JP2000202282A - Adsorbent of hydrocarbon in exhaust gas of automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure high hydrothermal stability and to efficiently adsorb lower hydrocarbons in the exhaust gas of an automobile by preparing a hydrocarbon adsorbent from a zeolite having a hydrophobic porous refractory layer on the outer surface and having a specified SiO2 to Al2O3 molar ration in its composition. SOLUTION: The adsorbent excellent in capability to adsorb hydrocarbons, particularly <=3C hydrocarbons in the exhaust gas of an automobile is prepared from a zeolite having a hydrophobic porous refractory layer on the outer surface and having an SiO2 to Al2O3 molar ratio of <=200 in its composition. The thickness of the refractory layer is <=500 nm. The zeolite contains at least one framework structure selected from MFI type, MEL type, BEA type, FAU type, MOR type, FER type, EUO type and NES type structures, etc., and at least one element selected from Ga, B, Ti, Zr, Co, Zn, In, Sn, Sb, P, etc., is contained in the framework.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an adsorbent for adsorbing and removing hydrocarbons in automobile exhaust gas.

[0002]

2. Description of the Related Art Exhaust gas from automobiles mainly contains hydrocarbons such as paraffinic hydrocarbons such as methane, ethane, propane, butane, pentane and hexane, and olefins such as ethylene, propylene, butene, pentene and hexene. It contains hydrocarbons and aromatic hydrocarbons such as benzene, toluene, xylene, and trimethylbenzene. The concentration of hydrocarbons in the exhaust gas varies depending on the type and operating state of the engine, but is generally 500 to 2
0000 ppm.

Conventionally, as a catalyst for purification of such automotive exhaust gases, hydrocarbons, and carbon monoxide oxidation, three-way catalyst to perform reduction of the NO _X at the same time is used. Such three-way catalysts exhibit sufficient catalytic activity above a predetermined reaction temperature. Normally, hydrocarbons in the exhaust gas of an automobile engine are emitted in a particularly large amount immediately after the engine is started. However, since the temperature of the exhaust gas at this time is not sufficiently high, there is a disadvantage that hydrocarbons cannot be efficiently purified by the three-way catalyst. Therefore, in order to compensate for such a disadvantage of the three-way catalyst, zeolite is arranged upstream of the three-way catalyst, and hydrocarbons discharged when the three-way catalyst is at a low temperature are temporarily adsorbed on the zeolite. Then, a method of burning and removing hydrocarbons with a three-way catalyst has been proposed (JP-A-2-75327, JP-A-2-13512).
No. 6). However, the adsorption capacity of the zeolite for hydrocarbons was not sufficient. On the other hand, the engine exhaust gas contains a large amount of water, and the temperature of the exhaust gas becomes high during operation of the engine. Therefore, the adsorbent for purifying hydrocarbons in the exhaust gas has high hydrothermal stability. Is required.

[0004] Among various zeolites, ZSM-5 is said to have the best hydrothermal stability.
-5 was not sufficiently satisfactory in terms of hydrothermal resistance in practice. That is, even if it exhibits its performance in the early stage of use, its ability to adsorb hydrocarbons decreases with use, and thus has not been adopted as a practical technique. Further, the conventional zeolite adsorbent has a drawback that even if the ability to adsorb C4 or more hydrocarbons is sufficient, the ability to adsorb C3 or less hydrocarbons is scarce.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made from the above viewpoint, and has high hydrothermal stability and can efficiently remove hydrocarbons in automobile exhaust gas, especially lower hydrocarbons having C3 or less. It is an object of the present invention to provide an adsorbent that can be adsorbed.

[0006]

Means for Solving the Problems The present inventors have conducted intensive research.
As a result, the specific zeolite, ie, SiO_Two/ Al_TwoO _Three
Molar ratio of 200 or less, hydrophobic porous refractory layer on outer surface
Of hydrocarbons in automobile exhaust gas by zeolite with carbon
Have excellent characteristics and can solve the above problems.
Thus, the present invention has been completed.

That is, the present invention is as follows. (1) having a hydrophobic porous refractory layer on the outer surface,
Substrate is SiO_Two/ Al _TwoO_ThreeZeola with a molar ratio of 200 or less
Hydrocarbon adsorbent in automobile exhaust gas composed of carbon dioxide. (2) The thickness of the hydrophobic porous refractory layer on the outer surface is 500
nm or less, and the zeolite of the substrate is SiO_Two/ Al_Two
O_ThreeThe hydrocarbon absorption according to (1), wherein the molar ratio is 30 to 200.
Lumber.

(3) The base zeolite is MFI type, M
EL type, BEA type, FAU type, MOR type, FER type, M
TW type, MTT type, TON type, ERI type, CHA type, L
The hydrocarbon adsorbent according to (1) or (2), which comprises at least one skeleton structure selected from TL type, LTA type, EUO type and NES type. (4) The hydrocarbon adsorbent according to (1) or (2), wherein the zeolite as the substrate comprises an MFI-type zeolite produced only from an inorganic compound.

(5) Ga, B, Fe, Ti, Zr, Co, Zn, In, S
The hydrocarbon adsorbent according to any one of (1) to (4), containing at least one element selected from n, Sb and P. (6) The hydrocarbon adsorbent according to any one of (1) to (5), wherein the base zeolite is a metal-supported zeolite.

(7) The hydrocarbon adsorbent according to (6), wherein the supported metal is silver. (8) The hydrocarbon adsorbent according to any one of (1) to (5), wherein the hydrophobic porous refractory layer on the outer surface is made of zeolite. (9) The hydrocarbon adsorbent according to (8), wherein the framework structure of the zeolite in the hydrophobic porous refractory layer on the outer surface is MFI type or MEL type.

(10) The hydrocarbon adsorbent according to (8) or (9), wherein the zeolite of the hydrophobic porous refractory layer on the outer surface has a skeletal structure different from that of the base zeolite. (11) Firing zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of 200 or less at 650 ° C. or more for 1 hour or more (8)
Or a method for producing the hydrocarbon adsorbent according to (9).

(12) The hydrocarbon adsorbent according to any one of (1) to (7), wherein the hydrophobic porous refractory layer on the outer surface is amorphous silica.

[0013]

Embodiments of the present invention will be described below. The hydrocarbon adsorbent used in the present invention is SiO ₂ / A
a zeolite having a l ₂ O ₃ molar ratio of 200 or less as a base,
It has a hydrophobic porous refractory layer on its outer surface.

The zeolite serving as the substrate of the hydrocarbon adsorbent of the present invention may have a molar ratio of SiO ₂ / Al ₂ O ₃ of 200 or less, preferably 30 to 200, more preferably 30 to 100. It is desirable to do. SiO
_{If the} molar ratio of ₂ / Al ₂ O ₃ is too large, the number of ion exchange sites, which are considered to be the adsorption points of zeolite, will decrease, and the adsorption capacity will decrease. In addition, SiO ₂ / Al ₂
If the O ₃ molar ratio is too small, the hydrothermal resistance of the zeolite will be low and the durability will be reduced, making it difficult to use.

As the zeolite serving as the substrate of the present invention, those having various skeletal structures can be used.
EA type, FAU type, MOR type, FER type, MTW type, M
TT type, TON type, ERI type, CHA type, LTL type, L
It preferably contains at least one skeleton structure selected from TA, EUO and NES types. These zeolites may be used as a mixture of two or more. Further, among them, MFI type, MEL type, FE
R-type zeolites are particularly preferred. MFI type, MEL
Type, FER type zeolite and SiO ₂ / Al ₂ O
Those with a molar ratio of ₃ in the range of 30 to 100 are the most preferred zeolites. The MFI-type zeolite used in the present invention refers to ZSM-5 and zeolites having a crystal structure similar thereto, for example, ZSM-5, ZS
M-8, zeta 1, zeta 3, Nu-4, Nu-5, T
Z-1, TPZ-1, ISI-3, ISI-5, AZ-
A zeolite such as 1 corresponds.

The zeolite as the base may contain other elements together with Al in the skeleton structure. Ga, B, Fe, Ti, Zr, C
o, Zn, In, Sn, Sb and P can be mentioned. These may be only one type or may include two or more types. As a contained element, Ga is particularly preferably used. Further, as the zeolite of the substrate of the present invention, a metal-supported zeolite supporting a metal element such as silver or gold is preferably used. Among them, silver-supported metal-supported zeolite exhibits an excellent ability to adsorb hydrocarbons, in particular, adsorbability of C3 or lower hydrocarbons, and is preferably used.

The hydrophobic porous refractory layer (hereinafter referred to as "hydrophobic layer") of the present invention is typically a layer made of a porous refractory mainly composed of silica or silica-alumina. This layer hardly adsorbs moisture as compared with certain zeolites. Usually, amorphous silica, amorphous silica alumina, etc. (collectively referred to as amorphous silica) or zeolite can be used as the hydrophobic layer. The hydrophobic layer is SiO ₂
The / Al ₂ O ₃ molar ratio may be greater than 200, but 50
Those having 0 or more are particularly preferred because of their high hydrophobicity. The zeolite as the hydrophobic layer may be a zeolite having a skeleton partially containing another element or a metal carrying silver or the like, similarly to the zeolite as the base. The zeolite in the hydrophobic layer has the same skeletal structure as the zeolite serving as the substrate, and may be made hydrophobic by increasing the molar ratio of SiO ₂ / Al ₂ O _3. Good. Further, the skeleton structure of the zeolite in the hydrophobic layer is preferably an MFI zeolite or a MEL zeolite.

When amorphous silica is used as the hydrophobic layer, various types of amorphous silica or amorphous silica containing a small amount of impurities may be used. The amorphous silica is not limited to pure amorphous silica, but may be a material containing aluminum such as silica-alumina or a material containing other elements such as phosphorus and titanium. Furthermore, a mixture with zeolite may be used. Also in this case, the amorphous silica forming the hydrophobic layer may be inferior in hydrophilicity to the zeolite as the base. Normally, the SiO ₂ / Al ₂ O ₃ molar ratio should be greater than 200, but those with 500 or more are particularly preferred because of their high hydrophobicity.

The role of the hydrophobic layer of the hydrocarbon adsorbent of the present invention is to enhance the selectivity of adsorption of hydrocarbons of the zeolite as a substrate, particularly the adsorption of lower hydrocarbons having a relatively low adsorption power of C3 or less. It is. Exhaust gas such as automobile exhaust gas generally contains a large amount of water, and the water is preferentially adsorbed to an adsorbent such as zeolite, and adsorbs hydrocarbons, especially C3 or lower hydrocarbons. Often hinders. However, by forming a hydrophobic porous layer on the outer surface of the base zeolite, which is the main body of the adsorbent,
It is considered that the approach of moisture to the zeolite portion (inside the hydrophobic layer on the surface) of the substrate is suppressed by the hydrophobic layer, and the adsorption of moisture to the zeolite of the substrate is also suppressed. As a result, it is considered that the adsorption of hydrocarbons, particularly the adsorption of lower hydrocarbons of C3 or lower, proceeds smoothly.

According to the above-described concept, it is considered that the thicker the hydrophobic layer, the more difficult it is to adsorb moisture to the zeolite of the substrate, and the higher the selectivity of hydrocarbon adsorption.
However, if the hydrophobic layer is too thick, the rate of permeation of hydrocarbons may be slowed down, which may be undesirable for hydrocarbon adsorption. The hydrophobic layer has a thickness of 500
nm or less, preferably 10 to 500 nm, more preferably 100 to 400 nm.

Next, the method for producing the adsorbent of the present invention will be described. First, the zeolite serving as the substrate may be a commercially available zeolite or a zeolite produced by a usual method. What is necessary is just to select suitably from the zeolites which have the said characteristic. In addition, there are natural and synthetic zeolites, but synthetic zeolites, especially synthetic zeolites produced using only inorganic compounds as raw materials, generally have high thermal stability and are less likely to lose ion exchange sites even in the operating temperature range. C3
The following hydrocarbons have excellent adsorption properties and are suitable zeolites. Further, the above zeolite is subjected to steaming treatment or treatment with an acid or alkali to form SiO ₂ / Al ₂ O.
The molar ratio of ₃ may be adjusted. Elements other than aluminum can be introduced by a commonly used ion exchange method or the like, or a metal such as silver can be supported by a normal supporting method.

The synthesized MFI-type zeolite is preferably of H-type or metal-exchanged type. The H-form may be subjected to ion exchange with hydrochloric acid, ammonium chloride, ammonium nitrate or the like by a usual method. The metal exchange type element is not particularly limited, but includes Ga, B, Fe, Ti, Zr, Co, Zn, and I.
n, Sn, Sb and P are preferable, and ion exchange may be performed by a usual method. The generated H-type or metal-exchanged zeolite is preferably calcined at 300 to 1000 ° C. In that case, you may perform in the presence of steam. Furthermore, the obtained MFI-type zeolite can be used after being appropriately treated with a substance such as an acid, an alkali, ammonia, a halogen, or another nonmetallic compound.

Next, a method for forming a hydrophobic layer on the outer surface of zeolite as a substrate will be described. As a method of forming the hydrophobic layer of zeolite on the outer surface of the base zeolite, the base zeolite is calcined at a high temperature, aluminum is desorbed from the zeolite framework structure on the outer surface, and the zeolite SiO ₂ / Al ₂ O By increasing the molar ratio of ₃ , hydrophobicity can be developed. SiO ₂ /
If the zeolite having a molar ratio of Al ₂ O ₃ of 200 or less is calcined to form a hydrophobic layer on its outer surface, the hydrocarbon adsorbent of the present invention can be easily produced. The firing conditions are at least 650 ° C, preferably at least 650-1000 ° C for 1 hour or more,
Preferably, it may be appropriately selected from 1 to 50 hours. Desorption of aluminum from the framework structure of the zeolite occurs from the outer surface of the zeolite and progresses to the inside over time. Therefore, the longer the baking is performed at a high temperature, the thicker the dealuminated hydrophobic layer becomes. By adjusting the firing temperature and time, a hydrophobic layer having a desired thickness can be formed.

As a method for forming amorphous silica on the outer surface of zeolite as a hydrophobic layer, there is a method by a CVD method using a silicon compound gas. Alternatively, a silica sol, a silicic acid aqueous solution, a silicate compound such as a silicate ester may be attached to the surface of the zeolite of the substrate, and then dried and fired. Baking is usually performed at 300 to 600 ° C. for about 0.5 to 10 hours. Attention must be paid to the fact that calcination at an excessively high temperature for a long time may destroy the framework structure of the zeolite of the substrate. The thickness of the hydrophobic layer may be adjusted by the amount of the silica source to be attached.

The hydrocarbon adsorbent obtained by the above method is
For example, molding may be performed using a binder such as silica, alumina, silica-alumina, magnesia, and zirconia. The shape of the hydrocarbon adsorbent obtained in the present invention is arbitrary, and may be, for example, a pellet, a plate, a column, or a lattice. Further, a substrate such as cordierite, mullite, alumina or the like such as a honeycomb or a lattice or a wire mesh may be coated with a hydrocarbon adsorbing material.

The hydrocarbon adsorbent of the present invention comprises other adsorbents,
For example, they may be used in combination with adsorbents having different pore structures. It can also be used in combination with an automobile exhaust gas purification catalyst, or carrying or compounding an automobile exhaust gas purification catalyst component. The hydrocarbon adsorbent of the present invention can be processed as described above and installed in the flow path of automobile exhaust gas to adsorb and remove hydrocarbons in automobile exhaust gas. The installation position may be, for example, immediately below the engine, upstream of the exhaust gas purifying catalyst, above, or downstream of another adsorbent. It is also possible to install in parallel with the exhaust gas flow path and introduce exhaust gas by a switching valve or the like only when necessary to adsorb and remove hydrocarbons.

[0027]

Next, the present invention will be described in detail with reference to examples.
However, the present invention is not limited to these examples.
No. [Example 1] Aluminum sulfate (18-hydrate) 17.0
g, sulfuric acid (97%) 14.5 g, water 250 g
Liquid (A liquid), water glass (JIS No.3 sodium silicate)
Use a solution consisting of 221 g and 250 g of water (referred to as solution B)
I thought. After mixing solution A and solution B, mordenite powder
After adding 0.3 g (manufactured by Tosoh), put it in an autoclave.
The mixture was kept at 160 ° C. with stirring for 5 days while being sealed.
After cooling, the reaction product 1 was filtered and washed,
Let dry. As a result of X-ray diffraction,
Zeolite. In addition, this zeolite is
It was calcined at 550 ° C. for 4 hours in a stream. Apply this zeolite
Perform ion exchange with a constant ammonium nitrate solution to obtain
After drying the ammonium-type zeolite at 120 ° C.,
It was calcined at 550 ° C. for 4 hours to obtain calcined zeolite 1. This
Of calcined zeolite 1_Two/ Al _TwoO_ThreeThe molar ratio is 3
It was 5.4. This calcined zeolite 1 is placed in a muffle furnace
After further calcination at 800 ° C for 4 hours, 0.5 mol
Treat with liquid, wash with water and dry. Then again at 550 ° C
It was baked for 4 hours. This is compression molded to 32 to 64 mesh
The hydrocarbon adsorbing material 1 was obtained by adjusting the particle size in the menu. This hydrocarbon
Table 1 shows the properties of the adsorbent 1.

Example 2 The calcined zeolite 1 obtained in Example 1 was calcined in a muffle furnace at 650 ° C. for 10 hours, treated with a 0.5 molar nitric acid solution, washed with water and dried in the same manner as in Example 1. Then, it was fired again at 550 ° C. for 4 hours. This was compression-molded to obtain a hydrocarbon adsorbent 2 having a uniform particle size of 32 to 64 mesh. Table 1 shows the properties of the hydrocarbon adsorbent 2.

Example 3 10 g of the calcined zeolite 1 obtained in Example 1 was immersed in a mixed solution of 50 ml of tetraethoxysilane and 20 ml of butyl alcohol. After being treated at 60 ° C. for 2 hours while refluxing, the immersion was filtered off and washed with water. After drying this at 120 ° C.,
The mixture was calcined at 00 ° C. for 4 hours to obtain a hydrocarbon adsorbent 3. Table 1 shows the properties of the hydrocarbon adsorbent 3. Although the silica-alumina ratio of the hydrocarbon adsorbent 3 as a whole does not change much, it can be seen that the silica-alumina ratio on the outer surface is high.

Example 4 12.2 g of tetrabutylammonium bromide, 6.3 g of sulfuric acid (97%), and 15 parts of water
Solution (hereinafter referred to as "solution A"), water glass (JIS)
A solution (hereinafter referred to as solution B) consisting of 52.5 g of No. 3 sodium silicate and 150 g of water was prepared. 40 g of the calcined zeolite 1 obtained in Example 1 was taken, put into 200 g of water, and stirred to form a slurry. Solution A and Solution B were added to the slurry and mixed well.
Hold at 25 ° C. with stirring for 25 hours, and calcine zeolite 1
The MEL type zeolite having a high silica composition was crystallized on the surface of the (MFI type). After cooling, the reaction product was filtered, washed, and dried at 120 ° C. As a result of X-ray diffraction, the product had a peak indicating the structure of MEL-type zeolite in addition to MFI-type zeolite. Further, the zeolite was calcined at 550 ° C. for 4 hours in an air stream. This zeolite is ion-exchanged with a 1N ammonium nitrate solution,
The obtained ammonium zeolite was dried at 120 ° C., and then calcined at 550 ° C. for 4 hours to obtain calcined zeolite 4. The SiO ₂ / Al ₂ O ₃ molar ratio of the calcined zeolite 4 was 46. The calcined zeolite 4 is compression-molded and the particle size is adjusted to 32 to 64 mesh.
I got This molded zeolite 4 is heated at 800 ° C. in a muffle furnace.
For 4 hours to obtain a hydrocarbon adsorbent 4. Table 1 shows the properties of the hydrocarbon adsorbent 4.

[Example 5]
Minium (18-hydrate) 17.0 g, sulfuric acid (97%) 1
A solution consisting of 4.5 g and 250 g of water (referred to as solution A), water
221 g of glass (JIS No. 3 sodium silicate), 250 g of water
Aluminum sulfate instead of a solution consisting of
Um (18 hydrates), gallium nitrate (9 hydrates)
From 1.9 g, 17.0 g of sulfuric acid (97%), and 250 g of water
Solution (A solution), water glass (JIS No. 3 silicate
A solution consisting of 212 g of water and 250 g of water (solution B)
Prepared). Autoclave as in Example 1
Thus, a reaction product 5 was obtained. This product 5 is placed in an air stream 55
Baking at 0 ° C. for 4 hours. This zeolite is treated with 1 N nitric acid
Ion exchange with ammonium solution
After drying the zeolite at 120 ° C., 550 ° C.
For 4 hours to obtain calcined zeolite 5. This fired ze
Olite 5 SiO_Two/ Al_TwoO_ThreeThe molar ratio is 47.3,
SiO_Two/ Ga_TwoO _ThreeThe molar ratio was 338. This yaki
The zeolite 5 was further calcined at 800 ° C. for 4 hours,
Treated with a 0.5 molar nitric acid solution as in Example 1, washed with water and dried
Dried. Next, it was baked at 550 ° C. for 4 hours. Press this
Shrink molding to uniform particle size to 32-64 mesh
Adhesive 5 was obtained. Table 2 shows the properties of the hydrocarbon adsorbent 5.

Example 6 The calcined zeolite 1 obtained in Example 1 was calcined in a muffle furnace at 650 ° C. for 10 hours, treated with a 0.5 molar nitric acid solution, washed with water and dried in the same manner as in Example 1. Then, it was fired again at 550 ° C. for 4 hours. 50 g of the zeolite obtained here was taken, and phosphorus was supported using 1.0 M orthophosphoric acid. Silver was supported on this using a 0.5N silver nitrate solution. The support was dried at 120 ° C., calcined in a muffle furnace at 650 ° C. for 4 hours, and compression-molded to obtain a hydrocarbon adsorbent 6 having a particle size of 32 to 64 mesh (Ag 4 wt. %, P1.5
4 wt% supported ZSM5 zeolite). Table 2 shows the properties of the hydrocarbon adsorbent 6.

[Comparative Example 1] The calcined zeolite 1 obtained in Example 1 was compression-molded to obtain a hydrocarbon adsorbent 7 having a uniform particle size of 32 to 64 mesh. Table 2 shows the properties of the hydrocarbon adsorbent 7.
Shown in Comparative Example 2 Commercially available MFI-type zeolite (UETIKO)
NZ PZ-2 900H zeolite, SiO ₂ / Al
₂ O ₃ molar ratio 900) was compression-molded to make the particle size uniform to 32 to 64 mesh to obtain a hydrocarbon adsorbent 8. Table 2 shows the properties of the hydrocarbon adsorbent 8.

Comparative Example 3 A commercially available MFI type zeolite (PZ-2 900H zeolite manufactured by UETIKON,
(SiO ₂ / Al ₂ O ₃ molar ratio 900) was calcined at 800 ° C. for 4 hours, treated with a 0.5 molar nitric acid solution, washed with water and dried as in Example 1. Next, it was baked at 550 ° C. for 4 hours. This was compression-molded to obtain a hydrocarbon adsorbent 9 having a uniform particle size of 32 to 64 mesh. Table 3 shows the properties of the hydrocarbon adsorbent 9.

Comparative Example 4 The same commercial MFI as Comparative Example 2 was used instead of 40 g of the calcined zeolite 1 obtained in Example 1.
A hydrocarbon adsorbent 10 was obtained in the same manner as in Example 4 except that 40 g of the zeolite was used. Table 3 shows the properties of the hydrocarbon adsorbent 10. Comparative Example 5 The calcined zeolite 1 obtained in Example 1 was loaded with Ag and P in the same manner as in Example 6, and then calcined in a muffle furnace at 500 ° C. for 4 hours. This is compression molded to 32
The particle size was adjusted to ~ 64 mesh to obtain a hydrocarbon adsorbent 11. Table 3 shows the properties of the hydrocarbon adsorbent 11.

Comparative Example 6 The calcined zeolite 1 of Example 6 was used.
Instead of using 50 g of the same commercially available MFI as in Comparative Example 2.
A hydrocarbon adsorbent 12 was obtained in the same manner as in Example 6, except that 50 g of the zeolite was used. Table 3 shows the properties of the hydrocarbon adsorbent 12. [Example 7, Comparative Example 7] The above Examples 1 to 6, Comparative Examples 1 to
A stainless steel reaction tube was filled with 50 mg of each of the hydrocarbon adsorbents 1 to 12 obtained in 6, and the hydrocarbon adsorption performance was evaluated.
Air (45cc / min) as carrier gas in the reaction tube
And kept at 80 ° C. for 1 hour while flowing a mixture of water and water (5 cc / min). Next, 0.2 cc of propylene gas as lower hydrocarbons was taken in a syringe, injected into the carrier gas, and propylene was introduced into the reaction tube in a pulsed manner. The propylene concentration of the gas at the outlet of the reaction tube was measured to calculate the amount of propylene adsorbed on the hydrocarbon adsorbent. The results are shown in Table 4 as the amount of propylene adsorbed per gram of adsorbent (g).

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

According to the hydrocarbon adsorbent in exhaust gas of the present invention, C3 hydrocarbons are adsorbed efficiently even at 80 ° C.

Claims (12)

[Claims] An outer surface having a hydrophobic porous refractory layer,
Internal substrate is SiO _Two/ Al_TwoO_ThreeMolar ratio of 200 or less
Hydrocarbon adsorbent in automobile exhaust gas composed of zeolite. 2. The method according to claim 1, wherein the thickness of the hydrophobic porous refractory layer on the outer surface is 500 nm or less, and the zeolite of the substrate is SiO ₂ /
Hydrocarbon adsorbent according to claim 1 wherein the al ₂ O ₃ molar ratio from 30 to 200. 3. The base zeolite is of MFI type, MEL
Type, BEA type, FAU type, MOR type, FER type, MTW
Type, MTT type, TON type, ERI type, CHA type, LTL
The hydrocarbon adsorbent according to claim 1, comprising at least one skeletal structure selected from a type, an LTA type, an EUO type, and a NES type. 4. The zeolite according to claim 1, wherein the zeolite as the substrate comprises an MFI-type zeolite prepared from only an inorganic compound.
A hydrocarbon adsorbent according to any of the preceding claims. 5. The method according to claim 1, wherein the skeleton structure of the base zeolite contains Ga,
B, Fe, Ti, Zr, Co, Zn, In, Sn, Sb
The hydrocarbon adsorbent according to any one of claims 1 to 4, comprising at least one element selected from P and P. 6. The hydrocarbon adsorbent according to claim 1, wherein the base zeolite is a metal-supported zeolite. 7. The hydrocarbon adsorbent according to claim 6, wherein the supported metal is silver. 8. The hydrocarbon adsorbent according to claim 1, wherein the hydrophobic porous refractory layer on the outer surface is made of zeolite. 9. The hydrocarbon adsorbent according to claim 8, wherein the framework structure of the zeolite of the hydrophobic porous refractory layer on the outer surface is MFI type or MEL type. 10. The hydrocarbon adsorbent according to claim 8, wherein the zeolite of the hydrophobic porous refractory layer on the outer surface has a skeleton structure different from that of the base zeolite. 11. An SiO ₂ / Al ₂ O ₃ molar ratio of 200
The method for producing a hydrocarbon adsorbent according to claim 8 or 9, wherein the following zeolite is calcined at 650 ° C or more for 1 hour or more. 12. The hydrocarbon adsorbent according to claim 1, wherein the hydrophobic porous refractory layer on the outer surface is made of amorphous silica.