JP2001012233A - Catalyst deterioration prediction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deterioration prediction method of a catalyst free to use for selection of an optimum catalyst suitable for various using environments. SOLUTION: A deteriorating state of a catalyst is predicted by computing a catalyst temperature distribution (n+1) and an oxygen density distribution (n+1) in accordance with a catalyst precious metal grain diameter distribution (n) and a reaction rate distribution (n), computing the catalyst precious metal particle size distribution (n+1) in accordance with them and a poisoning quantity distribution (n+1), computing a frequency factor distribution (n+1) in accordance with this and the poisoning quantity distribution (n+1) and computing the reaction rate distribution (n+1) in accordance with this.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting deterioration of a catalyst installed in an exhaust system of a vehicle-mounted engine and used for purifying exhaust gas.

[0002]

2. Description of the Related Art The exhaust system of an internal combustion engine such as an on-vehicle engine includes
A catalyst for exhaust gas purification is installed. The catalyst comprises a carrier and a heat-resistant cover for protecting the carrier. A fine noble catalytic noble metal such as platinum, rhodium or palladium is supported on the carrier. If the catalyst deteriorates due to aging or the like, the purifying action of the exhaust gas decreases. Therefore, when developing and designing an internal combustion engine, a deterioration durability test of the catalyst is performed, and a catalyst suitable for each internal combustion engine is selected.

[0003]

However, the deterioration and durability test of the catalyst usually takes several months to half a year, and requires enormous costs. Therefore, it is difficult to perform sufficient tests within a limited development period and development cost. For this reason, it was difficult to find the optimum catalyst in actual deterioration durability tests, and in order to meet the current strict exhaust gas regulations, it was often necessary to mount a catalyst that overspecified.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for predicting catalyst deterioration that can be used to select an optimum catalyst suitable for each use environment. .

[0005]

According to the first aspect of the present invention, a catalyst noble metal particle size distribution (n + 1) in a deterioration stage n is obtained in obtaining a reaction rate distribution (n + 1) in a deterioration stage n + 1 after a lapse of a time tn from a catalyst deterioration stage n. ) And the reaction rate distribution (n), the catalyst temperature distribution (n + 1) and the oxygen concentration distribution (n + 1) in the deterioration stage n + 1 are predicted by using a method for predicting the catalyst temperature and the oxygen concentration. Distribution (n +
1) The catalyst noble metal particle size distribution (n + 1) in the deterioration stage n + 1 using a method of predicting the catalyst noble metal particle size based on the oxygen concentration distribution (n + 1) and the poisoning amount distribution (n + 1) in the deterioration stage n + 1. And the frequency factor distribution of the reaction rate (n + 1) is predicted using the method of predicting the frequency factor of the reaction rate based on the catalyst noble metal particle size distribution (n + 1) and the poisoning amount distribution (n + 1). In addition, there is provided a catalyst deterioration prediction method characterized by predicting a deterioration state of a catalyst.

The object of the prediction method of the present invention is a catalyst constituted by supporting a catalyst precious metal on a carrier having an appropriate shape. By introducing exhaust gas into the carrier, pollutants contained in the exhaust gas are converted into harmless substances through a chemical reaction promoted by a catalyst. This purifies the exhaust gas.

The catalyst as shown in the first embodiment is supported on a columnar carrier, arranged in the exhaust gas flow of the exhaust system of an automobile engine, and configured to purify the exhaust gas. According to the present invention, for example, such catalyst deterioration can be predicted.

The "deterioration stage" will be described. The degradation stage of a new and unused catalyst is zero. When the exhaust gas comes into contact with the catalyst in the deterioration stage 0, exhaust gas purification by the catalyst starts. The catalyst gradually degrades over time. The deterioration stage at the time when the time t0 has elapsed since the start of purification by the catalyst is 1
And After a lapse of time t1 from the state of the degradation stage 1, the stage is the degradation stage 2. That is, after the time tn has elapsed from the degradation stage n, the degradation stage is n + 1. Note that time intervals t0, t1,. . . tn,. . . Need not be equal. Further, as described later, in the case of a catalyst mounted in an exhaust system of an automobile engine, each deterioration stage can be determined based on a traveling distance (see Embodiment 3).

The "catalyst noble metal particle size distribution" refers to the particle size distribution of the catalytic noble metal supported on the carrier at an arbitrary position and at an arbitrary deterioration stage of the carrier. The catalyst noble metal particle diameter when not used is equal to the atomic diameter of the catalyst noble metal, but the catalyst noble metal is aggregated due to exposure to a high temperature and an oxygen-excess atmosphere over time, and the particle diameter increases. The particle size distribution in this state is the “catalyst noble metal particle size distribution” at each deterioration stage. The catalyst noble metal particle size distribution (0) in the deterioration stage 0 needs to be given as an initial value of the “catalyst noble metal particle size distribution” in the present invention. This value has a fixed value corresponding to the type of the catalytic noble metal and the state of being supported on the carrier.

[0010] "Reaction rate distribution" refers to any location on the carrier,
It is the speed of various chemical reactions when exhaust gas is purified at any stage of degradation. The value of the reaction rate distribution (0) at the deterioration stage 0 can be obtained from actual measurement of a new and unused catalyst. In the present invention, this value needs to be given as an initial value of the “reaction rate distribution”.

"Catalyst temperature distribution" refers to any location on the carrier,
It is a temperature distribution at an arbitrary deterioration stage. The “oxygen concentration distribution” is a distribution of the concentration of oxygen gas at an arbitrary position on the carrier and at an arbitrary deterioration stage. Details of these prediction methods will be described later.

The "poisoning amount distribution" means any location on the carrier,
It is a distribution of the attached amount of the poisoning substance to the catalyst at an arbitrary deterioration stage. This poisoning substance is a substance contained in the exhaust gas and is a substance that adheres to the catalyst and inhibits purification of the exhaust gas by the catalyst. For example, in Embodiment 1 described below, phosphorus contained in exhaust gas is a poisoning substance.

Since the amount of the poisoning substance increases with the use time of the catalyst, the poisoning amount distribution increases with the deterioration stage.
The spatial profile of the poisoning amount distribution can be estimated from actual measurement of the deteriorated catalyst. Therefore, in the prediction method of the present invention, the poisoning amount distribution is given as a specific value corresponding to the deterioration stage.

The value corresponding to each deterioration stage can be obtained by actual measurement. For example, a catalyst used for purifying exhaust gas of an automobile engine is proportional to the engine oil consumption of the automobile engine. (See Embodiment 1).

The details of a method for predicting the "catalyst noble metal particle size" from the "catalyst temperature distribution", "oxygen concentration distribution" and "poisoning amount distribution" will be described later.

The "frequency factor distribution of the reaction rate" is the distribution of the frequency factor at an arbitrary position on a carrier and at an arbitrary deterioration stage. Frequency factor distribution at degradation stage n + 1 (n + 1)
Are the catalyst noble metal particle size distribution (n + 1) and the poisoning amount distribution (n +
1), and the detailed method will be described later.

In general, a reaction rate constant k is given by an Arrhenius type, and a frequency factor A, an activation energy E,
Using the gas constant R and the temperature T, it is given by the following equation. k = A × exp (−E / RT) Accordingly, the reaction rate distribution (n + 1) at the deterioration stage n + 1 can be obtained from the frequency factor distribution (n + 1).

The most remarkable point in the present invention is that, based on the catalyst noble metal particle size distribution (n) and the reaction rate distribution (n) at the deterioration stage n, the deterioration stage n + 1 after the lapse of time tn from the catalyst deterioration stage n To find the reaction rate distribution (n + 1) at Considering the case where n = 0, in order to obtain the catalyst noble metal particle size distribution (1) and the reaction rate distribution (1) in the degradation stage 1, the catalyst noble metal particle size distribution (0) and the reaction rate in the degradation stage 0 The distribution (0) is used.

The catalyst noble metal particle size distribution (0) and the reaction rate distribution (0) at the deterioration stage 0 are given as initial values. Based on these values, the catalyst temperature distribution (1) and the oxygen concentration distribution (1) in the deterioration stage 1 after the lapse of time t0 are obtained.

Next, using the estimated poisoning amount distribution (1) and the above results, a catalyst noble metal particle size distribution (1) is obtained.
The frequency factor distribution (1) of the reaction rate is obtained based on the catalyst noble metal particle size distribution (1) and the poisoning amount distribution (1) obtained in the above process. Reaction rate distribution (1) based on this frequency factor distribution (1)
Get.

Then, using the reaction rate distribution (1) and the catalyst noble metal particle size distribution (1) obtained from the above process, the catalyst noble metal particle size distribution (2) and the reaction rate distribution in the degradation stage 2 are similarly calculated. (2) can be obtained. Thereafter, by repeating such processing, the time t0. . . tn. . . The reaction rate distribution at each degradation stage separated by an interval can be obtained.

When the reaction rate (reaction rate distribution) at each position in the carrier decreases, the progress of the reaction by the catalyst slows down. That is, it is considered that the purification rate by the catalyst decreased and the catalyst deteriorated. Therefore, it can be determined that the catalyst has deteriorated at the time when the purification rate by the catalyst falls below an appropriate reference value. It is necessary to determine the reaction rate distribution of a plurality of chemical reactions depending on the type of the catalyst and the type of exhaust gas to be purified (for example, see Embodiment 1).

Next, the operation of the present invention will be described. By utilizing the method according to the present invention, it is possible to measure the performance of a catalyst in a limited condition without actually performing a long-term degradation durability test of the catalyst by measuring the performance of the catalyst in a limited state.
It is possible to estimate the state of deterioration of the catalyst at any location. For this reason, a sufficient simulation test can be repeated within a limited development period and development cost, and it is difficult to over-specify, and it is possible to select an optimal catalyst for each use environment.

As described above, according to the present invention, it is possible to provide a catalyst deterioration prediction method which can be used to select an optimum catalyst suitable for each use environment.

Next, as in the second aspect of the present invention, the method of predicting the catalyst temperature and the oxygen concentration is a method of calculating based on a heat-mass transport equation. The method of predicting the diameter is a method of calculating based on mathematical expressions including oxygen concentration, temperature and poisoning amount.
The method of estimating the frequency factor of the reaction rate is preferably a method of calculating based on a mathematical expression including the particle size and poisoning amount of the catalytic noble metal.

This makes it possible to precisely and accurately predict the state of deterioration inside the catalyst at any stage of deterioration, thereby making it possible to predict the purification performance and temperature characteristics of the catalyst at any stage of deterioration. Become. As a result, the performance of the deteriorated catalyst can be grasped without performing an actual durability test, and the enormous cost and time required for the experiment can be reduced.

The details of the heat and mass transport equations will be described later.
For details on the formula for calculating the catalyst noble metal particle size, see
As will be described later, it is basically calculated from a mathematical expression as shown in FIG.
it can. In the equation, h (P_wt) Gives a concrete function form
Thus, the equation shown in FIG. 8A can be obtained.
You. Also, h (P _wt) As other functions other than FIG.
Shapes can be used. Furthermore, the frequency factor of the reaction rate
The details of the formulas to be calculated will be described later.
7, it can be calculated from a mathematical expression. q (P
_wtFIG. 8 (b)
Can be obtained.

Next, as in the third aspect of the present invention, the method of predicting the catalyst temperature and the oxygen concentration is a method of calculating based on the transport equations of heat and substances shown in FIGS. The method of predicting the catalyst noble metal particle size is a method of calculating based on the mathematical expression of FIG. 8A including the oxygen concentration, the temperature, and the poisoning amount, and further predicts the frequency factor of the reaction rate. The method is preferably a method of calculating based on the mathematical formula of FIG. 8B including the particle size and poisoning amount of the catalytic noble metal.

This makes it possible to precisely and accurately predict the state of deterioration inside the catalyst at any stage of deterioration, thereby making it possible to predict the purification performance and temperature characteristics of the catalyst at any stage of deterioration. Become. As a result, the performance of the deteriorated catalyst can be grasped without performing an actual durability test, and the enormous cost and time required for the experiment can be reduced.

Next, the governing equations according to FIGS. 2 to 8 will be described. The equation according to FIG. 2 (a) shows the heat balance in the exhaust gas phase passing through the catalyst. Left side indicates the amount of heat transported by the exhaust gas flow velocity V _g, the right side indicates the amount of heat transferred from the exhaust gas to the carrier. Also, instead of the equation according to FIG. 2A, an equation according to FIG. 2B with an unsteady term added to the left side can be used.

The equation shown in FIG. 3A shows the heat balance in the carrier. The first term on the right side indicates the amount of heat conduction in the radial direction (heat conductivity λ _{w, r} ). The second term on the right side indicates the amount of heat conduction in the axial direction (thermal conductivity λ _{w, z} ). The third term on the right side shows the amount of heat transfer from the exhaust gas to the carrier. The fourth term QC _{, r} on the right side indicates the amount of heat generated. The left side is an unsteady term indicating the amount of change in the catalyst temperature per unit time due to excess or deficiency of the calorific value of each term on the right side. FIG. 3A shows a governing equation in a cylindrical coordinate system (r, θ, z).
The governing equation of FIG. 3B expressed in the orthogonal coordinate system (x, y, z) may be used.

The equation according to FIG. 4 (a) shows the mass balance in the exhaust gas phase passing through the catalyst. Left side shows the amount of the chemical species i transported by the exhaust gas flow velocity v _g. The right side shows the amount of chemical species i transferred from the exhaust gas to the carrier surface. The equation shown in FIG. 4B is obtained by adding a non-stationary term to the left side, and this equation can be used instead of FIG. 4A.

The equation according to FIG. 5 shows the material balance on the carrier surface. The left side shows the consumption of the species i by the catalytic reaction. The right side shows the amount of chemical species i transferred from the exhaust gas to the carrier surface.

The specific heat C _pw , the radial thermal conductivity λ _{w, r} , the axial thermal conductivity λ _{w, z} , and the geometric surface area S _geo of the carrier are as follows:
This is a unique value depending on the type and shape of the carrier. The exhaust gas density ρ _g , the exhaust gas specific heat C _pg , the exhaust gas flow rate v _g , the heat transfer coefficient h _z , and the mass transfer coefficient h _{D, i} are quantities that are theoretically estimated from the exhaust gas temperature and the chemical species concentration. The calorific value Q _{C, r} is determined by multiplying the consumption R _i of the chemical species i by the catalytic reaction by the enthalpy.

FIG. 8A is an equation showing the growth rate of the catalyst noble metal particle size. When the catalyst noble metal particle diameter D _n in the degradation stage n at any one point in the carrier is known from the equation according to FIG. 8A, the oxygen in the process of lapse of time tn from the degradation stage n to the degradation stage n + 1 is obtained. From the concentration [O ₂ ] and the catalyst temperature _Tw , the catalyst noble metal particle diameter D _{n + 1} in the deterioration stage n + 1 can be obtained.

FIG. 8B is an equation for obtaining a frequency factor of the reaction rate at an arbitrary point in the carrier at the deterioration stage n + 1. After obtaining the catalyst noble metal particle diameter D _{n + 1} at the degradation point n + 1 at an arbitrary point in the support by the equation according to FIG. 8A, the reaction rate at the degradation step n + 1 is determined by the equation according to FIG. 8B. it is possible to obtain the frequency factor a _{n + 1} of the.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 A catalyst deterioration prediction method according to an embodiment of the present invention will be described.
This will be described with reference to FIGS. Briefly describing the catalyst deterioration prediction method of this example, when calculating the reaction rate distribution (n + 1) in the deterioration stage n + 1 after the elapse of the time tn from the catalyst deterioration stage n, the catalyst noble metal particle size distribution (n ) And the reaction rate distribution (n),
5 to the catalyst temperature distribution (n + 1) and the oxygen concentration distribution (n +
1) is calculated.

Next, based on the catalyst temperature distribution (n + 1), the oxygen concentration distribution (n + 1), and the poisoning amount distribution (n + 1) in the deterioration stage n + 1, the equation in FIG. The catalyst noble metal particle size distribution (n + 1) is calculated. Next, based on the catalyst noble metal particle size distribution (n + 1) and the poisoning amount distribution (n + 1), the frequency factor distribution (n + 1) of the reaction rate is calculated using the equation of FIG. 8B. Next, a reaction rate distribution (n + 1) is calculated based on the reaction rate frequency factor distribution (n + 1). This makes it possible to predict the state of deterioration of the catalyst.

Hereinafter, a specific description will be given. In the exhaust system of an automobile engine, NO contained in exhaust gas from the engine
A catalyst capable of decomposing x, THC (CH ₄ , C ₃ H _6, etc.), CO, and the like by a chemical reaction described below is provided. This catalyst has a central axis C as shown in FIGS.
A carrier 10 made of a metal having a cylindrical shape with a cross section in a direction perpendicular to the cylinder and a rectangular cross section in a direction parallel to the central axis, the inside of which is formed in a honeycomb shape;
(Not shown).

In this example, a description will be given of prediction of deterioration of a Pt-Rh three-way catalyst used by being supported on a carrier in such a catalyst. Further, the deterioration prediction method of this example is realized as software. In the three-way catalyst, noble metal particles having an average particle size of 5 ° are uniformly supported on the entire wall surface constituting the honeycomb-shaped interior of the carrier 10. The carrier 10 has a diameter R of 86 mm and a length L as shown in FIG.
Is 120 mm.

Further, as shown in FIG. 10, in this example, a simulation is performed for a case where exhaust gas is uniformly introduced into the catalyst from the side surface of the carrier 10 having a circular shape. Therefore, it is considered that distributions such as a reaction rate distribution and a catalyst noble metal particle size distribution described later are concentric with the center axis C of the carrier 10. Therefore, the prediction in this example is performed on the assumption that the distributions in the governing equations and mathematical expressions according to FIGS. 2 to 8 described later are determined only by r and z.

Here, r is the carrier 1 as shown in FIG.
The length in the radial direction from the center O of the 0 side to the outer periphery of the carrier 10, and z is a numerical value expressing the position in the carrier by the axial length with respect to the center O of the carrier 10. In addition, it can be said that r and z are positions indicated by cylindrical coordinates with the center O as the origin and the center axis C as a reference.

When the exhaust gas touches the three-way catalyst of this example,
The following reaction occurs. (Chemical reaction 1) CO + 0.5O ₂ → CO ₂ . . . Reaction rate R1, (Chemical reaction 2) C ₃ H ₆ + 4.5O ₂ → 3CO ₂ + 3H ₂ O. . . Reaction rate R2, (Chemical reaction 3) CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O. . . Reaction rate R3, (Chemical reaction 4) CO + NO → CO ₂ + N ₂ . . . Reaction rate R4, (chemical reaction _{5) H 2 + 0.5O 2 →} H 2 O. . . Reaction rate R5

[0043] Thus, the rate of consumption of CO, etc., RCO = R1 + R4, RO 2 = 0.5R1 + 4.5R2 + 2.0R3 + 0.5R
_{5, RTHC = RC 3 H 6} + RCH 4 = R2 + R3, R N O = R4, RH 2 = R5, become.

[0044] Further, the reaction rate R1~R5 is, Rj = Aj × exp (-E / RT w) × [X] m [Y] n. . . Becomes Incidentally, Rj; one of R1 to R5, Aj; according to each frequency factor of the reaction 1 to 5, E: activation energy, R: gas constant, T _w: the catalyst temperature, [X],
[Y]. . . The concentration (C _w , _i ) of the chemical species involved in the chemical reaction at the catalyst surface. For example, in the case of (chemical reaction 1), the concentrations of CO (C _w , CO) and O ₂ (C _w , O ₂ ) correspond.

The higher the reaction rate, the higher the efficiency of exhaust gas purification by the catalyst. Therefore, catalyst degradation can be determined by following the distribution of the above reaction rates in the carrier in time series.

Next, the details of the method for predicting catalyst deterioration will be described. In this example, as shown in FIG. 1, the deterioration of the catalyst in the deterioration stage 1 after the elapse of the time t0 from the deterioration stage 0 is predicted. Here, t0 = 50 hours. During the period of time t0, the temperature of the exhaust gas flowing into the catalyst of this example is 900
° C, and the exhaust gas contains TH such as CO, CH ₄ and C ₃ H _6.
C, NOx, O ₂ , N _2, etc.
25%, THC 800ppm, NOx 1700pp
It is assumed that m and O ₂ are 0.55% and the others are N _{2 and the} like. These values are assumed to be constant during the period of time t0.
These conditions will be referred to as deterioration exposure conditions in the deterioration prediction of this example.

Next, the reaction rate distribution (0) of the above catalyst at the deterioration stage 0 was obtained as follows. The catalyst of this example was installed in the exhaust system of an automobile engine, and the engine operating conditions (speed, torque, air ratio) were set arbitrarily, and the exhaust gas amount, exhaust gas temperature, catalyst temperature, and catalyst were set for each operating condition. The pollutant concentration in the exhaust gas flowing in and the pollutant concentration in the exhaust gas flowing out of the catalyst were measured.

From the actual measurement results thus obtained, the temperature dependence and the concentration dependence of the reaction rate of each chemical reaction to be considered were specified. The reaction rate constant kj of each chemical reaction is expressed as kj = Aj × exp (−Ej / RT _w ). From the temperature dependence and the concentration dependence obtained from the actual measurement results, the frequency factor Aj and the activation energy Ej are obtained. Identified. That is, the reaction rate could be determined.

Since the catalyst in the deterioration stage 0 is a completely new catalyst, the activity of the catalyst, that is, the reaction rate is assumed to be equal in each part of the carrier 10. Therefore, the reaction rate distribution (0) of each chemical reaction is a constant value obtained by the above method regardless of (r, z). In this manner, the initial values of the catalyst noble metal particle size distribution (0) and the reaction rate distribution (0) were obtained by step 101 in FIG.

The catalyst noble metal particle size distribution (0),
Assuming the reaction rate distribution (0) as an initial value, it is substituted into the governing equations according to FIGS. 2 to 5, and further, various values described in the same figure are substituted. 1
It was solved numerically like 02. Thus, catalyst temperature distribution (1) and oxygen concentration distribution (1) were obtained. Here, Figure 2
The values substituted in FIG. 5 are σ = 0.7 and ρ _w = 2767 (kg / kg) in the case of the target catalyst in this example.
m ³ ), C _pw = 636 (J / (kg · K)), λ _{w, z} =
1.424 (W / (m · K)), λ _{w, r} = 0.359
(W / (m · K)) and S _geo = 2822 (m ² / m ³ ).

FIG. 11 shows the catalyst temperature distribution (1) obtained. In FIG. 9, as shown in FIG. 9, the center temperature O on the side surface of the support is taken as the origin, the z axis is taken in the axial direction, the r axis is taken in the radial direction, and the catalyst temperature distribution is described as a value for the distance (r, z). did. Thus, for example, the temperature at a position 20 mm in the axial direction and 20 mm in the radial direction from the center point O was predicted to be approximately 940 ° C. Similarly, FIG. 12 shows the oxygen concentration distribution obtained in step 102 of FIG.
According to the figure, for example, the oxygen concentration at a position 20 mm in the axial direction and 20 mm in the radial direction from the center point O is about 0.325.
%.

Subsequently, in step 103 of FIG.
The poisoning amount distribution (1) in the deterioration stage 1 is obtained. As described above, the catalyst of this embodiment is installed in the exhaust system of an automobile engine and purifies exhaust gas discharged from the engine. In this case, most of the poisoning substance is phosphorus contained in the engine oil. Since the consumption of the engine oil is proportional to the operation time of the engine (the traveling distance of the vehicle), it can be considered that the poisoning amount increases simply in proportion to the deterioration stage.

Regarding the spatial profile of where the poisonous substance reaches the carrier and how much, the carrier carrying the catalyst is installed in the exhaust system and the automobile engine is operated for a certain period of time. By measuring the state of adhesion of the poisoning substance, an appropriate poisoning amount distribution can be set.

Based on the above measured results, the deterioration stage 1
Of the poisoning amount distribution in the system, the axial distance z = 5
P in mm_wt= 0.83 (wt%), z = 15 mm
At P_wt= 0.55 (wt%), z = 30mm
And P_wt= 0.39 (wt%), z = 50 mm
P_wt= 0.22 (wt%), z = 70mm _wt
= 0.11 (wt%), z = 110 mm_wt=
The value was 0.037 (wt%).

In this example, the poisoning amount distribution (1) in the deterioration stage 1 was calculated from the above poisoning amount estimated value as a function formula of the axial distance z. In this example, the poisoning amount was constant in the radial direction.

Next, in step 104, based on the catalyst temperature distribution (1), the oxygen concentration distribution (1), and the poisoning amount distribution (1), the deterioration stage is determined using the equation of FIG. The catalyst noble metal particle size distribution (1) in No. 1 was calculated. Here, the values substituted into FIG. 8A are a = 1.2 × 10 ⁹ , b = 0.
67, η = 1.0, E = 95600 (J / mol).

FIG. 1 shows the obtained catalyst noble metal particle size distribution (1).
No. 3. From the figure, it was found that the catalyst noble metal particle diameter at a position 20 mm in the axial direction and 20 mm in the radial direction from the center point O is in the range of 255 to 260 μm.

Then, based on the obtained catalyst noble metal particle size distribution (1) and poisoning amount distribution (1), the frequency factor distribution (1) of the reaction rate is calculated using the mathematical expression of FIG. 8 (b). Calculated.
Here, the values substituted in FIG. 8B are ξ = 0.4 and D ₀ = 5 (Å) in the case of the target catalyst in this example.
It is.

Based on the frequency factor distribution (1) of the reaction rate of each chemical reaction obtained in this way, the above-mentioned relational expression with the chemical reaction rate, kj = Aj × exp (−Ej / RT _w ), is used. The reaction rate distribution (1) of each chemical reaction was calculated.

As described above, the catalyst noble metal particle size distribution (1) and the reaction rate distribution (1) in the deterioration stage 1 can be obtained from the catalyst noble metal particle size distribution (0) and the reaction speed distribution (0) in the deterioration stage 0. did it.

From this reaction rate distribution (1), it was possible to predict the purification performance of the catalyst targeted in this example in the deterioration stage 1. In a mode test to evaluate the fuel efficiency and exhaust purification performance of an automobile, time-series data such as the temperature of the exhaust gas flowing into the catalyst installed in the exhaust system, the amount of exhaust gas, and the concentration of pollutants contained in the exhaust gas (in this example, the mode FIG. 2 in which the reaction rate distribution (1) calculated as described above is taken into consideration with the input value from immediately after the start of operation to 120 seconds).
By numerically solving the governing equations shown in FIG. 5 in a time series, the concentration of pollutants in the exhaust gas flowing out of the catalyst could be predicted.

By integrating the time-series concentration data of CO and THC in the outflow exhaust gas thus predicted, the integrated emission of CO and THC after the deterioration stage 1, that is, continuous operation for 50 hours was predicted. This prediction result is shown in FIG.

Next, a new catalyst corresponding to catalyst deterioration stage 0, which is a target of prediction in this example, is actually mounted on the exhaust system of an automobile engine, and the temperature of the exhaust gas flowing into the catalyst and contained in the exhaust gas. The operating conditions of the engine were set so that the concentration of the pollutants would be the same as the above-mentioned degradation exposure condition, and 50
By performing continuous operation for a long time, a deteriorated catalyst corresponding to the deterioration stage 1 was obtained.

A mode operation test is performed with the deteriorated catalyst mounted, and the concentration of pollutants in the exhaust gas flowing out of the catalyst is determined.
The measurement was performed in time series using an exhaust gas analyzer. By integrating the time-series concentration data of CO and THC in the effluent gas thus measured, actual measured values of the integrated emissions of CO and THC after continuous operation for 50 hours were obtained. The results are plotted in FIG. As a result, it was found that the calculated prediction and the experimental result agreed well.

The operation and effect of this embodiment will be described. FIG.
As is clearer, by using the method of this example, it is possible to measure the performance of the catalyst only in a limited state without actually performing the degradation durability test of the catalyst, and to determine the degradation stage and the arbitrary level in the carrier. The state of deterioration of the catalyst at the location can be estimated. For this reason, a sufficient simulation test can be repeated within a limited development period and development cost, and it is difficult to over-specify, and it is possible to select an optimal catalyst for each use environment.

As described above, according to this embodiment, it is possible to provide a catalyst deterioration prediction method that can be used to select an optimal catalyst suitable for each use environment.

Further, in this example, the state of the catalyst in the deterioration stage 1 is predicted only. However, the state of deterioration after further lapse of time or the state of deterioration of the catalyst at finer time intervals is predicted. Can also.

Embodiment 2 In this embodiment, a catalyst metal is supported on a ceramic carrier different from that of Embodiment 1, and the deterioration state of a catalyst attached to an exhaust system of an automobile after traveling 100,000 miles is shown. To predict. Each degradation stage is assumed to be every 10,000 miles,
The deterioration was predicted by the same method as in the first embodiment.

The prediction of the catalyst noble metal particle size distribution according to step 102 in FIG. 1 is shown in FIG. 15 for 20,000 miles (deterioration stage 2), 50,000 miles, (deterioration stage 5), and 100,000 miles (deterioration stage 10). I do. Note that the catalyst noble metal particle size distribution in FIG. 15 only describes the relationship with the axial distance.

A new catalyst corresponding to the deterioration stage 0 of the predicted catalyst was actually mounted on the exhaust system of an automobile engine, and a 100,000 mile running test was performed.
0 (100,000 miles) of the deteriorated catalyst was obtained. The catalyst is decomposed into several parts in the axial direction, each of which is crushed, and X
The catalyst noble metal particle size was measured by X-ray diffraction (XRD). In this way, the relationship between the catalyst noble metal particle size and the axial distance in the deterioration stage 10 was measured and plotted in FIG. From FIG. 15, it was found that the predicted result and the measured result were in good agreement.

Next, the new catalyst (deterioration stage 0) placed in the normal temperature atmosphere and the deteriorated catalyst (deterioration stage 10) after traveling 100,000 miles similarly placed in the normal temperature atmosphere have the same conditions (exhaust gas). Temperature, flow rate, concentration of pollutants contained) The time series change of catalyst temperature and the time series change of purification rate of pollutants contained in exhaust gas when the exhaust gas was introduced stepwise were predicted.

That is, the purification performance of the degraded catalyst (deterioration stage 10), which predicts the purification performance of the new catalyst (deterioration stage 0) and simulates the degradation process from the new catalyst and predicts the degradation state after traveling 100,000 miles. We examined whether it was possible to predict the future.

In the case of a new catalyst (deterioration stage 0), time-series data such as the temperature and flow rate of exhaust gas flowing into the catalyst in a stepwise manner and the concentration of pollutants contained in the exhaust gas (in this example, immediately after the start of introduction) To 180 seconds) as input values,
The time series of the catalyst temperature and the purification rate of pollutants contained in the exhaust gas flowing out of the catalyst are obtained by numerically solving the governing equations shown in FIGS. 2 to 5 in consideration of the reaction rate distribution (0) in a time series. The change could be predicted.

In the case of the deteriorated catalyst (deterioration stage 10), the procedure from step 101 to step 106 in FIG. By solving the governing equations shown in FIGS. 2 to 5 in consideration of the reaction rate distribution (10) calculated by sequentially repeating the above processes up to numerical values in time series, the catalyst temperature and the exhaust gas flowing out of the catalyst are included. The time series change of the purification rate of pollutants can be predicted.

A new catalyst (deterioration stage 0) and a degraded catalyst after 100,000 miles (deterioration stage 10) were actually mounted on the exhaust system of an automobile engine, respectively, and kept in a room temperature atmosphere. After that, a test was conducted to introduce the exhaust gas in a stepwise manner, and the time series change of the catalyst temperature and the time series change of the purification rate of pollutants contained in the exhaust gas were measured.

FIG. 16 and FIG. 17 show both predicted results and measured results of the time-series changes in the catalyst temperature at points A to D inside the deteriorated catalyst (deterioration stage 10) after traveling 100,000 miles. Here, point A is as shown in FIG.
(R, z) = (20, 10) (unit is mm). B
The point is (r, z) = (30, 10), and the point C is (r, z) =
The points (50, 10) and D are (r, z) = (80, 10). In FIGS. 16 and 17, the portions indicated by broken lines are the prediction results, and the portions plotted with ○, ●, Δ, and Δ are the actual measurement results. From FIG. 16 and FIG. 17, it was found that the predicted result and the measured result are in good agreement.

The CO, TH of the new catalyst (deterioration stage 0) and the degraded catalyst after traveling 100,000 miles (deterioration stage 10) are calculated.
The relationship between the purification rates of C and NOx and the elapsed time from the time when the exhaust gas was introduced stepwise is described in FIGS. In FIGS. 18 to 20, the portion indicated by the broken line is the prediction result, the portion plotted by ○ is the actual measurement result of the new catalyst (deterioration stage 0), and the portion plotted by ● is the degraded catalyst (deterioration stage 10). ) Is the actual measurement result. FIG.
From FIG. 20, it was found that the predicted result and the measured result agree well.

Next, assuming that a new catalyst (deterioration stage 0) and a degraded catalyst after traveling 100,000 miles (deterioration stage 10) are installed in the exhaust system of an automobile engine, respectively, the fuel efficiency and exhaust purification performance of the automobile are assumed. In a mode test to evaluate the reaction rate distribution (0) or reaction rate distribution (1), time-series data such as the temperature of the exhaust gas flowing into the catalyst, the amount of exhaust gas, and the concentration of pollutants contained in the exhaust gas are used as input values.
The concentration of pollutants in the exhaust gas flowing out of the catalyst was predicted by numerically solving the governing equations according to FIGS. By integrating the time-series concentration data of CO, THC, and NOx in the outflow exhaust gas thus predicted, the integrated emission in the mode operation test of each catalyst was calculated. This value is standardized as 1 for the case of a new catalyst and is shown in FIG.

Further, a new catalyst (deterioration stage 0) and a degraded catalyst after traveling 100,000 miles (deterioration stage 10) were actually mounted on the exhaust system of an automobile engine, and a mode operation test was performed. The concentration of pollutants in the flue gas flowing out of the facility was measured in chronological order using a flue gas analyzer. Measured CO, THC, NOx in effluent exhaust gas
By integrating the time-series concentration data of the above, actual measured values of the integrated emission in the mode operation test of each catalyst were obtained. This value was standardized as 1 for a new catalyst, and is shown in FIG. 21 as an actually measured value.

As can be seen from the figure, the predicted result and the actually measured value agree very well. If the prediction method of the first embodiment is used, the engine can be continuously operated without performing the actual machine test on the catalyst. It was found that the performance of the catalyst after operation could be predicted, and the deterioration of the catalyst could be predicted.

[0081]

As described above, according to the present invention, it is possible to provide a catalyst deterioration prediction method which can be used to select an optimum catalyst suitable for each use environment.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a procedure of a prediction method according to a first embodiment.

FIG. 2 is an explanatory diagram showing an equation used for a prediction method in the first embodiment.

FIG. 3 is an explanatory diagram showing an equation used for a prediction method in the first embodiment.

FIG. 4 is an explanatory diagram showing equations used for a prediction method in the first embodiment.

FIG. 5 is an explanatory diagram showing an equation used for a prediction method in the first embodiment.

FIG. 6 is an explanatory diagram showing an equation for calculating a catalyst noble metal particle size.

FIG. 7 is an explanatory diagram showing an equation for calculating a frequency factor of a reaction rate.

FIG. 8 is an explanatory diagram showing an expression used for a prediction method in the first embodiment.

FIG. 9 is a perspective view of a carrier according to the first embodiment.

FIG. 10 is an explanatory sectional view of a carrier according to the first embodiment.

FIG. 11 is a diagram showing a predicted catalyst temperature distribution in the first embodiment.

FIG. 12 is a diagram showing a predicted oxygen concentration distribution in the first embodiment.

FIG. 13 is a diagram showing a predicted catalyst noble metal particle size distribution in the first embodiment.

FIG. 14 is a diagram showing a value obtained by predicting an integrated emission and a value obtained by actual measurement in the first embodiment.

FIG. 15 is a diagram showing a predicted catalyst noble metal particle size distribution and a measured value in Embodiment 2;

FIG. 16 is a diagram showing a predicted catalyst temperature distribution and measured values at points A and D according to the second embodiment.

FIG. 17 is a diagram showing a predicted catalyst temperature distribution and actual measurement values for points B and C in the second embodiment.

FIG. 18 is a diagram showing a predicted CO purification rate and a measured value in the second embodiment.

FIG. 19 is a diagram showing a predicted HC purification rate and an actually measured value in the second embodiment.

FIG. 20 is a diagram showing a predicted NOx purification rate and an actually measured value in the second embodiment.

FIG. 21 is an explanatory diagram showing a relative value of an integrated emission by prediction and a value by actual measurement in the second embodiment.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinichi Matsunaga 41-cho, Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central R & D Laboratories Co., Ltd. 41, Yokomichi, Toyota Central Research Institute, Inc. (72) Katsuyuki Osawa, Inventor Katsuyuki Osawa, Nagakute-machi, Aichi, Aichi Prefecture, Japan 41-Yokomichi, Toyota Central Research Institute, Inc. F-term (reference) AA02 AA17 AB03 BA14 BA15 BA19 BA33 DB06 DB10 DB13 EA17 EA18 EA21 EA30 EA33 EA38 FB03 FC02 GA06 GB01X GB05W GB06W GB10X GB17X HA36 HA37 HA42 4G069 AA20 BA17 BB02A BB02B BC69A BC71B BC07BEB19 EB03 EB03

Claims (3)

[Claims] When determining a reaction rate distribution (n + 1) in a deterioration stage n + 1 after a lapse of time tn from a catalyst deterioration stage n, a catalyst noble metal particle size distribution (n) and a reaction speed distribution (n) in a deterioration stage n The catalyst temperature distribution (n + 1) and the oxygen concentration distribution (n + 1) in the deterioration stage n + 1 are predicted using the method for predicting the catalyst temperature and the oxygen concentration based on (N +
Based on 1) and the poisoning amount distribution (n + 1) at the deterioration stage n + 1, the method of predicting the catalyst noble metal particle size is used to predict the catalyst noble metal particle size distribution (n + 1) at the deterioration stage n + 1. Based on the particle size distribution (n + 1) and the poisoning amount distribution (n + 1), the method of predicting the reaction rate frequency factor is used to predict the reaction rate frequency factor distribution (n + 1), and to determine the deterioration state of the catalyst. A catalyst deterioration prediction method characterized by predicting. 2. The method according to claim 1, wherein the method of predicting the catalyst temperature and the oxygen concentration is a method of calculating based on a heat and mass transport equation. This method is based on mathematical formulas including oxygen, oxygen concentration, temperature, and poisoning amount, and the method for predicting the frequency factor of the reaction rate is based on the mathematical formula including the particle size and poisoning amount of catalytic noble metal. A method for predicting catalyst deterioration. 3. The method according to claim 1 or 2, wherein the method of predicting the catalyst temperature and the oxygen concentration is a method of calculating based on transport equations of heat and substances shown in FIGS.
The method of estimating the catalyst noble metal particle size is a method of calculating based on the mathematical expression of FIG. 8A including the oxygen concentration, the temperature and the poisoning amount, and further a method of estimating the frequency factor of the reaction rate. Fig. 8 contains the particle size and poisoning amount of catalytic noble metal.
A method for predicting catalyst deterioration, which is a method for calculating based on the mathematical expression of (b).