FIELD OF INVENTION
The field of the present invention is related to Selective Catalytic Reduction (SCR)
catalyst to abate NOx from the exhaust of a lean burn automotive engine. More
particularly, this invention discloses a DeNOx catalyst consisting of one or more
5 transition metal-doped loaded zeolite/zeolite-type materials, coated on honeycomb
monolith and a method of preparing the same.
BACKGROUND OF THE INVENTION
Air pollution has become a significant global problem not only in terms of global
warming but also poses serious health hazards. The major pollutants in automotive
10 exhaust system include emissions such as oxides of Nitrogen (also known as NOx),
carbon monoxide, unburned hydrocarbons and particulate matter. Amongst the
above, NOx plays a prominent role in the formation of smog, acid rain, ground level
ozone and fine particulate matters (PM). It is therefore, become very imperative to
drastically reduce or eliminate NOx emissions. In addition, the legislative emission
15 norms have globally become more and more stringent.
The use of SCR for reduction of NOx pollutants from vehicular emissions is well
known in prior art. These are known to use zeolite/zeolite-type based catalysts for
selective catalytic reduction of NOx to nitrogen (N2) gas and steam/water (H2O).
However, such catalysts are known to have lower conversions at lower
20 temperatures and may lose structural stability at higher temperatures.
The present invention discloses the composition and method to prepare a novel SCR
catalyst, which not only gives a reasonably high, low-temperature NOx conversion
but also high temperature structural stability and durability.
OBJECTIVES OF THE INVENTION
25 The primary objective of this invention is to formulate a SCR or DeNOx catalyst
which can reduce the NOx emissions from the exhaust tail pipe of said automotive
engines.
3
Another objective of the instant invention, is to exhibit a reasonably high NOx
conversion at low temperatures during cold start operations.
Yet another objective of the instant invention, is to exhibit high temperature
structural stability, during extremely long periods of operation on road.
5 Yet another objective of the instant invention is to be highly selective towards NO
reduction to N2 compared to NO2, over a metal(s) loaded zeolite/zeolite-type based
SCR catalysts during the entire temperature range of SCR system.
Yet another objective of this invention is to improve performance of the metal(s) or
transition metal(s) or combination of metal(s) loading by inventive method on
10 zeolite/zeolite-type based SCR catalysts during entire temperature range of SCR
system.
Yet another objective of this invention is to recover >99% performance of the
metal(s) loaded zeolite/zeolite-type based SCR catalysts after sulphur aging.
To achieve the aforesaid objectives of this instant invention, the following actions
15 were taken (1) judicious selection of zeolite/zeolite-type material(s), (2) choice of
metal(s)/transition metal(s) and their combinations, (3) metal doping/loading,
(4) incorporating suitable binding agent(s) and (5) optionally, incorporating
promoter(s).
SUMMARY OF THE INVENTION
20 The instant invention discloses a metal(s) loaded zeolite/zeolite-type based catalyst
and a method of manufacturing said metal(s) loaded zeolite/ zeolite-type based SCR
catalyst. Specifically, the metal(s) loaded zeolite/zeolite-type based SCR catalyst
include CHA structure type materials such as silico-aluminophosphates,
aluminophosphates (AlPO-34, SAPO-34, MeAPO-34, MeAPSO-34, AlPO-47,
25 SAPO-47, MeAPO-47, MeAPSO-47) and/or aluminosilicates loaded with metal
elements such as transition metals Cu, Fe, Ni, Mn, Co, V, Ti and Zn or their
combinations thereof.
4
Aspects of the present invention include a method of making the metal(s) loading
on zeolite/zeolite-type materials by wet and instant dry method. The method
includes a first step, in which an aqueous solution containing metal(s) is prepared
by simple mixing of water and metal salts under stirring, a second step, in which,
5 the zeolite/zeolite-type materials is added slowly with simultaneous mixing to the
above solution, a third step, in which, the solution is stirred at elevated temperatures
for few hours, a fourth step, in which, the solution is exposed suddenly at above
water-evaporation temperatures until dryness, a fifth step, in which, the collected
dried sample at ambient is heated in an oven again for few hours to remove any
10 occluded water molecules and/or volatile components, a final step, in which, the
sample is calcined for few hours and cooled to ambient temperature, preferably
naturally.
Aspects of the present invention include a method of making the metal(s) loaded
zeolite/zeolite-type based SCR catalyst. The method includes a first step, in which,
15 a slurry of the metal(s) zeolite/zeolite-type mixture is prepared; a second optional
step, in which, the slurry is coated on a honeycomb structure; a third step, in which,
the slurry or the coated honeycomb is subjected to calcination; and a fourth step in
which, the coated honeycomb monolith is post-treated by air-moisture mixture.
The post-treatment step includes heating the coated and calcined honeycomb
20 monolith slowly from ambient to a high temperature while passing air-moisture
mixture through it. After a holding period at the desired temperature, the said
honeycomb monolith is allowed to reach ambient naturally.
One of the main advantages of this instant invention is that it will optionally
eliminate/reduce the requirement/dependency of an upstream DOC (Diesel
25 Oxidation Catalyst) in lean burn diesel engines.
Other aspects, advantages, and salient features of the current invention will become
apparent to those skilled in the art, from the following detailed description which,
when taken in conjunction with the annexed drawings, discloses exemplary
embodiments of the invention.
5
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figures 1 illustrate preferred embodiment process for preparing, coating and posttreating the transition metal(s) loaded zeolite/zeolite-type based SCR catalyst of the
instant invention.
5 Figure 2 illustrate a comparative study of the X-Ray Diffraction (XRD) patterns of
CuZ catalyst before and after post-treatment process.
Figure 3 illustrates a comparative NH3-TPD study of CuZ catalyst before and after
post-treatment process.
Figure 4 illustrate a comparative solid state Al27 MAS NMR study of CuZ catalyst
10 before and after post-treatment process.
Figure 5 illustrate test results of NOx conversion efficiency over transition metal(s)
loaded zeolite/zeolite-type based SCR catalyst such as CuZ, FeCuZ, FeZ and
CuFeZ catalysts.
Figures 6A to 6C illustrate test results of NOx conversion efficiency Vs each mode
15 in 7-mode cycle over CuZ catalyst, where Figure 6A shows the test results of NOx
conversion efficiency, and where Figure 6B shows the test results of NO conversion
efficiency, and where Figure 6C shows the test results of NO2 conversion
efficiency.
Figures 7A and 7B illustrate test results of NOx conversion efficiency Vs
20 temperatures over CuZ catalyst, where Figure 7A shows the test results of NOx
conversion efficiency between post-treated and 3 cycles of sulphur aged at 200°C
for 20 hours, where Figure 7B shows the test results of NOx conversion efficiency
between post-treated and 3 cycles of regeneration at 650°C after each sulphur aged
cycles.
25 DETAILED DESCRIPTION
The following detailed description should be read with reference to the drawings.
6
The following section full-forms of acronyms used in this specification. If any
acronym or word is not defined or elaborated in this section, then said acronym or
word will have a meaning commonly defined and acceptable in the art at the time
of the filing of this application.
5 SCR: Selective Catalytic Reduction
SAPO: Silico-aluminophosphate
AlPO: Aluminophosphate
SSZ: Aluminosilicates
CHA: Chabazite
10 The present invention discloses a transition metal(s) loaded zeolite/zeolite-type
SCR catalyst. The performance of transition metal(s) loaded catalyst is attributed to
the change in acidic nature of the zeolite/zeolite-type based SCR catalyst by (1) the
choice of the method of preparation of the said catalyst, (2) coating of this material
on honeycomb monolith and (3) post-treatment process.
15 Furthermore, the performance of the transition metal(s) loaded zeolite/zeolite-type
SCR catalyst is attributed to (1) judicious selection of zeolite/zeolite-type
material(s), (2) choice of transition metal(s) and their combinations, (3) metal
doping/loading, (4) incorporating suitable binding agent(s) and (5) optionally,
incorporating promoter(s).
20 The present invention discloses transition metal(s) loading on zeolite/zeolite-type
materials and a method of manufacturing said metal(s) loaded zeolite/zeolite-type
SCR catalyst.
It is a preferred embodiment to prepare the metal(s) loading by wet and instant dry
method comprising the steps of:
25 a) Preparing an aqueous solution containing metal(s) by mixing of
water and metal salts under stirring,
7
b) Adding slowly the zeolite/zeolite-type materials with simultaneous
mixing to the solution of step a),
c) Stirring the solution at elevated temperatures for few hours,
d) Exposing the solution suddenly at above water-evaporation
5 temperatures until dryness to obtain dry sample,
e) Re-heating the collected dried sample at above water evaporation
temperature for few hours to remove any occluded water molecules
and/or volatile components,
f) Subjecting the sample for calcination for few hours at high
10 temperature followed by cooling to ambient temperature
It is a further preferred embodiment to prepare the DeNOx catalyst by preparing a
slurry of metal(s) loaded zeolite/zeolite-type material, with a binder and optionally
with a promoter; optionally coating said slurry on a honeycomb structure monolith,
15 subjecting the said slurry for calcination and then having a post treatment step. The
post treatment is by heating slowly from ambient temperature to high temperature
while passing air-moisture mixture through it, holding for a period at the desired
high temperature in the presence of air-moisture mixture, and finally cooling to
ambient temperature in the presence of air-moisture mixture to obtain the DeNOx
20 catalyst with enhanced properties.
The transition metal(s) loaded zeolite/zeolite-type based SCR catalyst involves the
use of microporous zeolite (aluminosilicates type) or zeolite-type (silicoaluminophosphates/aluminophosphates type) and loaded with Cu (copper) or Fe
(Iron) or combinations thereof.
25 Furthermore, the Cu (copper) content in the transition metal(s) loaded
zeolite/zeolite-type based SCR catalyst is in the range of 0.01 to 0.02 Mol %.
Alternatively, the Fe (Iron) content in the transition metal(s) loaded zeolite/zeolitetype based SCR catalyst is in the range of 0.003 to 0.005 mol %.
8
The composition of the zeolite/zeolite-type in the transition metal(s) loaded zeolite
based SCR catalyst is in the range of 45 to 95 wt%, preferably between 80% and
90%.
The composition of a binder such as zirconium sol or silica sol or alumina sol or
5 titania sol or their combinations thereof, in the transition metal(s) loaded
zeolite/zeolite-type based SCR catalyst is in the range of 5 to 55 wt%, preferably
between 10% and 20%.
Optionally, promoters, such as titania, zirconia, ceria-zirconia, silica, alumina,
silica-alumina, alkaline and alkaline earth metals incorporated either individually
10 or in combinations thereof, on the transition metal(s) loaded zeolite/zeolite-type
based SCR catalyst, is in the range of 0.1 to 15 wt%.
In a preferred embodiment the metal(s) loaded zeolite/zeolite-type based SCR
catalyst is made by the process illustrated in the flow chart shown in Figure 1 and
is described as below.
15 In Figure 1, the said process includes a first step, in which an aqueous solution
containing metal(s) is prepared by simple mixing of water and metal salts under
stirring, a second step, in which, the zeolite/zeolite-type materials is added slowly
with simultaneous mixing to the above solution, a third step, in which, the solution
is stirred at elevated temperatures for few hours, a fourth step, in which, the solution
20 is exposed suddenly at above water-evaporation temperatures until dryness, a fifth
step, in which, the collected dried sample at ambient is re-heated in an oven again
for few hours to remove any occluded water molecules and/or volatile components,
a final step, in which, the sample is calcined for few hours and cooled naturally.
The slurry mixture includes a first slurry of the above described metal(s) loaded
25 zeolite/zeolite-type materials and water and a second slurry of a suitable binder and
water, optionally, a promoter. The two slurries are mixed together. The mixed slurry
has a solid concentration of 10 to 45% and a viscosity (cP) <2500. The particle size
distribution of the slurry D50 (µm) ranges between 1.5 to 7.5 µm, preferably in the
9
range of 2.0 µm to 4.5 µm. The pH of the slurry is maintained in between 2.5 to
6.5, preferably 3.0 to 4.0.
In the next process step, the slurry is coated on a honeycomb monolith structure.
The honeycomb monolith structure can be ceramic or metallic. The ceramic
5 substrates may be either a flow-through type or a wall-flow filter type.
In the next step, the slurry or the coated honeycomb is subjected to calcination for
4 to 10 hours with the temperature ranging between 400℃-600℃.
In the next step, post-treatment process is conducted as depicted in Figure 1. In this
process, the transition metal(s) loaded zeolite/zeolite-type based SCR catalyst
10 (coated on honeycomb monolith) is placed inside a furnace and heated up to
designated temperatures. An air stream containing 4.5 to 15% of moisture content
is forced through the furnace with heating, holding and cooling steps.
The transition metal(s) loaded zeolite/zeolite-type based SCR catalyst after airmoisture mixture post-treatment process exhibit enhanced NOx conversion
15 efficiency even at low temperatures as compared to transition metal loaded
zeolite/zeolite-type based SCR catalyst without the air-moisture mixture posttreatment process.
The NOx (NO+NO2) emitted from the DOC+DPF system placed upstream to the
said SCR becomes the inlet feed to the said SCR. Hence, the selectivity in reduction
20 efficiency between NO and NO2 becomes more critical in overall NOx reduction.
The above detailed study shown in the figure 6A-6C indicate the NOx conversion
efficiency is superior to NO reduction rather than NO2.
Recent developments in engine technology have reduced NO2 formation, since their
operating temperatures are lower. Therefore, overall composition of NOx in the
25 exhaust assembly is shifting towards higher proportions of NO as compared to NO2.
The transition metal(s) loaded zeolite/zeolite-type based SCR catalyst of the instant
invention, due to its preferred selectivity of NO to N2, eliminate/reduce the
requirement/dependency of an upstream DOC to produce NO2, since there is no
necessity for NO2 production.
10
Various other modifications, adaptations, and alternative designs are of course
possible in light of the above learnings. Therefore, it should be understood at this
time that within the scope of the appended claims the invention might be practiced
otherwise than as specifically described herein.
5
Characterization of SCR Catalyst Powder
Characterization and evaluation to measure the performance of the transition
metal(s) loaded zeolite/zeolite-type based SCR catalyst powder of the instant
invention was conducted and the results are disclosed in the following passages.
Techniques like XRD, Surface Area analysis, NH3-TPD and Al 10 27 MAS NMR were
used to understand the topological changes brought about on the surface of the
catalyst by the air-moisture mixture post-treatment process.
X-Ray Diffractions Studies
A comparative study of the X-Ray Diffraction (XRD) patterns of the transition
15 metal(s) loaded zeolite/zeolite-type based SCR catalyst before and after the airmoisture mixture post-treatment process is shown in Figure 2 respectively.
The enhanced sharp peaks intensity in Figure 2 top pattern line in comparison to
the one below (bottom pattern line) indicates the improved crystalline nature of the
transition metal(s) loaded zeolite/zeolite-type based SCR catalyst could due to
20 healing of the defect sites leading to more ordered orientation at atomic level during
the air-moisture mixture post-treatment process. This enhanced crystalline nature
of transition metal(s) loaded zeolite/zeolite-type based SCR catalyst is results in
increase of active sites, which consequently leads to increase in conversion
efficiency.
25 NH3-Temperature Programmed Desorption (TPD) Studies
A comparative NH3-TPD study of transition metal(s) loaded zeolite/zeolite-type
based SCR catalyst before and after air-moisture mixture post-treatment process is
11
disclosed in Figure 3. NH3-TPD results exhibit an improvement of 12 - 17% in the
ammonia adsorption capacity after air-moisture mixture post-treatment process.
The NH3-TPD profile (Figure 3) also exhibits the presence of stronger acid sites
after air-moisture mixture post-treatment process at the high temperature range of
5 300 - 500℃ is attributed to the formation of strong acid sites either from the healed
defective ones or masked ones or both. These acid sites where later identified to be
the come from tetrahedral Al sites (attributed to BrØnsted acid type) by Al27 MAS
NMR technique.
Surface Area Measurements
10 Surface area is an indicator of the available area on the support material on which
the incoming feed gas can diffuse and react with the active sites therein. Once posttreated, the surface area of the transition metal(s) zeolite/zeolite-type found to be
enhanced by 10 - 12 %. This is again could be attributed to healing of defect sites.
Solid State Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR)
15 Spectroscopy
Solid state Al27 MAS NMR studies on transition metal(s) loaded zeolite/zeolitetype based SCR catalyst before and after air-moisture mixture post-treatment
process were recorded. The NMR profile, clearly, exhibits enhanced tetrahedral Al
(AlT4) species (chemical shift 54 ppm) after post-treatment process in comparison
20 to the one before by more than 3/2 fold, while the octahedral Al (AlT6) species
(chemical shift 0-10 ppm) as well as pentahedral Al (AlT5) species (chemical shift
18 ppm) are reduced after post-treatment process. The presence of enhanced
tetrahedral Al species after post-treatment process, is evident due to the presence of
more Al species in the framework of zeolite/zeolite-type materials, as one could
25 assign as strong acid sites (BrØnsted), which is not the case, before post-treatment
process.
The current inventions were demonstrated by the examples provided below. All the
experiments are carried out using zeolite/zeolite-type materials belonging to CHA
structure type. More specifically, SAPO and SSZ of above said type is used.
12
Example 1
Cu containing zeolite/zeolite-type material preparation
Copper containing zeolite/zeolite-type materials were prepared by wet and instant
dry method. An aqueous solution of copper salt containing 0.015 mol of Cu was
5 prepared by simple mixing of water and copper salt with stirring for 15 minutes. To
this copper containing aqueous solution, a defined amount of zeolite or zeolite-type
powder samples were added slowly for 30 minutes with simultaneous mixing. This
solution was stirred at elevated temperatures of 70°C to 80°C for 5 to 6 hours and
then exposed suddenly to temperatures >110°C. Preferably the solution was stirred
10 at elevated temperature of 75°C for preferably 5.5 hours prior to the sudden
exposure to preferable temperatures of 190°C. The thus dried sample was collected
and reheated to remove any trapped, occluded water molecules and/or volatile
compounds in the zeolite and zeolite-type materials. Finally, it was calcined at
550°C for 4 to 6 hours. This catalyst powder sample was denoted as CuZ.
15 Example 2
FeCu containing zeolite/zeolite-type material preparation
Iron/Copper containing zeolite/zeolite-type materials were prepared by the wet and
instant dry method. First, the CuZ-1 was prepared by the same procedure as
mentioned in the Example 1. The calcined and finely grounded CuZ powder sample
20 of defined amount was added slowly for 30 minutes with simultaneous mixing into
an aqueous solution of iron salt containing 0.004 mol of Fe which was pre-prepared
by simple mixing of water and Iron salt with stirring for 15 minutes. This solution
was stirred at elevated temperatures such as 70°C to 80°C for 5 to 6 hours and then
exposed suddenly to temperatures >110°C. Preferably the solution was stirred at
25 elevated temperature of 75°C for preferably 5.5 hours prior to the sudden exposure
to preferable temperatures of 190°C. The thus dried sample was collected and
reheated to remove any trapped, occluded water molecules and/or volatile
13
compounds in the zeolite/zeolite-type materials. Finally, it was calcined again at
550°C for 4 to 6 hours. This catalyst powder sample was denoted as FeCuZ.
Example 3
Fe containing zeolites/zeolite-types preparation
5 Iron containing zeolite/zeolite-type materials were prepared by the wet and instant
dry method. An aqueous solution of iron salt containing 0.004 mol of Fe was
prepared by simple mixing water and of Iron salt and stirred for 15 minutes. To this
iron containing aqueous solutions, defined amount of zeolite/zeolite-type powders
were added slowly for 30 minutes with simultaneous mixing. This solution was
10 stirred at elevated temperatures of 70°C to 80°C for 5 to 6 hours and then exposed
suddenly to temperatures >110°C. Preferably the solution was stirred at elevated
temperature of 75°C for preferably 5.5 hours prior to the sudden exposure to
preferable temperatures of 190°C. The thus dried sample was collected and reheated
to remove any trapped, occluded water molecules and/or volatile compounds in the
15 zeolite/zeolite-type materials. Finally, it was calcined at 550°C for 4 to 6 hours. This
catalyst powder sample was denoted as FeZ.
Example 4
CuFe containing zeolite/zeolite-type material preparation
Iron/Copper containing zeolite/zeolite-type materials were prepared by wet and
20 instant dry method. First, the FeZ was prepared by the same procedure as mentioned
in the Example 2. The calcined and finely grounded FeZ zeolite/zeolite-type
powder sample of defined amount was added slowly for 30 minutes with
simultaneous mixing into an aqueous solution containing of copper salt containing
0.015 mol of Cu which was pre-prepared by simple mixing of water and copper salt
25 with stirring for 15 minutes. This solution was stirred at elevated temperatures such
as 70°C to 80°C for 5 to 6 hours and then exposed to temperatures >110°C.
Preferably the solution was stirred at elevated temperature of 75°C for preferably
5.5 hours prior to the sudden exposure to preferable temperatures of 190°C. The
14
thus dried sample was collected and reheated to remove any trapped, occluded
water molecules and/or volatile compounds in the zeolite/zeolite-type materials.
Finally, it was calcined again at 550°C for 4 to 6 hours. This catalyst powder sample
was denoted as CuFeZ.
5
Example 5
Catalyst Preparation Method
The prepared CuZ containing zeolite/zeolite-type powder samples were re-slurried
10 with water and suitable binder under controlled pH conditions. This slurry was
stirred vigorously for 3 to 5 hours (preferably 4 hours) and coated on ceramic
honeycomb monolith having 400 cpsi cell density and 4 mil wall thickness. The
coated ceramic honeycomb was post-treated as discussed elsewhere.
Similar process was employed to prepare coated FeCuZ, FeZ, and CuFeZ catalysts.
15 Example 6
Testing Conditions
A steady state cycle test run was operated in the temperature range from 80°C to
550°C with urea dosing from 170°C to 550°C. The conditions are summarized in
Table 1.
20 Table 1
Parameters Conditions
NO (ppm) 600
NO2 (ppm) 400
Total NOx (ppm) 1000
NH3 (ppm) 1000
O2 (%) 6
H2O (%) 10
N2 Balance
15
Rising Temp. Speed
(℃/min.) 15
Test Temp. Range 80° to 550°C
Ammonia Dose At 170°C
Space Velocity (h-1
) 50,000
NOx/NH3Ratio 1
NO2/NH3 Ratio 0.4
Gas Flow including
H2O (LPH) 1060
The transient seven mode test cycle run operated at varying temperatures, space
velocities and feed gas compositions whereas NH3 is dosed at 170°C. The
conditions are summarized below in Table 2.
5 Table 2
Mode
No.
Temp.
( °C )
Space
Velocity
(h-1
)
NOx Conc.
Inlet (ppm)
NO
(ppm)
NO2
Fraction
(%)
NO2
(ppm)
NH3
(ppm)
Total
NOx+NH3
(ppm)
O2
(%)
H2O
(%) N2
Mode-1 432 75000 959 643 33 316 959 1918
6 8 Bal.
Mode-2 375 60000 821 443 46 378 821 1642
Mode-3 311 45000 609 329 46 280 609 1218
Mode-4 217 25000 303 215 29 88 303 606
Mode-5 435 50000 1196 849 29 347 1196 2392
Mode-6 386 45000 1087 630 42 457 1087 2174
Mode-7 360 30000 823 403 51 420 823 1646
Example 7
Performance Results
Table 3
Temperature
(℃)
NOx Conversion (%)
CuZ
Post-treated
FeZ
Post-treated
FeCuZ
Post-treated
CuFeZ
Post-treated
16
180 18 32 28 21
200 92 42 48 43
250 94 48 67 72
300 98 42 83 87
350 98 51 85 91
400 97 68 85 88
450 99 72 79 89
500 97 60 78 91
550 95 62 75 89
Figure 5 and Table 3 discloses the steady state cycle test results of NOx conversion
>92% for post-treated CuZ catalyst in comparison with that for other post-treated
catalysts in the temperature range of 200°C to 550°C. Light off temperature is also
5 significantly enhanced.
Figure 6A discloses the transient 7 mode test results of NOx conversion efficiency
before and after post-treatment process over CuZ. The results in Table 4 were
obtained at varying temperature, space velocities and feed gas concentrations for
each mode.
10 It is observed that at low temperatures of 217℃ (Mode-4), the fresh NOx conversion
is 64% whereas after post-treatment process, the NOx conversion is improved to
97%. From the temperature range of 311℃ to 435℃ that include another 6 modes
at varying space velocities and feed gas concentrations, the NOx conversions after
post-treatment process are improved from 84-90% range to 92-98%.
15 Further, Figure 6B discloses the results of selective NO reduction efficiency of
before and after post-treatment process over CuZ catalyst.
It is observed that at low temperatures of 217℃ (Mode-4), the NO conversion is
50% whereas after post-treatment process, the NO conversion is improved to 98%.
In the case of other 6 different temperature modes, operated at varying space
20 velocities and feed gas concentrations, ranges between 311℃ to 435℃, the NO
conversion after post-treatment process substantially increases from 74-86% to
90-99%.
17
Figure 6C discloses the results of NO2 reduction efficiency before and after posttreatment process over CuZ catalyst.
It is observed that at low temperatures of 217℃ (Mode-4), the NO2 conversion is
97% whereas after post-treatment process, the NO2 conversion is decreases to 94%.
5 From the temperature range of 311℃ to 435℃, another 6 modes at varying space
velocities and feed gas concentrations, the NO2 conversion is marginally altered
(~1%) after post-treatment process.
Table 4
Conversion (%) of CuZ
NOx NO NO2
Post-treatment Process
Before After Before After Before After
Mode-1 86 92 82 90 95 98
Mode-2 85 96 74 94 98 97
Mode-3 84 98 74 99 97 96
Mode-4 64 97 50 98 97 94
Mode-5 90 97 86 96 99 98
Mode-6 90 95 83 94 98 98
Mode-7 88 96 77 95 98 98
10 Example 8
Sulphur Aging and Regeneration
The post-treated catalyst was treated at 200°C for 20 hours in SO2 environment and
then regenerated by heating to 650°C. The catalyst was tested, as mentioned in
Example 6, before and after each sulphur aging cycles and also after each
15 regeneration cycle for a total 3 cycles.
Example 9
Testing Results
18
Figure 7A and Figure 7B discloses the results of steady state three cycles of NOx
conversion after sulphur aging for post-treated CuZ catalyst and its subsequent
regeneration of the same as mentioned in Example 8.
The results in the Table 5 discloses that the NOx conversion drops for each of the
5 three cycles of sulphur aging catalysts. Furthermore, Table 5 also discloses that the
NOx conversion restored back to its initial conversion after regeneration for each
sulfur aged catalysts.
Table 5
Temperature
(℃)
NOx Conversion (%) of CuZ
Post-treated
Sulphur Aged Regenerated
1st
Cycle
2nd
Cycle
3rd
Cycle
1st
Cycle
2nd
Cycle
3rd
Cycle
180 18 6 11 0 12 12 0
200 92 55 42 33 52 53 45
250 94 74 67 58 86 84 79
300 98 84 78 70 98 97 95
350 98 85 78 71 98 98 98
400 97 85 80 72 99 98 97
450 99 93 79 73 99 98 97
500 97 85 78 70 98 97 96
550 95 82 75 70 96 97 97
10
19

WE CLAIM:
1. A method for preparing a DeNOx catalyst comprising:
a. Preparing a slurry of metal(s) loaded zeolite/zeolite-type material,
5 with a binder and optionally with a promoter,
b. Coating said slurry on a honeycomb structure monolith,
c. Subjecting the said slurry of step a. or the slurry coated honeycomb
monolith of step b. for calcination,
d. Post-treating the calcined product of step c. by air moisture mixture,
10 wherein said post-treatment comprises:
i. heating slowly from ambient temperature to high
temperature while passing air-moisture mixture through it,
ii. holding for a period at the desired high temperature in the
presence of air-moisture mixture,
15 iii. cooling to ambient temperature in the presence of airmoisture mixture.
2. A method for making a DeNOx catalyst as claimed in claim 1, wherein said
metal(s) loaded zeolite/zeolite-type material of step a. is prepared by wet
20 and instant dry method comprising the steps of:
a) Preparing an aqueous solution containing metal(s) by mixing of
water and metal salts under stirring,
b) Adding slowly the zeolite/zeolite-type materials with simultaneous
mixing to the solution of step a),
25 c) Stirring the solution at elevated temperatures for few hours,
d) Exposing the solution suddenly at above water-evaporation
temperatures until dryness to obtain dry sample,
e) Re-heating the collected dried sample at above water evaporation
temperature for few hours to remove any occluded water molecules
30 and/or volatile components,
20
f) Subjecting the sample for calcination for few hours at high
temperature followed by cooling to ambient temperature
3. The method as claimed in claim 1, wherein said DeNOx catalyst in an
5 enhanced catalytically active tetrahedral framework Al species related to
BrØnsted acidity; having an enhanced selectivity of NO to N2 rather than to
NO2 even at low temperatures; and having an enhanced thermal and
structural stability at temperatures up to 800°C.
10 4. The method as claimed in claim 1, wherein said honeycomb structure
monolith is either flow through type or wall flow type.
5. The method as claimed in claim 1 or 2, wherein said zeolite/zeolite-type
material is selected from the CHA structure type comprising
15 AlPO-34, SAPO-34, MeAPO-34, MeAPSO-34, AlPO-47, SAPO-47,
MeAPO-47, MeAPSO-47, SSZ-13 and SSZ-62, preferably SAPO-34,
SAPO-47, SSZ-13 and SSZ-62.
6. The method as claimed in claim 1 or 2, wherein metal(s) comprises of, but
20 not limited to, Cu, Fe, Ni, Mn, Co, V, Ti and Zn, used independently or in
combinations thereof, preferably Cu or Fe or in combination thereof.
7. The method as claimed in claim 1, wherein said slurry is prepared in
aqueous medium with a binder, wherein said binder comprises of, but not
25 limited to sols of silica, alumina, zirconia and titania or in combinations
thereof, preferably silica sol or alumina sol or in combination thereof.
8. The method as claimed in claim 1, wherein said slurry has zeolite/zeolite30 type material in the range of 45% to 95%, preferably between 80% and 90%.
21
9. The method as claimed in claim 1 or 7, wherein said slurry has the binder
in the range of 5% to 55%, preferably between 10% and 20%.
10. The method as claimed in claim 1 or 7, wherein said binder has surface area
in the range of 150 m2
/g to 350 m2
/g, preferably above 200 m2 5 /g.
11. The method as claimed in claim 1, wherein said slurry pH is in the range of
2.5 to 6.5, preferably in the range 3.0 to 4.0; solid content is in the range of
20 % to 45 %, preferably in the range of 25 % to 35 %, particle size is in the
10 range of 1.5 µm to 7.5 µm, preferably in the range of 2.0 µm to 4.5 µm, and
viscosity is in the range of 1000 cP to 5000 cP, preferably in the range of
2000 to 2500 cP.
12. The method as claimed in claim 1, wherein said slurry is prepared in
15 aqueous medium with a promoter, wherein said promoter comprises of
titania, zirconia, ceria-zirconia, silica, alumina, silica-alumina, alkaline and
alkaline earth metals incorporated either individually or in combinations
thereof in the range of 0.1 to 15 wt%.

20 13. The method as claimed in claim 1, wherein said calcination in step c. is for
4 to 10 hours at temperature in the range of 400℃-600℃.
14. The method as claimed in claim 1, wherein said post-treatment in step d. at
high temperature is at 650°C-750°C while passing air-moisture mixture
25 through it in a stream of air laden with 4.5 to 15% of moisture,
15. A DeNOx catalyst having enhanced catalytically active tetrahedral
framework Al species related to BrØnsted acidity; an enhanced selectivity
of NO to N2 rather than to NO2 even at low temperatures; and an enhanced
30 thermal and structural stability at temperatures up to 800°C.
22
16. A DeNOx catalyst comprising metal(s) loaded zeolite/zeolite-type material
including CHA structure type materials such as silico-aluminophosphates,
aluminophosphates (AlPO-34, SAPO-34, MeAPO-34, MeAPSO-34, AlPO47, SAPO-47, MeAPO-47, MeAPSO-47) and/or aluminosilicates loaded
5 with metal elements such as transition metals Cu, Fe, Ni, Mn, Co, V, Ti and
Zn or their combinations thereof having enhanced catalytically active
tetrahedral framework Al species related to BrØnsted acidity and an
enhanced thermal and structural stability at temperatures up to 800°C.
10 17. A DeNOx catalyst as and when prepared by a method as claimed in claims
1-15.