FIELD OF THE INVENTION
The present invention relates to art ammonium Fait coated Cu.....X
,zeolite for promotion of selective catalytic reduction of Auto NO
emisGiori and a process for preparing the same.
BACKGROUND OF THE INVENTION
Nitrogen oxide 'chan9pel ireolites c an s e 1 ec t i ve I y c on ver t n i t roqei"i oxides
over a much wider range of air.....fuel ratios than noble-metal
catalyst1;;. Copper ion e -:ch anqed X.....zeolites are less active than
Cu.....ZSM5 zeolites. However, X —zeolites having gn;ater pore dimen-
sions can retain larger amounts of metal ions, f-urthermore, they
are less expensive, can be synthesized more easily and are
commercially available. From the view point of practical use, it
seems desirable to enhance the catalytic activity of copper
e;¦:changee:! X.....2:eo 1 i te .
However, copper-.....exchanged X.....zeolites are unable to reduce the NO
emissions of a lean burn engine to the same level as present day
spark-igni t :i on engines fitted with three-way catalytic converters
at 7\. :::: I- Hence, a further reduction is necessary.
Among the known processes for reducing MIL ,, the selective cata-
lytic reduction (SCR) technique seems to be the most promising.
Reducing agents, such as ammonia, urea may he used for this SCR
process. Although some power stations use ammonia as a reducing
agent, but due to the high temperature required for the reduction
o
viz. 800.....1000 C, and also because of pollution hazards that may
be caused by ammonia slip, ie. leakage of unreacted ammonia, this
is not a viable option for automobiles.
Urea on the other hand may be regarded as safe from to>: icological
o
aspects. Tt is highly soluble in water (:l 0S gm in 100 ml at 20 C)
and hence high concentrations may be transported in a storage
tank. But urea infusion also implies infusion of water into the
catalytic chamber which has a deactivating effect on zeolites and
hence close metering of the urea dosage is required.
OBJECTS OF THE.1" INVENTION
I t is therefore an object of this invention to provide a cheap
a n d c:: o m lit e r <:: i a 1 1 y a v a i I. a b I e m o d i. f i e d X.....z e o 1. i t e w h i c h may serve a s
a better substitute for noble.....mptal catalysts which are
e:-: pen si ve ,.
ft is a further object of this invention to provide a modified X -
zeolite which unlike the noble-metal catalysts does not show any
x :.! and CCuA 3 respectively and
thus facilitate the continuation of the redo;-: cycle involving the
metal ions,,
Lu, "¦¦ Lu
That the ammonium salts may undergo hydrolytic decomposition is
i;s!l so sutost ant :i a ted by the? production of ammonia which I»a '::i- been
detected in the.? exhaust gas during catalysis with ammonium salt
.1 o a d i n g .
It is also significant that in thp absencp of copper ions, depo.....
sit ion of ammonium salts causes a depreciation of catalytic
activity toy about 5J3V. as compared to thp copppr.....ammonium salt
based catalysts. Apparently, the ammonium and copper ions act in
conjunction, their mutual interaction being necessary for
improved N0 conversi on .
The pressure drop which arises across the catalyr-t bed has a
deterring effect on engine performance.. But the pressure drop in
this case was found to be well within acceptable .limits. For the
entire range of operation, the back.....pressure developed varied
from 20mm to <'!0mm of water column.
The percent power loss due to back.....pressure is insensitive to the
particular engine being tested and the average power loss per mm
of mercury is 0. 032V;» The corresponding power loss for the
f-.'*:perimerit under study was calculated to be varying from 0,0'-17 VI
to 0.094%. On performing an uncertain!ty analysis, the uncer.....
t a in i ty was seen to be varying between 2."?"' to 4*/. which may he
c o n s i;.:! e r e d w i. t h i n a c c e p b a b 1 e 1 :i m i t s .
The d*d vantages of the ammon i urn salt coated X-zeoIite will now be
explained with the help of the following experimental set-up
and using three sets of samples.
EXPERIMENTAL PROCEDURE
Three sets of samples were used for the experiment —
m -¦¦ Copp e'- ex c h an g e d X.....z e o 1 i t e ;
C ..... Copper- exchanged X.....zeolite with ammonium carbonate deposition;
D- Copper exchanged X-zeolite with ammonium sulphate deposition.
Reauired amounts of X-Zeo i : ¦:*> are slurried in distil.! nd
water and 13.5 ml aliqucts of 1M HCj are a»csd u-ith constant
stirring to maintain a Ph = 6.
Calculated amoant ai transition metai salt is added to the
slurry.
Tne mixture is stirred for 6-7 hours at a temperature
o
maintained between 70-83 C.
The slurry is filtered and washed i«ith distilled water to
remove the HC1.
Zeolites are overs-dried for 24 hours 3"; a temperature of
120°C.
Catalyst is activated by heating at 4t*$ C for 3 hours in a
furnace and then cooled inside the furnace itself to retain its
mechanical properties.
Catalyst is stored in dessicator till use.
Samples C and D were treateu wit"; concentrated solutions of
Ammonium Carbonate and Ammonium So Ian ate respectively anci stirred
continuously for 3—4 hours while maintaining the temperature
o
within 70 - 8$ C. Then, they wer»h ty-twA - X -¦¦iwws 4- 4-fc-e- - w-a 4>r+ - •s^mw^u i ius- -»uAf*h. s4-e—(4 ef*€:«s-i- 444H+.
A commercial 3.....cylinder, 4-stroke, mater......cooled, ST engine
(Marut i ¦¦¦¦Si.izuk :i. ) with a displacement volume of B00co coupled with
a hydrsulii: dynamometer war used for evaluating the performance
of the catalysts. An electro.....chemical type on.....line gas analyser
was used for the gas analysis.
The set.....up may be outlined as follows ;
Type i Four1 stroke, water cooled.
Bor& : 68.5 mm
Stroke : 72 mm
Number of cylinders : 3
Compression ratio "¦: 8.7:1
Ignition timing : 7 + 1 before TDC
Dyn amome ter
A hydraulic dynamometer is used for testing the power of the
engine and to apply external load. The power absorbed is calcu-
lated by the formula ::
P-WN/C-WN./2000 hp
where ;
P :: Power absorbed by dynamometer, hp;
W :::: Load indicated by the weighing device, kg;
N ¦-¦ SI i a ft speed in rpm;
C = D y n amom e t e r c on s t a n t ::~ 2 0 0M.
l-ias Ana!! yser*
Thp yas analysing equipment (TNT.....J6-B) is used for the experiment
to measure CO, N0X , gas temperature, etc.. "I he sensor is
connected through a filter to the gas analyser. The analyser
calibrates itself automatically with normal room temperature. The
various parametorE are measured ss follows :
Carbon monoxide - This is measured by an electro.....chemical sensor
having a range of 0.0 to 4.0'A.
Nitrogen oxides ..... This is ml so measured by an electro-chemical
sensor having a range of 0 to 2000 ppm.
Exhaust gas temperature ..... I hi.s is measured by a Ni.....Or thermo.....
o
couple having a range of 0 to 1000 C.
M e o s u j- e m e n t o t v o 11 .i m e t r i c f 1 o w r a t e o f g a s e s
The volumetric flow rate of the gas through the catalyst bed is
measured by using an orifice meter in the exhaust line. An
orifice of 16 mm diameter- in a cylindrical pipe of 5:1 mm internal
d i a meter. A I.J ¦¦-1 u b e m a n o mete r i s <:: o n n e c t e d s c r o s s t h e o r i f i c e
which measures the pressure difference in terms of water column.
A bypass valve is provided before the converter to control the
volumetric flow rate through the converter.
Measurement of catalyst bed temperature
Chrome 1-alume1 thermocouple connected to a panel board is used to
me a;™ u re the catalyst bed temperature. An electric heating coil is
wound around the converter with proper insulation using asbestos
paper arid asbestos rope to heat the catalyst bed. "I he heating
coil is connected to a variac to establish control over the
quantity of heat supplied.
Measurement of back pressure
A U.....tube manometer1 with water as the manometric fluid is
connected across the catalyst bed to measure the back pressure
developed by the catalytic converter.
Fuel supply system
The fuel measuring apparatus consists of a gasoline tank of a
volume of 4 .1 .. 'The fuel flow is measured by noting the time taken
fnr a metered quantity of fuel to flow to the origins?.
A :i i" s i..i p p .'I y s y s t e m
A large circular drum having an orifice meter at the top of the
tank is connected to the engine. A (J--tube manometer connected
across the orifice meter measures air consumption in terms of mm
o<: water column,, Calibration curve of the air supply systpm
available in the laboratory is utilized in calculating the air
supply.
(Z a t a 1 y t i c c on v e r t e r-
Thp converter had the following specifications s
SI'i ap e ; Cy 1 i nd r i c: a .1 5
D:i sme ter : 5 cm 5
Length : '?•. 9 cm;
Volume ; 120 cc;
Packing ; Pelleted catalysts in packed bed.
Eng i n e cond i t i oris
Borne engine parameters were kept constant in order to facilitate
<:::omparison of ob. ., which :i =¦¦¦ usually the exhaust
temperature of an au toe-, jd :i. I e and hencp this method is sui t abl e
for practical use,, Fu ther, ammonium sa'its reduce the problem of
deactivation of zeolites in presence? of water- which is a perti-
nent probl '"¦ -i with urea infusion, and the emission of ammonia was
rather low for the ammonium salt based catalysts, it is possible
that the ammonium salts ensure easy reduc :i. h i J. :i ty of (.;u. and
stabi !. i ty of Cu , thus facilitating the redox cycle involving
these ions which :is considered the key to the catalytic activity
o f Cu¦¦¦¦ X Z eo I. i t e s .
wE CLAir":
1. A process for oreoanng a--» jnwionium -salt coateo Cu-X
zeolite for promotion of selective catalytic reduction of Auto NO^
emission, comprising the s-tea of ^estirvg a samoie of a Cu-X
Zeolite with a concentrated solution of an ammonium salt such as
herein described to ontain the ammonium salt coated Cu-X Zeolite
which is then subjected drying.
2. The process as claimed in claim 1 uherein said ammonium
salt is selected from ammonium carbonate and ammonium sulphate.
3. The process as ciai*sd in ciann- 1 wnerein the treatment
with the ammonium salt is effected unoer stirring for a period of
3 to 4 hrs.
4. The process as claimed in claim 1 wherein the treatment
with the ammonium salt is effected ait a temperature of 70 to
80° C.
5. The process as claimed in clam 1 nine re in the Cu-X
zeolite is prepared uy subjecting X-zeoiite to trie step of
slurrying and adding a mineral acio aid a transition metal salt
thereto followed by stirring the slurry, filtering, washing and
drying the same to ontain, trie Cu —X-zeoiites and further
O 0
activating the same -by heating at a teaperature cf 35fc* to 420 C
for a period of 3 to 3 Vl hrs.
6. The arocsss as claimed in cia;^ 5 herein the X-rsoiits is
slurried in distilled water.
7. The process as ciaiased in ciaisr. 5 <,*.r„e r-# ir,. t'-.S to 1.21"! of a
mineral acid such as lycrochioric acid is auded to the slurry.
8. The process as ciai.metJ in ciaifir 5 wherein the mineral acid ¦
is added to maintain a cH of 5.8 to 6.4
9. The process as dawned in c'siist 5 wherein said transition
metal salt is cupnc acetate lCu (OAc )z 3 .
10. The process as claimed in clam 5 wherein after addition
of said transition ^etai salt, the slurry is stirred for a period
of 6 to 7 hrs. at a temperature between 70 to B0 C.
11. The process as claimed in claim 5 wnerein the slurry .is
washed with distilled water.
12. The process as claimeo in claim 5 wherein the slurry is
oven-dried for 2*3 to 30 hrs. it a t t-flsperature in the range of 110
to 130°C.
13. The process for preparing an ammonium salt coated Cu-X
zeolite substantially as herein described and illustrated.

This invention relates to a process for preparing an
ammonium salt coated Cu-X zeolite for promotion of selective
catalytic reduction of Auto NOx emission, comprising the step of
treating a sample of a Cu-x Zeolite with a concentrated solution
of an ammonium salt such as herein described to obtain the
ammonium salt coated Cu-x Zeolite which is then subjected to
drying.