that is:

λ ₂ <λ ₃ <λ ₁ ; a ₂ <a ₃ <a ₁ ; c ₁ <c ₃ <c ₂

This can improve the thermal conductivity and thermal diffusion performance of the coating structure, improve the thermal conductivity and thermal diffusion performance of the catalytic converter, and quickly increase the internal temperature of the N ₂ O catalytic converter under the same engine low-temperature starting conditions.

(2)Stability

Graphene has a very stable honeycomb lattice structure and super hydrophobicity, and molecular sieve has a silicon-oxygen tetrahedron or aluminum-oxygen tetrahedron structure. After graphene modifies the molecular sieve, the structural stability and hydrophobicity of the graphene/molecular sieve material can be improved. .

(3) Adsorption performance

The specific surface area S ₁ of graphene is much larger than the specific surface area S ₂ of molecular sieve. After the molecular sieve is modified by graphene, the specific surface area S ₃ of the graphene/molecular sieve material should be between graphene and molecular sieve, that is:

S ₂ <S ₃ <S ₁

This can improve the surface and internal adsorption performance of the N ₂ O catalytic converter.

(4) Catalytic decomposition process

The schematic diagram describing the physical and chemical processes of N ₂ O in the N ₂ O catalytic converter of a gasoline engine is shown in Figure 8, including: the diffusion and adsorption process of N ₂ O in the nanoporous material on the surface of the catalyst carrier channel and inside the graphene/molecular sieve structure , the N ₂ O catalyzed chemical reaction process between the coating surface and the nanoporous material inside the graphene/molecular sieve structure.

The N ₂ O catalytic decomposition reaction is:

2N ₂ O → 2N ₂ + O ₂ (1)

The possible reaction processes for the catalytic decomposition of N ₂ O on the catalyst are:

1) N ₂ O is adsorbed on the surface of the precious metal catalyst T* to obtain N ₂ O*

2) N ₂ O* decomposes into N ₂ (g) and adsorbed oxygen species O*

N ₂ O*→N ₂ +O* (3)

3) Through the Langmuir-Hinshelwood (L-H) mechanism, the adsorbed oxygen species recombines and regenerates vacancies

4) N ₂ O combines with the adsorbed oxygen species O* to obtain N ₂ (g), O ₂ (g) and regenerated precious metal catalyst T*

N ₂ O+O*→N ₂ +O ₂ +T* (5)

5) N ₂ O is adsorbed on the surface of the precious metal catalyst T* and reacts to obtain N ₂ (g) and adsorbed oxygen species O*

N ₂ O+T*→N ₂ +O* (6)

Energy change ΔE _ads during adsorption process:

ΔE _ads =E _{catalyst+adsorbate} -(E _catalyst +E _adsorbate ) (7)

In the formula, E _{catalyst+adsorbate} is the energy of the adsorbate adsorbed by the catalyst, E _catalyst is the energy of the catalyst, and E _adsorbate is the energy of the adsorbate.

Activation energy ΔE of the reaction process:

ΔE＝E _TS -E _IS (8)

In the formula, E _IS is the total energy of the initial state, and E _TS is the total energy of the transition state.

Reaction rate constant:

In the formula, k _B is Boltzmann's constant, h is Planck's constant, R is the universal gas constant, T is the temperature, and ΔE is the reaction activation energy.

The gasoline engine N ₂ O zero emission catalyst and catalytic converter provided by the present invention have the following advantages:

(1) The multi-level staggered structure of graphene/molecular sieve modified by graphene changes the pore structure of the coating, increases the specific surface area of the material, and is beneficial to increasing the adsorption capacity of N ₂ O.

(2) According to the size and polarity of N ₂ O molecules, the structural controllability of graphene molecules is used to change the pore structure and adsorption polarity of molecular sieves, so that the modified graphene/molecular sieve pore structure changes the effect of N ₂ O has shape-selective catalysis.

(3) The multi-level staggered structure and the increased specific surface area of the material can change the diffusion performance of N ₂ O in the pore structure and extend the diffusion time, which will help the catalyst have enough time to increase the temperature and reach the temperature for N ₂ O catalytic decomposition.

(4) In the multi-level staggered structure of graphene/molecular sieve, graphene has very good thermal conductivity and thermal diffusivity, and a low specific heat capacity, which is beneficial to the thermal diffusion and temperature increase inside the catalyst, and shortens the ignition time of the catalyst.

(5) The multi-level staggered structure of Rh catalyst and CeO ₂ cocatalyst increases the internal active sites of the catalyst, which can improve the oxygen storage and oxygen release control capabilities inside the catalyst and the catalytic performance of N ₂ O.

The above-described embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims (8)

1. Petrol engine N ₂ The O zero emission catalyst is characterized in that the catalyst takes Rh as a main catalyst and CeO ₂ The catalyst is a cocatalyst, and graphene/molecular sieve modified by graphene is used as a coating with a multi-layer structure and honeycomb cordierite ceramic is used as a carrier.

2. The catalyst of claim 1 wherein the coating order on the cordierite support is a multi-layered structure of graphene/molecular sieve/graphene, and the channel surface layer is graphene.

3. The catalyst of claim 1 wherein the order of coating on the cordierite support is a multi-layered structure of molecular sieves/graphene/molecular sieves, etc., and the surface layer of channels is a molecular sieve.

4. The catalyst according to claim 1, wherein the cordierite carrier is divided into a front part and a rear part along the channel direction, the coating sequence of the front part is a multi-layer structure of graphene/molecular sieve/graphene and the like, and the surface layer of the channel is graphene; the coating sequence of the latter half part is a multi-layer structure of molecular sieve/graphene/molecular sieve, etc., and the surface layer of the channel is the molecular sieve.

5. The catalyst according to claim 1, wherein the cordierite carrier is divided into a front part and a rear part along the channel direction, the coating sequence of the front part is a multi-layer structure of molecular sieve/graphene/molecular sieve and the like, and the surface layer of the channel is the molecular sieve; the coating sequence of the latter half part is a multi-layer structure of graphene/molecular sieve/graphene and the like, and the surface layer of the channel is graphene.

6. The catalyst according to any one of claims 1 to 5, characterized in that the Rh catalyst, ceO ₂ The cocatalyst is directly coated on the surface of the graphene or molecular sieve channel.

7. The catalyst according to claim 6, wherein the Rh catalyst, ceO ₂ The promoter is also coated on the graphene or molecular sieve surface inside the structure.

8. Petrol engine N ₂ The catalyst for zero emission of O, which is characterized by being encapsulated by the catalyst as claimed in any one of claims 1 to 7.