U.S. patent application number 14/131653 was filed with the patent office on 2014-06-19 for method for coating a catalysed particulate filter and a particulate filter.
This patent application is currently assigned to Haldor Topsoe A/S. The applicant listed for this patent is Par L. Gabrielsson, Keld Johansen. Invention is credited to Par L. Gabrielsson, Keld Johansen.
Application Number | 20140170033 14/131653 |
Document ID | / |
Family ID | 46320938 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140170033 |
Kind Code |
A1 |
Gabrielsson; Par L. ; et
al. |
June 19, 2014 |
METHOD FOR COATING A CATALYSED PARTICULATE FILTER AND A PARTICULATE
FILTER
Abstract
Method for the preparation of a wall flow particulate filter
catalysed at its inlet side with a first catalyst having activity
in the removal of residual hydrocarbons and carbon monoxide and
catalysing at rich burn engine operation conditions the reaction of
nitrogen oxides with hydrogen and/or carbon monoxide to ammonia and
catalysed at its outlet side with a second catalyst having activity
in the selective reduction of NOx by reaction with ammonia being
formed in the inlet side. The method involves the provision of a
first catalyst having a particle size smaller than the filter wall
mean pore size, and a second catalyst having a particle size larger
than the filter wall mean pore size, and mixing the first and
second catalyst into one suspension, which is used for wash-coating
from the outlet end. The first catalyst thereby diffuses into the
partition wall.
Inventors: |
Gabrielsson; Par L.;
(Helsingborg, SE) ; Johansen; Keld;
(Frederikssund, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gabrielsson; Par L.
Johansen; Keld |
Helsingborg
Frederikssund |
|
SE
DK |
|
|
Assignee: |
Haldor Topsoe A/S
Kgs. Lyngby
DK
|
Family ID: |
46320938 |
Appl. No.: |
14/131653 |
Filed: |
June 14, 2012 |
PCT Filed: |
June 14, 2012 |
PCT NO: |
PCT/EP2012/061328 |
371 Date: |
January 8, 2014 |
Current U.S.
Class: |
422/181 ;
427/244 |
Current CPC
Class: |
Y02T 10/24 20130101;
B01D 2255/20738 20130101; B01J 23/63 20130101; B01D 2255/1023
20130101; F01N 3/2073 20130101; B01J 29/85 20130101; B01J 37/0219
20130101; B01D 2255/9155 20130101; B01J 37/0246 20130101; F01N
3/2832 20130101; F01N 2510/0684 20130101; Y02T 10/12 20130101; B01J
35/04 20130101; B01D 53/9468 20130101; F01N 3/035 20130101; B01D
2255/50 20130101; B01D 53/9422 20130101; B01D 2255/20761 20130101;
B01D 53/9418 20130101; B01J 37/0036 20130101; B01J 37/0244
20130101 |
Class at
Publication: |
422/181 ;
427/244 |
International
Class: |
F01N 3/28 20060101
F01N003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2011 |
DK |
PA 2011 00537 |
Claims
1. Method of preparation a catalysed wall flow filter, comprising
the steps of a) providing a wall flow filter body with a plurality
longitudinal inlet flow channels and outlet flow channels separated
by gas permeable porous partition walls; b) providing a catalyst
washcoat comprising a first catalyst composition being active in
reaction of nitrogen oxides with carbon monoxide and hydrogen to
ammonia and a second catalyst composition being active in selective
reduction of nitrogen oxides by reaction with ammonia to nitrogen,
the first catalyst composition has a mode particle size being
smaller than average pore diameter of the porous partition walls
and the second catalyst composition has a mode particle size being
larger than the average pore diameter of the porous partition
walls; c) coating the filter body with the catalyst washcoat by
introduction of the washcoat into outlet end of the outlet
channels; and d) drying and heat treating the coated filter body to
obtain the catalysed particulate filter.
2. The method of claim 1, wherein the catalyst being active in
conversion of nitrogen oxides to ammonia includes palladium,
platinum, a mixture of palladium and rhodium and a mixture of
palladium, platinum and rhodium.
3. The method of claim 1, wherein the catalyst being active in
conversion of nitrogen oxides to ammonia consists of palladium.
4. The method according to claim 1, wherein the catalyst being
active in the selective reduction of nitrogen oxides comprises at
least one of a zeolite, a silica aluminum phosphate, an ion
exchanged zeolite, silica aluminum phosphate promoted with iron
and/or copper, one or more base metal oxides.
5. The method according to claim 1, further comprising the steps of
providing a second washcoat containing a catalyst composition being
active in the oxidation of ammonia; and coating a part of outlet
channels at region at the outlet end with the second washcoat.
6. A catalysed wall flow filter being prepared in accordance with
claim 1.
Description
[0001] The present invention relates to a multifunctional catalysed
engine exhaust particulate filter. In particular, the invention is
a method for the preparation of a multifunctional catalysed
particulate filter being catalysed with a three way catalyst (TWC)
and a catalyst being active in removing nitrogen oxides by the
known NH3--selective catalytic reduction (SCR) process, and
optionally with a catalyst having activity in the oxidation of
excess ammonia to nitrogen.
[0002] The multifunctional catalysed filter is in particular useful
for the cleaning of exhaust gas from lean burn gasoline engines,
such as the gasoline direct injection (GDI) engine.
[0003] GDI engines generate more carbonaceous soot than gasoline
premixed injection engines. In Europe the Euro 5+ Diesel
legislation is expected to be used for GDI in the future with a
particulate mass limit at 4.5 mg/km, which requires filtration of
the engine exhaust in order to reach the above limit.
[0004] Typically, filters for use in automotive applications are
the wall flow type filter consisting of honeycombed structured
body, wherein particulate matter is captured on or in partition
walls of the honeycomb structure. These filters have a plurality
longitudinal flow channels separated by gas permeable partition
walls. Gas inlet channels are open at their gas inlet side and
blocked at the opposite outlet end and the gas outlet channels are
open at the outlet end and blocked the inlet end, so that a gas
stream entering the wall flow filter is forced through the
partition walls before into the outlet channels.
[0005] In addition to soot particles, exhaust gas from gasoline
engines contains nitrogen oxides (NOx), carbon monoxide and unburnt
hydrocarbons, which are chemical compounds representing a health
and environmental risk and must be reduced or removed from the
exhaust gas.
[0006] Catalysts being active in the removal or reduction of NOx,
carbon monoxide and hydrocarbons to harmless compounds are per se
known in the art.
[0007] The patent literature discloses numerous cleaning systems
comprising separate catalyst units for the removal of harmful
compounds from engine exhaust gas.
[0008] Also known in the art are exhaust gas particulate filters
coated with catalysts catalysing oxidation of hydrocarbons and
particulate matter together with selective catalytic reduction
(SCR) of NOx by reaction with ammonia being added as such or as
precursor thereof into the exhaust gas.
[0009] Multifunctional diesel particulate filters coated with
different catalysts catalysing the above mentioned reactions are
also known in the art.
[0010] In the known multifunctional filters, the different
catalysts are segmentarily or zone coated in different zones of the
filter.
[0011] Segmentary or zone coating of different catalysts on the
filter is an expensive and difficult preparation process.
[0012] Compared to known technique, the present invention suggests
an easier method for the preparation of particulate filers
catalysed with different catalysts for the selective reduction of
nitrogen oxides with ammonia and removal of hydrocarbons, carbon
monoxide and excess ammonia.
[0013] Thus, the invention provides a method of preparation a
catalysed wall flow filter, comprising the steps of
[0014] a) providing a wall flow filter body with a plurality
longitudinal inlet flow channels and outlet flow channels separated
by gas permeable porous partition walls;
[0015] b) providing a catalyst washcoat comprising a first catalyst
composition being active in reaction of nitrogen oxides with carbon
monoxide and hydrogen to ammonia together with a second catalyst
composition being active in selective reduction of nitrogen oxides
by reaction with ammonia to nitrogen, the first catalyst
composition has a particle size being smaller than average pore
diameter of the porous partition walls and the second catalyst
composition has a particle size with is larger than the average
pore diameter of the porous partition walls;
[0016] c) coating the filter body with the catalyst washcoat by
introduction of the washcoat into outlet end of the outlet
channels; and
[0017] d) drying and heat treating the coated filter body to obtain
the catalysed particulate filter.
[0018] The advantage of either the first catalyst has a smaller
particle size than the mean pore diameter of the partition walls
and the second catalyst particles have a larger particle size than
the mean pore diameter of the walls is to allow the first catalyst
particles to diffuse effectively into the partition walls and to
prevent the second catalyst from diffusing into the channels where
the specific catalytic activity is nor desired.
[0019] It is then possible to coat the filter body with different
catalysts inlet and outlet flow channels with a single
washcoat.
[0020] Useful catalyst for the reaction of Nox to ammonia by the
following reaction:
NOx+H.sub.2/CO=NH.sub.3+CO.sub.2+H.sub.2O
are palladium, platinum, a mixture of palladium and rhodium and a
mixture of palladium, platinum and rhodium.
[0021] These catalysts catalyse the ammonia formation under rich
burn operating conditions of the gasoline engine, i.e.
.lamda.<1. Palladium is the preferred catalyst with the highest
ammonia formation.
[0022] Ammonia being thus formed within the inlet channels by the
above reaction permeates through the partition walls of the filter
into the outlet channels and is during the rich operating
conditions adsorbed in the SCR catalyst in the outlet flow
channels.
[0023] Both the ammonia forming catalyst and the SCR catalyst are
preferably deposited on the partition walls on the sides facing the
inlet channel and the outlet channel, respectively.
[0024] In a subsequent lean burn operation cycle of the engine, NOx
being present in the exhaust gas reacts with the ammonia stored in
the SCR catalyst by the following reaction:
NOx+NH.sub.3=N.sub.2+H.sub.2O
[0025] As already mentioned above, SCR catalyst are per se known in
the art. For use in the invention, the preferred catalyst being
active in the selective reduction of nitrogen oxides comprises at
least one of a zeolite, a silica aluminum phosphate, an ion
exchanged zeolite, silica aluminum phosphate promoted with iron
and/or copper, one or more base metal oxides.
[0026] A further preferred SCR catalyst for use in the invention is
a silica aluminium phosphate with chabazite structure, such as SAPO
34, promoted with copper and/or iron.
[0027] In order to remove the excess ammonia having not reacted
with NOx, the wall flow filter comprises in an embodiment of the
invention additionally an ammonia oxidation catalyst arranged in
each outlet flow channel at least in the region of the outlet end
of the filter.
[0028] A preferred ammonia oxidation catalyst comprises palladium,
platinum or a mixture thereof.
[0029] By contact with the ammonia oxidation catalyst, ammonia is
oxidised to nitrogen and water.
[0030] The ammonia oxidation catalyst may be deposited directly on
the partition wall in the outlet channels of the filter in the
outlet region or provided as surface layer on surface of the SCR
catalyst layer.
[0031] The invention provides additionally a method of preparation
of a catalysed wall flow filter.
[0032] In its broad embodiment the invention provides a of
preparation a catalysed wall flow filter, comprising the steps
of
[0033] a) providing a wall flow filter body with a plurality
longitudinal inlet flow channels and outlet flow channels separated
by gas permeable porous partition walls;
[0034] b) providing a catalyst washcoat comprising a first catalyst
composition being active in reaction of nitrogen oxides with carbon
monoxide and hydrogen to ammonia and a second catalyst composition
being active in selective reduction of nitrogen oxides by reaction
with ammonia to nitrogen, the first catalyst composition has a mode
particle size being smaller than average pore diameter of the
porous partition walls and the second catalyst composition has a
mode particle size being larger than the average pore diameter of
the porous partition walls;
[0035] c) coating the filter body with the catalyst washcoat by
introduction of the washcoat into outlet end of the outlet
channels; and
[0036] d) drying and heat treating the coated filter body to obtain
the catalysed particulate filter.
[0037] Specific catalyst compositions for use in the invention are
mentioned hereinbefore and further disclosed in claims 2 to 4.
[0038] In further an embodiment of the invention, the filter is
additionally coated with a so called ammonia slip catalyst, which
is a catalyst being active in the oxidation of excess of ammonia to
nitrogen and water.
[0039] Thus in this embodiment the inventive method comprises the
steps of
[0040] providing a second washcoat containing a catalyst
composition being active in the selective oxidation of ammonia;
and
[0041] coating at least a part of the outlet channels with the
washcoat subsequently to the coating with the catalyst
washcoat.
[0042] When preparing the washcoats for use in the invention, the
catalysts being usually in particle form are milled or agglomerated
to the required particle size and suspended in water or organic
solvents, optionally with addition of binders, viscosity improvers,
foaming agents or other processing aids.
[0043] The filter is then washcoated according to common practice,
including applying vacuum in the filter, pressurizing the washcoat
or by dip coating.
[0044] The amount of the first catalyst coated on the filter is
typically 10 to 140 g/l, and the amount of the second catalyst on
the filter is typically 10 to 100 g/l. The total catalyst loading
on the filter is typically in the range of 40 to 200 g/l.
[0045] Examples of suitable filter materials for use in the
invention are silicon carbide, aluminium titanate, cordierite,
alumina, mullite or combinations thereof.
EXAMPLE
[0046] A suspension of the first catalyst composition is in a first
step prepared from a powder mixture of palladium rhodium deposited
on cerium oxide and alumina particles of a particle size smaller
than the filter wall mean pore size.
[0047] A suspension of the mixture first catalyst is prepared by
mixing 20 g of these powders in 40 ml demineralised water pr liter
filter. A dispersing agent Zephrym PD-7000 and an antifoam agent
are added. The suspension is milled in a bead mill. The particle
sizes of the final suspension must be smaller than the mean pore
diameter of the pores in the wall of the wall flow filter
[0048] A suspension of a second catalyst is made by mixing and
dispersing 100 g of silica aluminium phosphate SAPO-34 promoted
with 2% copper in 200 ml demineralised water pr liter filter. A
dispersing agent Zephrym PD-7000 and an antifoam agent are added.
The particle sizes must be larger than the mean pore diameter of
the pores in the wall of the wall flow filter
[0049] The suspensions of the first catalyst and the second
catalyst are then mixed to one suspension.
[0050] A high porosity (approximately 60% and wall mean pore size
approx 18 .mu.m) conventionally plugged SiC wall flow filter is
used.
[0051] The mixed suspensions of first and the second catalyst is
washcoated from the filters outlet end of the filters permeate side
by standard washcoat methods permeate side, dried and calcined at
750.degree. C.
* * * * *