Method for evaluating hydrothermal aging performance of selective catalytic reduction reactor in temperature sub-zone

Abstract

The application discloses a kind of selective catalytic reduction reactor hydrothermal ageing performance temperature domain evaluation method, the inside of the reactor is equipped with multiple SCR single channel, the channel in the square cylinder structure surrounded by catalytic coating is main channel;First, establish SCR single channel mathematical model, and given limit condition, form closed equation group, then based on the model expansion hydrothermal ageing parameter is carried out temperature domain evaluation to the reactor hydrothermal ageing performance.The application can obtain the nitrogen oxide conversion rate of reactor under different hydrothermal ageing degree, for theoretical model, the cost of reactor evaluation is low, and efficiency is high.By defining relative Brønsted acid site, copper site and physical adsorption site concentration, the quantitative characterization of the influence of mild hydrothermal ageing on catalyst active site distribution is realized, and the severe hydrothermal ageing performance of the reactor is evaluated by defining the standard hydrothermal ageing catalytic active site total concentration, to provide accurate control index for anti-aging catalyst design.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diesel engine exhaust treatment, and particularly relates to a method for evaluating the hydrothermal aging performance of a selective catalytic reduction reactor in different temperature zones. BACKGROUND

[0002] Heavy commercial vehicles have large load, long operation time, high stability operation quality requirement, and very poor working conditions in some cases. New energy heavy commercial vehicles are difficult to meet the needs of commercial transportation market in a short time. Diesel engines have become the main power source in the commercial transportation field due to their high fuel economy, low carbon dioxide emissions and strong torque output. For long-distance transportation and heavy-load vehicles, diesel engines can significantly reduce operating costs while ensuring power and reducing carbon emissions, meeting the current dual needs of environmental protection and economy. These advantages make diesel engines dominate the commercial vehicle market, especially playing an important role in industries such as logistics, freight transportation and public transportation. However, although the proportion of heavy commercial vehicles such as heavy trucks and large buses is not high, the proportion of nitrogen oxide (NO X ) emissions in the transportation field is high. Therefore, heavy commercial vehicles have become the focus of pollution reduction and carbon reduction in the transportation field.

[0003] At present, selective catalytic reduction (SCR) technology based on copper-based molecular sieve catalyst is widely recognized as one of the most effective technologies for reducing nitrogen oxide (NO x ) emissions in diesel engine exhaust.

[0004] Among them, Cu-SSZ-13 molecular sieve has unique CHA topological structure, high specific surface area and regular channels, and exhibits excellent NH3-SCR activity, N2 selectivity and durability, becoming the current mainstream commercial catalyst. Durability is a main index for evaluating the performance of a catalyst. With the increase of driving mileage of heavy commercial vehicles powered by diesel engines, the performance of the molecular sieve catalyst of the selective catalytic reduction reactor gradually deteriorates, resulting in reduced reaction activity and decreased conversion efficiency. At present, the NO x emissions in the exhaust of heavy commercial vehicles powered by diesel engines can be reduced by more than 90% through the SCR technology. Due to the increasingly stringent emission regulations, it is necessary to ensure that the SCR catalyst has stable high conversion efficiency in long-term operation, and higher requirements are put forward for the durability of the catalyst. Hydrothermal aging mechanism and anti-aging strategy are the key to the development of high-efficiency and durable SCR catalysts.

[0005] We need to seek a low-cost, reliable method to evaluate the hydrothermal stability of SCR catalysts under different hydrothermal aging temperature ranges, in order to know the effect of SCR catalysts on the treatment of diesel engine exhaust during use. SUMMARY

[0006] In view of the above problems existing in the prior art, the purpose of the present application is to provide a hydrothermal aging performance evaluation method for a selective catalytic reduction reactor, an SCR single channel mathematical model is established, and the nitrogen oxide conversion rate can be obtained through the model, the mathematical model is a theoretical model, and the reactor evaluation cost is low and efficient. By defining the relative Brønsted acid site, copper site and physical adsorption site concentration, the quantitative characterization of the influence of mild hydrothermal aging on the active site distribution of the catalyst is realized, and accurate control indicators are provided for the design of the anti-aging catalyst. The total concentration of the standard hydrothermal aging catalytic active site is used to quantify the degree of severe hydrothermal aging, and a direct correlation model between the aging degree and the NO x conversion rate is established. Through the mapping relationship between the total concentration of the core parameter standard hydrothermal aging catalytic active site and the NO x conversion rate, a rapid aging evaluation standard is established.

[0007] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0008] The hydrothermal aging performance evaluation method for a selective catalytic reduction reactor, the reactor is provided with a plurality of SCR single channels inside, the SCR single channel is a square cylindrical structure, the side wall of the square cylindrical structure is a catalytic coating formed by a catalyst, the channel in the square cylindrical structure surrounded by the catalytic coating is a main channel, there are many pores in the catalytic coating, and ammonia molecules are adsorbed on the active sites of the catalyst and selective catalytic reduction reaction is carried out;

[0009] First, an SCR single channel mathematical model is established, and then the hydrothermal aging performance of the reactor is evaluated based on the model to extend the hydrothermal aging parameters, and the establishment method of the mathematical model includes the following steps:

[0010] Step S1: establishing an SCR single channel mathematical model, the equation set corresponding to the model includes a component balance equation of gas phase matter in the main channel, a momentum balance equation of gas phase matter in the main channel, an enthalpy balance equation of gas phase matter in the main channel, a gas phase component balance equation in the catalytic coating, a gas phase enthalpy balance equation in the catalytic coating, an NH3 coverage balance equation in the catalytic coating, a component balance equation of the gas phase-coating interface, and an enthalpy balance equation of the gas phase-coating interface;

[0011] Step S2: Given the initial and boundary conditions of the SCR single-channel mathematical model, and based on the characteristics of the SCR single channel, limit the values ​​or expressions of some unknown parameters in the equation set in step S1, substitute the limited parameter values ​​or expressions into each equation in step S1 to obtain the closed equation set corresponding to the SCR single-channel mathematical model.

[0012] When evaluating the hydrothermal aging performance of the reactor by temperature range, it is assessed from two states: mild hydrothermal aging and severe hydrothermal aging. The hydrothermal aging temperature is 550°C to 750°C, and the hydrothermal aging temperature is above 750°C. During mild hydrothermal aging, the aging performance of the reactor is evaluated by the concentration of Brønsted acid sites, copper sites, and physical adsorption sites. During severe hydrothermal aging, the aging performance of the reactor is evaluated by the standardized total concentration of hydrothermal aging catalytic active sites.

[0013] The relative concentration of Brønsted acid sites was calculated. With hydrothermal aging time t a and aging temperature T a The relationship, in which:

[0014] ;

[0015] ;

[0016] ;

[0017] For the standardized concentration of Brønsted acid sites, This represents the concentration of Brønsted acid sites. The concentration of Brønsted acid sites in the catalyst before hydrothermal aging, k a The pre-exponential factor for the Arrhenius kinetics of mild hydrothermal aging is given, where Ea is the activation energy, R is the ideal gas constant, and c is a constant. It is the total concentration of catalytic active sites in hydrothermal aging.

[0018] The relative copper site concentration was calculated. With hydrothermal aging time t a and aging temperature T a The relationship, in which:

[0019] ;

[0020] ;

[0021] It is the concentration of copper sites. is the copper site concentration at zero Brønsted acid site concentration, for a specific catalyst, is constant, a is the coefficient of the linear function of copper site concentration and Brønsted acid site concentration.

[0022] The relative physical adsorption site concentration is calculated as as a function of hydrothermal aging time t a and aging temperature T a , where:

[0023] ;

[0024] ;

[0025] ;

[0026] is the physical adsorption site concentration.

[0027] The global or local performance evaluation method for severe hydrothermal aging is to calculate the normalized total hydrothermally aged catalytic active site concentration to obtain the NO X conversion or the NO X concentration distribution in the catalytic coating at different temperatures and , where

[0028] ;

[0029] is the total catalytic active site concentration in the unhydrothermally aged state.

[0030] In step S2, the defined unknown parameters include: the mass transfer coefficient of any component on the surface of the catalytic coating, the diffusion coefficient of any component in the main channel and in the catalytic coating respectively, the specific surface area of the catalyst in the catalytic coating, the reaction rate expression of each chemical reaction involved in the SCR single channel, the total hydrothermally aged catalytic active site concentration in the catalytic coating.

[0031] The component balance equation of the gas phase in the main channel is:

[0032] ;

[0033] where t represents time; z represents the axial direction; p represents the exhaust gas density, i.e. the gas density in the main channel; v represents the exhaust gas velocity, i.e. the gas velocity in the main channel; y i represents the mass fraction of component i in the main channel; D i represents the diffusion coefficient of component i in the main channel;

[0034] The momentum balance equation for the gas phase in the main channel is:

[0035] ;

[0036] where μ represents the dynamic viscosity; p represents the pressure;

[0037] The enthalpy balance equation for the gas phase in the main channel is:

[0038]

[0039] where c p represents the specific heat capacity of the gas in the main channel; λ g represents the thermal conductivity of the gas in the main channel; T g represents the temperature of the gas in the main channel;

[0040] The gas phase component balance equation in the catalytic coating is:

[0041]

[0042] where, p w is the density of the gas in the catalytic coating; x represents the radial direction; y w,i is the mass fraction of component i in the catalytic coating; D w,i is the diffusion coefficient of component i in the catalytic coating; a c is the specific surface area of the catalyst in the catalytic coating; γ i,j is the stoichiometric ratio of component i in chemical reaction j; M i is the molar mass of component i; T w is the temperature of the gas in the catalytic coating; r j (T w ) is the reaction rate of chemical reaction j at the temperature of the gas in the coating T w ;

[0043] The gas phase enthalpy balance equation in the catalytic coating is:

[0044] ;

[0045] where λ w is the thermal conductivity of the gas in the catalytic coating; is the standard enthalpy of formation of chemical reaction j;

[0046] The NH3 coverage balance equation in the catalytic coating is:

[0047] ;

[0048] where θNH3 coverage of adsorbed NH3on the catalytic coating reaction surface; γ NH3,j stoichiometric ratio of NH3in chemical reaction j;

[0049] The component balance equation of the gas-coating interface is:

[0050] ;

[0051] wherein, k m,i mass transfer coefficient of component i on the coating surface;

[0052] The enthalpy balance equation of the gas-coating interface is:

[0053] ;

[0054] wherein, d h the hydraulic diameter of the main channel, k h the heat transfer coefficient of the gas-coating interface.

[0055] The initial conditions of the SCR single-channel mathematical model are:

[0056] , , ;

[0057] The boundary conditions are:

[0058] ;

[0059] ;

[0060] ;

[0061] ;

[0062] wherein, T in T0represents the temperature at the inlet of the reactor, T 0is the initial temperature, p atm P0is the atmospheric pressure under standard conditions, v in V0is the gas flow rate at the inlet of the reactor, v 0is the initial gas flow rate, p out Pis the pressure at the outlet of the reactor, L is the length of the main channel, which is the axial length; δw for the catalytic coating thickness; for the coverage of the initially adsorbed NH3 on the reaction surface of the catalytic coating.

[0063] The nitrogen oxides in the exhaust gas of a diesel engine include nitrogen monoxide and nitrogen dioxide, and the conversion rate of the nitrogen oxides is :

[0064] ;

[0065] wherein, and are the NO X concentrations at the inlet and outlet of the reactor, respectively.

[0066] The beneficial effects of the present application are:

[0067] (1) An SCR single-channel mathematical model is established, and the conversion rate of nitrogen oxides can be obtained through the model, so that the emission reduction performance of the reactor can be evaluated or assessed.

[0068] (2) The SCR single-channel mathematical model takes into account the influence of the degree of hydrothermal aging of the catalyst, and the evaluation of the emission reduction performance of the reactor is more accurate.

[0069] (3) The theoretical model established can be used to capture the mechanism of hydrothermal aging and its corresponding influence on the performance of the catalyst, and can more accurately describe the influence of aging temperature and aging time on the performance of the SCR during the hydrothermal aging process of the copper-based molecular sieve catalyst.

[0070] (4) The mathematical model is a theoretical model, and the evaluation of the reactor is low in cost and high in efficiency.

[0071] (5) By defining the relative concentrations of Brønsted acid sites, copper sites and physical adsorption sites, the quantitative characterization of the influence of mild hydrothermal aging on the distribution of active sites of the catalyst is realized, and accurate control indicators are provided for the design of anti-aging catalysts.

[0072] (6) The degree of severe hydrothermal aging is quantified by using the standardized total concentration of hydrothermal aging catalytic active sites, and a direct correlation model between the degree of aging and the NO x conversion rate is established. Through the mapping relationship between the total concentration of hydrothermal aging catalytic active sites of the core parameter and the NO x conversion rate, a rapid aging evaluation standard is established.

[0073] (7) The model established can simulate the axial / radial concentration field distribution, accurately locate the "dead zone" of the unreacted NO x in the aged catalyst, and guide the optimization of the catalyst structure.

[0074] (8) Couple the NH3 coverage equation with the active site concentration parameter to realize dynamic early warning of ammonia escape risk of aging catalyst. Attached Figure Description

[0075] Figure 1 This is a schematic diagram of the SCR single-channel model of the present invention.

[0076] Figure 2 It represents the relative Brønsted acid site concentration and the relationship between hydrothermal aging time and temperature.

[0077] Figure 3 It represents the relationship between relative copper site concentration and hydrothermal aging time and temperature.

[0078] Figure 4 It represents the relationship between the relative concentration of physical adsorption sites and the hydrothermal aging time and temperature.

[0079] Figure 5 NO at different temperatures and aging levels X Conversion rate.

[0080] Figure 6 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 1.0 and a temperature of 100℃.

[0081] Figure 7 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 1.0 and a temperature of 300℃.

[0082] Figure 8 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 1.0 and a temperature of 350℃.

[0083] Figure 9 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 1.0 and a temperature of 400℃.

[0084] Figure 10 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 1.0 and a temperature of 500℃.

[0085] Figure 11 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 0.8 and a temperature of 300℃.

[0086] Figure 12 It is Ω Total_norm The NO concentration distribution of the catalytic coating at a value of 0.8 and a temperature of 350℃.

[0087] Figure 13 It is Ω Total_normNO concentration profile of the catalytic coating for 0.8 and temperature of 400 °C.

[0088] Figure 14 Ω Total_norm NO concentration profile of the catalytic coating for 0.6 and temperature of 300 °C.

[0089] Figure 15 Ω Total_norm NO concentration profile of the catalytic coating for 0.6 and temperature of 350 °C.

[0090] Figure 16 Ω Total_norm NO concentration profile of the catalytic coating for 0.6 and temperature of 400 °C. DETAILED DESCRIPTION

[0091] The specific embodiments of the present application will be described in detail below with reference to the attached drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory in nature and are not intended to limit the application.

[0092] For the purposes of this description, spatially relative terms such as "beneath", "below", "lower", "above", "upper" and the like can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0093] A method for evaluating the hydrothermal aging performance of a selective catalytic reduction reactor in different temperature zones, the reactor can be regarded as having a plurality of SCR single channels inside. Diesel engine exhaust enters the reactor, and the exhaust as a reactant passes through the SCR single channels to achieve catalytic reduction, and the generated products are discharged from the reactor.

[0094] First, a mathematical model of the SCR single channel is established, and then the model is expanded based on the hydrothermal aging parameters to evaluate the hydrothermal aging performance of the reactor in different temperature zones.

[0095] The schematic diagram of the SCR single channel model is as follows: Figure 1As shown, the SCR single channel is a square cylinder structure, the side wall of the square cylinder structure is a catalytic coating formed by a catalyst, the channel in the square cylinder structure surrounded by the catalytic coating is a main channel, there are many pores in the catalytic coating, and ammonia molecules are adsorbed on active sites of the catalyst. In other words, the SCR single channel includes a main channel and a catalytic coating surrounding the main channel. Figure 1 X and Z respectively represent the radial direction and the axial direction of the main channel. The mass transfer process of reactants and products in the main channel and the interior of the catalytic coating is divided into two types: intraphase mass transfer and interphase mass transfer. There are a large amount of nitrogen oxides (NO X ) and oxygen (O2) in the main channel, and these components enter the catalytic coating, and this mass transfer process is interphase mass transfer. The generated products include water and nitrogen, and these harmless products are first generated in the interior of the catalytic coating and are transported through the porous structure of the coating. The above products diffuse from the active sites in the coating to the outside through the pores of the catalytic coating, and this mass transfer process is intraphase mass transfer. The pore structure of the coating determines the speed and efficiency of product transfer, ensuring that the products can quickly leave the reaction sites and be transported to the surface of the coating. When H2O and N2 pass through the catalytic coating by intraphase mass transfer and reach the surface, they enter the interface between the gas phase and the solid phase, i.e., the gas phase channel in the reactor. In this process, the products enter the macroscopic channel from the microscopic pores of the coating and enter the gas phase from the solid coating by interphase mass transfer mechanism. The whole process involves complex multiple mass transfer and reaction mechanisms, including axial convection and diffusion in the gas phase, mass transfer at the gas-solid interface, and radial diffusion and catalytic reaction in the interior of the catalytic coating. Each process interacts to ensure that the reactants enter the catalytic coating from the gas phase and effectively complete the chemical conversion in the coating to generate the target products.

[0096] The SCR reactor has the following structural characteristics: small size main channels in parallel, large length-to-width ratio of the main channel, negligible heat loss, and uniform radial flow distribution. It can be reasonably assumed that all SCR single channels exhibit consistent flow and reaction behavior in the reactor. This assumption simplifies the analysis of the performance of the reactor and provides consistent expectations for the overall system behavior. The specific assumptions include the following:

[0097] A1) In the model, the axial diffusion effect in the main channel and in the interior of the catalytic coating is ignored. This assumption simplifies the mathematical description of gas transport and reaction processes, because axial diffusion usually contributes less to the overall mass transfer in actual reactors. By ignoring this factor, more focus can be placed on the analysis of dominant processes such as convection and radial diffusion, thereby reducing computational complexity.

[0098] A2) The model assumes that the gas flow in the main channel is in a laminar state, meaning that there is no significant turbulent effect of the fluid in the main channel. The laminar assumption is helpful to simplify the fluid mechanics analysis and to provide more accurate mass transfer and reaction calculation results, based on the geometry of the main channel and the inlet conditions.

[0099] A3) In the model, the gas is uniformly distributed at the SCR single channel inlet, i.e. the gas flow rate, velocity, temperature and concentration at each main channel inlet are the same.

[0100] A4) The model assumes that the catalyst active material and coating are uniformly distributed in all single channels, and the porous medium of the coating is also uniform and isotropic.

[0101] A5) The model divides the catalyst coating area into high-permeability and low-permeability areas. In the high-permeability area, the gas mass transfer process is dominated by convection, i.e. the gas can quickly pass through the catalyst pores and enter the reaction area; while in the low-permeability area, the mass transfer process is dominated by diffusion, and the gas molecules slowly move in smaller pores through the diffusion mechanism. The mass transfer in the copper-based molecular sieve catalyst coating does not consider convective mass transfer.

[0102] A6) Nuclear magnetic resonance experiments show that there is no evidence of dealumination of the copper-based molecular sieve catalyst at a mild aging temperature, indicating that the performance degradation of the copper-based molecular sieve catalyst at a mild aging temperature can be assumed to be the reduction of its active sites, so the influence of mild hydrothermal aging can be reflected by the change of the concentration of the molecular sieve active sites.

[0103] Based on the above six assumptions, the modeling method of the SCR single channel mathematical model includes the following steps:

[0104] Step S1: Establishing the SCR single channel mathematical model, the equation set corresponding to the model includes the component balance equation of the gas phase material in the main channel, the momentum balance equation of the gas phase material in the main channel, the enthalpy balance equation of the gas phase material in the main channel, the gas phase component balance equation in the catalyst coating, the gas phase enthalpy balance equation in the catalyst coating, the NH3 coverage balance equation in the catalyst coating, the component balance equation of the gas phase-coating interface, and the enthalpy balance equation of the gas phase-coating interface.

[0105] In this embodiment, each equation of the equation set is as follows:

[0106] 1) Component balance equation of gas phase material in main channel

[0107] (1)

[0108] Wherein, t represents time; z represents the axial direction; p represents the exhaust gas density, i.e. the gas density in the main channel; vwhere, u represents the exhaust velocity, i.e. the gas velocity in the main channel; y i where, y represents the mass fraction of component i in the main channel; D i where, D represents the diffusion coefficient of component i in the main channel.

[0109] 2) Momentum balance equation for gas phase species in the main channel

[0110] (2)

[0111] where, μ represents the dynamic viscosity; p represents the pressure.

[0112] 3) Enthalpy balance equation for gas phase species in the main channel

[0113] (3)

[0114] where, c p represents the specific heat capacity of the gas in the main channel; λ g represents the thermal conductivity of the gas in the main channel; T g represents the gas temperature in the main channel.

[0115] 4) Gas phase component balance equation in the catalytic coating

[0116] (4)

[0117] where, p w is the density of the gas in the catalytic coating; x represents the radial direction; y w,i is the mass fraction of component i in the catalytic coating; D w,i is the diffusion coefficient of component i in the catalytic coating; a c is the specific surface area of the catalyst in the catalytic coating; γ i,j is the stoichiometric ratio of component i in chemical reaction j; M i is the molar mass of component i; T w is the gas temperature in the catalytic coating; r j (T w ) is the reaction rate of chemical reaction j at the gas temperature T w in the coating.

[0118] 5) Gas phase enthalpy balance equation in the catalytic coating

[0119] (5)

[0120] where, λ w is the thermal conductivity of the gas in the catalytic coating; is the standard enthalpy of formation of chemical reaction j.

[0121] 6) NH3 coverage balance equation in catalytic coating

[0122] (6)

[0123] where, is the total concentration of catalytic active sites after hydrothermal aging; θ NH3 is the coverage of adsorbed NH3 on the coating reaction surface; γ NH3,j is the stoichiometric ratio of NH3 in chemical reaction j.

[0124] 7) Component balance equation at gas-coating interface

[0125] (7)

[0126] where, k m,i is the mass transfer coefficient of component i on the coating surface. d h is the main channel width.

[0127] 8) Enthalpy balance equation at gas-coating interface

[0128] (8)

[0129] where, k h is the heat transfer coefficient at the gas-coating interface.

[0130] Step S2: Given the initial conditions and boundary conditions of the SCR single-channel mathematical model, limit the values or expressions of some unknown parameters in the equation set in step S1 according to the characteristics of the SCR single channel, and substitute the limited parameter values or expressions into each equation in step S1 to obtain the closed equation set corresponding to the SCR single-channel mathematical model.

[0131] First, the initial conditions and boundary conditions of the SCR single-channel mathematical model are given in equations (9) and (10) respectively:

[0132] , , (9)

[0133] ;

[0134] ;

[0135] ;

[0136] (10)

[0137] wherein, T in T represents the temperature at the reactor inlet, T 0 is the initial temperature, p atm P is the atmospheric pressure at standard conditions, v in V represents the gas flow velocity at the reactor inlet, v 0 is the initial gas flow velocity, p out P represents the pressure at the reactor outlet, L is the length of the main channel, which is the axial length; δ w is the coating thickness; is the coverage of the initially adsorbed NH3 on the coating reaction surface.

[0138] In the NH3-SCR reaction, the Eley-Rideal (E-R) mechanism is applied to the SCR kinetic model.

[0139] wherein, it is considered that NH3 is adsorbed on the catalytic surface and NO X in the gas phase reacts.

[0140] The ammonia adsorption reaction is:

[0141] (11)

[0142] The ammonia desorption reaction is:

[0143] (12)

[0144] The nitric oxide oxidation reaction is:

[0145] (13)

[0146] The ammonia oxidation reaction is:

[0147] (14)

[0148] The standard SCR reaction is:

[0149] (15)

[0150] The fast SCR reaction is:

[0151] (16)

[0152] The slow SCR reaction is:

[0153] (17)

[0154] where S represents the catalytically active sites. During the adsorption of NH3, it was found that the process belongs to the non-activated adsorption type, which means that the adsorption reaction does not require additional activation energy.

[0155] The Temkin relationship takes into account the change in adsorption heat and is applicable to desorption behavior under conditions of surface non-uniformity. In the desorption process of NH3, it was found that the activation energy (E des ) can be described by the Temkin expression (18).

[0156] (18)

[0157] where E 0 des is the initial desorption activation energy; a is the coefficient; θ NH3 is the coverage of adsorbed NH3 on the coating reaction surface.

[0158] Arrhenius' law describes the effect of temperature on the rate of a chemical reaction. Specifically, the reaction rate increases with increasing temperature, which can be quantitatively described by the Arrhenius equation. Arrhenius' law indicates that there is an exponential relationship between the reaction rate and the activation energy of the reactants and the absolute temperature. Each reaction rate expression represented by equations (19) - (25) is an expression that conforms to this law.

[0159] The ammonia adsorption reaction rate expression is:

[0160] (19)

[0161] The ammonia desorption reaction rate expression is:

[0162] (20)

[0163] The nitric oxide oxidation reaction rate expression is:

[0164] (21)

[0165] The ammonia oxidation reaction rate expression is:

[0166] (22)

[0167] The standard SCR reaction rate expression is:

[0168] (23)

[0169] The fast SCR reaction rate expression is:

[0170] (24)

[0171] The slow SCR reaction rate expression is:

[0172] (25)

[0173] where r ads and k ads are the ammonia adsorption reaction rate and rate constant; r des and k des are the ammonia desorption reaction rate and rate constant; r NO and k NO are the NO oxidation reaction rate and rate constant; r NH3 and k NH3 are the NH3 oxidation reaction rate and rate constant; r stand and k stand are the standard SCR reaction rate and rate constant; r rapid and k rapid are the fast SCR reaction rate and rate constant; r slow and k slow are the slow SCR reaction rate and rate constant; c NH3 , c NO、 c NO2 and c O2 are the molar concentrations of NH3, NO, NO2, and O2, respectively. is the maximum coverage of NH3 on the coated reaction surface; is the critical coverage of NH3 on the coated reaction surface; is the reaction equilibrium constant.

[0174] The parameters of the kinetic model for fresh catalyst (i.e., catalyst that has not been hydrothermally aged) are shown in Table 1.

[0175] Table 1. Parameters of the kinetic model for fresh catalyst

[0176]

[0177] The nitrogen oxides in diesel exhaust primarily include nitric oxide and nitrogen dioxide, and the nitrogen oxides conversion rate is the performance index of the model, which can be expressed as:

[0178] (26)

[0179] where and are the NO X concentrations at the inlet and outlet of the reactor, respectively.

[0180] Based on the above, the closed equation set corresponding to the SCR single-channel mathematical model is obtained, and the nitrogen oxide concentration at the outlet can be obtained, and then the nitrogen oxide conversion rate can be obtained, which reflects the emission reduction performance of the reactor.

[0181] The simulated inlet gas components include 900 ppm NO, 100 ppm NO2, 1000 ppm NH3, 5% O2, and 7% H2O, the space velocity is 40,000 h⁻¹, and the SCR main structure and material parameters are shown in Table 2.

[0182] Table 2 SCR main structure and material parameters

[0183]

[0184] Based on the above, the SCR single-channel mathematical model is established.

[0185] Next, the hydrothermal aging performance of the reactor is evaluated in different temperature zones. The performance is evaluated from three aspects: mild hydrothermal aging, overall performance of severe hydrothermal aging, and local performance of severe hydrothermal aging.

[0186] In this embodiment, the copper-based molecular sieve is Cu-SSZ-13.

[0187] The implementation of evaluating the hydrothermal aging performance of the reactor in different temperature zones is based on the establishment of the SCR single-channel mathematical model, and mainly applies the results of step S2 from three aspects: direct application of the equation set, parameterized expansion, and implementation of evaluation in different temperature zones.

[0188] The direct application of the equation set refers to directly using the closed equation set (including 8 equations of component balance, momentum balance, and enthalpy balance) established in step S2 as the basis for calculation or analysis during the evaluation in different temperature zones. For example: the NO concentration is obtained by solving equations (1)-(8), and the conversion rate is calculated. The influence of aging on adsorption sites is analyzed using the NH3 coverage balance equation, i.e., formula (6). x

[0189] Parameterized expansion mainly refers to the quantification of active sites. Specifically, based on the kinetic parameters of step S2 (such as Table 1), the hydrothermal aging parameters are expanded: the standardized concentrations of Brønsted acid sites, copper sites, and physical adsorption sites are defined by formulas (27)-(39), and the active site model (Ω, ) of step S2 is associated with aging conditions (temperature and time). The aging rate function, i.e., formula (28), is derived using the Arrhenius equation of step S2, i.e., formulas (19)-(25).

[0190] The implementation of evaluation in different temperature zones refers to simulating the performance under different aging conditions through the equation set of step S2.​

[0191] The theoretical model of step S2 is transformed into a tool to quantitatively assess the aging performance by parameter extension (aging time / temperature) and scenario subdivision (mild / severe hydrothermal aging).

[0192] The hydrothermal aging of Cu-SSZ-13 catalysts is divided into two states, mild and severe. Under the “mild” aging state (from 550 °C to 750 °C), there are two major structural changes, including dealumination of the zeolite and redistribution of the exchanged Cu species, but NO X conversion is almost unchanged. Under the “severe” aging state (above 750 °C), there are almost no Brønsted acid sites left in the zeolite, and the structure of the catalyst starts to collapse, leading to a decrease in NO x conversion, oxidation function, and NH3 storage.

[0193] Four NH3 adsorption sites are found in Cu-SSZ-13, including physical adsorption sites, two types of exchanged copper sites (ZCuOH and Z2Cu), and Brønsted acid sites. Two different copper sites are responsible for low-temperature NH3 storage, and the Brønsted acid sites are responsible for high-temperature NH3 storage. With the progress of mild hydrothermal aging, the total storage amount of NH3 remains unchanged. The decrease in the number of Brønsted acid sites in Cu-SSZ-13 during mild hydrothermal aging is not due to dealumination, but due to the transformation of copper sites. It is worth noting that the total number of active sites remains unchanged during mild hydrothermal aging, and this transformation almost does not change the total storage amount of NH3, NO X conversion efficiency is almost unaffected, but the proportion of the number of active sites of different categories changes.

[0194] For the Brønsted acid sites, the normalized Brønsted acid site concentration of the hydrothermally aged catalyst relative to the fresh catalyst can be defined as follows:

[0195] (27)

[0196] wherein, is the normalized Brønsted acid site concentration, is the Brønsted acid site concentration, is the Brønsted acid site concentration of the non-hydrothermally aged catalyst.

[0197] The reactor model is based on the assumption that the mild hydrothermal aging process can be considered as a chemical reaction, and the rate of this reaction can be expressed by Arrhenius kinetics. That is, the degree of mild hydrothermal aging is calculated by the loss of catalytically active sites to calculate the hydrothermal aging rate, is the aging temperature (T a) and aging time (t a The integrated form of the mild hydrothermal aging calculation function is shown in equation (28).

[0198] (28)

[0199] where k a is the mild hydrothermal aging Arrhenius kinetic pre-exponential factor; Ea is the activation energy; R is the ideal gas constant, and c is a constant.

[0200] The relative Brønsted acid site concentration is defined as :

[0201] (29)

[0202] where is the total concentration of hydrothermally aged catalytic active sites.

[0203] Substituting equations (27) and (28) into (29) gives

[0204] (30)

[0205] The calculated relative Brønsted acid site concentration as a function of hydrothermal aging time and temperature is shown in Figure Figure 2 Brønsted acid sites are the main sites for NH3storage at high temperatures. The lower the relative Brønsted acid site concentration, the smaller the NH3storage capacity, especially at > 300 °C for the maintenance of reactant coverage (0 NH3 ). The decrease in the relative Brønsted acid site concentration leads to a decrease in the NO x conversion in the high temperature region (300 - 400 °C) of the catalyst and a shift of the peak temperature to higher temperatures. High catalysts show a slower activity decay in mild hydrothermal aging, thus extending the reactor lifetime.

[0206] For the copper site concentration, the copper site concentration can be described as a linear function of the Brønsted acid site concentration, which indicates that the NH3storage capacity on the copper sites is unique at a given concentration of Brønsted acid sites. The implication of the calculations shown here is that for a known temperature exposure time, the equivalent hydrothermal aging can be estimated, and for a known hydrothermal aging, the copper and Brønsted acid site concentrations can be predicted. These predictions can be further used to calculate the total NH3storage and the storage at specific sites.

[0207] (31)

[0208] where, It is the concentration of copper sites. This is the copper site concentration when the Brønsted acid site concentration is 0. For a specific catalyst, is a constant. a is the coefficient of the linear function of copper site concentration and Brønsted acid site concentration.

[0209] Define relative copper site concentration :

[0210] (32)

[0211] Substituting equations (27), (28), and (31), we can obtain...

[0212] (33)

[0213] The relationship between relative copper site concentration and hydrothermal aging time and temperature can be calculated as follows: Figure 3 As shown, copper sites dominate NH3 storage at low temperatures, and their increased concentration can partially compensate for the loss of high-temperature storage capacity due to Brønsted acid sites. Increased copper site concentration can also compensate for the decrease in reaction rate caused by the reduction of Brønsted acid sites. Increased copper site concentration is a hallmark feature of the mild hydrothermal aging of Cu-SSZ-13, reflecting the thermodynamic stabilization process of copper species. Although it can partially maintain NH3 storage and high-temperature SCR activity, reactor performance needs to be comprehensively evaluated in conjunction with the decline of Brønsted acid sites.

[0214] For the physical adsorption sites, combined with equation (31), the physical adsorption sites are calculated as shown in equation (34).

[0215] (34)

[0216] It is the concentration of physical adsorption sites.

[0217] Assumption:

[0218] (35)

[0219] but:

[0220] (36)

[0221] Define the relative concentration of physical adsorption sites :

[0222] (37)

[0223] Substituting equations (27), (28), and (36), we can obtain

[0224] (38)

[0225] The relationship between the relative physical adsorption site concentration and the hydrothermal aging time and temperature is shown in Figure 4 . The physical adsorption site concentration is positively correlated with the Brønsted acid site concentration, which decreases due to copper site migration, resulting in simultaneous decay. Although the physical adsorption site is not an active center, it serves as a temporary repository for NH3, and its reduction will weaken the NH3 buffering capacity of the catalyst at low temperatures, resulting in insufficient NH3 supply under transient conditions. The rapid decay of (especially at >600°C) is an early sign of framework dealumination, indicating subsequent accelerated copper site aggregation and acid site loss, which requires early intervention to avoid a performance cliff. The decrease in physical adsorption site concentration is a structural indicator of mild hydrothermal aging of Cu-SSZ-13, reflecting the degradation of the molecular sieve framework integrity. Although it does not directly participate in the SCR reaction, its decay will indirectly reduce low-temperature activity by weakening NH3 storage and mass transfer, and it indicates a more serious aging risk. The changes in and should be combined to comprehensively evaluate the catalyst state.

[0226] The global performance analysis of severe hydrothermal aging is as follows:

[0227] Under severe hydrothermal aging conditions, hydrothermal aging significantly reduces the total concentration of active sites of Cu-SSZ-13 catalysts by destroying the molecular sieve framework structure, reducing Brønsted acid sites, changing the distribution and aggregation state of Cu species, etc. How aging temperature (above 750°C) and aging time quantitatively affect active site concentration is still unknown. According to the site theory, the adsorption of NH3 on the catalyst is related to the distribution of Brønsted acid sites. As the aging temperature increases, the activity of Brønsted sites decreases, the proportion of inactive sites increases, the coverage of the aged catalyst significantly decreases, the adsorption capacity of NH3 decreases, and the amount of adsorbed NH3 decreases, but the basic reaction mechanism does not change. Therefore, the present application uses the ratio of the total concentration of catalytic active sites after hydrothermal aging of the catalyst to the total concentration of catalytic active sites in the fresh state to represent the aging degree of the catalyst.

[0228] (39)

[0229] Figure 5 In the present application, the two graphs are cloud displays under certain conditions, including the graph of and the graph of

[0230] AsFigure 5 The molecular sieve catalysts with various ammonia storage capacities were shown to have NO X conversion rates, especially a large increase in catalytic activity at 200-300°C, and a maximum NO X conversion rate at 300-400°C, followed by a decrease in NO X conversion rate with increasing temperature. This is because at low temperatures, the low molecular energy results in a low chemical reaction rate, and NO X cannot fully react with NH3; with increasing temperature, the catalyst becomes active, and the SCR reaction can proceed rapidly, and NO X reacts fully with NH3 in a short time, achieving the highest NO X conversion rate. However, when the temperature further increases to above 400°C, the non-selective oxidation of NH3 causes a decrease in NO X conversion rate.

[0231] However, with increasing decreasing ammonia storage capacity, the degree of catalyst aging increases, and NO X conversion rate decreases, and a higher temperature is required to accelerate the SCR reaction and improve NO X conversion rate. This is because the decrease in ammonia storage capacity results in a decrease in the total concentration of hydrothermally aged catalytically active sites, and the peak NO X conversion rate moves toward high temperatures. A higher temperature is required to accelerate the SCR reaction and improve NO X conversion rate. Moreover, at high temperatures, the NO X conversion rate of a catalyst with a high degree of aging decreases rapidly.

[0232] The local performance of a severely hydrothermally aged catalyst is analyzed as follows:

[0233] To improve the catalytic efficiency of an aged catalyst for the SCR reaction, the effect of the degree of aging on the SCR reaction was studied. The simulated inlet gas composition included 1000 ppm NO, 1000 ppm NH3, 5% O2, and 7% H2O. The concentration distribution of NO in the catalytic coating at different temperatures is shown in FIG. 1. Because there is no NO2 in the inlet gas, and the amount of generated NO2 is very small, the small amount of generated NO2 is also consumed, and the concentration distribution of NO2 is not considered here. Figures 6-16 (1) Below 350°C, the overall concentration of NO in the catalytic coating continuously decreases with increasing temperature, while above 350°C, it instead increases. On the one hand, this is because of the equilibrium limitation of NO oxidation, which moves toward the direction of NO2 decomposition with increasing temperature; on the other hand, this is because, after 350°C, the SCR reaction slows down, and less NO is consumed.

[0234]

[0235] ​(2) At different temperatures, the concentration at the inlet is large, and the concentration at the outlet is small. Along the axial direction of the gas flow, the NO concentration is continuously decreasing.

[0236] (3) In the radial direction, below 350°C, the NO concentration continuously decreases from the gas-solid interface to the inside of the catalytic coating. Above 350°C, the NO concentration at the back end of the inside of the catalytic coating is lower than that at the gas-solid interface. The concentration decreases in the low-temperature region because NO is rapidly consumed (SCR reaction dominates) when it diffuses from the gas phase to the inside of the coating in the near-interface region. In the internal region, due to the reactant concentration gradient and diffusion resistance, the penetration depth of NO is limited, forming a decreasing concentration from the surface to the inside. Moreover, the higher the temperature, the more the low-NO-concentration region at the back end extends to the inside of the catalytic coating. The expansion of the internal low-concentration region in the high-temperature section is due to the fact that the SCR reaction rate decreases at high temperatures, the NO consumption rate slows down, the reaction region extends to a deeper layer of the coating, leading to the expansion of the low-concentration region to the inside, and on the other hand, the high temperature exacerbates the temperature gradient inside the coating, and the thermal migration effect promotes the diffusion of NO to the high-temperature area (such as the center of the coating), further expanding the range of the internal low-concentration region.

[0237] (4) As the total concentration of standardized catalytic active sites decreases , the NH3 adsorption capacity decreases, the standard SCR reaction slows down, and the NO concentration in the coating increases. Moreover, the overall concentration of NO in the catalytic coating changes becomes sluggish. The overall concentration response of NO is sluggish due to the weakening of the reaction kinetics. When is low, the diffusion-reaction competition in the catalytic coating is unbalanced: the mass transfer rate of NO from the gas phase to the inside is relatively high compared to the limited surface reaction rate, resulting in a gentle change in concentration gradient and a more uniform overall distribution. This phenomenon is more pronounced in the low-temperature section because the SCR reaction is already slow at low temperatures, and the reduction of active sites further amplifies the kinetic inertia, reducing the sensitivity of the system to changes in operating conditions.

[0238] (5) The critical temperature of the NO concentration reduction point at the back end increases. A higher critical temperature is required for the significant reduction of NO concentration at the back end of the coating (near the outlet region), which is the result of the shift of the catalyst activity window. When the total concentration of standardized catalytic active sites decreases, the reaction rate per unit area decreases, and the temperature must be increased to compensate for the loss of kinetics: high temperature (> 350°C) can temporarily enhance the reactivity of oxygen active sites, promote NO adsorption and conversion, but only under more severe conditions. Although temperature rise accelerates the reaction, it also intensifies the side reaction, further delaying the effective consumption of NO at the back end, and pushing up the critical temperature threshold.

[0239] In summary, based on the different hydrothermal aging characteristics of the selective catalytic reduction reactor based on Cu-SSZ-13 at different hydrothermal aging temperatures, a temperature domain evaluation method for the hydrothermal aging performance of the selective catalytic reduction reactor is proposed.

[0240] Finally, it is necessary to explain here that: the above examples are only used to make further detailed description of the technical solutions of the present application, and cannot be understood as a limitation on the protection scope of the present application. Some non-essential improvements and adjustments made by the skilled in the art based on the above content of the present application all belong to the protection scope of the present application.

Claims

1. A method for evaluating hydrothermal aging performance of a selective catalytic reduction reactor in a temperature zone, characterized in that, The interior of the reactor is provided with a plurality of SCR single channels, the SCR single channel is a square cylinder structure, the side wall of the square cylinder structure is a catalytic coating formed by a catalyst, the channel in the square cylinder structure surrounded by the catalytic coating is a main channel, the catalytic coating has a plurality of pores inside, and the active sites of the catalyst adsorb ammonia molecules and perform selective catalytic reduction reactions; First, a SCR single channel mathematical model is established, and then based on the model, water thermal aging parameters are expanded to evaluate the water thermal aging performance of the reactor in a temperature domain. The establishment of the mathematical model includes the following steps: Step S1: establishing a SCR single channel mathematical model, the equation set corresponding to the model includes a component balance equation of a gas phase substance in a main channel, a momentum balance equation of the gas phase substance in the main channel, an enthalpy balance equation of the gas phase substance in the main channel, a gas phase component balance equation in a catalytic coating, a gas phase enthalpy balance equation in the catalytic coating, an NH3 coverage balance equation in the catalytic coating, a component balance equation of a gas phase-coating interface, and an enthalpy balance equation of the gas phase-coating interface; Step S2: given initial conditions and boundary conditions of the SCR single channel mathematical model, a closed equation set corresponding to the SCR single channel mathematical model is calculated; When the water thermal aging performance of the reactor is evaluated in a temperature domain, the performance is evaluated from two states of mild water thermal aging and severe water thermal aging respectively. The water thermal aging temperature corresponding to the mild water thermal aging is 550-750 DEG C, and the water thermal aging temperature corresponding to the severe water thermal aging is above 750 DEG C. When the mild water thermal aging is performed, the aging performance of the reactor is evaluated by Brønsted acid site concentration, copper site concentration and physical adsorption site concentration. When the severe water thermal aging is performed, the aging performance of the reactor is evaluated by the normalized total concentration of water thermal aging catalytic active sites. The relative Brønsted acid site concentration was calculated with the hydrothermal aging time t a and the aging temperature T a , wherein: ； ； ； is the concentration of standardised Brønsted acid sites, is the concentration of Brønsted acid sites, is the concentration of Brønsted acid sites of the unhydrothermally aged catalyst, k a is the Arrhenius kinetic pre-exponential factor for the mild hydrothermal ageing, Ea is the activation energy; R is the ideal gas constant, c is a constant, is the total concentration of hydrothermally aged catalytically active sites; The relative copper site concentration was calculated with the hydrothermal aging time t a and the aging temperature T a wherein: ； ； is the copper site concentration, is the copper site concentration at zero Brønsted acid site concentration, for a particular catalyst, is a constant, a is a coefficient of a linear function of the copper site concentration and the Brønsted acid site concentration; The relative physisorption site concentration was calculated with the hydrothermal aging time t a and the aging temperature T a , wherein: ； ； ； is the physical adsorption site concentration.

2. The evaluation method according to claim 1, characterized by: The method for the global or local performance evaluation at severe hydrothermal aging is: calculating the normalized total concentration of hydrothermally aged catalytic active sites , obtaining the NO X conversion at different temperatures and or the NO X concentration profile in the catalytic coating, wherein: ； is the total concentration of catalytically active sites in the unhydrothermally aged state.

3. The evaluation method according to claim 1 or 2, characterized by: In step S2, given the initial conditions and boundary conditions, the values or expressions of part of the unknown parameters in the equation set in step S1 are limited according to the characteristics of the SCR single channel, the values or expressions of the limited unknown parameters are substituted into each equation in step S1, and a closed equation set corresponding to the SCR single channel mathematical model is obtained. The limited unknown parameters include: the mass transfer coefficient of any component on the surface of the catalytic coating, the diffusion coefficient of any component in the main channel and in the catalytic coating respectively, the specific surface area of the catalyst in the catalytic coating, the reaction rate expression of each chemical reaction involved in the SCR single channel, and the total concentration of water thermal aging catalytic active sites in the catalytic coating.

4. The evaluation method according to claim 1 or 2, characterized by: The component balance equation of the gas phase substance in the main channel is: ； where t denotes time; z denotes the axial direction; The momentum balance equation of the gas phase substance in the main channel is: denotes the exhaust density, i.e. the gas density in the main channel; v denotes the exhaust velocity, i.e. the gas velocity in the main channel; y i denotes the mass fraction of component i in the main channel; D i denotes the diffusion coefficient of component i in the main channel; Wherein, μ represents dynamic viscosity; p represents pressure; ； The enthalpy balance equation of the gas phase substance in the main channel is: The gas phase component balance equation in the catalytic coating is: ； where c p represents the specific heat capacity of the gas in the main channel; λ g represents the thermal conductivity of the gas in the main channel; T g represents the temperature of the gas in the main channel; The gas phase enthalpy balance equation in the catalytic coating is: ； wherein, The NH3 coverage balance equation in the catalytic coating is: w is the density of the gas within the catalytic coating; x denotes the radial direction; y w,i is the mass fraction of component i within the catalytic coating; D w,i is the diffusion coefficient of component i within the catalytic coating; a c is the specific surface area of the catalyst in the catalytic coating; γ i,j is the stoichiometric ratio of component i to chemical reaction j; M i is the molar mass of component i; T w is the temperature of the gas within the catalytic coating; r j (T w ) is the reaction rate of chemical reaction j at a gas temperature of T w within the coating; The component balance equation of the gas phase-coating interface is: ； where λ w is the thermal conductivity of the gas within the catalytic coating; is the standard enthalpy of formation of chemical reaction j; The enthalpy balance equation of the gas phase-coating interface is: ； where θ NH3 is the coverage of adsorbed NH3on the catalytic coating reaction surface; γ NH3,j is the stoichiometric ratio of NH3in the chemical reaction j; The initial conditions of the SCR single channel mathematical model are: ； wherein k m,i is the mass transfer coefficient of component i at the coating surface; The boundary conditions are: ； where d h is the hydraulic diameter of the main channel, k h is the heat transfer coefficient at the gas-coating interface.

5. The evaluation method according to claim 4, characterized by: ​ , , ； ​ ； ； ； ； wherein T in T0is the temperature at the reactor inlet, T 0 is the initial temperature, p atm P0is the atmospheric pressure at standard conditions, v in V0is the gas flow velocity at the reactor inlet, v 0 is the initial gas flow velocity, p out P1is the pressure at the reactor outlet, L is the length of the main channel, which is the axial length; δ w d is the thickness of the catalytic coating; 0 is the initial coverage of the catalytic coating reaction surface by adsorbed NH3.

6. The evaluation method according to claim 1, characterized by: The nitrogen oxides in the exhaust gas of diesel engines include nitric oxide and nitrogen dioxide, and the conversion rate of nitrogen oxides is : ； wherein, and NO concentrations at the reactor inlet and outlet, respectively. X concentrations.

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