Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a carrier-supported catalyst
and to a process for making it.
Carbon monoxide and hydrocarbons are oxidized in contact with
catalysts, wherein the active ingredients are either noble metals belonging
to group VIII of the Periodic System or are mixed oxides, e.g. of copper,
manganese and nickel, the mixed oxides, which are less costly, being preferr-
ed so as to enable wide use to be made of those catalysts, e.g. for ~he
decontamination of automobile exhaust gas. The catalysts used to this end
are required to be abrasion proof, to be thermally shockproof, to be sinter-
proof, to have a low starting temperature, if possible lowerthan 200C, andto have a constant activity, even if heated for prolonged periods of time to
temperatures of at least 800C.
United States Patent Specification 3,~93,325 describes a catalyst
deposited, e.g. on gel-like or activated alumina, for the catalytic oxidation
of exhaust gas of internal combustion engines. The active ingredients
applied to the carrier are selected from oxides of copper, nickel, cobalt,
iron, chromium, manganese or mixtures thereof.
A further catalyst has been described in German Patent Specification
1~272,896, which is deposited on a carrier containing at least 30 weight %
of alumina together with alkali metal and alkaline earth metal oxides, and
heat-resistant filler materials. The catalytically active ingredients
inter alia include oxides of copper, nickel, cobalt, manganese and cerium.
These prior art catalysts are not fully satisfactory, however,
as their activity varies depending on whether they are contacted with an
oxidizing or reducing gas. More particularly, they are highly active if
contacted with a mixture consisting of the gas to undergo oxidation and a
stoichiometric or slightly understoichiometric proportion of oxygen, whilst
they are less active if contacted with a mixt~re containing an excess of
oxygen.
In other words, it is necessary for those prior art catalysts
to be contacted with a gas mixture containing a s~iochiometric proportion
of oxygen, based on the carbon monoxide and hydrocarbons present in the
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gas mixture. This is especially necessary in an attempt (a) to maintain
the catalyst active and (b) to ensure complete combustion of the gas to under-
go oxidation. It should be borne in mind, however, that the exhaust gases
of internal combustion engines always contain variable proportions of carbon
monoxide and hydrocarbons so that considerable expenditure in respect of
equipment is at least necessary to achieve this, if at all.
It is accordingly an object of the present invention to provide
a carrier-supported catalyst whose activity remains unaffected in contact
with gas mixtures, irrespective of the oxygan concentration therein, and
which additionally has a low starting temperature.
Accordingly, the present invention provides for a carrier-support-
ed catalyst~ wherein the active ingredient consists essentially of cerium in
oxide form and wherein 0.2 to 10 weight % of cerium, based on the carrier, is
deposited thereon and wherein the carrier consists essentially of a mixture
of delta-alumina and alpha-alumina with an alkali content of up to 0.2
weight %; said carrier having been produced by suspending aluminum oxide
selected from the group consisting of delta-alumina and boehmite, and having
- an al~ali content of up to 0.2 weight %, in water; heating the resulting
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highly viscous magma so as to form a dry mass; admi~ing graphite to the dry
mass and grinding it; compressing the ground graphite-containing mass into
shapes; burning off the graphite from the shapes at temperatures within the
range 550 to 750C; and calcining the shapes for periods within the range 10
to 20 hours at temperatures within the range lO00 to 1250C.
The in~ention also provides a process for making the carrier-
supported catalyst which comprises suspending aluminum oxide selected from
the group consisting of delta-alumina and boehmite, and having an alkali
content of up to 0.2 weight %, in water; heating the resulting highly vis-
cous magma so as to form a dry mass, admixing graphite to the dry mass and
grinding it; compressing the ground graphite-containing mass into shapes;
burning off the graphite from the shapes at temperatures within the range 550
to 750C; calcining the shapes for periods within the range 10 to 20 hours
at temperatures within the range 1000 to 1250C so as to convert said alumi-
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num oxide into a mixture of delta-alumina and alpha-alumina; impregnating
the shapes with an aqueous solution of a cerium salt of a readily decompos-
able acid; drylng the cerium salt so applied to the shapes for periods with-
in the range 16 to 64 hours at temperatures within the range 130 to 150C;
decomposing the dry cerium salt by heating theshapes first at temperatures
within the range 200 to 300C and thereafter at temperatures within the
range 450 to 550C, respectively; and annealing the resulting shapes contain-
ing cerium oxide at temperatures within the range 700 to 900C.
Further preferred features of the present invention for making
the carrier-supported catalyst provide: -
a) for between 3 and 10 weight percent of graphite to be admixed to the
dry mass prior to grinding it.
b) for cerium nitrate to be used as the cerium salt of a readily decomposable
acid.
The carrier-supported catalyst of the present lnvention is particul-
arly useful for the oxidation of carbon monoxide and hydrocarbons with an
excess of oxygen to ensure complete combustion thereof.
Vital to the present catalyst is more particularly the alumina
' carrier, which is partially converted to d~-A1203. Carrier-supported catalysts
ha~ing the catalytically active cerium oxide applied to incompletely dehyd-
rated aluminum oxide monohydrate or to highly crystalline ~ -A1203 are con-
siderably less active catalytically.
A carrier of high activity is obtained when the carrier consists
of a mixture of delta-A1203 and alpha-A1203.
In addition to this, it is necessary for the alumina carrier to
contain little alkali as alkalles are known to increase the starting tempera-
ture of carrier-supported catalysts.
The cerlum salt used in aqueous solution for impregnating the
carrier and applying the catalytically active ingredient thereonto should
haye an anlon which can be completely remoyed later, during calcination.
The prefer~ed cerium salt is cerium nitrate. Cerium sulfate produces
catalysts of reluctant activity.
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The carrier should preferably be impregnated with a quantity of
cerium salt solution which just corresponds to its volume of pores. In
other words 9 it is the concentration of the cerium salt solution used for
impregnation and the volume of pores of the carrier which determine the
- cerlum content of the resulting carrier-supported catalyst.
With respect to catalysts having a low starting temperature, it is
necessary for them to be made with the use of very pure cerium salt. So-
called cerium mixed metal salts should conveniently not be used.
Qualitatively highly reliable carrier-supported catalysts are
obtained in those cases in which the cerium salt applied to the carrier is
dried over a prolonged period of time within the range 16 and 64 hours, for
example,
The carrier-supported catalysts used in the following Examples
were cylindrical shapes 3 mm in diameter and 3 mm long. 17 normal liters
~S.T.P.), per cc of catalyst per hour, of a test gas mixture was oxidized in
contact therewith. The gas mixture contained 3 % by volume of 2~ 2 % by
v.olume of Co~ 1000 ppm of n-hexane, 2.5 % by volume of steam, the balance
being N2~ and was heated in each particular case to the testing temperature.
The residual concentrations of C0 and n-hexane were identified in the
oxidized gas and the conversion in % of *hese two substances was calculated
therefrom.
The temperatures at which 50 and 90 %, respectively, of C0 and
n-hexane, respectively, were found to have been converted to CO2 and H20
(U50 C0; Uso co; U50 Hex.; Ugo Hex ) were used as the activity indexes of
the catalyst.
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EX~PLE 1: (Comparative Example)
Ce(NO3)3 . 6 H20 was dried until the nitrate commenced decomposition and
compressed into shapes. The~shapes were heated for 10 hours to temperatures
within the range 500 and 800C, with the supply of air. The catalytic
activity was determined and the following results were obtained:
~50 ~ = 430C U H = 560C`
UgO CO' UgO H = 660C
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EXAMPLE 2: (Invention)
~-A1203 (Aluminum oxide "C", a product of Degussa) was suspended in water
and compacted therein. The resulting highly viscous magma was dried, admixed,
with 3 weight % of graphite and ground. The ground material was compressed
into shapes which were first heated to 650C to burn off the graphite and
then annealed for 20 hours at 1100C. The carrier so made was impreganted
with a cerium (III) nitrate solution and dried for 64 hours at 140C. To
decompose the cerium nitrate, the carrier was first heated for 3 hours to
250C and then for 10 hours to 500C. The resulting cerium oxide-containing
shapes were finally annealed for 10 hours at 800C. Catalys~s containing 2,
4 and 6 weight %, respectively, of cerium were made in this manner. Their
activity was determined and the following results were obtained:
Ce-content in weight %
2 4 6
U50 C0 [ Cl190 170160
_ ,
UgO CO [C]270 240205
50 Hex [ C] 565 540 505
` .
EXAMPLE 3: (Invention)
A1203 tAluminum oxide "C", a product of Degussa) was made into shapes in -
`~ the manner described in Example 2. The graphite used as a compression aid
was burnt off and shape specimens were annealed in each case for 20 hours
at temperatures of 950C, 1000C, 1050C, 1100C, 1150C, 1200C, 1250C ;~
and 1300C, respectively. Following this, 6 weight % of cerium was applied
ko the individual specimens, in the manner described in Example 2. The
activity of the resulting catalysts was determined and the following results ;~-
were obtained:
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Carrier annealed [C]
at C 50 CO 90 CO 50 Hex 90 Hex
_
~9SO) 500 730 620 740
1000 450 580 620 740
1050 260 380 560 700
1100 160 205 505 640
1150 190 270 560 670
1200 190 305 565 680 : .
1250 240 350 570 690
(1300) 270 390 600 730
. . .
EXAMPLE 4: (Invention)
Boehmi.te (AlOOH) containing 0.03 weight % of sodium was compressed
into shapes in the manner described in Example 2. The graphite used as a
compression aid was burnt off and shaped specimens were annealed in each
particular case for 20 hours at temperatures of 900C, 1000C, 1100C, 1200C
and 1250C, respectively. Following this~ 6 weight % of cerium was applied
to the individual specimens, in the manner described in Example 2. The
activity of the resulting catalysts was determined and the following results
were obtai~ed:
[C] Carrier annealed at C
_ .
, 900 1000 1100 1200 1250
50 CO 460 420 . 400 360 280 : :
'` I' _ _ .
U90 CO 610 530 510 450 450
':,:
U 590 600 580 610 600 `
50 ~lex _ :
EXAMPLE 5: (Carrier containing alkali)
'
The carrier-supported catalyst prepared in the manner described in
Example 2 was impregnated with the quantity of potassium carbonate solution
which was necessary to incorporate 0.5 weight % of K2C03 therein~ then dried
at 140C and annealed for 10 hours at 800C. The activity was determined
and the following results were obtained:
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U50 C0 = 335C
UgO C0 = ~50C
U50 Hex = 620 C
EXAMPLE 6. (Carrier containing alkali)
Bayerite ("Martifin"*, a product of Martinswerk, Bergheim) contain-
ing about 0.25 weight % of sodium (this is sodium originating from the
particular process used for making the product~ was compressed into shapes,
in the manner described in Example 2. The graphite ~Ised as a compression
aid was burnt off and shape specimens were annealed in each particular case
for 20 hours at temperatures of 900C, 1000C, 1100C, 1200C and 1300C,
respectively. Following this, 6 weight % of cerium was applied to the
individual carrier specimens, in the manner described in Example 2. The
activity of the resulting catalysts was determined and the following results -
were obtained:
[C] Carrier annealed at C
900 1000 ~ 1100 ~ 1200 1300
:' ~ _ ._
50 C0 510 430 410 320 330
' ~ _ _ I ,
UgO C0 620 - 510 530 450 460
50 Hex 590 570 610 600 610
, . .
EXAMPLE 7: (Less readily decomposable cerium salt)
, A catalyst containing 6 weight % of cerium was prepared in the
manner described in Example 2 save that cerium sulfate was substituted for
cerium nitrate. The activity of the catalyst so made was determined in a
series of tests. Between the individual tests, the catalyst below the test `
gas mixture was annealed in each particular case for 10 minutes at 800C.
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Activity determination 50 C0 [ C] UgO C0 ~ C] U50 Hex ~oc3.,
1 ~30 530 590
_ _ .
2 350 450 580
3 290 390 560
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4 260 360 5~0
f-
240 340 530
_ ,
6 220 330 530
EXAMPLE 8: (Mix-ture of rare earths)
Catalysts containing 6 weight % of rare earths were prepared in
.
the manner described in Example 2 save that the cerium nitrate was replaced
by salt solutions produced by dissolving cerium mixed metals of the follow-
ing composition:
Alloy A: 56 % of Ce Alloy B: 49 % of Ce
,~28 % of La 23 % of La
:.10 % of Nd 15 % of Nd
~4 % of Pr 12 % of Pr ~ Y
:2 % of further r.e. i % of further r.e.
.' in nitric acid. The activity was determined and the following results were
.; obtained:
Cerium mixed metal alloy:
~ A B
.. . ~_. _ .
, U50 C0 [ C~ 280 330
_
'': UgO C0 [ C] 380 430 :~:
. _
`~ 10U50 Hex [ ] _ _ 550 525
:~ EXAMPLE 9: ~Annealing period and temperature)
-`. The catalyst prepared in the manner described in Example 2 which
.
: had the Pollowing activity:
. U50 C0 = 160 C
UgO C0 = 205 C
. U50 H = 505 C
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was annealed for 13 hours at 1100C and then had the following activity:
U50 CO = 185C
UgO CO = 280C
~ U50 Hex = 530 C
; A catalyst was prepared in the manner described in Example 2 save
that the annealing step at 700-900C was omitted and replaced by heat treatment
at 300-400C, after decomposition of the cerium salt. The catalyst so made
had the following activity:
U50 CO 185 C
UgO C0 = 355C
50 Hex 535 C
EXAMPLE 10
Basic aluminum chloride A12(0H)5Cl. 3 H20 ~"Locron", * a product
of Farbwerke Hoechst AG) was dissolved in water and the solution was admixed
with the quantity of ceriumnitrate necessary to obtain a catalyst containing
6 % of cerium. The whole was admixed with ammonia to jointly precipitate the
Al and Ce hydroxides. The precipitate was filtered off, scrubbed with water
and drled. After the addition of 5 weight % of graphite, the dry precipitate
was compressed into shapes. The graphite was burnt off at 650C and the
shapes were annealed for 20 hours at 800C. The activity was determined and ~ ~ ;
the following results were obtained:
U = 330C
UgO C0'= 450C
50 Hex -
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~ U90 Hex = 640 C
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