U.S. patent application number 13/056281 was filed with the patent office on 2011-06-23 for catalysts for nox reduction employing h2 and a method of reducing nox.
This patent application is currently assigned to HEESUNG CATALYSTS CORPORATION. Invention is credited to Hyun-Sik Han, Eun-seok Kim, Yun-Je Lee, Se-Min Park, Gon Seo.
Application Number | 20110150742 13/056281 |
Document ID | / |
Family ID | 41610806 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110150742 |
Kind Code |
A1 |
Han; Hyun-Sik ; et
al. |
June 23, 2011 |
CATALYSTS FOR NOX REDUCTION EMPLOYING H2 AND A METHOD OF REDUCING
NOX
Abstract
Disclosed is a catalyst composition for reducing NOx through two
steps including reacting NOx with H2 thus producing ammonia which
is then reacted with NOx, instead of direct NOx reduction by H2,
and a method of reducing NOx using the catalyst composition.
Inventors: |
Han; Hyun-Sik; (Ansan-city,
KR) ; Kim; Eun-seok; (Siheung-si, KR) ; Seo;
Gon; (Gwangju-city, KR) ; Park; Se-Min; (Yeosu
si, KR) ; Lee; Yun-Je; (Buk-Gu, KR) |
Assignee: |
HEESUNG CATALYSTS
CORPORATION
Shiheung-city
KR
|
Family ID: |
41610806 |
Appl. No.: |
13/056281 |
Filed: |
August 6, 2008 |
PCT Filed: |
August 6, 2008 |
PCT NO: |
PCT/KR08/04571 |
371 Date: |
January 27, 2011 |
Current U.S.
Class: |
423/351 ;
502/313; 502/316; 502/318; 502/319; 502/324; 502/74 |
Current CPC
Class: |
B01D 2255/91 20130101;
B01D 2255/20761 20130101; B01J 23/8986 20130101; B01D 53/9418
20130101; B01J 37/033 20130101; Y02C 20/10 20130101; B01J 37/0201
20130101; B01J 29/7615 20130101; B01D 2255/20738 20130101; B01D
2255/1023 20130101; B01J 23/002 20130101; B01J 23/8472 20130101;
B01D 2255/2073 20130101; B01D 2255/20753 20130101; B01J 23/6562
20130101; B01J 23/868 20130101; B01D 2255/1021 20130101; B01D
2255/20746 20130101; B01J 37/18 20130101; B01J 23/34 20130101; B01J
35/002 20130101; B01J 23/8993 20130101; B01D 2251/202 20130101;
B01J 23/8892 20130101; B01D 2255/20723 20130101; B01J 2523/00
20130101; B01J 23/898 20130101; B01D 53/9427 20130101; B01J 23/862
20130101; B01J 37/08 20130101; B01D 2255/20769 20130101; B01J
2523/00 20130101; B01J 2523/17 20130101; B01J 2523/25 20130101;
B01J 2523/67 20130101; B01J 2523/00 20130101; B01J 2523/25
20130101; B01J 2523/67 20130101; B01J 2523/842 20130101; B01J
2523/00 20130101; B01J 2523/25 20130101; B01J 2523/67 20130101;
B01J 2523/72 20130101 |
Class at
Publication: |
423/351 ;
502/318; 502/316; 502/324; 502/319; 502/313; 502/74 |
International
Class: |
B01J 23/86 20060101
B01J023/86; B01J 23/889 20060101 B01J023/889; B01J 23/34 20060101
B01J023/34; B01J 29/072 20060101 B01J029/072; B01J 37/03 20060101
B01J037/03; B01J 37/08 20060101 B01J037/08; B01J 37/18 20060101
B01J037/18; C01B 21/02 20060101 C01B021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2008 |
KR |
10-2008-0075102 |
Claims
1. A mixed oxide catalyst for reducing NO.sub.x using H.sub.2 as a
reducing agent, comprising one or more A metal oxides selected from
the group of consisting of Fe.sub.2O.sub.3, CO.sub.2O.sub.3, NiO
and CuO; and one or more B metal oxides selected from the group
consisting of V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO.sub.2 and
MoO.sub.3, which are co-precipitated and mixed.
2. The mixed oxide catalyst according to claim 1, wherein a ratio
of A metal oxide to B metal oxide ranges from 2:1 to 1:0.5.
3. The mixed oxide catalyst according to claim 1, wherein a
precious metal selected from the group consisting of platinum and
palladium is supported in an amount of from 0.1 to 2 wt %.
4. The mixed oxide catalyst according to claim 3, further
comprising an ammonia-selective catalytic reduction catalyst.
5. A method of preparing a mixed oxide catalyst for reducing
NO.sub.x using H.sub.2 as a reducing agent, comprising: dissolving
in aqueous nitrate or acetate one or more metal oxide precursors of
A metal oxides, wherein the A metal oxides are selected from the
group consisting of Fe.sub.2O.sub.3, CO.sub.2O.sub.3, NiO and CuO,
and one or more metal oxide precursors of B metal oxides, wherein
the B metal oxides are selected from the group consisting of
V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO.sub.2 and MoO.sub.3, thus
preparing a solution; adding barium nitrate oxide to the solution;
adding ammonia water or aqueous sodium bicarbonate as a
precipitating agent to the solution so that pH of the solution is
from 7 to 7.3, thus forming a precipitate; and subjecting the
precipitate to post treatment comprising filtering, washing, drying
and burning.
6. The method according to claim 5, wherein a ratio of A metal
oxide to B metal oxide ranges from 2:1 to 1:0.5.
7. The method according to claim 5, further comprising, after
subjecting the precipitate to post treatment, supporting either or
both precious metals of platinum and palladium in an amount of from
0.1 to 2 wt % on the catalyst, burning the precious metal-supported
catalyst, and subjecting the burned catalyst to reduction treatment
using a gas mixture containing N.sub.2 and H.sub.2 at a molar ratio
of 1.
8. A method of reducing NO.sub.x at from 150 to 350.degree. C.
using H.sub.2 as a reducing agent in presence of the mixed oxide
catalyst of claim 1.
9. The method according to claim 8, wherein the method is performed
under conditions in which O.sub.2 content is equal to or less than
10% by volume based on a volume of the NO.sub.x.
Description
TECHNICAL FIELD
[0001] As a system for reducing NO.sub.x from diesel exhaust gas,
selective catalytic reduction (SCR) and NO.sub.x storage reduction
(NSR) are known. In the SCR method, a reducing agent is
continuously sprayed into exhaust gas and selectively reacted with
NO.sub.x in a catalyst bed so that NO.sub.x is converted into
N.sub.2. This method is classified into NH.sub.3-SCR, Urea-SCR,
HC-SCR and H.sub.2-SCR depending on the type of reducing agent such
as ammonia, urea, hydrocarbon and H.sub.2. On the other hand, in
the NSR method, NO.sub.x is stored in an oxidation atmosphere and
then desorbed in a reduction atmosphere formed through spray of
fuel, thus reducing NO.sub.x.
BACKGROUND ART
[0002] Generally, NO.sub.x emitted from large-scale boilers or
nitric acid plants can be effectively removed through NH.sub.3-SCR
which supplies ammonia as a reducing agent to a catalyst bed
composed of titania-supported vanadia or iron-containing zeolite.
Ammonia is highly reactive and selective and is thus very effective
for removing NO.sub.x from the exhaust gas of fixed facilities even
in the presence of O.sub.2. However, the use of ammonia to remove
NO.sub.x from diesel exhaust gas is very dangerous because a diesel
vehicle should be driven in a state of always being loaded with
ammonia which is highly toxic. So, aqueous urea is used instead of
ammonia as a reducing agent therein. The urea is decomposed into
ammonia and carbon dioxide in the catalyst bed so that NO.sub.x is
reduced to N.sub.2. Although the urea-SCR method is advantageous
because NO.sub.x removal performance is high, it is problematic in
that a tank for storing aqueous urea and a device for spraying such
urea should be additionally mounted to a diesel vehicle. As has
been done for fuel, a sales network of aqueous urea should be
constructed. As well, the urea-SCR method is difficult to apply to
a diesel vehicle, due to problems including low solubility of urea,
freezing, and ammonia slip.
[0003] Among the SCR methods, H.sub.2-SCR using H.sub.2 as a
reducing agent instead of the aqueous urea is receiving attention
because the construction of an apparatus thereof is simple and
there is no concern about secondary pollution. However, it is
difficult to construct the supply network of H.sub.2 and to load it
into a vehicle. Further, O.sub.2 in the diesel exhaust gas may
first react with H.sub.2, undesirably lowering NO.sub.x selective
removal efficiency by H.sub.2. Thus, the application of the above
method has not been considered to date. The reason is described
below.
[0004] The temperature and O.sub.2 content of diesel exhaust gas
greatly vary depending on driving conditions of vehicles.
[0005] During normal high-speed driving, the temperature may be
300.degree. C. or higher and also the O.sub.2 content may exceed
10% under lean burn. Further, in order to allow NO.sub.2 to be
directly reduced to N.sub.2 by H.sub.2, H.sub.2 should be strongly
activated. In this case, however, a probability of reacting such
H.sub.2 with O.sub.2 is increased, undesirably lowering the
NO.sub.x removal efficiency. Namely, to increase the NO.sub.x
removal efficiency by H.sub.2, the probability of reacting H.sub.2
with O.sub.2 should be inhibited while increasing the degree of
activation of H.sub.2, which is difficult. Hence, limitations are
imposed on applying the H.sub.2-SCR method to diesel vehicles.
DISCLOSURE
Technical Problem
[0006] Accordingly, the present inventors have directed their
attention to a method of reducing NO.sub.x using H.sub.2 as a
reducing agent in the presence of ammonia, in lieu of conventional
direct NO.sub.x reduction by H.sub.2, to selectively reduce
NO.sub.x while inhibiting excessive activation of H.sub.2. The
present inventors have devised two-step NO.sub.2 removal, including
activating H.sub.2 only to the appropriate level so that it can
thus react with NO.sub.x, giving ammonia, which is then reacted
with NO.sub.x.
[0007] Therefore, an object of the present invention is to provide
a catalyst composition for reducing NO.sub.x through two steps
including reacting NO.sub.x with H.sub.2, thus preparing ammonia,
which is then reacted with NO.sub.x, thereby removing NO.sub.x,
instead of direct NO.sub.x reduction by H.sub.2.
[0008] Another object of the present invention is to provide a
hybrid catalyst composition having not only a function as an SCR
catalyst of reaction between a reducing agent and NO.sub.x but also
an NSR function for storing NO.sub.x on the surface of the catalyst
to thus react with the reducing agent, so that part of the reducing
agent is adsorbed on the surface of the catalyst and thus NO.sub.x
storage sites are formed, in order to efficiently remove NO.sub.x
regardless of changes in the concentration of NO.sub.x.
[0009] A further object of the present invention is to provide a
catalyst composition suitable for a H.sub.2-SCR method using
H.sub.2 as a reducing agent including the two steps of producing
ammonia and then removing NO.sub.x, in which the temperature range
of the catalyst composition usable in diesel vehicles is wide and
is on the order of 150.about.300.degree. C.
[0010] Still another object of the present invention is to provide
a catalyst composition including the catalyst composition according
to the present invention and a conventional NH.sub.3-SCR catalyst
composition, which are mixed together.
[0011] Yet another object of the present invention is to provide a
method of reducing NO.sub.x using the catalyst composition.
Technical Solution
[0012] In order to accomplish the above objects, the present
invention provides a mixed oxide catalyst, a method of preparing
the catalyst and a method of reducing NO.sub.x using the
catalyst.
[0013] According to the present invention, the mixed oxide catalyst
for reducing NO.sub.x using H.sub.2 as a reducing agent includes
one or more selected from the group of A metal oxides consisting of
Fe.sub.2O.sub.3, CO.sub.2O.sub.3, NiO and CuO, and one or more
selected from the group of B metal oxides consisting of
V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO.sub.2 and MoO.sub.3, which are
co-precipitated and mixed. The present invention has the following
features, but is not limited thereto.
[0014] In the mixed oxide catalyst, the weight ratio of A metal
oxide to B metal oxide may range from 2:1 to 1:0.5.
[0015] On the mixed oxide catalyst, a precious metal selected from
the group consisting of Pt and Pd may be supported in an amount of
0.1.about.2 wt %.
[0016] The mixed oxide catalyst may further include a conventional
NH.sub.3-SCR catalyst. As such, an example of the conventional
NH.sub.3-SCR catalyst may include, but is not limited to, a
titania-supported vanadia catalyst or an iron-containing zeolite
catalyst.
[0017] In addition, the method of preparing the mixed oxide
catalyst for reducing NO.sub.x using H.sub.2 as a reducing agent
includes dissolving in aqueous nitrate or acetate one or more metal
oxide precursors selected from the group of A metal oxides
consisting of Fe.sub.2O.sub.3, Co.sub.2O.sub.3, NiO and CuO, and
one or more metal oxide precursors selected from the group of B
metal oxides consisting of V.sub.2O.sub.5, Cr.sub.2O.sub.3,
MnO.sub.2 and MoO.sub.3, thus obtaining a solution, adding barium
nitrate for improving structural stability of the mixed oxide to
the solution, adding ammonia water or aqueous sodium bicarbonate as
a precipitating agent to the solution so that pH of the solution is
7.about.7.3, thus forming a precipitate, and subjecting the
precipitate to post treatment including filtering, washing, drying
and burning. The present invention has the following features, but
is not limited thereto.
[0018] In the method, the ratio of A metal oxide precursor to B
metal oxide precursor may range from 2:1 to 1:0.5.
[0019] The method may further include, after subjecting the
precipitate to post treatment, supporting either or both precious
metals of Pt and Pd in an amount of 0.1.about.2 wt % on the
catalyst, burning the precious metal-supported catalyst, and
subjecting the burned catalyst to reduction treatment using a gas
mixture containing N.sub.2 and H.sub.2 at a molar ratio of 1.
[0020] In addition, the method of reducing NO.sub.x includes
reducing NO.sub.x at 150.about.350.degree. C. using H.sub.2 as a
reducing agent in the presence of the above mixed oxide catalyst.
This method may be performed even under conditions in which O.sub.2
content is 0.about.10% by volume based on the volume of NO.sub.x,
but the present invention is not limited thereto.
Advantageous Effects
[0021] According to the present invention, oxides of A metals
including Cu, Fe, Co and Ni and oxides of B metals including Cr,
Mn, Mo and V are co-precipitated and mixed, thus preparing mixed
oxide catalysts and ternary mixed oxide catalysts. These catalysts
exhibit superior activity for production of ammonia through
selective reaction between NO.sub.2 and H.sub.2 even in the
presence of 5% or 10% O.sub.2, and simultaneously, manifest very
high NO.sub.2 and NO storage performance. Thereby, the catalysts
can exhibit superior NO.sub.x reduction performance through
injection of H.sub.2 even in the presence of O.sub.2. In
particular, because NO.sub.x is removed via ammonia, the NO.sub.x
removal performance is high. The catalysts according to the present
invention have high Pt or Pd dispersability and high hydrothermal
stability and poisoning resistance to sulfur and thus can
significantly remove NO.sub.x from diesel exhaust gas. Also, the
catalysts can be typically easily prepared from transition metal
precursors which are inexpensive with high durability to water or
heat and to sulfur poisoning.
DESCRIPTION OF DRAWINGS
[0022] FIG. 1 shows X-ray diffraction patterns of A-B mixed oxide
catalysts in which the B metal is Cr and the A metal is Fe, Co, Ni
and Cu, after a burning process;
[0023] FIG. 2 shows X-ray diffraction patterns of A-B mixed oxide
catalysts in which the A metal is Cu and the B metal is Cr, V, Mo
and Mn, a Cr--Mn catalyst, and a Fe--Mn catalyst, after a burning
process;
[0024] FIG. 3 shows X-ray diffraction patterns of Pt(2.0)-Cu--Cr
and Pt(2.0)-Fe--Mn catalysts, which are Pt-supported catalysts;
[0025] FIG. 4 shows IR spectra of the process of storing NO.sub.2
(a) and the process of reducing NO.sub.2 by H.sub.2 (b) in the
Cu--Cr catalyst;
[0026] FIG. 5 shows IR spectra of the process of producing ammonia
from NO.sub.2 through injection of H.sub.2 in the absence of
O.sub.2 (a) and in the presence of O.sub.2 (b) in the Cu--Cr
catalyst which is a mixed oxide catalyst;
[0027] FIG. 6 shows IR spectra of the Cu--Mn catalyst, the Fe--Cr
catalyst and the Fe--Mn catalyst in the presence of O.sub.2;
[0028] FIG. 7 schematically shows a flow reactor used for
H.sub.2-SCR;
[0029] FIG. 8 shows NO.sub.2 reduction results by H.sub.2 of the
Pt(2.0)-Fe catalyst (a), the Pt(2.0)-Mn catalyst (b) and the
Pt(2.0)-Fe--Mn catalyst (c) under flow of 500 ppm NO.sub.2
containing 10% O.sub.2; and
[0030] FIG. 9 shows NO.sub.2 reduction behavior by H.sub.2 of the
Pt(2.0)-Fe--Mn catalyst with Fe-BEA zeolite.
MODE FOR INVENTION
[0031] A catalyst for effectively and selectively reducing NO.sub.x
using H.sub.2 gas in the presence of O.sub.2 should have the
following three functions, namely, high NO.sub.x adsorption,
appropriate activation of H.sub.2, and activation of adsorbed
NO.sub.x. Specifically, NO.sub.x is adsorbed or stored on the
surface of the catalyst because of having reacted therewith and
thus should be concentrated on the catalyst. In this case, part of
NO.sub.x should be activated so that it is converted into ammonia
through reaction with H.sub.2. As well, when H.sub.2 is adsorbed on
the surface of the catalyst and thus activated in an atomic state,
it may be reacted with NO.sub.x, thus producing ammonia.
[0032] Taking into consideration the above reasons, the present
inventors selected, as oxides of A metals which exhibit superior
NO.sub.x storage performance, Fe.sub.2O.sub.3, CO.sub.2O.sub.3, NiO
and CuO, and as oxides of B metals which are able to adsorb
NO.sub.x in an activated state, V.sub.2O.sub.5, Cr.sub.2O.sub.3,
MnO.sub.2 and MoO.sub.3. In the present invention, the oxides of
the A and B metals are co-precipitated and combined, thus preparing
mixed oxides, thereby maximizing NO.sub.x storage capacity and
NO.sub.x reduction performance at the same time. Further, to
inhibit the sintering of the B metal, barium nitrate is added as a
structure stabilizer. As a precious metal, Pt or Pd is supported on
the catalyst. Depending on the type of catalyst, two or more kinds
of A metal or B metal are added, thus preparing ternary or more
mixed oxide catalysts, after which a precious metal is supported
thereon. Accordingly, H.sub.2 is activated in an atomic state on
the surface of precious metal to thus react with NO.sub.x adsorbed
on the surface of the mixed oxide, thereby producing ammonia. In
the present invention, the mixed oxide according to the present
invention promotes the ammonia and NO.sub.x reduction and
ultimately reduces NO.sub.x to N.sub.2.
[0033] For mass production of the mixed oxide catalyst at low cost,
a general co-precipitation method is applied, and inexpensive
starting materials are used. When ammonia water or sodium
bicarbonate is added to the mixed solution to appropriately adjust
the pH of the solution, a highly active catalyst is prepared. The
precious metal is supported in an amount of 0.1.about.2%, and the
reduction reaction is operated in the temperature range of
150.about.350.degree. C. Even when the concentration of O.sub.2 in
NO.sub.x exceeds 10% by volume, the above catalyst can exhibit
superior NO.sub.x selective reduction by H.sub.2.
[0034] A better understanding of the present invention may be
obtained through the following examples which are set forth to
illustrate, but are not to be construed to limit the present
invention.
Example 1
Preparation of Mixed Oxide Catalysts
[0035] Mixed oxide catalysts were prepared from oxides of A metals
(Cu, Fe, Co, Ni) and B metals (Cr, Mn, Mo, V) through
co-precipitation and mixing. The weight ratio of A metal oxide to B
metal oxide was adjusted to 2, 1 and 0.5. As a precipitating agent,
ammonia water or aqueous sodium bicarbonate was used, and pH of the
mixed solution was adjusted to 6.0.about.8.0. Any one A metal was
reacted with any one B metal, thus preparing binary mixed oxide
catalysts, and also, multicomponent mixed oxide catalysts were
prepared using two or more kinds of these metals. The method of
preparing some catalysts which are regarded as important is
described below.
[0036] a) Cu--Cr Mixed Oxide Catalyst
[0037] A solution of 15.2 g of copper nitrate and 1.60 g of barium
nitrate in 152 g of water was mixed with a solution of 15.4 g of
potassium dichromate in 154 g of water, thus preparing a mixed
solution. For sufficient mixing, the mixed solution was stirred for
30 min and then ammonia water was slowly added thereto so that the
pH thereof was 7.0.about.7.5. The resultant precipitate was
filtered using filter paper, sufficiently dried in an oven at
80.degree. C., and then ground using a mortar and a pestle, thus
obtaining fine powder. The powder was transferred into an electric
furnace so that it was burned at 500.degree. C. for 4 hours, giving
10.9 g of a Cu--Cr mixed oxide catalyst represented by a Cu--Cr
catalyst.
[0038] b) Fe--Cr Mixed Oxide Catalyst
[0039] A solution of 24.7 g of iron nitrate and 1.6 g of barium
nitrate in 247 g of water and a solution of 15.4 g of potassium
dichromate in 154 g of water were prepared. These two solutions
were mixed and stirred for 30 min to provide for sufficient mixing,
after which ammonia water was slowly added thereto so that the pH
thereof was 7.0.about.8.0. The resultant precipitate was filtered
using filter paper, dried in an oven at 80.degree. C., and then
ground using a mortar and a pestle, thus obtaining fine powder. The
powder was transferred into an electric furnace so that it was
burned at 500.degree. C. for 4 hours, giving 8.5 g of a Fe--Cr
mixed oxide catalyst represented by a Fe--Cr catalyst.
[0040] c) Cu--Mn Mixed Oxide Catalyst
[0041] A solution of 20.6 g of copper nitrate in 206 g of water and
a solution of 24.6 g of manganese nitrate in 246 g of water were
prepared. These two solutions were sufficiently mixed for 30 min,
after which a 1 M sodium bicarbonate solution was slowly added
thereto so that the pH thereof was 7.0.about.7.8. The resultant
precipitate was filtered using filter paper, dried in an oven at
80.degree. C., and then ground using a mortar and a pestle, thus
obtaining fine powder. The powder was transferred into an electric
furnace so that it was burned at 500.degree. C. for 4 hours, giving
21 g of a Cu--Mn mixed oxide catalyst represented by a Cu--Mn
catalyst.
[0042] d) Fe--Mn Mixed Oxide Catalyst
[0043] A solution of 35.9 g of iron nitrate in 359 g of water and a
solution of 25.5 g of manganese nitrate in 255 g of water were
prepared. These two solutions were sufficiently mixed for 30 min,
after which a 1 M sodium bicarbonate solution was slowly added
thereto so that the pH thereof was 6.5.about.7.5. The resultant
precipitate was filtered using filter paper, dried in an oven at
80.degree. C., and then ground using a mortar and a pestle, thus
obtaining fine powder. The powder was transferred into an electric
furnace so that it was burned at 500.degree. C. for 4 hours, giving
15 g of a Fe--Mn mixed oxide catalyst represented by a Fe--Mn
catalyst.
[0044] e) Mn--Cr Mixed Oxide Catalyst
[0045] A solution of 17.6 g of manganese nitrate and 1.6 g of
barium nitrate in 176 g of water and a solution of 15.4 g of
potassium dichromate in 154 g of water were prepared. These two
solutions were mixed and stirred for 30 min to provide for
sufficient mixing, after which ammonia water was slowly added
thereto so that the pH thereof was 7.0.about.7.5. The resultant
precipitate was filtered using filter paper, dried in an oven at
80.degree. C., and then ground using a mortar and a pestle, thus
obtaining fine powder. The powder was transferred into an electric
furnace so that it was burned at 500.degree. C. for 4 hours, giving
12.1 g of a Mn--Cr mixed oxide catalyst represented by a Mn--Cr
catalyst.
[0046] The other mixed oxide catalysts were prepared through the
above procedures. Also, mixed oxide catalysts having a composition
ratio of 2 and 0.5, in addition to 1, were prepared. Each of the
catalysts thus prepared was reduced under flow of a reducing gas
mixture containing H.sub.2 and N.sub.2 at a molar ratio of 1:1 at
400.degree. C. and a flow rate of 120 ml/min, before being
used.
[0047] f) Synthesis of Fe-BEA Zeolite (NH.sub.3-SCR Catalyst)
[0048] To a solution of 377 g of tetraethyl ammonium hydroxide and
312 g of colloidal silica, 31 g of sodium aluminate was dropped
with stirring, thus preparing a synthesis mother solution having a
composition of 1.5Na.sub.2O:20SiO.sub.2:Al.sub.2O.sub.3:
2.46(TEA).sub.2O:416H.sub.2O. This solution was stirred for 2
hours, placed in a high-pressure autoclave and thus heated to
165.degree. C. for 3 hours, and then subjected to hydrothermal
reaction while maintaining the above temperature for 90 hours, thus
obtaining 28 g of BEA zeolite having a molar ratio of Si/Al of 10.
10 g of the synthesized BEA zeolite was added to 100 ml of a 0.2 N
iron chloride solution, ion-exchanged at 60.degree. C. for two
days, filtered, washed, and then burned, giving Fe-ion-exchanged
Fe-BEA zeolite.
Example 2
Preparation of Pt- or Pd-supported Mixed Oxide Catalyst
[0049] To evaluate NO.sub.2 reduction performance by a H.sub.2
reducing agent, Pt was supported in an amount of 0.1, 0.2, 1.0 and
2.0% by weight on the mixed oxide catalyst of Example 1. As a Pt
precursor, hexachloroplatinic acid was dissolved in an amount of
each of 0.1, 0.2, 1.1 and 2.1 g in 35 g of water, thus preparing a
Pt solution, which was then added to 50 g of the mixed oxide
catalyst. The catalyst reached equilibrium after 24 hours, and then
dried in an oven at 80.degree. C. and thus dewatered. The solution
was burned in an electric furnace at 400.degree. C. for 2 hours,
placed in a quartz tube and then subjected to reduction treatment
using a gas mixture containing N.sub.2 and H.sub.2 mixed at an
equal ratio. The Pt-supported Cu--Cr catalysts and Fe--Mn catalysts
were represented by Pt(0.1)-Cu--Cr, Pt(0.2)-Cu--Cr, Pt(1.0)-Cu--Cr,
Pt(2.0)-Cu--Cr, Pt(0.1)-Fe--Mn, Pt(0.2)-Fe--Mn, Pt(1.0)-Fe--Mn, and
Pt(2.0)-Fe--Mn.
[0050] On the other hand, Pd-supported mixed oxide catalysts were
prepared using a palladium nitrate precursor through procedures
similar to the above Pt supporting procedures. Specifically,
palladium nitrate was dissolved in an amount of each of 0.1, 0.2,
1.1 and 2.2 g in 35 g of water, thus preparing a Pd solution which
was then added to 50 g of the mixed oxide catalyst, dried, burned
in an electric furnace at 400.degree. C. for 2 hours, and then
subjected to reduction treatment, yielding Pd-supported mixed oxide
catalysts. The Pd-supported Cu--Cr catalysts and Fe--Mn catalysts
were represented by Pd(0.1)-Cu--Cr, Pd(0.2)-Cu--Cr, Pd(1.0)-Cu--Cr,
Pd(2.0)-Cu--Cr, Pd(0.1)-Fe--Mn, Pd(0.2)-Fe--Mn, Pd(1.0)-Fe--Mn, and
Pd(2.0)-Fe--Mn.
Example 3
X-ray Diffraction Pattern of A-B Mixed Oxide Catalyst
[0051] Among the A-B mixed oxide catalysts prepared in Example 1,
the catalysts in which the B metal was Cr and the A metal was Fe,
Co, Ni and Cu were burned, after which X-ray diffraction patterns
thereof were measured. The results are shown in FIG. 1. The
diffraction pattern of the mixed oxide catalyst was very
complicated because the diffraction peaks of metal oxides alone and
in combinations thereof coexisted. In the Cu--Cr catalyst, the
diffraction peaks of CuO, CuCr.sub.2O.sub.4 and BaCrO.sub.4 were
shown. In any catalyst, the diffraction peak of BaCrO.sub.4 added
to improve structural stability of the catalyst was distinctly
observed. In the Cu--Cr and Fe--Cr catalysts, the diffraction peak
of CuO or Fe.sub.2O.sub.3 was strongly observed. In the Fe--Cr and
Co--Cr catalysts, the diffraction peaks difficult to confirm were
present, and thus the mixed oxide catalysts were seen to have a
complicated structure.
[0052] FIG. 2 shows the X-ray diffraction patterns of the A-B mixed
oxide catalysts in which the A metal was set and the kind of B
metal was changed to Cr, V, Mo and Mn. In the Cu--V catalyst, the
diffraction peaks of Cu.sub.2V.sub.2O.sub.7 and V.sub.2O.sub.5 were
observed. In the Cu--Mn catalyst, the peak of CuO and CuMnO.sub.4
was observed together. Whereas, in the Cu--Mo catalyst, the
diffraction peak of the copper compound was unclear, and only the
diffraction peaks of MoO.sub.2 and MoO.sub.3 were greatly observed.
The diffraction peaks of the Cr--Mn catalyst prepared from only B
metals and the Fe--Mn catalyst prepared through crossing of A-B
metals were observed. Depending on the kind of metal, the
diffraction pattern of the catalyst was seen to considerably vary.
In the Cu--Mn catalyst, the diffraction peaks of CuO and
CuMnO.sub.4 were observed, whereas in the Cr--Mn catalyst the
diffraction peaks of MnO.sub.2 and BaCrO.sub.4 were observed. Also,
in the Fe--Mn catalyst, the diffraction peaks of Fe.sub.2O.sub.3
and NaMnO.sub.4 were observed. From this, the oxides of A and B
metals could be seen to be present in different forms depending on
the kind of metal.
[0053] FIG. 3 shows X-ray diffraction patterns of, as Pt-supported
catalysts, Pt(2.0)-Fe, Pt(2.0)-Mn, Pt(2.0)-Fe--Mn,
Pt(2.0)-Fe--Mn(2/1) and Pt(2.0)-Fe--Mn(1/2) having different Fe/Mn
composition ratios, and Pt(2.0)-Cu--Cr catalysts, and as a
Pd-supported catalyst, Pd(2.0)-Fe--Mn, which were prepared in
Example 2. In the Pt(2.0)-Fe catalyst, the diffraction peaks of
NaFeO.sub.2 and Fe metal were observed. In the Pt(2.0)-Mn catalyst,
the diffraction peaks of MnO were greatly observed. In the
Pt(2.0)-Fe--Mn, Pt(2.0)-Fe--Mn(2/1) and Pt(2.0)-Fe--Mn(1/2)
catalysts containing Fe and Mn, not only the diffraction peaks of
MnO and Fe metal but also the diffraction peak of MnFe.sub.2O.sub.4
were observed, from which it could be seen that Fe and Mn were not
present alone. The diffraction peak of the Pd-supported catalyst,
namely, the Pd(2.0)-Fe--Mn catalyst was similar to that of the
Pt-supported catalyst, namely, Pt(2.0)-Fe--Mn catalyst, with the
exception that the diffraction peaks of NaFeO.sub.2 were weakly
observed. The Pt(2.0)-Cu--Cr catalyst had complicated diffraction
peaks, unlike the Cu--Cr catalyst. The diffraction peak of Pt in
all of these catalysts was not observed. This was judged to be
because Pt did not aggregate on the surface of the catalyst but was
well dispersed thereon.
Example 4
NO.sub.2 Storage Performance of Mixed Oxide Catalyst
[0054] The NO.sub.2 storage performance of the catalysts prepared
in Examples 1 and 2 was evaluated. To this end, the catalyst was
loaded into a gravimetric adsorption system provided with a quartz
spring and then exhausted at 300.degree. C. for 1 hour, after which
measurement was performed at 150.degree. C. in consideration of the
temperature of diesel exhaust gas. The results of measurement of
the storage performance of the Cu--Cr catalyst and the Fe--Mn
catalyst among the above mixed oxide catalysts are summarized in
Table 1 below. The NO.sub.2 storage performance of the catalyst was
greatly changed depending on catalyst pretreatment conditions. The
storage performance was represented into a storage amount in a
state where the catalyst was exposed to NO.sub.2 at 30 Torr and a
storage amount in a state where NO.sub.2 was emitted. Before
reduction treatment, an adsorption amount was slightly larger than
the storage amount. However, after the reduction treatment, the
adsorption amount became similar to the storage amount. This is
considered to be because part of NO.sub.2 is weakly adsorbed on the
surface of the catalyst before the reduction treatment, but the
entirety thereof is strongly stored thereon after the reduction
treatment. Thus, the performance of the catalyst was determined
only by the storage amount with no consideration being given to the
adsorption amount. In the case of the Fe catalyst prepared from
only Fe, the amount of stored NO.sub.2 was increased about 23 times
from 7 mg/g to 161 mg/g through reduction treatment. Also, in the
case of the Mn catalyst prepared from only Mn, the amount of stored
NO.sub.2 was increased about 6 times from 13 mg/g to 79 mg/g
through the reduction treatment. The Fe--Mn mixed oxide catalyst
containing these two components increased the storage amount about
7 times before the reduction treatment but about 2 times after the
reduction treatment, compared to that of the catalyst composed
exclusively of Fe or Mn. In the case of the Fe--Mn catalyst, the
amount of stored NO.sub.2 was remarkably larger than that of the
Cu--Cr catalyst, and thus the NO.sub.2 storage performance could be
seen to greatly vary depending on the kind of metal. As such,
although the storage amount may vary depending on the kind of metal
and the reduction treatment, NO.sub.2 may be typically adsorbed in
a large amount on many O vacancies formed on the surface of the
catalyst after the reduction treatment. After the reduction
treatment, the amount of NO.sub.2 stored on the Fe--Mn catalyst was
174 mg/g, which was evaluated to be superior.
[0055] Table 1 below shows the NO.sub.2 adsorption and storage
amounts of the mixed oxide catalysts at 50.degree. C.
TABLE-US-00001 TABLE 1 NO.sub.2 Adsorption and Storage Amounts
(mg/g) Before Reduction After Reduction Adsorption Storage
Adsorption Storage Catalyst Amount Amount Amount Amount Fe 15 7 161
161 Mn 24 13 79 79 Fe--Mn 90 83 174 174 Cu--Cr 22 15 50 43 Pt
(2.0)--Fe -- -- 254 254 Pt (2.0)--Mn -- -- 106 106 Pt (2.0)--Fe--Mn
-- -- 182 181 Pt (2.0)--Cu--Cr -- -- 39 36
[0056] When Pt was supported on the metal oxide catalyst, the
amount of stored NO.sub.2 was greatly changed. After reduction
treatment of the precious metal-supported catalyst, namely, the
Pt(2.0)-Fe catalyst, the amount of stored NO.sub.2 was 254 mg/g,
which was esteemed to be very high. The Pt(2.0)-Mn catalyst also
increased the storage amount from 79 mg/g to 106 mg/g, which was
smaller than that of the Pt(2.0)-Fe catalyst. The Pt(2.0)-Fe--Mn
catalyst slightly increased the storage amount from 170 mg/g to 181
mg/g, compared to that of the Fe--Mn catalyst containing no Pt.
However, the Cu--Cr catalyst slightly decreased the storage amount
from 43 mg/g to 36 mg/g when Pt was supported thereon. This is
considered to be because, when Pt is supported, the activation of
H.sub.2 is increased upon reduction treatment and thus many O
vacancies of the surface of the catalyst are formed. However, in
the case of the Pt(2.0)-Cu--Cr catalyst, the amount of stored
NO.sub.2 was decreased, and thus the storage performance of the
catalyst could be seen to greatly vary depending on the kind of
metal. The storage state of the adsorbed NO was checked using an IR
spectrometer (BIO-RAD, 175C) equipped with an in-situ cell. The
NO.sub.2 storage behavior and the NO.sub.2 desorption behavior by
H.sub.2 in the Pt(2.0)-Cu--Cr catalyst of Example 1 are shown in
FIG. 4. The reduction treatment was performed at 250.degree. C.
using H.sub.2 at a flow rate of 100 ml/min, after which 2000 ppm
NO.sub.2 by volume was allowed to flow at 200.degree. C. and thus
the process of storing NO.sub.2 was measured (a). Also, while
N.sub.2 gas containing 20% H.sub.2 by volume was allowed to flow,
the process of desorbing the stored NO.sub.2 was measured (b). When
NO.sub.2 was stored, initial absorption bands were shown at 1540,
1420 and 1240 cm.sup.-1. After 10 min, the absorption bands were
greatly increased at 1440 and 1340 cm.sup.-1. Initially, NO.sub.2
was stored in the form of bidentate nitrate and ionic nitrite, and
then was converted into ionic nitrate over time. When H.sub.2 was
allowed to flow to the Pt(2.0)-Cu--Cr catalyst to which NO.sub.2
was stored, the absorption bands were rapidly decreased and then
almost none thereof was seen after 15 min. This was because
NO.sub.2 stored on the catalyst by H.sub.2 was rapidly reduced and
desorbed.
Example 5
Production of Ammonia in Mixed Oxide Catalyst
[0057] In the mixed oxide catalyst, ammonia was produced through
reaction between H.sub.2 and NO.sub.2. The produced ammonia was
strongly adsorbed on acid sites and could thus be detected using an
IR spectrometer used in Example 4. A mesoporous material (MCM-41)
having a sulfonic acid group able to strongly adsorb ammonia was
used as a test catalyst. The test catalyst was fixed to the path
through which IR beams were passed. While the catalyst was heated
to 250.degree. C. using a heater, H.sub.2 was added at 30 Torr and
thus reduction treatment was performed for 1 hour. After exhaust,
NO.sub.2 was fed at 20 Torr at the same temperature. Because
NO.sub.2 was not stored on acid sites, there was no difference in
the test sample. Subsequently, H.sub.2 was added at 20 Torr so that
the reaction was performed for 20 min and cooling to 50.degree. C.
was performed, thus checking whether ammonia was produced.
[0058] To evaluate the effect of O.sub.2, O.sub.2 was added at 20
Torr after NO.sub.2 adsorption. FIG. 5 shows the results of the
production of ammonia by adding H.sub.2 to the Cu--Cr mixed oxide
catalyst of Example 1 to which NO.sub.2 was adsorbed, in the
absence of O.sub.2 (a) and in the presence of O.sub.2 (b). In the
absence of O.sub.2, reduction treatment was performed at
250.degree. C., after which the absorption band of sulfonic acid
was greatly observed at 1377 cm.sup.-1. However, when H.sub.2 was
injected and reaction and then cooling to 50.degree. C. were
performed, the absorption band at 1377 cm.sup.-1 became small and
novel absorption bands were shown at 1440 and 1410 cm.sup.-1. From
these absorption bands shown due to the presence of the ammonium
ion, ammonia could be confirmed to be produced and adsorbed to the
sulfonic acid group. While ammonia was produced and adsorbed to the
sulfonic acid group, the absorption band at 1377 cm.sup.-1 was
decreased, and the absorption band of ammonium ion was shown. In
the presence of O.sub.2, the absorption bands of ammonium ion were
observed at 1440 and 1410 cm.sup.-1, which were smaller than in the
absence of O.sub.2. This means that ammonia was produced through
reaction between NO.sub.2 and H.sub.2.
[0059] FIG. 6 shows IR spectra of the Cu--Mn catalyst, the Fe--Cr
catalyst and the Fe--Mn catalyst, in addition to the Cu--Cr
catalyst, in the presence of O.sub.2. As in the Cu--Cr catalyst,
the absorption bands of ammonium ion were shown at 1440 and 1410
cm.sup.-1 in the presence of O.sub.2, although being small. As
such, the degree of production of ammonia greatly varied depending
on the kind of component of the catalyst. In the case of the Fe--Cr
catalyst and the Cu--Mn catalyst, the absorption band of ammonium
ion was very small. In the Fe--Mn catalyst, the absorption band of
ammonium ion was large, from which more production of ammonia could
be confirmed.
Example 6
H.sub.2-SCR in Flow Reactor
[0060] The NO.sub.2 reduction performance of the catalyst using a
H.sub.2 reducing agent was measured by use of a normal pressure
flow reactor. The construction of the flow reactor used in the
H.sub.2-SCR reaction is shown in FIG. 7. 0.1 g of the Pt-supported
catalyst was loaded in a quartz tube having an outer diameter of 10
mm and then activated at 500.degree. C. for 1 hour. In
consideration of the temperature of diesel exhaust gas, cooling to
150.degree. C. was performed, and a gas mixture of 520 ppm NO.sub.2
by volume and 5% O.sub.2 by volume was supplied at a flow rate of
100 ml/min and thus saturated and adsorbed to the catalyst. While
the gas mixture of NO.sub.2 and O.sub.2 was allowed to flow, 2 ml
of the H.sub.2 reducing agent was injected five times at intervals
of 5 min, thus evaluating the NO.sub.2 reduction performance. Using
a NO.sub.2 sensor (NGK, TCNS6005-C3) and a mass spectrometer
(Balzer, QMS200) provided to the ends of the reactor, the amount of
reduced NO.sub.2 and the amount of consumed H.sub.2 were measured.
As such, not only NO.sub.2 but also N.sub.2O and NH.sub.3 can be
sensed by use of the NO.sub.2 sensor provided to the end of the
reactor, and thus a decrease in the concentration of NO.sub.2 may
be connected with conversion of the entirety of NO.sub.2 into
N.sub.2. Using the mass spectrometer, it could be seen to produce
H.sub.2 at m/e of 2 and water at m/e of 17 and 18. The m/e of NO is
44, and thus the amount of NO.sub.2 converted into NO can be
detected. The amount of supported precious metal, partial pressure
of O.sub.2, and activity of Pd-supported catalyst were
evaluated.
[0061] FIG. 8 shows the results of H.sub.2-SCR reaction in the
Pt(2.0)-Fe catalyst (a), the Pt(2.0)-Mn catalyst (b) and the
Pt(2.0)-Fe--Mn catalyst (c) under conditions of 10% O.sub.2.
H.sub.2 was supplied to the NO.sub.2 gas at a predetermined flow
rate, thus measuring the NO.sub.2 conversion. The SCR performance
by H.sub.2 in the metal oxides alone and in combinations thereof
greatly varied. Specifically, in the Pt(2.0)-Fe catalyst, the
reduction reaction using H.sub.2 was barely performed at
150.about.300.degree. C. Also in the Pt(2.0)-Mn catalyst, the
reduction reaction was barely performed even in the presence of
H.sub.2 at 150.degree. C., but the NO.sub.2 reduction reaction
using H.sub.2 proceeded at 200.about.250.degree. C. Because of the
injection of H.sub.2, part of the NO.sub.2 was desorbed from the
surface of the catalyst and thus the concentration of NO.sub.2
became larger than the initial concentration, but was immediately
decreased and thus NO.sub.2 was reduced. However, at 300.degree.
C., in lieu of the reduction reaction, the NO.sub.2 desorption
became extreme due to the injection of H.sub.2. The reaction
results for the Pt(2.0)-Fe--Mn catalyst which is a mixed catalyst
of Fe and Mn are shown in (c) of FIG. 8. At 150.degree. C., the
NO.sub.2 reduction reaction using H.sub.2 slightly proceeded, but
considerably progressed due to the injection of H.sub.2 at
200.degree. C., thus remarkably lowering the concentration of
NO.sub.2. At 250.about.300.degree. C., part of NO.sub.2 was
desorbed because of the injection of H.sub.2 but the reduction
reaction considerably proceeded. The reduction performance of the
catalyst at 200.about.300.degree. C. was evaluated to be superior
to the extent that the concentration of NO.sub.2 was close to
zero.
TABLE-US-00002 TABLE 2 NO.sub.2 Reduction by H.sub.2 in Pt- or
Pd-supported Mixed Oxide Catalyst Loaded O.sub.2 Removal NO.sub.2
H.sub.2 Amount Content Temp. Limit. Convers. Effi. Catalyst (g) (%)
(.degree. C.) (ppm) (%) (%) Pt(0.2)--Fe--Mn 0.1 5.sup.a) 150 371 8
1 200 231 18 2 250 317 14 2 300 188 42 5 Pt(2.0)--Fe--Mn '' '' 150
385 17 2 200 34 124 16 250 21 128 17 300 30 89 12 Pt(2.0)--Cu--Mn
'' '' 150 386 8 1 200 374 2 1 250 385 15 2 300 394 17 2
Pt(2.0)--Cu--Mo '' '' 150 384 10 1 200 385 14 2 250 379 14 2 300
364 16 2 Pd(2.0)--Fe--Mn '' '' 150 355 7 1 200 32 129 17 250 43 112
15 300 72 87 12 Pd(2.0)--Cu--Cr '' '' 150 374 14 2 200 188 34 5 250
159 72 10 300 248 21 3 Pt(2.0)--Fe '' 10.sup.b) 150 470 7 1 200 475
3 1 250 463 11 1 300 475 1 0 Pt(2.0)--Mn '' '' 150 299 7 1 200 58
60 8 250 68 59 8 300 146 39 5 Pt(2.0)--Fe--Mn '' '' 150 379 8 1 200
53 108 14 250 26 109 14 300 33 79 10 Note: NO.sub.2 gas:
.sup.a)NO.sub.2 505 ppm/O.sub.2 5%/N.sub.2 balance .sup.b)NO.sub.2
524 ppm/O.sub.2 10%/N.sub.2 balance
[0062] As seen in FIG. 8 showing the NO.sub.2 reduction using
H.sub.2, removal limitation, NO.sub.2 conversion and H.sub.2
efficiency were calculated. The removal efficiency represents the
minimum concentration of NO.sub.2 lowered due to the injection of
H.sub.2. The NO.sub.2 conversion and the H.sub.2 efficiency are
defined as Equations 1 and 2 below.
number of moles of NO 2 reduced number of moles of NO 2 fed for 25
min .times. 100 Equation 1 number of moles of NO 2 reduced number
of moles of H 2 injected .times. 100 Equation 2 ##EQU00001##
[0063] As above, the results of NO.sub.2 reduction by injecting
H.sub.2 to the flow of NO.sub.2 in the presence of 5% O.sub.2 and
10% O.sub.2 by volume are shown in Table 2. As is apparent from
these results, the NO.sub.2 reduction performance could be seen to
greatly vary depending on the amount of supported precious metal,
the kind of precious metal, and the component of mixed oxide. When
the O.sub.2 content was 5%, the Pt(0.2)-Fe--Mn catalyst in which Pt
was supported in an amount of 0.2% by weight exhibited the NO.sub.2
conversion of 8.about.42% at 150.about.300.degree. C., which was
not so high. However, the Pt(2.0)-Fe--Mn catalyst in which the
amount of supported Pt was 2.0% had the NO.sub.2 conversion of 17%
at 150.degree. C. but exhibited the NO.sub.2 conversion exceeding
100% at 200.degree. C. and 250.degree. C. When the amount of
supported Pt was not 0.2% but 2.0%, the NO.sub.2 reduction
performance was superior. The effect of increasing the NO.sub.2
conversion exceeding 100% is caused by reducing the fed NO.sub.2 by
produced ammonia, adsorbing the remaining ammonia to the surface of
the catalyst or removing lattice O from the surface of the catalyst
to thus additionally remove NO.sub.2. Because ammonia is produced
from NO.sub.2 and is used to remove NO.sub.2, the point of time at
which H.sub.2 is supplied does not agree with the point of time at
which NO.sub.2 is removed.
[0064] In the Pt(2.0)-Cu--Mn catalyst and the Pt(2.0)-Cu--Mo
catalyst, having different components, the NO.sub.2 conversion was
very low to the level of 2.about.17%. On the other hand, the
Pd(2.0)-Fe--Mn catalyst in which Pd was supported in place of Pt
had the reduction performance similar to that of the Pt(2.0)-Fe--Mn
catalyst, and thus exhibited the NO.sub.2 conversion of 129% at
200.degree. C. which was evaluated to be very high. The
Pd(2.0)-Cu--Cr catalyst exhibited the NO.sub.2 conversion of 72% at
250.degree. C., which was smaller than that of the Pd(2.0)-Fe--Mn
catalyst but was evaluated to be high. As shown in FIG. 7, for a
considerably long period of time after completion of the injection
of H.sub.2, the phenomenon in which the concentration of NO.sub.2
is lowered, briefly, the reduction reaction, slowly proceeds. This
is because the produced ammonia reduces the surface of the catalyst
to thus produce NO.sub.x adsorption sites or is adsorbed unchanged
and then reacted with fed NO.sub.x.
[0065] The mixed oxide catalyst, for example, the Pt(2.0)-Fe--Mn
catalyst, exhibiting excellent performance in the presence of 5%
O.sub.2, was evaluated for reduction performance under an excessive
O.sub.2 content of 10%. In the Pt(2.0)-Fe catalyst, the NO.sub.2
conversion was very low on the order of 10% or less. In the
Pt(2.0)-Mn catalyst, the NO.sub.2 conversion was considerably high
on the order of 60%. In the Pt(2.0)-Fe--Mn catalyst, the NO.sub.2
conversion exceeded 100% and the removal limitation was very low on
the order of 26 ppm. Even under an excessive O.sub.2 content of
10%, the NO.sub.2 reduction performance was superior.
Example 7
H.sub.2-SCR in Reactor Packed with Precious Metal-Supported Mixed
Oxide Catalyst and NH.sub.3-SCR Catalyst
[0066] The reactor was packed with the Pt(2.0)-Fe--Mn catalyst
having superior NO.sub.2 reduction performance by H.sub.2 in Table
2 and the NH.sub.3-SCR catalyst prepared in Example 1, for example,
the Fe-BEA zeolite, and NO.sub.2 reduction performance by H.sub.2
was evaluated. As shown in FIG. 9, almost all of NO.sub.2 was
removed at 200.about.300.degree. C. due to injection of H.sub.2.
After completion of the injection of H.sub.2, the concentration of
NO.sub.2 was maintained low for a considerably long period of time,
from which the reduction performance was evaluated to be high. The
reaction results are shown in Table 3 below. At 200.degree. C., the
NO.sub.2 conversion was 133% which was evaluated to be very
high.
TABLE-US-00003 TABLE 3 NO.sub.2 Reduction by H.sub.2 in Reactor
packed with Fe-BEA Zeolite and Mixed Oxide Catalyst O.sub.2 Re-
Con- moval NO.sub.2 H.sub.2 Loaded tent Temp. Limit. Convers. Effi.
Catalyst Amount (%) (.degree. C.) (ppm) (%) (%) Pt(2.0)--Fe--Mn 0.1
g 10 150 379 8 1 200 53 108 14 250 26 109 14 300 33 79 10
Pt(2.0)--Fe--Mn + Each 0.1 g, '' 150 372 10 1 Fe-BEA Total 0.2 g
200 24 133 16 250 26 111 14 300 33 91 11 Note: NO.sub.2 gas:
NO.sub.2 505 ppm/O.sub.2 10%/N.sub.2 balance
Example 8
Hydrothermal Treatment of Mixed Oxide Catalyst
[0067] In diesel exhaust gas containing a considerable amount of
water, when the temperature of exhaust gas is widely changed
depending on driving conditions, the catalyst should be used
without exchange for a long period of time and thus should have
high hydrothermal stability. Thus, the hydrothermal stability of
the mixed oxide catalyst was evaluated.
[0068] The precious metal-supported mixed oxide catalyst was loaded
in an alumina crucible, and was placed in a quartz tube of a
circular burning furnace and thus subjected to hydrothermal
treatment. Then, N.sub.2 was allowed to flow into a steam
evaporator in a precision constant temperature circulator, thus
preparing and supplying a gas mixture containing N.sub.2 and 10%
steam by volume. While the N.sub.2 gas containing steam was
supplied at a flow rate of 100 ml/min, the treatment was performed
at 750.degree. C. for 4 hours.
[0069] The catalyst was washed with water and the decrease in the
activity of the mixed oxide catalyst was evaluated. 10 g of the
Pt(2.0)-Fe--Mn catalyst as the Pt-supported catalyst was added to
1000 g of water, strongly stirred at room temperature, treated for
1 hour, filtered using filter paper and then dried in an oven at
80.degree. C.
TABLE-US-00004 TABLE 4 Amount of NO.sub.2 Stored on Pt-supported
Mixed Oxide Catalyst after Waste Treatment & Hydrothermal
Treatment NO.sub.2 Adsorption Amount (mg/g) Adsorption Storage
Catalyst Amount Amount Pt (2.0)--Fe--Mn 182 181 Pt (2.0)--Fe--Mn
(Water Treatment) 72 66 Pt (2.0)--Fe--Mn (Hydrothermal Treatment)
84 82
[0070] The amount of NO.sub.2 stored on the Pt(2.0)-Fe--Mn catalyst
subjected to water treatment and hydrothermal treatment is shown in
Table 4. The amount of stored NO.sub.2 through water treatment and
hydrothermal treatment was lowered from 181 mg/g to 66 mg/g and 82
mg/g respectively. The amount of stored NO.sub.2 was considerably
lowered through hydrothermal treatment.
[0071] Table 5 below shows the results of NO.sub.2 reduction by
H.sub.2 in the Pt-supported Fe--Mn catalyst subjected to water
treatment and hydrothermal treatment. The reduction performance of
the Pt(2.0)-Fe--Mn catalyst subjected to water treatment was
similar to that before the treatment. The removal performance was
slightly decreased at high temperatures, but was greatly increased
at low temperatures. In the conventional Pt(2.0)-Fe--Mn catalyst,
the NO.sub.2 conversion and the H.sub.2 efficiency at 150.degree.
C. were 17% and 2% respectively, and thus the removal performance
was poor. In the water treated catalyst, the NO.sub.2 conversion
and the H.sub.2 efficiency were considerably increased to 73% and
10% respectively, but were slightly decreased at 250
.about.300.degree. C.
[0072] In the Pt(2.0)-Fe--Mn catalyst subjected to hydrothermal
treatment, the NO.sub.2 reduction performance at
150.about.200.degree. C. was considerably deteriorated, and was
greatly improved at temperatures not lower than 250.degree. C. The
Pt(2.0)-Fe--Mn catalyst exhibited had the NO.sub.2 conversion and
the H.sub.2 efficiency of 89% and 12% respectively at 300.degree.
C., and the NO.sub.2 conversion and the H.sub.2 efficiency of the
Pt(2.0)-Fe--Mn catalyst subjected to hydrothermal treatment were
considerably improved to 121% and 16% respectively.
TABLE-US-00005 TABLE 5 NO.sub.2 Reduction by H.sub.2 in
Pt(2.0)--Fe--Mn Catalyst Loaded O.sub.2 Removal NO.sub.2 H.sub.2
Amount Content Temp. Limit. Convers. Effi. Catalyst (g) (%)
(.degree. C.) (ppm) (%) (%) Pt(2.0)--Fe--Mn 0.1 5 150 385 17 2 200
34 124 16 250 21 128 17 300 30 89 12 Pt(2.0)--Fe--Mn '' '' 150 66
73 10 (Water Treatment) 200 39 114 15 250 26 107 14 300 50 81 11
Pt(2.0)--Fe--Mn '' '' 150 450 2 1 (Hydrothermal 200 147 28 4
Treatment) 250 86 84 11 300 39 121 16
Example 9
Durability of Precious Metal-Supported Mixed Oxide Catalyst to
Sulfur Poisoning
[0073] The diesel exhaust gas contains sulfur compounds including
SO.sub.2, undesirably deteriorating the activity of the
catalyst.
[0074] To evaluate the durability of the precious metal-supported
mixed oxide catalyst to sulfur poisoning, the catalyst was poisoned
with SO.sub.2. The catalyst was exhausted, activated and then
sufficiently poisoned with SO.sub.2 gas at 10 Torr at 150.degree.
C. for 1 hour, before storing NO.sub.2. After exhaust for 1 hour,
NO.sub.2 at 30 Torr was supplied and thus the adsorption amount
thereof was measured.
[0075] The amount of adsorbed SO.sub.2 and the amount of stored
NO.sub.2 after poisoning are shown in Table 6 below. At 150.degree.
C., SO.sub.2 was not adsorbed in a large amount. Upon treatment
with SO.sub.2, the amount of stored NO.sub.2 was decreased by
almost half.
TABLE-US-00006 TABLE 6 Amounts of SO.sub.2 and NO.sub.2 Stored on
Pt (2.0)--Fe--Mn catalyst SO.sub.2 Adsorption NO.sub.2 Adsorption
Amount (mg/g) Amount (mg/g) Before After Before After Catalyst
Exhaust Exhaust Exhaust Exhaust Pt (2.0)--Fe--Mn -- -- 182 181 Pt
(2.0)--Fe--Mn 13 13 68 64 (Poisoned)
[0076] The deterioration in the reduction performance of the
precious metal-supported mixed oxide through sulfur poisoning at
150.degree. C. and 200.degree. C. was evaluated. 2 ml of SO.sub.2
gas amounting to 8 times that of NO.sub.2 supplied for 5 min after
NO.sub.2 saturation and adsorption was injected, thus poisoning the
catalyst. Subsequently, H.sub.2 was injected and thus the
deterioration in the activity of the catalyst was measured.
[0077] The NO.sub.2 removal performance by H.sub.2 after sulfur
poisoning is shown in Table 7 below. The NO.sub.2 reduction
performance of the Pt(2.0)-Fe--Mn catalyst poisoned with SO.sub.2
was almost the same as that before sulfur poisoning. The NO.sub.2
conversion and the H.sub.2 efficiency were slightly decreased, but
the NO.sub.2 removal limitation at 200.degree. C. was 35 ppm which
was equivalent to that before sulfur poisoning.
TABLE-US-00007 TABLE 7 NO.sub.2 Reduction by H.sub.2 in
Pt(2.0)--Fe--Mn Catalyst poisoned with Sulfur Loaded O.sub.2
Removal NO.sub.2 H.sub.2 Amount Content Temp. Limit. Convers. Effi.
Catalyst (g) (%) (.degree. C.) (ppm) (%) (%) Pt(2.0)--Fe--Mn 0.1 5
150 385 17 1 200 34 124 16 Pt(2.0)--Fe--Mn '' '' 150 285 15 2
(Poisoned) 200 35 108 14
* * * * *