JP3177678B2 - NOx adsorbent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing low-concentration NOx from a gas in which a large amount of moisture coexists with low-concentration nitrogen oxides (NOx) of several ppm, such as road tunnel ventilation gas.
The present invention relates to a NOx adsorbent that efficiently adsorbs and removes NOx.

[0002]

2. Description of the Related Art Conventionally, adsorbents for low-concentration NOx as described above include ruthenium,
NOx adsorbents carrying cerium and the like, and manganese salts added as manganese salts as surface modifiers for amorphous titanium oxide
There has been proposed a NOx adsorbent or the like in which ruthenium and cerium are sequentially supported on an n-Ti-based surface-modified titanium oxide carrier, and silver, copper, manganese and the like are added thereto.

[0003]

SUMMARY OF THE INVENTION N using ruthenium
It is considered that the NOx adsorption ability (expressed by NOx adsorption speed, NOx adsorption capacity, and the like) of the Ox adsorbent can be improved by increasing the surface of the supported ruthenium particles and / or the interface between ruthenium and other components. That is, if the degree of dispersion of ruthenium on the adsorbent is constant, the NOx adsorption ability is considered to be proportional to the amount of ruthenium carried.

However, in the adsorbent obtained by the above-described conventional supporting method, as shown in FIG.
The x-adsorbing ability is saturated at a ruthenium addition amount of 2 (wt%) or more with respect to the weight of the carrier, and the effect of increasing the ruthenium addition amount is hardly recognized.

[0005] Further, the NOx adsorbing ability after heating at 400 ° C is generally low, and the effect of increasing the amount of added ruthenium is hardly recognized.

From the above facts, in the conventional loading method, as the loading amount increases, the degree of dispersion of ruthenium decreases, and the surface and interface of the ruthenium particles are not proportional to the loading amount of ruthenium. It is not proportional to the load. Further, since thermal aggregation is more likely to occur as the degree of dispersion decreases, it is considered that the NOx adsorbing ability after heating at 400 ° C. becomes larger as the amount of ruthenium supported increases, and the effect of increasing the supported amount cannot be recognized.

[0007] The present invention provides a method for producing NO per ruthenium supported amount.
An object of the present invention is to increase the initial value of the x-adsorbing ability and at the same time, prevent a decrease in performance in repeated use of adsorption and desorption.

[0008]

In order to increase the ruthenium surface and / or interface per the amount of ruthenium supported, it is important to support the ruthenium particles with a high degree of dispersion.

It is known that when a porous carrier having an acidic point is immersed in an aqueous ruthenium chloride solution, ruthenium ions are adsorbed to the acidic point of the carrier. If this is dried and fired, a NOx adsorbent in which ruthenium is highly dispersed and supported can be prepared. However, if free acid sites remain around the adsorbed and supported ruthenium, or free ruthenium that is not adsorbed and supported remains, ruthenium ions can easily move on the supported surface, drying and firing, and regeneration of the adsorbent. It is considered that coagulation occurs due to the heating of, and the degree of dispersion of ruthenium decreases.

In order to prevent this, other inexpensive metal ions may be adsorbed and carried on the free acid sites of the carrier (see FIG. 2). It is preferable that the metal ion species to be added have the same or slightly weaker adsorbability to ruthenium as the carrier. This is because if the adsorbability to the carrier is too strong, ruthenium ions are eliminated and the added metal fills the acidic sites, while if it is too weak, it is not effectively adsorbed to the free acidic sites, preventing the surface diffusion of ruthenium. Can not. The addition time of the other metal may be any time before the coagulation of the adsorbed and supported ruthenium occurs, but practically, it is preferable to perform the addition simultaneously with the operation of adsorbing and supporting the ruthenium.

[0011] The present inventors have proposed iron ions (F) as metal ions having the same adsorptivity to an acidic carrier as ruthenium ions.
e ²⁺ and / or Fe ³⁺ ) have been found to be suitable. So we changed to the conventional ruthenium loading method ,
Ruthenium and iron are supported simultaneously or sequentially, and
A NOx adsorbent carrying aluminum
When the deposition amount was measured, it was found that the initial NOx was higher than before.
It has been found that the compound has an adsorption ability and the effect of increasing the amount of supported ruthenium also increases. For example, a mixture of ruthenium chloride and iron chloride
The carrier is impregnated with the combined aqueous solution, dried and calcined.
NOx adsorbent loaded with carbon dioxide (Samples A to D described later)
And the NOx saturation absorption with respect to the amount of ruthenium carried
When the amount of deposition was measured, this was
Higher initial NOx adsorption capacity than NOx adsorbents
The effect of increasing the amount of ruthenium supported was also high (see FIG. 3).
See).

[0012] This means that the mixed loading of ruthenium and iron improves the degree of dispersion of the loaded ruthenium, and
This indicates that iron was well adsorbed and supported on the acidic points between the ruthenium particles, so that aggregation of the ruthenium particles during drying and firing could be prevented.

Therefore, it is considered that the principle of the method according to the present invention is effective in all cases in which a small amount of ions are adsorbed and supported on a carrier having an acidic point in a highly dispersed manner.

Further, in order for the NOx adsorbent to withstand repeated use, it is necessary to suppress the agglomeration of the ruthenium particles due to heating during regeneration of the adsorbent and, at the same time, to suppress the thermal change of the substance forming the interface with ruthenium. is there.

Therefore, after preparing a NOx adsorbent having high initial performance by the above-mentioned method, and further adding manganese (sample E), deterioration due to repeated NOx adsorption and regeneration by heating at 300 ° C. could be prevented. (See FIG. 4).

It is desirable that the addition of manganese be performed using the same nitrate as the cerium raw material after all the steps up to the loading of cerium are completed. Also, instead of manganese, silver, copper,
The same effect was obtained by using iron nitrate.

The first NOx adsorbent according to the present invention is a NOx adsorbent comprising ruthenium and cerium supported on a carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide.
In the adsorbent, the carrier carries ruthenium and iron,
Thereafter, it is obtained by supporting cerium.

A second NOx adsorbent according to the present invention is a NOx adsorbent comprising ruthenium and cerium supported on a carrier comprising titanium oxide or a Mn-Ti-based surface-modified titanium oxide.
The adsorbent is obtained by supporting ruthenium and at least one of iron, nickel and chromium on the carrier, and then supporting cerium.

In order to produce the first NOx adsorbent, iron chloride is used in an amount of 0.01 to 1 (mol / l), preferably 0.5 to 1 (mol / l).
A method is preferred in which a carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide is immersed in a ruthenium supporting solution containing 0.3 (mol / l), baked at 150 to 300 ° C, and then cerium is supported. .

To produce the second NOx adsorbent, iron,
A total concentration of at least one chloride of nickel and chromium of 0.01 to 2 (mol / l), preferably 0.02
A carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide is immersed in a ruthenium-supporting solution containing 5 to 0.5 (mol / l), and baked at 150 to 300 ° C.
Thereafter, a method of supporting cerium is preferable.

In the second method for producing a NOx adsorbent, ruthenium and at least one of iron, nickel and chromium are supported on a support made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide. The obtained ruthenium carrier is immersed in an aqueous solution containing 2.0 to 3.2 (mol / l), preferably 2.8 to 3.2 (mol / l) of cerium nitrate, at 250 to 380 ° C, preferably 300 ~
It is preferable to carry cerium by firing at 350 ° C.

In the first or second NOx adsorbent,
The support made of a Mn-Ti-based surface-modified titanium oxide is obtained, for example, by adding a manganese compound to amorphous titania and firing.

In the first or second NOx adsorbent,
The loading of ruthenium and iron on the carrier may be simultaneous or sequential.

[0024] The first or second NOx adsorbent may further contain at least one of silver, manganese, copper and iron.

In order to produce the first or second NOx adsorbent containing silver, manganese, copper and / or iron, ruthenium and iron are added to a carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide. , Nickel and chromium, and the obtained ruthenium-supported material was converted from cerium nitrate to 2.0 to 3.2 (mol / l), preferably 2.8 to 3.2 (mol / l). ), And calcined at 250 to 380 ° C., preferably 300 to 350 ° C., and the obtained cerium carrier is mixed with at least one nitrate of at least one of silver, manganese, copper and iron.
3 to 1.5 (mol / l), preferably 0.5 to 1.0
(Mol / l), immersed in an aqueous solution containing 250 to 380 ° C,
Desirably, a method of firing at 300 to 350 ° C. is preferable.

It is also preferable that the first or second NOx adsorbent is a plate-like NOx adsorbent obtained by holding the NOx adsorbent on a noncombustible fiber preform.

The NOx adsorbent according to the present invention is effective in efficiently adsorbing and removing low-concentration NOx from a gas in which a large amount of moisture coexists with a low concentration of several ppm NOx, such as a road tunnel ventilation gas. It is a target.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

EXAMPLES Preparation of Samples A to E Sample A A titanium oxide colloid solution (solid content of 32 parts by weight) obtained by a nitrate hydrolysis method was impregnated and held in a ceramic paper having a thickness of 0.5 mm, dried at 110 ° C., and dried to form an amorphous material. A plate-like material holding 165 g / m ^{2 of high} quality titanium oxide was obtained. This was immersed in a 1.0 (mol / l) manganese nitrate aqueous solution for 6 minutes and dried at 110 ° C. This plate was fired at 450 ° C. for 3 hours in an air stream to obtain a surface-modified plate-shaped titanium oxide support.

This plate-like carrier was coated with ruthenium 17 (g / g).
l), iron 4 (g / l) ruthenium chloride / iron (II) chloride
After immersion in a mixed aqueous solution for 5 minutes and drying at 110 ° C.,
It was baked at 30 ° C. for 1 hour. Furthermore, this is cerium 400
(G / l) in cerium nitrate aqueous solution for 10 minutes,
After drying at 10 ° C., it was baked at 330 ° C. for 3 hours.
Was prepared.

Sample B Sample B was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A was 12 (g / l).

Sample C Sample C was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A was 7 (g / l).

Sample D Sample D was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A was 3 (g / l).

Sample E A sample prepared under the same conditions as in Sample C was further immersed in a 0.5 (mol / l) aqueous solution of manganese nitrate for 10 minutes.
After drying at 0 ° C., the sample was fired at 330 ° C. for 3 hours to prepare Sample E.

The carrier compositions of Samples A to E and 200
Table 1 shows the NOx saturated adsorption amount (initial) in a gas containing ppm NO.

[0035]

[Table 1]

Comparative Example Preparation of Samples A 'to D' Sample A 'A surface-modified plate-like titanium oxide carrier similar to that used in Sample A was immersed in a ruthenium chloride aqueous solution of ruthenium 17 (g / l) for 5 minutes. After drying at 110 ° C.,
Fired for hours. This was immersed in a cerium nitrate aqueous solution of cerium 400 (g / l) for 10 minutes, dried at 110 ° C., and baked at 330 ° C. for 3 hours to prepare a sample A ′.

[0037]

Sample B 'Sample B' was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A 'was 12 (g / l).

Sample C 'Sample C' was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A 'was changed to 7 (g / l).

Sample D 'Sample D' was prepared in the same manner as Sample A, except that the ruthenium concentration of the immersion liquid of Sample A 'was changed to 3 (g / l).

The carrier composition of Samples A ′ to D ′, and 2
Table 2 shows the NOx saturated adsorption amount (initial and after heating at 400 ° C. for 10 hours) in a gas containing 00 ppm of NO.

[0042]

[Table 2]

[0043]

As is clear from FIG. 4, the NOx adsorbent in which ruthenium is supported on the carrier in a highly dispersed state by the method of the present invention and the structure is stabilized with manganese is higher than that of the conventional method. It turns out that it shows activity and stability.

[Brief description of the drawings]

FIG. 1 is a graph showing a ruthenium addition effect of a conventional NOx adsorbent.

FIG. 2 is a schematic view showing an image of preventing ruthenium aggregation.

FIG. 3 is a graph showing a comparison of a ruthenium addition effect of a NOx adsorbent.

FIG. 4 is a graph showing a comparison of durability.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiro Kondo 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Inside Tachibashi Shipbuilding Co., Ltd. (72) Atsushi Fukuju 5-3-3 Nishikujo, Konohana-ku, Osaka No. 28 Inside Tachibana Shipbuilding Co., Ltd. (56) References JP-A-8-192045 (JP, A) JP-A 8-196900 (JP, A) JP-A-7-60114 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) B01J 20/00-20/34

Claims (9)

(57) [Claims] 1. A NOx adsorbent comprising ruthenium and cerium supported on a carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide, wherein ruthenium and iron are supported on the carrier, and then cerium is supported. A NOx adsorbent characterized by being obtained by: 2. A NOx adsorbent comprising ruthenium and cerium supported on a carrier made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide, wherein the carrier comprises at least one of ruthenium, iron, nickel and chromium. Characterized in that the NOx adsorbent is obtained by supporting cerium and then supporting cerium. 3. A NOx adsorbent obtained by further adding at least one of silver, manganese, copper and iron to the NOx adsorbent according to claim 1. 4. The NO according to claim 1, wherein
A plate-like NOx adsorbent, wherein the x-sorbent is held by a noncombustible fiber preform. 5. A solution for supporting ruthenium containing 0.01 to 1 (mol / l) of iron chloride, wherein titanium oxide or Mn-T
A carrier made of i-type surface-modified titanium oxide is immersed in
A method for producing a NOx adsorbent, characterized in that the NOx adsorbent is calcined at a temperature of up to 300 ° C. and then cerium is supported. 6. A total concentration of at least one chloride of iron, nickel and chromium of 0.01 to 2 (mol / l).
The titanium oxide or M
dipping a carrier made of n-Ti-based surface-modified titanium oxide,
A method for producing a NOx adsorbent, characterized in that the NOx adsorbent is calcined at 150 to 300 ° C. and then cerium is supported. 7. A support made of titanium oxide or a Mn-Ti-based surface-modified titanium oxide, on which ruthenium and at least one of iron, nickel and chromium are supported. 2.0 ~
Immersed in an aqueous solution containing 3.2 (mol / l),
A method for producing a NOx adsorbent, characterized by firing at 0 ° C. 8. A support made of titanium oxide or a Mn—Ti-based surface-modified titanium oxide, on which ruthenium and at least one of iron, nickel and chromium are supported. 2.0 ~
Immersed in an aqueous solution containing 3.2 (mol / l),
Baking at 0 ° C., then the obtained cerium carrier
Dipping in an aqueous solution containing 0.3 to 1.5 (mol / l) of at least one nitrate of silver, manganese, copper and iron;
A method for producing a NOx adsorbent, characterized by firing at 250 to 380 ° C. 9. The NOx according to claim 1, wherein:
A NOx removal method characterized by contacting a gas containing NOx with an adsorbent to adsorb NOx in the gas.