JPH0780302A - Nox removing catalyst consisting of transition metal boride - Google Patents

Abstract

PURPOSE:To obtain a catalyst capable of removing NOx contained in an exhaust gas and capable of removing NOx even from an oxygen-excess exhaust gas by forming the catalyst with at least one kind of transition metal boride expressed by a specified formula. CONSTITUTION:This NOx removing catalyst consists of at least one kind of transition metal boride expressed by MaBb, where M is a transition metal, B is boron, (a) and (b) are a real number, and 0<b/a<200. In this case, when only one kind of M is used in the MaBb, Pm in the Lanthanide series and Pa Cm Bk Cf Es, Fm, Md, No and Lr in the Actinide series are not incorporated into the catalyst. The NOx contained in the exhaust gas are removed by this catalyst, and further even the NOx in the oxygen-excess exhaust gas are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst having the property of removing nitrogen oxides from exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for removing nitrogen oxides, an ammonia selective reduction method or a so-called ternary catalyst of Pt-Pd-Rh system has been used. However, in the ammonia selective reduction method, the fact that denitration must be performed using NH ₃ which is a dangerous substance is a major obstacle to practical use.
Further, the ternary catalyst has a drawback that it is poisoned by oxygen coexisting in the exhaust gas and its activity is significantly reduced.

At present, in addition to such a method, oxides such as alumina and zirconia are used to produce propylene,
A catalyst for removing nitrogen oxides using a hydrocarbon such as propane as a reducing agent has been proposed (Catalyst, 33, (2), 61).
-64 (1991)). Further, as a catalyst for decomposing nitrogen oxides without using hydrocarbons, perovskite type oxides utilizing oxygen defects as active sites have been proposed (Chemical Society of Japan, (5), 604-610 (199).
1)).

However, the nitrogen oxide removing mechanism of a catalyst for removing nitrogen oxides by using such hydrocarbons as a reducing agent is centered on a redox reaction for partially oxidizing hydrocarbons and simultaneously reducing nitrogen oxides. Therefore, the catalytic activity is largely controlled by the combustion of hydrocarbons, that is, the oxidation behavior, and in the so-called lean burn region where oxygen is excessive, the complete combustion of hydrocarbons has priority, so the decomposition and removal characteristics of nitrogen oxides are sufficient. The perovskite-type oxide catalyst, which decomposes nitrogen oxides without using hydrocarbons, has the disadvantage that its decomposition activity is significantly reduced in the presence of oxygen. However, it is not in practical use yet because it does not have sufficiently high catalytic activity and has no long-term stability.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a catalyst having a characteristic of removing nitrogen oxides from exhaust gas even in the presence of oxygen and having excellent durability. .

[0006]

In the present invention, as a result of continuous research to develop a catalyst having a characteristic of removing nitrogen oxides from exhaust gas even in the presence of oxygen and having excellent durability, the general formula In the boride represented by MaBb (M = transition metal, B = boron, a and b are real numbers), 0 <
We have found that boride of at least one transition metal having b / a <200 has a high ability to remove nitrogen oxides in exhaust gas and is excellent in durability, and has found the present invention. .

Next, the present invention will be described in detail.

The composition of the nitrogen oxide removing catalyst of the present invention is 0 <b / a <20 in the boride represented by the general formula: MaBb (M = transition metal, B = boron, a and b are real numbers).
It must be a boride of at least one transition metal that is zero.

However, in the boride represented by MaBb in the present invention, when M is one kind, Pm of the lanthanoid series, Pa, Cm, Bk, Cf of the actinide series,
Borides containing Ms of Es, Fm, Md, No, and Lr are not included. This is because borides containing only these elements are unstable, and borides do not exist under normal circumstances.

Examples of borides represented by MaBb include ScB ₂ and Sc when M is a group IIIa element.
_{B 4, ScB 6, ScB 12} , YB 2, YB 4, YB 6, YB
_In the case of group IVa elements such as ₁₂ , YB ₆₆ , LaB ₂ , LaB ₄ , LaB ₆ , LaB ₁₂ , Ti ₂ B, TiB, Ti ₃
B ₄ , TiB ₂ , ZrB, ZrB ₂ , ZrB ₆ , ZrB ₁₂ ,
In the case of a Va group element such as HfB and HfB ₂ , V ₂ B,
V ₃ B ₂ , VB, V ₃ B ₄ , V ₂ B ₃ , VB ₂ , Nb ₂ B, Nb
₃ B ₂ , NbB, Nb ₃ B ₄ , NbB ₂ , Ta ₂ B, Ta
₃ B _2, TaB, Ta ₂ etc. B _3, TaB _2, in the case of Group VIa _{elements, Cr 4 B, Cr 2 B} , Cr 5 B 3, Cr 3 B 2,
CrB, Cr ₃ B ₄ , CrB ₂ , CrB ₄ , CrB ₆ , Mo ₂
B, Mo ₃ B ₂ , MoB, MoB ₂ , Mo ₂ B ₄ , MoB ₃ ,
MoB ₁₂ , W ₂ B, WB, WB ₂ , W ₂ B ₅ , WB ₄ , Cr
In the case of a Group VIIa element such as B ₁₂ , Mn ₄ B, Mn ₂
B, MnB, Mn ₃ B ₄ , Mn ₃ B ₂ , MnB ₂ , MnB ₄ ,
Tc ₃ B, Tc ₇ B ₃ , TcB, Tc ₃ B ₄ , TcB ₂ , Re
₄ B, Re ₃ B, Re ₇ B ₃ , Re ₂ B ₂ , ReB, Re
₃ B ₄ , Re ₂ B ₃ , ReB ₂ , Re ₂ B ₅ , ReB _3, etc., V
In the case of a group III element, Fe ₂ B, FeB, Ru
₇ B ₃ , Ru ₁₁ B ₈ , RuB _1.1 , Ru ₂ B ₃ , RuB ₂ , R
u ₂ B ₅ , OsB, OsB ₂ , Os ₂ B ₅ , Co ₃ B, Co ₂
B, CoB, Rh ₇ B ₃ , Rh ₂ B, RhB ₁ . ₁ , Rh
B ₂ , IrB _1.1 , IrB ₂ , Ni ₃ B, Ni ₂ B, Ni ₃ B
₂ , Ni ₄ B ₃ , NiB, Ni ₂ B ₃ , NiB ₂ , NiB ₁₂ ,
Pd ₃ B, Pd ₅ B ₂ , Pd ₂ B, Pt ₃ B, Pt ₂ B, Pt
_In the case of a group Ib element such as ₃ B ₂ or PtB, CuB ₂₂ ,
In the case of lanthanoid series elements such as AgB ₂ and AuB ₂ , CeB ₄ , CeB ₆ , PrB ₄ , PrB ₆ , NdB ₄ ,
NdB ₆ , SmB ₄ , SmB ₆ , EuB ₄ , EuB ₆ , Gd
B ₂ , GdB ₄ , GdB ₆ , GdB ₁₀₀ , TbB ₂ , Tb
_{B 4, TbB 6, TbB 12} , TbB 70, DyB 2, Dy
B ₄ , DyB ₆ , DyB ₁₂ , HoB ₂ , HoB ₄ , Ho
_{B 6, HoB 12, HoB 70} , ErB 2, ErB 4, Er
_{B 6, ErB 12, TmB 4} , TmB 6, TmB 12, Yb
B ₄ , YbB ₆ , YbB ₁₂ , YbB ₇₀ , LuB ₂ , Lu
In the case of actinoid series elements such as B ₄ , LuB ₆ , and LuB ₁₂ , ThB ₄ , ThB ₆ , ThB ₁₈ , ThB ₆₆ , U
B ₂ , UB ₄ , UB ₁₂ , NpB ₂ , NpB ₄ , NpB ₆ , N
pB ₁₂ , PuB, PuB ₂ , PuB ₄ , PuB ₆ , PuB
₁₂ , PuB ₁₀₀ , AmB ₄ , AmB _{6 and the} like.

Further, the above boride may be used in combination of two or more kinds. In that case, lanthanoid series Pm, actinide series Pa, Cm, Bk, C.
A boride having M of f, Es, Fm, Md, No, and Lr can also be included. Also, IIb group Zn, Cd, H
g, IIIb group Ga, In, Tl, IVb group Ge,
It is also possible to simultaneously use Sn, Pb, Vb group Bi borides.

Of the above borides, from the viewpoint of being excellent in oxidation resistance, preferably IIIa group, IVa group,
It is practically suitable to use a boride of a Va group transition metal.

The method for producing the nitrogen oxide removing catalyst of the present invention is not particularly limited, and powdered MaBb (M represents at least one transition metal) may be used as it is. MaBb in the form of particles may be obtained by directly boring the metal M. To obtain fine powder, the oxide of M is reduced with a reducing metal (eg, Mg, Al, Zn, etc.) in an inert atmosphere. It can also be obtained by reacting with boron. However, in this case, as a post-treatment, it is necessary to remove the by-product transition metal oxide with a dilute acid or the like. It is also possible to obtain a boride by a liquid phase reaction using an alkoxide or an inorganic salt for M or boron.

When powdered MaBb is used, BE
The larger the T value (specific surface area), the higher the catalytic activity. However, under low SV, the removal efficiency of nitrogen oxides is good if it is 0.1 m ² / g or more, but under high SV, this value is larger. Is preferred.

Further, MaBb is formed on the porous catalyst carrier.
When used as a MaBb film by coating
After immersing the porous catalyst carrier in an aqueous solution or a non-aqueous solution in which MaBb is dispersed, it is baked in a reducing atmosphere, or boron is added to the surface of M oxide (M is at least one or more transition metal elements) Implanting using the sputtering method or the ion plantation method, Ma on the surface
A Bb film may be formed.

Furthermore, as is generally seen in conventional oxide catalysts such as alumina and zirconia, a noble metal such as platinum, palladium or rhodium or an active metal species such as copper, cobalt, nickel or iron is supported. Is also effective as a method for improving the nitrogen oxide removal catalyst function.

The boride-based exhaust gas purifying catalyst of the present invention is used for removing nitrogen oxides from oxygen-excess exhaust gas. The removal of nitrogen oxides in the oxygen excess exhaust gas can be performed by bringing the exhaust gas removal catalyst of the present invention into contact with the exhaust gas containing nitrogen oxides. The exhaust gas targeted by the present invention may be any exhaust gas containing nitrogen oxides. Further, in addition to nitrogen oxides, exhaust gas containing oxygen in excess of the amount of oxygen required to completely oxidize carbon monoxide, hydrocarbons and hydrogen generally contained in exhaust gas may be used, Further, it may actually contain carbon monoxide, hydrocarbons, hydrogen and water. Specific examples of such exhaust gas include exhaust gas discharged from an internal combustion engine such as an automobile, particularly exhaust gas in a state where the air-fuel ratio is large (so-called lean region). The use condition of the catalyst is not particularly limited, but the temperature range is 100 to 1000 ° C, and further 500 to 800 ° C.
Is preferred. For SV, 500h ^{-1 to} 500
It may be 000 h ^-1 .

[0018]

As described above, the present invention has a characteristic of removing nitrogen oxides contained in exhaust gas, and further has a characteristic of removing nitrogen oxides even in exhaust gas with excess oxygen. Is provided.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 LaB ₆ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² and then adjusted to a particle size of 12 mesh or more and 20 mesh or less, and then kept at a usual size. NO = 1300p by pressure fixed bed flow reactor
Nitrogen oxide removal activity was measured in the temperature range of 400-800 degreeC in SV = 2500 / h using the reaction gas of pm. The results are shown in Table 1.

[0021]

[Table 1]

Example 2 LaB ₆ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² and then adjusted to a particle size of 12 mesh or more and 20 mesh or less, and then kept in a usual state. NO = 1300p by pressure fixed bed flow reactor
pm, using a reaction gas of propylene = 800 ppm,
Nitrogen oxide removal activity of 40 at SV = 2500 / h
It measured in the temperature range of 0-800 degreeC. The results are shown in Table 2.
Shown in.

[0023]

[Table 2]

Example 3 ZrB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² and then adjusted to a particle size of 12 mesh or more and 20 mesh or less, and then was usually used. NO = 1300p by pressure fixed bed flow reactor
Nitrogen oxide removal activity was measured in the temperature range of 400-800 degreeC in SV = 2500 / h using the reaction gas of pm. The results are shown in Table 3.

[0025]

[Table 3]

Example 4 ZrB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² , and was then adjusted to a particle size of 12 mesh or more and 20 mesh or less and then kept at normal pressure. NO = 1300p by pressure fixed bed flow reactor
pm, using a reaction gas of propylene = 800 ppm,
Nitrogen oxide removal activity of 40 at SV = 2500 / h
It measured in the temperature range of 0-800 degreeC. The results are shown in Table 4.
Shown in.

[0027]

[Table 4]

Example 5 TiB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² and then adjusted to have a particle size of 12 mesh or more and 20 mesh or less, and then the same as usual. NO = 1300p by pressure fixed bed flow reactor
Nitrogen oxide removal activity was measured in the temperature range of 400-800 degreeC in SV = 2500 / h using the reaction gas of pm. The results are shown in Table 5.

[0029]

[Table 5]

Example 6 TiB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² , and was then adjusted to a particle size of 12 mesh or more and 20 mesh or less and then kept at normal pressure. NO = 1300p by pressure fixed bed flow reactor
pm, using a reaction gas of propylene = 800 ppm,
Nitrogen oxide removal activity of 40 at SV = 2500 / h
It measured in the temperature range of 0-800 degreeC. The results are shown in Table 6.
Shown in.

[0031]

[Table 6]

Example 7 TaB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² and then adjusted to a particle size of 12 mesh or more and 20 mesh or less. NO = 1400p by pressure fixed bed flow reactor
Nitrogen oxide removal activity was measured in the temperature range of 400-800 degreeC in SV = 2500 / h using the reaction gas of pm. The results are shown in Table 7.

[0033]

[Table 7]

Example 8 TaB ₂ powder (manufactured by Nippon Shinkin Co., Ltd., BET value = 1 m ² / g) was uniaxially pressure-molded at a pressure of 500 kg / cm ² , and was then adjusted to a particle size of 12 mesh or more and 20 mesh or less and kept in a usual state. NO = 1400p by pressure fixed bed flow reactor
pm, using a reaction gas of propylene = 800 ppm,
Nitrogen oxide removal activity of 40 at SV = 2500 / h
It measured in the temperature range of 0-800 degreeC. The results are shown in Table 8
Shown in.

[0035]

[Table 8]

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01J 21/02 ZAB A 8017-4G 23/20 ZAB A 8017-4G

Claims (1)

[Claims] 1. Nitrogen comprising at least one transition metal boride represented by the general formula: MaBb (M = transition metal, B = boron, a and b are real numbers and 0 <b / a <200). Oxide removal catalyst.