JP2010031820A - Exhaust emission control method and exhaust emission control catalyst device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively control alcohol discharged from an engine in an unburned state; and to restrain it from being discharged to the atmosphere. <P>SOLUTION: The alcohol discharged from the engine 1 is once adsorbed to an alcohol adsorption layer 6 of a first catalyst converter 3, and then, is converted to aldehyde by an aldehyde generation catalyst layer 7, and the aldehyde is once adsorbed to an aldehyde adsorption layer 9 of a second catalyst converter 4, and then, is controlled through oxidization by a three-way catalyst layer 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

    The present invention relates to an exhaust gas purification method and an exhaust gas purification catalyst device.

With the challenge of reducing environmental burdens, in particular, reducing CO ₂ emissions, commercialization of automobiles using bioethanol produced from cereals as a raw material has been promoted. Such automobiles are known as FFVs (flexible fuel vehicles) and have been researched and developed for decades, but as the proportion of ethanol in the fuel increases, HC compounds in the exhaust gas Purification of (organic compounds) becomes a problem. That is, since the amount of heat generated by ethanol combustion is less than that of gasoline, the exhaust gas temperature of the engine is lower than when only gasoline is used as fuel. Therefore, there is a problem that the amount of alcohol discharged in an unburned state increases immediately after the engine is started, or the amount of aldehyde discharged by partially oxidizing alcohol increases.

On the other hand, Patent Document 1 relates to a method for catalytic oxidation of alcohol contained in exhaust gas. During cold start of the engine, while the temperature of the catalyst is raised to 200 ° C., a large amount of uncontained material contained in the exhaust gas is disclosed. It is difficult to detoxify the combustion methanol, where the exhaust gas is treated with a first catalyst containing Pd and Rh or CeO ₂ to convert the alcohol to CO ₂ and water vapor, and this treatment Is converted to CO ₂ and water vapor by treating with a second catalyst containing silver, in which case the excess air ratio λ of the exhaust gas is reduced to 0.8 to 8.0. Disclose that it is preferable to adjust.
Japanese Unexamined Patent Publication No. 63-141631

    An object of the present invention is to solve the problem that immediately after the engine is started, the amount of alcohol discharged in an unburned state from the engine or the amount of aldehyde generated by partial oxidation of alcohol increases. It is an object of the present invention to provide a new exhaust gas purification system that can efficiently suppress emission into the interior.

    In the present invention, the alcohol discharged from the engine is once adsorbed on the adsorbent and converted into aldehyde, and the aldehyde is further adsorbed on the adsorbent and then oxidized and purified.

That is, the invention according to claim 1 is an exhaust gas purification method for an engine operated by a fuel containing alcohol,
Adsorbing alcohol discharged in an unburned state from the engine to the first adsorbent;
Desorbing alcohol from the first adsorbent;
Converting the alcohol desorbed from the first adsorbent to an aldehyde by the first catalyst material;
Adsorbing the aldehyde to a second adsorbent;
Desorbing aldehyde from the second adsorbent,
And a step of oxidizing and purifying the aldehyde desorbed from the second adsorbent by a second catalyst material.

In this way, alcohol discharged in an unburned state from the engine is not directly oxidized and decomposed to CO ₂ and H ₂ O by the first catalyst, but is partially oxidized by the first catalyst material to form a highly active aldehyde. After the conversion, the second catalytic material is used for the oxidative decomposition, so that the oxidative decomposition proceeds efficiently.

    Thus, in the present invention, alcohol is once adsorbed on the first adsorbent, then converted to aldehyde by the first catalyst material, the aldehyde is once adsorbed on the second adsorbent, and then the second adsorbent is used. Since oxidation purification is performed by the catalyst material, before the first catalyst material and the second catalyst material are activated, the alcohol and aldehyde are prevented from being discharged into the atmosphere without being purified. That is, alcohol and aldehyde can be adsorbed and held by the first and second adsorbents until the first and second catalyst materials are activated, and the purification rate of alcohol and aldehyde is reduced when the engine is cold started. You can avoid doing that.

The invention according to claim 2 is an exhaust gas purification catalyst device of an engine operated by a fuel containing alcohol,
A first adsorbent that adsorbs alcohol; a first catalyst material that converts the alcohol into an aldehyde; a second adsorbent that adsorbs the aldehyde; and a second catalyst material that oxidizes and purifies the aldehyde;
Alcohol discharged in an unburned state from the engine is adsorbed by the first adsorbent, and alcohol desorbed from the first adsorbent as the temperature rises is converted to aldehyde by the first catalyst material, and In the exhaust passage of the engine, the first adsorbent is adsorbed on the second adsorbent and desorbed from the second adsorbent as the temperature rises by the second catalyst material. And the first catalyst material is arranged upstream of the second adsorbent material and the second catalyst material in the exhaust gas flow.

    Therefore, with the catalyst device according to claim 2, alcohol discharged from the engine is once adsorbed on the first adsorbent, and then converted into aldehyde by the first catalyst, and the aldehyde is once adsorbed on the second adsorbent. Then, the invention according to claim 1 in which the second catalyst material is oxidized and purified can be implemented. The aldehyde discharged from the engine is oxidized and purified by the second catalyst material.

The invention according to claim 3 is the invention according to claim 2,
The first adsorbent that adsorbs the alcohol and the first catalyst material that converts the alcohol into an aldehyde are arranged in layers such that the former is a lower layer and the latter is an upper layer on the same carrier. And

    Accordingly, the alcohol discharged from the engine is adsorbed by the lower first adsorbent, and when the alcohol desorbed from the first adsorbent as the temperature rises passes through the upper layer, the upper first catalyst material. Will be converted to aldehydes.

The invention according to claim 4 is the invention according to claim 2,
The first adsorbent that adsorbs the alcohol is disposed upstream of the first catalyst material that converts the alcohol into an aldehyde in the exhaust gas flow direction.

    Therefore, the alcohol discharged from the engine is adsorbed by the first adsorbent disposed on the upstream side, and the alcohol desorbed from the first adsorbent as the temperature rises flows downstream to pass the first catalyst material. When passing, it is converted to aldehyde by the first catalyst material.

The invention according to claim 5 is any one of claims 2 to 4,
The second adsorbent that adsorbs the aldehyde and the second catalyst material that oxidizes and purifies the aldehyde are arranged in layers such that the former is a lower layer and the latter is an upper layer on the same carrier. To do.

    Accordingly, the aldehyde generated from the alcohol by the first catalyst material is adsorbed by the lower second adsorbent, and the aldehyde that is desorbed from the second adsorbent as the temperature rises passes through the upper layer. The second catalyst material is oxidized and purified.

The invention according to claim 6 is any one of claims 2 to 4,
The second adsorbent that adsorbs the aldehyde is disposed upstream of the second catalyst material that oxidizes and purifies the aldehyde in the exhaust gas flow direction.

    Therefore, the aldehyde generated from the alcohol by the first catalyst material is adsorbed by the second adsorbent disposed upstream, and the aldehyde that is desorbed from the second adsorbent as the temperature rises flows downstream. When passing through the second catalyst material, the second catalyst material is oxidized and purified.

The invention according to claim 7 is the invention according to any one of claims 2 to 6,
The 1st catalyst material which converts the said alcohol into an aldehyde contains the aluminate containing the at least 1 sort (s) of metal chosen from Cu, Co, and Ni, It is characterized by the above-mentioned.

    With such an aluminate, alcohol can be efficiently converted to an aldehyde even at a relatively low temperature.

The invention according to claim 8 is any one of claims 2 to 7,
The first adsorbent that adsorbs the alcohol and the second adsorbent that adsorbs the aldehyde are both composed of zeolite, and the zeolite composing the first adsorbent constitutes the second adsorbent. It is characterized in that the Keiban ratio (SiO ₂ / Al ₂ O ₃ molar ratio) is larger than that.

    That is, as the first adsorbent and the second adsorbent, zeolite that is widely used as an HC (hydrocarbon) adsorbent for exhaust gas can be adopted, but the first adsorbent is more than the second adsorbent. Since it is arranged on the upstream side of the exhaust gas flow, it is easily affected by the heat of the exhaust gas. Therefore, in the present invention, zeolite having a high heat resistance and a large Keiban ratio is employed for the upstream first adsorbent. On the other hand, the second adsorbent on the downstream side, which is less affected by the heat of the exhaust gas, employs zeolite with a low cayban ratio, but a low cayban ratio means that there are many acid sites, It is advantageous for adsorption and adsorption of alcohol flowing downstream without being adsorbed by the first adsorbent or without being converted to aldehyde by the first catalyst material.

    As described above, according to the present invention, the alcohol discharged from the engine is once adsorbed on the first adsorbent, then converted into aldehyde by the first catalyst material, and the aldehyde is once adsorbed on the second adsorbent. Since the second catalyst material is oxidized and purified, the alcohol can be efficiently oxidatively decomposed, and the alcohol and aldehyde are first and second activated until the first and second catalyst materials are activated. The adsorbent of 2 can be adsorbed and held, and it can be avoided that the purification rate of alcohol or aldehyde is reduced when the engine is cold started.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

    In FIG. 1, reference numeral 1 denotes an engine that is operated by a fuel containing alcohol. A first catalytic converter 3 is provided in the exhaust gas passage 2, and an exhaust gas passage downstream of the exhaust gas flow from the first catalyst 3. 2 is provided with a second catalytic converter 4. The exhaust gas purification catalyst device shown in the figure includes a first adsorbent that adsorbs alcohol, a first catalyst material that converts the alcohol into an aldehyde, a second adsorbent that adsorbs the aldehyde, and oxidatively purifies the aldehyde. And a second catalyst material.

That is, as shown in FIG. 2, the first catalytic converter 3 contains, in the honeycomb carrier 5, an alcohol adsorption layer 6 containing a first adsorbent that adsorbs alcohol, and a first catalyst material that converts alcohol into an aldehyde. The aldehyde generation catalyst layer 7 is arranged in layers so that the former is the lower layer and the latter is the upper layer. On the other hand, the second catalytic converter 4 includes an aldehyde adsorption layer 9 containing a second adsorbent that adsorbs aldehyde on the honeycomb carrier 8, and a second catalyst material (three-way catalyst) that oxidizes and purifies the aldehyde into CO ₂ and water vapor. ) -Containing three-way catalyst layer 10 is arranged in layers so that the former is the lower layer and the latter is the upper layer.

    The alcohol adsorption layer 6 and the aldehyde generation catalyst layer 7 of the first catalytic converter 3 do not have the layered arrangement shown in FIG. 2, but the alcohol adsorption layer 6 is on the upstream side of the exhaust gas flow, as shown in FIG. A tandem arrangement in which the aldehyde generation catalyst layer 7 is on the downstream side can be employed. Further, the aldehyde adsorption layer 9 and the three-way catalyst layer 10 of the second catalytic converter 4 are not arranged in the layered arrangement shown in FIG. 2, but the aldehyde adsorption layer 9 is located upstream of the exhaust gas flow as shown in FIG. Thus, a tandem arrangement in which the three-way catalyst layer 10 is on the downstream side can be achieved. Further, the alcohol adsorption layer 6 and the aldehyde generation catalyst layer 7 of the first catalytic converter 3 are arranged in a layered arrangement as shown in FIG. 2, and the aldehyde adsorption layer 9 and the three-way catalyst layer 10 of the second catalytic converter 4 are shown in FIG. The tandem arrangement may be adopted, or the alcohol adsorption layer 6 and the aldehyde generation catalyst layer 7 of the first catalytic converter 3 may be arranged in a tandem arrangement as shown in FIG. 3 to form the aldehyde adsorption layer 9 and the three-way catalyst layer 10 of the second catalytic converter 4. May be a layered arrangement as shown in FIG.

<About the first and second adsorbents>
As the first adsorbent for adsorbing alcohol, β-type zeolite having a Keiban ratio of 150 or more is preferably employed, but other zeolites such as ZSM5 and USY can also be employed. As the second adsorbent for adsorbing aldehyde, β-type zeolite having a Keiban ratio of 40 or more and less than 150 is preferably used, but other zeolites such as ZSM5 and USY can also be used.

    The amount of the first adsorbent carried on the honeycomb carrier 5 of the first catalytic converter 3 (the amount carried per 1 L of the carrier; hereinafter the same), and the second adsorbent carried on the honeycomb carrier 8 of the second catalytic converter 4. The amount may be, for example, 100 g / L or more and 200 g / L or less.

<About the first catalyst material>
As the first catalyst material for converting alcohol to aldehyde, various oxidation catalysts can be adopted, but it is comparatively possible to employ an aluminate containing at least one metal selected from Cu, Co and Ni. A high aldehyde conversion rate can be obtained from a low temperature. The content of these metals is preferably 2% by mass or more and 8% by mass or less. The amount of the first catalyst supported on the honeycomb carrier 5 may be, for example, 50 g / L or more and 150 g / L or less. The aluminate can be obtained by impregnating alumina powder with a solution of at least one metal selected from Cu, Co, and Ni (for example, nitric acid solution) and baking at a high temperature of about 800 ° C.

When the aldehyde conversion was measured for Cu aluminate containing 5% by mass of Cu, the results shown in Table 1 were obtained. The test material used for the measurement had a carrier capacity of 25 mL, a Cu aluminate loading of 100 g / L, and the composition of the model exhaust gas was 500 ppmC ethanol, 1.0% oxygen, and the balance nitrogen. The flow rate was 100 mL / min, and the aldehyde conversion rate was determined by changing the sample material inlet gas temperature in various ways. Aldehyde conversion rate is the CH out-of-plane of CHO group detected when ethanol and oxygen are introduced with respect to the absorption intensity of OH stretching vibration (3200-3500 cm ⁻¹ ) when only ethanol is introduced at each temperature. It calculated from the ratio of the absorption intensity of variable-angle vibration (1390cm < ^-1 >).

    Although the aldehyde conversion rate increases as the temperature increases, the aldehyde conversion rate is relatively high at 23% even at a low temperature of 150 ° C., and the aluminate is useful as the first catalyst material. I understand that.

<About the second catalyst material>
As the second catalyst material for oxidizing and purifying the aldehyde, various oxidation catalysts can be employed, but it is preferable to employ a three-way catalyst to simultaneously purify CO and NOx contained in the exhaust gas. As the three-way catalyst, it is preferable to employ a combination of Pd and Rh as the catalyst metal and a combination of alumina and a Ce-based oxygen storage material as the support material for the catalyst metal. As the oxygen storage material, it is preferable to employ a composite oxide containing Ce, Zr, and Nd. For example, the three-way catalyst has a two-layer structure in which the lower layer is a Pd-supported alumina-containing layer and the upper layer is a Rh-supported ZrCeNd composite oxide-containing layer, and the supported amount of each component is Pd supported amount = 4.5 g / L, Rh loading amount = 0.9 g / L, alumina (γ-alumina) loading amount = 50 g / L, ZrCeNd composite oxide loading amount = 75 g / L. The composition of the ZrCeNd composite oxide may be, for example, ZrO ₂ : CeO ₂ : Nd ₂ O ₃ = 80: 10: 10 (mass ratio).

<Purification of alcohol by the catalytic device>
Therefore, according to the exhaust gas purification catalyst device, the alcohol contained in the exhaust gas discharged from the engine 1 into the exhaust gas passage 2 activates the catalyst layers 7 and 10 of the first catalytic converter 3 and the second catalytic converter 4. When it is not converted (for example, when the temperature is 150 ° C. or lower), it is adsorbed by the first adsorbent contained in the alcohol adsorption layer 6 of the first catalytic converter 3. Alcohol passing through the first catalytic converter 3 is adsorbed by the second adsorbent contained in the aldehyde adsorption layer 9 of the second catalytic converter 4. The aldehyde discharged from the engine 1 is also adsorbed by the first adsorbent and the second adsorbent. Therefore, before the catalyst layers 7 and 10 are activated, the alcohol and aldehyde are prevented from being discharged into the atmosphere without being purified.

    When the temperature of the alcohol adsorption layer 6 of the first catalytic converter 3 increases due to the heat of the exhaust gas, desorption of alcohol from the alcohol adsorption layer 6 starts, and at the same time, the first catalyst of the aldehyde generation catalyst layer 7 The activity of the material will also increase. When the alcohol desorbed from the first adsorbent in the alcohol adsorbing layer 6 passes through the aldehyde-generating catalyst layer 7, it is partially oxidized by the first catalyst material in the catalyst layer 7 and converted into an aldehyde.

    The aldehyde produced by the first catalyst material flows downstream and is adsorbed by the second adsorbent contained in the aldehyde adsorption layer 9 of the second catalytic converter 4. The second catalytic converter 4 is on the downstream side of the first catalytic converter 3, and the temperature rise due to the heat of the exhaust gas is delayed from the first catalytic converter 3, so the temperature at which the first adsorbent desorbs alcohol. Even in this case, the temperature of the second adsorbent is not yet high, and the aldehyde produced by the first catalyst can be adsorbed. Further, the alcohol flowing downstream without being converted by the first catalyst material is also adsorbed by the second adsorbent. Therefore, it is suppressed that alcohol and aldehyde are discharged into the atmosphere without purification.

When the temperature of the aldehyde adsorption layer 9 of the second catalytic converter 4 increases due to the heat of the exhaust gas, desorption of alcohol and aldehyde from the aldehyde adsorption layer 6 starts, and at the same time, the third catalyst layer 10 2 The activity of the catalyst material is also increased. The alcohol and aldehyde desorbed from the aldehyde adsorption layer 9 and the alcohol and aldehyde flowing downstream through the first catalytic converter 3 are oxidized and purified to CO ₂ and water vapor by the three-way catalyst of the three-way catalyst layer 10. Therefore, it is suppressed that alcohol and aldehyde are discharged into the atmosphere without purification. In this case, the aldehyde obtained by partially oxidizing the alcohol has high activity (unstable), and therefore, it is efficiently oxidized and decomposed by the three-way catalyst.

    As the first adsorbent, β-type zeolite having a large Keiban ratio and thus high heat resistance is adopted, so even in the first catalytic converter 3 on the upstream side that tends to become high temperature due to the heat of the exhaust gas, There is little thermal deterioration and the alcohol adsorption performance is maintained over a long period of time. On the other hand, the second adsorbent of the second catalytic converter 4 that is relatively less affected by the heat of the exhaust gas is a β-type zeolite that has a low cayban ratio, and therefore has a high acid point and excellent adsorbability of hydrocarbon compounds. Since it is adopted, it is advantageous for suppressing the discharge of alcohol and aldehyde into the atmosphere.

    Note that the same adsorbent may be employed for the first adsorbent and the second adsorbent.

1 is a configuration diagram of an exhaust gas purification catalyst device for an engine according to the present invention. FIG. It is sectional drawing which shows an example of a 1st catalytic converter and a 2nd catalytic converter. It is sectional drawing which shows the other example of a 1st catalytic converter and a 2nd catalytic converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust gas passage 3 1st catalyst converter 4 2nd catalyst converter 5 Honeycomb carrier 6 Alcohol adsorption layer 7 Aldehyde production catalyst layer 8 Honeycomb carrier 9 Aldehyde adsorption layer 10 Three-way catalyst layer

Claims (8)

An exhaust gas purification method for an engine operated by a fuel containing alcohol,
Adsorbing alcohol discharged in an unburned state from the engine to the first adsorbent;
Desorbing alcohol from the first adsorbent;
Converting alcohol desorbed from the first adsorbent to an aldehyde by the first catalyst material;
Adsorbing the aldehyde to a second adsorbent;
Desorbing aldehyde from the second adsorbent,
And a step of oxidizing and purifying the aldehyde desorbed from the second adsorbent with a second catalyst material. An exhaust gas purification catalyst device for an engine operated by a fuel containing alcohol,
A first adsorbent that adsorbs alcohol; a first catalyst material that converts the alcohol into an aldehyde; a second adsorbent that adsorbs the aldehyde; and a second catalyst material that oxidizes and purifies the aldehyde;
Alcohol discharged in an unburned state from the engine is adsorbed by the first adsorbent, and alcohol desorbed from the first adsorbent as the temperature rises is converted to aldehyde by the first catalyst material, and In the exhaust passage of the engine, the first adsorbent is adsorbed on the second adsorbent and desorbed from the second adsorbent as the temperature rises by the second catalyst material. And the first catalyst material is disposed upstream of the second adsorbent material and the second catalyst material in the exhaust gas flow. In claim 2,
The first adsorbent that adsorbs the alcohol and the first catalyst material that converts the alcohol into an aldehyde are arranged in layers such that the former is a lower layer and the latter is an upper layer on the same carrier. Exhaust gas purification catalyst device. In claim 2,
The exhaust gas purifying catalyst device, wherein the first adsorbent that adsorbs the alcohol is disposed upstream of the first catalyst material that converts the alcohol into an aldehyde in the exhaust gas flow direction. In any one of Claims 2 thru | or 4,
The second adsorbent that adsorbs the aldehyde and the second catalyst material that oxidizes and purifies the aldehyde are arranged in layers such that the former is a lower layer and the latter is an upper layer on the same carrier. Exhaust gas purification catalyst device. In any one of Claims 2 thru | or 4,
The exhaust gas purifying catalyst device, wherein the second adsorbent that adsorbs the aldehyde is disposed upstream of the second catalyst material that oxidizes and purifies the aldehyde in the exhaust gas flow direction. In any one of Claims 2 thru | or 6,
The exhaust gas purification catalyst apparatus, wherein the first catalyst material for converting the alcohol into an aldehyde contains an aluminate containing at least one metal selected from Cu, Co, and Ni. In any one of Claims 2 thru | or 7,
The first adsorbent that adsorbs the alcohol and the second adsorbent that adsorbs the aldehyde are both composed of zeolite, and the zeolite composing the first adsorbent constitutes the second adsorbent. An exhaust gas purifying catalyst device characterized in that the Keiban ratio is larger than that.

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