Note: Descriptions are shown in the official language in which they were submitted.
Lo~7~3~
This invention relates to catalysts catalytic struc-
tures comprising a substrate, an intermediate oxide layer and
a catalytic layer, and to procedures for their manufacture.
The catalysts of various aspects of this invention
may be us~d for a wide variety of catalytic reactions, e.g.
the catalytic oxidation of ammonia in the manufacture of
nitric acid and the catalytic oxidation of organic compounds
(e.g. methane, ethane and propylene) for heating purposes
and carbon contain~ng compounds, e.g. carbon monoxide and
for catalytic reduction, e.g. the catalytic reduction of
oxides of nitrogen with a reducing fuel and for use in aut~-
mobile exhaust control units. The catalysts of aspects of
this invention may also be used in NOX Abatement units ad-
a~ted to be attached to plants for the manufacture of nitric
acid.
Many nitric acid plants use hig~ pressure processes
in which the oxidat~on of ammonia is carried out in the presence
, . .
of solid rhodium-platinum wire which has beon woven into a
' gauze. I-t is also highly advantageous to recover from the r
~- 20 tail gas plant, energy which can be utilised to supply power
~'' .
~- to the system. In some systems sufficient energy can be re-
-i covered for the process to be self-sustaining and even to
provide additional power. This is nor~ally carried out as a
catalytic process inlwhich the oxides of nitrogen are reacted !:'
... . .
with a gaseous reducing fuel. It is important that the cat-
alyst used be highly active, exhibit a minimum re~istance to
` gas flow and catalyse the reaction at low initial reaction or
,,: ..
` ignition temperatures. The catalyst itself, should however
,:
still have reasonably high (e.g. 750-800 C) temperature sta- -
bility.
-2
:3~
10'783~;~
Air pollution control by catalytic combustion ihposes
a number of restrictions on the type of catalyst which may be
used. In addit20n to a requirement that the catalyst should
be active at low temperatures, it should be stable under both
oxidising and reducing conditions. Further, when the catalyst
is p~cked into a reactor it should be~t~
thermal and mechanical shock and clogging by dust particles.
It is an object of a broad aspect of the present in-
vention to provide improved catalytic structures for uses as
above described.
-' , ,
i,
:
''".`.'
.
. .
`'~'
-
' ,'
:
-2a-
"--`-` 1078364
which are alternative to the ones now in use.
An object of another aspect of this invention is to provide
methods for the preparation of such catalysts.
According to one broad aspect of this invention, a catalyst is
provided comprising: a metal substrate made from a heat and oxidation
resistant alloy of iron including chromium (3 - 40) wt. %, aluminum
(trace - 10) wt. %, cobalt (0 - 5.0) wt. %, nickel (trace - 72) wt. %,
and carbon (0 - 0.5) wt. %, balance essentially iron, the metal sub-
,. ..
strate being in ~éxtended form; (b) an aluminum oxide film on the surface
of the extended metal substrate, the film being formed by oxidizing thesurface of the metal substrate; (c) a high surface area alumina coating
disposed over the aluminum oxide film and keyed to the substrate through
the film; and (d) a catalytic layer comprising at least one metal
selected from the group consisting of ruthenium, rhodium, palladium,
.:' `
iridium, platinum, silver, gold, and alloys of at least one of such
metals with at least one additional element comprising a base metal
selected from the group consisting of aluminum, magnesium, chromium,
molybdenum, tungsten, manganese, iron, rhenium, cobalt, titanium, vana-
dium, copper, zinc, cadmium, indium, thorium, bismuth, tin, lead, anti-
mony, a lanthanide or an actinide, the base metal being present in an
~-~ amount from a trace to 25 wt. % on the high surface area alumina coating.
. ,~. . .
by another aspect of this invention, a catalyst is provided
consisting essentially of: (a) a metal substrate having a high surface
area and made from a heat and oxidation resistant alloy of iron including
:
~` chromium (3 - 40) wt. %, aluminum (trace - 10) wt. %, cobalt (0 - 5.0)
.,
~; wt. ~, nickel (trace - 72) wt. % and carbon (0 - 0.5) wt. %, balance
: `;::'
! essentially iron, the metal substrate comprising an assembly of at least
two juxtaposed sheets made from such alloy with at least one sheet shaped
; so that when contacted with an adjacent sheet channels are formed there-
between for the passage of gaseous reactants through the substrate; (b)
.: . .,., ~,- . :. :. : : ,... , ... ,, . : :.
" . . : ;., ~:: . : ' ' - -:: . , ,
836~
an aluminum oxide film on the surface of the substrate, the film being
formed by oxidizing the surface of the substrate; (c) a layer of alumina
applied to the sheets and calcined; and (d) a catalytic layer applied
to the first layer, the second layer consisting essentially of one or
more metals selected from the group consisting of ruthenium, rhodium,
palladium, iridium, platinum, silver, gold, and alloys of at least one
of such metals with at least one additional element comprising a base
metal selected from the group consisting of aluminum, magnesium, chromium,
molybdenum, tungsten, manganese, iron, rhenium, cobalt, titanium, vana-
dium, copper, zinc, cadmium, indium, thorium, bismuth, tin, lead, anti-
mony, a lanthanide or an actinide, the base metal being present in an
amount from a trace to 25 wt. %.
By one variant, the metal substrate (a) is made from a heat
and oxidation resistant alloy of iron including at least one of the
;` elements chromium (3 - 40) wt. %, aluminum (1 - 10) wt. %, cobalt
(trace - 5.0) wt. %, nickel (trace - 72) wt. %, and carbon (trace - 0.5)
wt. %.
By another variant, no more than 10 wt. % of the alloy of iron
consists of one or more of the additional elements silicon, manganese,
~ 20 zirconium, copper, tungsten, vanadium, molybdenum, cerium, niobium,
- tantalum and titanium.
`~ By variations thereof, not more than 5 wt. %, e.g., not more
~ than 3 wt. % of the alloy of iron consists of one or more of the addi-
; tional elements.
By still another variant, the metal substrate (a) is made from
a heat and oxidation resistant alloy of iron which comprises, apart from
impurities, at least one of the elements Cr (3 - 30) wt. %, Al (l - lO)
wt. %, C (a trace to 0.5) wt. %, Co (a trace to 5.0) wt. %, Ni (a trace
to 15.0) wt. % and balance iron.
By another variant, the metal substrate (a) is made from a
H ` 4 -
,'
1~7~3364
heat and oxidation resistant alloy of iron which comprises, apart from
impurities, at least one of the elements Cr (13 - 24) wt. %, Al (3.5 -
6.5) wt. %, C (a trace - 0.1) wt. %, Co (0.2 - 0.8) wt. %, Ni (a trace -
5.0) wt. %, balance iron.
- By a further variant9 the metal substrate (a) is made from a
heat and oxidation resistant alloy which includes one or more of the
additional elements: Si (0.2 - 0.9) wt. %, Mn (0.2 - 0.7) wt. %,
Zr (0.01 - 0.20) wt. %, Cu (0.01 - 0.15) wt. %, Nb (0.01 - 0.3) wt. %,
Ta (0.8 - 1.2) wt. %, Ti ~0.8 - 1.2) wt. %, Co (0.01 - 1.0) wt. %,
Ca (0.01 - 0.5) wt. %, C (0.01 - 0.1) wt. %.
By yet another variant, the metal substrate (a) is made from a
: ::
- heat and oxidation resistant alloy of iron which comprises 0.09 wt. % C,
22.60 wt. % Cr, 2.0 wt. % Co, 4.5 wt. % Al and balance iron.
By a still further variant, the metal substrate (a) is made
",,:
,~'r from a heat and oxidation resistant alloy of iron which comprises Cr 30
' wt. %, Fe 65 wt. % and Al 5 wt. %.
By yet another variant, the metal substrate (a) is made from a
. ~
heat and oxidation resistant alloy of iron which comprises C 0.08 wt. %,
Cr 18.00 wt. %, Ni 10.00 wt. %, Ti 0.40 wt. % and balance iron.
By a further variant, the metal substrate (a) is made from a
^` heat and oxidation resistant alloy of iron which comprises Cr (10 - 40)
::
; wt. %, Al (1 - 9) ~t. %, Fe (51 - 88.9) wt. %, Ta (0.1 - 5) wt. %, Ce
(0.01 - 1) wt. %.
By yet another variant, the metal substrate (a) is made from a
`~ heat and oxidation resistant alloy of iron which comprises Cr (10 - 40)
wt. %, Al (1 - 9) wt. %, Fe (51 - 88.9) wt. %, Ta (0.1 - 5) wt. %, Ce
(0.01 - 1) wt. % and wherein Ce is partially replaced by Ca.
By other variants, the second catalytic layer may comprise a
7-1/2 wt. % Rh/Pt alloy; or may comprise a 10 wt. % Rh/Pt alloy; or
may comprise a 20 - 50 wt. % Rh/Pt alloy; or may comprise a 1 - 50 wt. %
- 5 -
, ~
:: . ~ - ,. : .:. ........ :
:: :,: '.:, . . : ': .
: .: i .: ., ,:
. ., , ,, .:
:: ~ :::: , ., :
1078364
rhodium, 0.01 - 25 wt. % base metal, balance platinum.
By another variant, the layer of alumina comprises calcined
. O
crystal aggregates having a diameter of 20 - lOOA and a pore diameter
of 40A.
By a further variant, the juxtaposed sheets are helically
wound together to form a metallic monolith.
By yet another variant, one sheet is corrugated and another,
adjacent sheet is plain.
By a further variant, the two separate thin metal sheets have
a thickness within the range 0.0015 to 0.0045 inches.
By one variation thereof, the sheets are corrugated of such
dimensions that the wound up structure has between 200 and 800 cells per
' ' ''!
~' - square inch when considered in cross section.
By another variation thereof, the catalyst has a substrate
- ; composed of metal sheets of approximate thickness 0.002 inches assembled
.:,'`'
to form a structure having approximately 400 cells per square inch when
considered in cross section and a surface to volume ratio of approximate-
.. ,:.
ly 1200 sq. ft. per cubic foot.
,: .
- ~y another aspect of this invention, a method is provided for
making a catalyst consisting essentially of a substrate having a high
surface area and made from a heat and oxidation resistant alloy of iron
including chromium (3 - 40) wt. %, aluminum (trace - 10) wt. %, cobalt
(0 - 5.0) wt. %, nickel (trace - 72) wt. %, and carbon (0 - 0.5) wt. %,
balance essentially iron, the substrate comprising at least two juxta-
posed sheets made from such alloy with at least one sheet shaped so that
when contacted with an adjacent sheet channels are formed therebetween
for the passage of gaseous reactants through the substrate, such method
comprising the steps of: (a) treating the substrate assembly to oxidize
its surface, thereby to provide an aluminum oxide film thereon; (b)
applying a first layer containing alumina to the sheets; (c) calcining
. ~ .
~t ~: - 6 -
1~78364
.
the sheets of (b) so that the first layer is bonded to the underlying
sheet and serves to bond adjacent and contacting sheets together; and
(d) applying a second and catalytic layer to the first layer, the second
-layer consisting of one or more metals selected from the group consisting
of ruthenium, rhodium, palladium, iridium, platinum, silver, gold, and
alloys of at least one of such metals with at least one additional metal
comprising a base metal selected from the group consisting of aluminum,
magnesium, chromium, molybdenum, tungsten, manganese, iron, rhenium,
; cobalt, titanium, vanadium, copper, zinc, cadmium, indium, thorium, bis-
muth, tin, lead, antimony, a lanthanide or an actinide, the base metal
; being present in an amount from a trace to 25 wt. %.
By a variant thereof, the juxtaposed sheets are helically
wound together to form a metallic monolith.
By another variant, one sheet is corrugated and another, adja-
cent sheet is plain.
By a further variant, the two separate thin metal sheets have
a thickness within the range of 0.0015 to 0.0045 inches.
By a variation thereof, the sheets are corrugated of such
-~ dimensions that the wound up structure has between 200 and 800 cells per
square inch when considered in cross section.
By another variation, the substrate is composed of metal sheets
of approximate thickness 0.002 inches assembled to form a structure having
approximately 400 cells per square inch when considered in cross section
and a surface to volume ratio of approximately 1200 sq. ft. per cubic
foot.
By yet another vacia~lt, the alumina is calcined to form chi and
gamma alumina.
By another variant of this invention, the extended metal sub-
strate (a) is made from a heat and oxidation resistant alloy containing
nickel and/or chromium having an aggregate nickel and/or chromium content
Y ~ 7 -
- . .: ;. - . , . : :
. I . . ! . , , , ' ~ i
1C~783~;4
of greater than 20 wt. %.
By a variant thereof, the catalyst includes one or more of the
additional elements Si (0.2 - 0.9) wt. %, Mn (0.2 - 0.7) wt. %, Zr
(0.01 - 0.20) wt. %, Cu (0.01 - 0.15) wt. %, Nb (0.01 - 0.3) wt. %,
Ta (0.8 0 1.2) wt. %, Ti (0.8 - 1.2) wt. %, Co (0.01 - 1.0) wt. %,
Ca (0.01 - 0.5) wt. %, C (0.01 - 0.1) wt. %.
By a variation thereof, the alloy of nickel and chromium com-
prises not less than 72 wt. % nickel, not more than 0.15 wt. % carbon,
not more than 1.00 wt. % manganese, 8.00% iron, not more than 0.015 wt. %
sulphur, not more than 0.50 wt. % silicon, not more than 0.50 wt. %
- copper and 15.50 wt. % chromium.
By another variation, the alloy of nickel and chromium con~
:
~ prises 60.50 wt. % nickel, ~3 wt. % chromium, 14.10 wt. % iron, 1.35 wt.
: . ~
% aluminum, not more than 0.50 wt. % manganese, not more than 0.25 wt. %
~;~ copper, not more than 0.25 wt. % silicon, not more than 0.50 wt. %
..':
carbon and not more than 0.007 wt. % sulphur.
By a further variation, the alloy of nickel and chromium com-
~; prises 32.50 wt. % nickel, not more than 21 wt. % chromium, not more
than 44 wt. % iron, not more than 0.10 wt. % carbon, not more than 1.50
wt. % manganese, not re than 0.15 wt. % sulphur, and not more than 0.75
wt. % copper.
By yet another variation, the alloy of nickel and chromium
comprises 20.0 wt. % chromium, not more than 77.5 wt. % nickel, 1.0 wt. %
iron, not more than 1.0 wt. % silicon, 0.4 wt. % manganese and not more
than 0.1 wt. % carbon.
By another variant, the catalyst consists essentially of (a) a
substrate comprising an assembly of at least two juxtaposed sheets made
from an alloy with one sheet being corrugated and the other sheet being
plain, so that channels are formed therebetween for the passage of
gaseous reactants through the substrate, the juxtaposed sheets being
~ 7a -
:~ : , . . .
:, ., .. :, ~:.
1C~78364
helically wound togethe~ to form a metallic monolith, the alloy having
the composition, in weight percert, carbon (0.09); chromium (22.60);
cobalt (2.0); aluminum (4.5); and iron, balance; (b) an aluminum oxide
film on the surface thereof, being produced by thermal oxidation; (c)
a catalytic layer washcoat of alpha aluminum trihydrate formed by con-
tacting the surface thereof with sodium aluminate solution containing
excess aluminum and caustic soda at 80C. and then firing, the catalytic
:: .~: .,
layer being metallized with a 7-1/2% Rh/Pt alloy to give a metal loading
of 30 g/ft .
By variants thereof, the washcoat loading may be 3.17 g/in3;
or 1.48 g/in3, or 0.7 g/in3.
" .
By another variant, the catalyst was formed by impregnating
....
; the metal substrate with a slurry of a pre-activated alumina trihydrate
` and an alumina monohydrate having a solid:liquid ratio between 25 and
50% and a pH less than 7, drying the substrate in warm air and firing
at 450C. for 2 hours to form chi and gamma alumina in an adherent
coating of up to 0.002 in. thick in the metal substrate.
,'' .::
By a variation thereof, the catalyst includes a loaded washcoat
~ by the step of immersing the support in a solution of a water-soluble
; 20 inorganic salt or salts of the platinum group metals.
By a further variant, the solution is of chloroplatinic acid,
- rhodium trichloride and nickel chloride.
By another variant, the loading is with 7-1/2% Rh/Pt.
By another aspect, the process involves using the catalyst
which comprises one of the steps of (a) manufacturing nitric acid by the
catalytic oxidation of ammonia; or (b) chemically reducing an oxide of
nitrogen with a gaseous reducing fuel in the presence of the catalyst.
The oxygen in the first layer may be present as an oxide
selected from the group consisting of alumina, silica, titania, zirconia,
hafnia, thoria, beryllia, magnesia, calcium oxide, barium oxide, chromia,
boria, scandium oxide~ yttrium oxide, and oxides of the lanthanides.
~ - 7b -
'' , '''. , "1., ' . ' . , , ' ' , ., ,:
, : : :: : :: ::, . ::: .:, :: . :
. - ~ : -
1C~78364
Alternatively, the oxygen in the first layer is present as an oxygen
containing anion selected from the group consisting of chromate, phos-
phate, silicate and nitrate. Preferably it is an aluminum oxide film.
The base metal alloyed to the platinum metal and included in
the second and catalytic layer may be aluminum, magnesium, chromium,
.,
molybdenum, tungsten, manganese, iron, rhenium, cobalt, titanium, vana-
; dium, copper, zinc, cadmium, iridium, thorium, bismuth, tin, lead, anti-
mony, a lanthanide or an actinide, present in an amount of from a trace
to 25 wt. %.
One particular catalyst according to an aspect of the present
; invention comprises an extended metal substrate containing 3 - 40 wt. %
i~ chromium, 1 - 10 wt. % aluminum, a trace to 3 wt. % of one or more
-; of the additional elements and the balance, apart from impurities, iron,
and in which the second and catalytic layer comprises a metal selected
from the group consisting of ruthenium, rhodium, palladium, iridium,
; platinum, silver, gold, or an alloy containing at least 10% by weight
of one of those metals with at least one of the base metals.
The catalytic layer comprising one or more of the platinum
group metals listed above or an alloy containing at least one of the
platinum group metals is preferably deposited upon the oxide coating
or film. It may be deposited in a form which directly possesses cataly-
tic activity or in a form which is capable of being rendered catalyti-
cally active by subsequent treatment.' Catalytic structures according
to aspects of the present invention are extremely robust and effective
in catalytic reactions under the stated reaction conditions.
Moreover, it has been found that in some reaction environments,
e.g., automobile exhaust purification, the metal substrate on the cata-
lyst of aspects of this invention causes the catalyst to reach running
temperature much more quickly and therefore considerably more efficiently
than conventional catalysts, e.g., those having a ceramic substrate.
- 7c _
.: , ; . : ,: ~ ~
`: ~078364
In this specification, the term "extended metal substrate" means
a metallic substrate which has been mechanically deformed in such a way
~- that, when compared with a plain non-deformed substrate, a very much
,~
increased surface area is obtained. Typically the increased surface
area may be achieved by corrugating or folding in a former and winding
up a flat roll and a corrugated foil together into a tube having a
~ spiral cross section.
-i In the accompanying drawing, the single Figure is a photograph
of one variant of a metallic substrate for use in providing the catalyst
structure of an aspect of this invention.
In a preferred embodiment of the present invention, the
metallic substrate which is employed in the catalytic structure is first
crimped, corrugated, folded, indented and/or perforated in such a way
that a very much extended surface area is produced. Such a surface area
is normally much greater than that obtained with a ceramic honeycomb
; or with particulate catalyst supports for the same given volume. An
example of a metallic substrate made in accordance with these teachings
comprises a roll of corrugated sheet of a heat resisting alloy inter-
leaved with a non-corrugated sheet of such alloy to form a metallic
monolith, is shown in the attached drawing. Alternatively, two corru-
gated sheets may be used with the corrugations in each sheet parallel
with each other or at an angle to each other. A coated substrate is
then provided with a firmly adherent oxide coating which is porous and
~ 7d _
:
~0783f~4
` - sbsorbent and ha~ a high surface area and which acts as the carrier for
- the second catalytically active layer containing one or more of the
platinum group metals as herein defined.
The heat resistant alloys comprising the extended metal sub-
~trate are preferably alloys having a minimum nickel plus chromium con-
tent of 20~ by weight. Typical alloys which therefore may be-used for
; the extended metal substrate are high nickel and chromium stainless
steels and proprietary products, e.g., those known by the Trade Marks of
"INCONEL" 600 and "INCONEL" 601.
It is preferred to provide the metallic substrate with a first
firmly adherent oxide layer in an essentially two stage process. In the
first stage the metallic substrate is thermally oxidized to provide a
thin first oxide layer which acts as a key. It is preferred to carry
out thermal oxidation by maintaining the formed metallic substrate at
from 1000 - 1200C. in air or moist cracked ammonia vapour for 1 hour.
The higher temperature is required with very oxidation-resistant alloys,
e.g., those high chromium stainless steel alloys known as KANTHAL
(registered Trade Mark) and the moist hydrogen atmosphere is preferred
with alloys having a high Ni content.
The adherent oxygen-containing or oxide film may be produced
by any one of several known procedures~including chemical techniques.
The film must be of sufficient thickness to provide adequate absorptive
capacity for retaining the catalytically active alloy comprising one
or more of the platinum group metals. The film is preferably from 0.004
to 0.001 inches thick.
Where aluminum is present in the alloy forming the extended
metal substrate, the oxide film may be produced by treating the aluminum-
containing surface with a solution of an alkaline carbonate, usually a
sodium carbonate chromate solution. The film may be produced by the
anodic oxidation of the metal surface whereby the metal is made the
- i~
` 1~78364
,
anode i~ an electrolytic solution. In anodizing aluminum-containing sur-
faces, a 15~ sulphuric acid solution is commonly employed as the electro-
lyte but other acid electrolytes, e.g., chromic acid, oxalic acid, phosphor-
ic acid and sometimes boric acid may be used. The oxide film in catalysts
according to which aspects of this invention relates is deliberately posi-
;; tioned and does not include the relatively thin natural oxide films which
sometimes occur on metal surfaces which have been exposed to the atmosphere.
One method of forming an alumina layer on these alloys which do
~-- not contain sufficient aluminum to form their one alumina layer upon oxi-
dation is the use of a procedure known by the Trade Mark of CALORISING.
This involves the vapour deposition of an aluminum coating followed by
anodizing or heating in an oxygen-containing gas. Alternative coatings,
e.g., chromate, phosphate, silica or silicate or zirconia may all be de-
posited by known methods. The many different techniques for the prepara-
tion of a high surface area catalytically active refractory metal oxide wash
coat containing one or more of the refractory metal oxides which confer
beneficial properties as regard ageing and inertness to platinum group
metals at high temperature under oxidizing and reducing conditions ~s well
known in the art and in the interests of brevity need not be reproduced
here.
A preferred adherent oxide coating deposited upon the extended
metal substrate is alumina.
One method for the deposition of hydrous alumina is proposed in
United States Patent No. 2,406,420 issued August 27, 1946 to H.B. Weiser
.
et al. Any convenient aluminum compound e.g. alkali metal aluminates and
aluminum salts may be used as the starting material. Either acidic or
basic precipitants are used, depending upon the character of the starting
material. Suitable acidic precipitants are ammonium chloride, ammonium
sulphate, ammonium nitrate,
~ _ 7 f _
...... . . ..
1(~78364
- hydrochloric acid, nitric acid, etc. Suitable basic precipitants are
ammonium hydroxide, sodium hydroxide, hexa-methylene tetramine, etc.
One method is to precipitate the hydrous alumina from an
alkali metal aluminate solution containing excess aluminum and alkali
metal hydroxide directly on to the extended metal substrates forming
~ part of the catalyst of an aspect of the present invention. If the
; aluminate solution is maintained at a temperature of 60 - 85C., a film
or coating of alpha alumina trihydrate (Gibbsite) is deposited. Subse-
quent heating at 150 - 180C. converts the tri-hydrate to the monohydrate
and subsequent heating at 540C. converts the monohydrate to gamma
alumina without loss of the very high surface area coating which is pro-
duced by this method. The high surface area results from the formation
of hexagonal crystal aggregates of approximate size 8x8x20 microns.
Micropores of size of 40A diameter are present in the hexagonal crystal
aggregates but appear to play no part in the catalytic activity of the
structure. The high surface area is demonstrated (in Example 12) by
resistance to lead and phosphorous poisoning after deposition of
catalytic metal.
The heat-and-oxidation resistant alloys comprising the
extended metal substrate used in the catalysts of aspects of the present
invention comprise alloys of iron, chromium and aluminum in which the
elements cobalt, nickel and carbon are preferably also present. Ranges,
apart from
.
,`~ .
,, .. , ., ~,. .
. . .
- . ~ - . : ,, . : -. ,, - , .
11~783~;4
: ` i
trace elPments and impurities, for each element which may be present in
` the alloy are as follows;
..,
,,' . % ' .w/w
. .
Cr 3 - 30
. Al 1 - 10
...
~ 0 - 0.5
Co 0 ~ 5.0
- Ni 0 - 15.0 ~:
Fe Balance
'
Preferred ranges for the above mentioned ele~ents are:
,
% w/w
Cr 13 - 24
Al 3,5 - 6.5
~' , ' ' `' `
.
- 8 -
10783~4
.`
, . ,
. - % WtW
. _
' C O - 0.1
Co 0.2 - 0.8
Ni o - 5 o
Fe Balance I
: Typical quantities of trace elements which may be present in the
~: alloy to improve strength, oxidation-resistance and heat-resistance are:
% WIW
Si 0.2 - 0.9
Mn 0.2 - 0.7
Zr 0.01 - 0.20
~ Cu 0.01 - 0.15
:~ Nb 0.01 - 0.3
Ta 0.8 - 1.2
Ti 0.8 - 1.2
Co 0.01 - 1.0
: Ca 0.01 - 0.5
- C 0.01 - 0.1
Specific heat-and-oxidation-resistant alloys suitable for use
in carrying out the present invention are given in the following examples:
EXAMPLE 1
Kanthal D (Registered Trate Mark): a proprietary product supplied by
the Kanthal Company of Sweden, and having the composition:
.
-: :
.
.. :: -. - . :,. ,: , :: : . . ... :: : .. : ;, ...
\\
1C1 78364
, ,
% W/W
C o.~s -
. Cr 22,60
Co 2.0
. .
Al 4 5
Fe Balance
EXAMPLE 2-
Megapyr (Registered Trade Mark): supplied by Telcon Metals Ltd.
and having the composition:
% W/W
.
Cr 30
Fe 65
Al 5
EXAMPLE 3
Stainless Steel 316 (one of the standard range of austenitic
stainless steels):
:`
% W/W
.
C 0.08 .
Cr 18.00
`20 Ni lO.00
Ti 0 40
Fe Balance
: EXAMPLE 4
The following range of alloys is supplied by the Kanthal Company
of Sweden:
-- 10 --
. . . . , . ,, .. : ... ~ ::
., : . . .. ~
:. . : .: : :
:: : . : .: :: ,
, ~: : . :: ,.: : ,,
i
:
% w/w
Cr 10 - 40
Al 1 - 9
; Fe 51 - 88.9
Ta 0.1- 5
Co 0 . 1- 1
In the above composition Ta may be partially replaced
by Ti, and Ce may be partially replaced by Ca.
Optionally the following constituents may be present
to impDOve the mechanical strength and oxidation resistance
of the alloys:
% w/w
Mn 0 - 2
Si - 0 - 2
:~ ~ 0'5
0 - 5
Nb 0 - 2
Mo 0 - 1.5
Th 0 - 0.2
Zr 0.01- 1, and
P and A may be present as impurities.
Examples in thi~ range are as follows:
:` . ( 1 ) .96 . . .. .w./w
,~ Cr 20 - 30
Al 3.5 - 6
Ta 2,5
~ Ce 0.15
- Fe Balance
~`
--11--
: 107836~ i
Y
Cr 20 - 30
~l 3 5 6 ~ .
~,. .I. 2 . 5
Ta . . 0.1
C~
Co 0.~ - 5
Fe ~3al ance
Cr 3.5 - 1
Al 5 - . 9
. . . .
~b 1 . 5
~r 0,15
- Ta o.i - 5
Fe i~alallce
( i v j 1~ W/~r
Cr 10 - 15
hl 3 _ 5 5
. . - . . ' 1
. Th 0.1
Ta 0.1 - 5
.', ~,~ ' . 0.01 - 1
Fe i3alance
12
.. ~ .......
, . ,
.
10783~;4
EXAMPLE 5
~` Immaculate 5 tregistered Trade Mark): a proprietary product supplied by
Firth Vickers Ltd.
% w/w
~ Cr 23.0
: - Ni 21.0
C 0.1
Fe Balance
EXAMPLE 6
10 Inconel 600 (registered Trade Mark): a proprietary product supplied
by Henry Wiggin Ltd.
%W/W!
Ni not less than - 72.00
- . C not more than - 0.15
Mn not more than - 1.00
Fe 8.00
S not more than - 0.015
Si not more than - 0.50
Cu not more than - 0.50
Cr 15.50
~ Inconel 601 ~registered Trade Mark)
,~ ~ % w/w
~,
Ni 60.50
Cr 23.00
Fe 14.10
Al 1.35
;
::
- 13 -
--~` 10783~4
Mn not more than - 0.50
Cu not more than ~ 0.25
Si not more than - 0.25
C not more than - 0.50 ;~
S not more than - 0.007
- EXAMPLE 7
Inconley 800 (Registered Trade Mark); a proprietary
product supplied by Henry Wiggin Ltd.
% W/W
Ni 32.50
C not more than - 0.10
Mn not more than - 1.50
S not more than - 0.15
Cu not more than - 0.75
Cr not more than - 21,00 ~:
Fe Balance
: EXAMPLE 8
.,
~ Brightray S (Registered Trade Mark); a proprietary
.,
.~- product supplied by Henry Uiggin Ltd.
~ ~ W/W
- Cr 20.0
::~ Fe 1.0
Si not ore than - 1.0
Mn not more than - 0.4
C not more than - O,1
Ni Balance
,~ .
-14_
1~78364
,
.
EXAMPLE 9
Stainless Steel No: 309
% _ W/W
Cr 22 - 24
Ni 12 - 15
C not more than - 0.2
Mn not more than - 2.0
- Si not re than - 1.0
Fe Balance
EXAMPLE 10
Stainless Steel No: 310 (Supplied by the British Steel Corporation)
W/W
Cr 24 - 26 (prefera-
bly 25)
Ni 10 -. 22 " ;~ ~
C not more than - - 0.25 n O.1
~: Mn not more than - 2.0 " 1.8
Si not more than - 2.0 " 1.5
. Pe Balance Balance
: EXAMPLE 11
_
Stainless Steel No: 321
~ % _ W/W
Cr 17 - 19
Ni 9 - 12
C 0.8
Mn not more than - 2.0
Si not more than - 1.0
Ti not more than - 0.4
Fe Balance
- , ,,. ~., .. .... :. :
1078364
EX~PLE 12 '~
Armco 18SR supplied by the Armco Corporation
% _ _ _ w/w
- Cr 18
Al 2
- Ti 0 4
si
C 0.05
Fe Balance
. ''' ' `'
Generally speaking, in the Fe-Cr-Al system, there are very few ferritè steels
having less than 12-12.5% by weight Cr which are satisfactory. Also the
- aluminum content for alloys which function satisfactorily is rarely outside
the range 1-6% by weight.
.
. . ~ .
The metal substrate used in the catalyst of aspects of the
present invention is deformed so as to present a large surface area to the
. , .
vapour phase reactants whose reaction is to be catalysed. This may be
carried out, for example, by first producing the alloy in thin sheet form
by rolling, corrugating by passage through fluted forming rolls, spirally
winding the thin corrugated sheet so that a round sieve-like body is formed,
the openings of which correspond to the depths of the grooves in the said
corrugated sheet. The two sheets may be wound simultaneously, one of the
,
sheets being corrugated and the other plain, corrugated to a different con-
figuration when compared with the first mentioned corrugated sheet or with
the corrugations of the sheets having the same or a different corrugation
configuration and with the corrugations in the respective sheets disposed
at angles to each other. Where a flat and a corrugated sheet in strip form
is used, the leading edges thereof are spot-welded together and strips of
a certain length are fed into a device which rolls the strips between three
sprung rollers to form a spirally wound collar-like or generally annular-
shaped module as shownSin the accompanying single figure in the drawings.
- 16 -
- 1~78364
Extended metal substrates used in the catalyst of aspects of
the present invention possess 1-1/2 - 3 times the surface to volume
ratio that can be obtained with a ceramic honeycomb substrate. The
normal substrate is 600 - 700 sq. ft. per cubic foot of substrate.
Examples are the products EX 20 (registered Trade Mark Corning) a
ceramic honeycomb substrate which has a surface area of 576 sq. ft./ft ;
and Grace 400 (registered Trade Mark) which has a surface area of 780
sq. ft./ft.3 for 0.003" thick Kanthal D ~registered Trade Mark) sheet
and 2000 sq.ft./ft.3 for 0.002 thick Kanthal D (registered Trade Mark)
sheet.
It is preferred to use foil of thickness between 0.0015 and
0.0045 inch and more preferably of thickness 0.002 inch corrugated and
assembled to form a structure having approximately ~00 cells per square
inch when considered in cross section. A preferred range of cell sizes
is 200 - 800 cells per square inch. Suitable surface to volume ratios
are 1200 sq. ft. per cubic foot with 400 cells per sq. inch and 2000 sq.
ft. per cubic foot with 800 cells per square inch.
An alternative method of forming the module comprising spot-
welding the two strips of foil to a stainléss steel tube of, for example,
20 1/~ inch outside diameter, which aids winding and module formation.
In yet another method, the two strips of foil to be simultane-
ously wound are spot-welded together along their leading edges and then
wound upon a hollow cone-shaped former, thereafter using friction rollers
and slides in the cone, the strip is wound up and is forced into a
retaining collar or shell in one operation.
Where a retaining collar or shell is not used, it is desirable
to weld successive convolutions of the module by forming one or more
radially extending runs of weld on the ends of the module. Other methods
of securing successive convolutions or at least the outermost convolu-
tions by stitching or tack-welding may be employed in order to prevent
' 't`' ~- 17 -
.. : - : .- ~
`` -` 1~'783~
the spir~lly wound modules from~unwinding.
After forming the modules into finished units, they
are pre~erably cleaned before the formation of the adherent
oxygen containing film or coating, and this is preferably
carried out by a vapour degreasing technique with a halogen
containing solvent, e.g., trichloroethylene followed
..... .
-17a-
~ 10783~
. by washing in acetone and drying.
- ~XAMPLE 13
In this example Gibbsite was deposited on thermally oxidised
Kanthal D modules as shown in the accompanying single figure of the drawing
. by contact with sodium aluminate solution containing excess aluminum and
caustic soda at 80"C. After firing the ~7ashcoat
,'; ' .
.
- , .
,
.
.
~ .
~ 18 ~
r
107836~
`~ was found to be almost pure gamma alumina. The washcoat was metallized
with a 7-1/2% Rh/Pt alloy using known techniques to give a metal loading
- of 30 g/ft of volume of the whole catalyst structure. Such structures
have been found to have better poison resistance than washcoated
ceramics and unwashcoated metallic substrates. This is demonstrated
by results obtained from Qimulated load and phosphorous trials on
catalyst structures with metal and ceramic substrates:
(a) Simulated lead poisoning trials
The test exhaust gas contained:
.
Hydrocarbons 1000 ppm
CO 2.5%
~:
NOX 1000 ppm
Pb 0,5 gm/hr balance N2
Washcoat : Gamma alumina
Metallized with : 7-1/2% Rh/Pt
:"
-~ Substrate Washcoat Metal Hydrocarbon conversion efficiency
load~ng load~ng after
~ g/in g/ft 1 hour 3 hours 7 hours
::
Kanthal D 3.17 30 79% 69% 52%
(registered
Trade Mark)
:
~anthal D 1.48 30 74% 63% 56%
(registered
Trade Mark)
Kanth?l D 0.7 30 67% 48% 36%
(registered
Trade Mark)
_ _
Ceramic
Ex 20 2.0 30 56-75 40-54 27-39
~registered
Trade Mark)
(Corning~
(range of
results)
...
-- 19 --
`'- ' ' '.:. :; ' . ' ' ,. : ,
,: ' . ., .'. :; ' . "' '' -, '' ,. ; ' ;,'' '' ',, . ' ': ' ' ' . ' : '
,: ' . ' '. , ''' '.; '' . ,, , ' , ' ' "
`10'7~3~
(b) Simulated phosphorous poisoning tr~ls
Washcoat : Gamma alumina t
Metallized with : 7-1/2~ RhtPt
_ .
~-~ Substrate Washcoat ~Metal~. Hydrocarbon conversion efficiency
- loading load~g~,after
~ g/in3 g/ft~ 1 hour 3 hours 7 hours
. .
Kanthal D 2.5 30 98~ 97% 97%
; (registered
Trade Mark)
" .
Kanthal D 1.8 30 96.5~ 95.0% 93%
(registered
Trade Mark~
Ceramic ~~ ~ - ~- -~ - ~- `
Ex 20 2.0 3~ 85% 76.5~ 59%
(registered
Trade Mark)
(Corning)
. . _ . . . _
Instead of Pb, the test exhaust gas contained 1000 ppm in P in
the form of 1~ tributylphosphate/toluene in air having a space
velocity of 100,000 hr 1.
A washcoat loading is preferred which is within the
range of 5 - 30~ by weight of the metallic monolith substrate.
A suitable loading of A1203 on Kanthal D (registered Trade Mark)
having 400 cells per square inch is 10~ by wei~ht. The surface
area of the alumina is 50 - 500 square meters per gram of alumina.
The aluminate method of deposition of alumina, described above,
gives a surface area of from 120 - 160 square per gram of alumina.
An alternative preferred method for the deposition of an
adherent alumina washcoat on the metallic substrate is to prepare
a siurry of a pre-activated Gibbsite (alumina trihydrate) and an
alumine monohydrate having a solid:liquid ratio of between 25 and
50% and a pH less than 7 and usi~ this to impregnate the shaped
substrate by complete immersion. The exact strength of the slurry
used twhich may be determined by trial and error) should be
sufficient to produce an alumina
-20-
1(~7836~
washcoat of the required thickness. The substrate is then allowed to
dry in warm air and finally fired for 2 hours at 450C. to form chi and
gamma alumina in adherent coating up to 0.002 in. thick on the metallic
substrate. Crystal aggregates of diameter 3 - 7 microns are produced
having micropores of approximately the same size, i.e., 40A in diamet~r.
A further alternative method of deposition of an adherent
alumina washcoat on the metallic substrate is to use a slurry of alpha
alumina monohydrate. After firing at 450C. gamme alumina is formed
having a surface area between 180 and 300 square meters per gram. Gamma
alumina is added to alpha alumina monohydrate at the slurrying stage
before firing in order to form a thixotropic mixture. Crystallite or
crystal aggregates of 20 - 100A diameter are formed. Micropore diameters
remain the same at 40A.
Suitable proprietary alumina trihydrates (Gibbsite) are "FRF
80" (registered Trade Mark) supplied by British Aluminium Chemicals Ltd.
and "C 333" (registered Trade Mark) supplied by Aluminum Company of
America. Suitable alumina monohydrates (Boehmite) are "SOL-GE~ ALUMINA"
(registered Trade Mark) supplied by the United Kingdom Atomic Energy
Authority. "DISPAL M" (registered Trade Mark~ supplied by Conoco and
"CONDEA F" (registered Trade Mark) supplied by the Condea Group. Gibb-
site is added to "SOL-GEL" (registered Trade Mark) alumina, which is
microcrystalline Boehmite, at the slurrying stage in order to form a
thixotropic mixture.
Optionally, one or more of the oxides titania, zirconia,
hafnia and thoria may be present in the alumina for the purpose of pro-
viding additional stabilization of the intermediate oxide (washcoat)
layer as described in British Patent No. 1,401,022. If desired, rare
earth oxides, alkaline earth oxides and alkali metal oxides may be used.
Many of the aluminum-containing metallic substrates used in
; 30
- 21 _
. :
: , ...
- : , . .
1(~78364
- - the catalyst of aspects of the present invention have the property of
oxidizing "inwards". That is to say it is believed that a factor con-
tributory to the success of the catalysts of aspects of the present
invention is the fact that the extended metal substrate itself, which
forms part of the catalytic structure of aspects of the present inven-
- - tion has a tendency to oxidize under very strong oxidizing conditions in
such a way that the first layer of adherent oxide film does not tend to
grow over or cover the outermost layer of the alloy-containing platinum
group metal, silver or gold.
Impregnation or deposition of the alloy of platinum group
metals, silver and gold and optionally base metal upon the first oxygen
containing adherent layer may be accomplished by known methods of
deposition of catalytically active metals on washcoats or other supports,
e.g. if a high surface area refractory metal oxide is the adherent
oxygen containing film, the support may be immersed in a solution of
water-soluble inorganic salt or salts of platinum group metal, e.g.
platinum, rhodium and nickel. In this case chloroplatinic acid, rhodium
trichloride and nickel chloride would be used.
It is preferred that the composition of the outermost layer of
catalystic metal consist of platinum group metals or alloys of the
platinum group metals with each other and with base metals. Particularly
preferred combinations are 7-1/2~ Rh/Pt for ~OX abatement, i.e., reduc-
tion of oxides of nitrogen with a gaseous reducing fuel in nitric acid
tail gas purification.
Particularly preferred alloys of platinum, rhodium and base
'
'' '
~ ' ~
~ 30
... ..
~ 22 _
-: . . :. . . . :.. .:: ;:: . : ~ .
~1;)'~83~
metal which in the catalyst of aspects of the present invention
are suitable in the outermost catalytic metal alloy layer of the
catalyst structure are alloys containing:
w/w
Rh 1 ~ 50
Base Metal 0.01 - 25
Pt Balance
in which the base metal is selected from the group consisting of
Al, Mg, Cr, Mo, W, Mn, Fe, Co, Ni, Ti, V, Th, U, Cu, Ag, Zn, Cd,
Hg, In, Tl, Bi, Sn, Pb, the lanthanides and the actinides. This
combinatinos is useful for the oxidation and reduction reactions
and also in the steam reforming of naphtha and naphthadistillates.
The base metals mentioned above, however, are also
useful in other platinum group metal ~lloy combinations and also,
when employing catalytic structures according to aspects of the
present invention in which the outermost catalytic metal layer
contains silver or
: .
.~-r
-23-
` or gold. Ruthenium is use ~ ~ ~O~ ~6 ~ecomposition of NOX in automobile
exhaust purification.
EXA~'LE 14
A three inch wide piece of Kanthal D (registered Trade Mark)
three-thousandths of an inch thick had fifty -thousandths corrugations
formed in it by the method described above and was formed into a spiral
- module. It was oxidized for one hour at 1200C. to form an alumina
layer adherent upon the substrate. A 7-1/2% rhodium platinum alloy was
then deposited upon the alunina and the catalytic structure was sub-
~ected to oxidation trials using a space velocity of an automobile
englne exhaust of 80,000 hours 1. The initial hydrocarbon conversion
was 73%, after 100 hours it was 66%. The initial light off was 265C.,
after 100 hours it was 320C.
EXA~PLE 15
A corrugated spiral module formed as described above from a
one inch piece of 321 stainless steel was calorized to form an alumanum
- ; coating which was then oxidized for one hour at 1000C. and a loading of
25 grams per cubic foot of 7-1/2% rhodium platinum was placed on the
oxide coated substrate. Using a space velocity of 240 thousand hours 1
the following results were obtained:
Initial hydrocarbon conversion was 72%, after 24 hours 77%;
initial light off 230C.; after 24 hours 290C.
EXAMPLE 16
A one inch piece of 316 stainless steel was calorized and
oxidized for one hour at 1200C.~ using the same loading of rhodi~m
-, platinum alloy and space velocity as described in Example 14 the
following results were obtained:
'~ Initial hydrocarbon conversion was 76%, after initial light
, off at 195C.; after 24 hours light off was at 290C.
. .~
- 24 -
, . . _ . _ . : . ,
~ ' " , ,, ', , , , ' " ' .
~ 1078364
EXAMPLE 17
Using foil 0.002" thick made of (a) stainless steel 310SS
supplied by the British Steel Corporation and (b) Lanthal D (registered
Trade Mark) supplied by the Kanthal Company of Sweden two cylindrical
motules were made up 3" long, 2" in diameter having 800 cells per square
inch (cross section). A high surface area alumina washcoat was
deposited on both by the aluminate method described above and 40 gm/cu.
ft. platinum was deposited upon the alumina by known techniques.
Both units were then engine tested using low-lead fuel accor-
ding to specification of the Environmental Protection Agency of theUnited States.
Hydrocarbon Carbon Monoxide
Conversion_ Conversion
Kanthal D (registered 90.8% 99.2%
Trade Mark)
(100 hours)
310 SS 79,4% 90.3%
(200 hours~ -
E ~YPLE 18
In this example a ceramic monolith is compared with a Kanthal
D tregistered Trade Mark) module both of which have a high loading FRF
80 (registered Trade Mark) /Sol-Gel (registered Trade Mark) alumina
washcoat with a 100% Pt catalytic layer and also included is a Kanthal
(registered Trade Mark) module having a high loading hydrolytic
alumina taluminate method) washcoating and also h~aving a 100% Pt
:.~
catalytic layer.
.
`:
25 -
, .
-, - ~,
, . . . .
1078364
Washcoat Dimensions Effective Effective
~ frontal vol.
- area
..... _
Ceramic FRF 80 (registered Trade 4" x 6" 11.1 sq.in.66.4 cu.in.
Mark)/Sol Gel (registered
Trade Mark)
A1203
Kanthal D " " " " " " 10.75 " " 64.7 " "
(registered
Trade Mark)
Kanthal D Hydrolytic " 11.4 " " 66.5 " i'
~registered (Aluminate)
Trade Mark~
Results
o
The results are sum weighted for automobile engine operation
under different conditions:
Hydrocarbon conversion Carbon monoxide conversion
0 hrs 100 hrs 200 hrs 300 hrs 0 hrs 100 hrs 200 hrs 300hrs
-
Ceramic +92.9 76.677.0 75.1 96.1 89.7 94.6 98.2
FRF 80(regis-
tered Trade
Mark/Sol Gel
(registered
Trade Mark)
Kanthal D87.8 71.875.3 63.0 88.5 90.5 79.5 80.0
(regis~ered
Trade Mark) +
FRF 80 (regis-
j tered Trade
Mark)/Sol Gel
;~ (registered
Trade Mark)
.,
Kanthal D92.3 79.380.2 75.0 95.4 87.6 91.1 90.0
~registered
i Trade Mark) +
Hydrolytic
' alumina
,, ~
These results show good comparability of metal supports with
ceramic substrates both as regards performance and stability.
.:
:.
~`~- 30
. .
; , ,', ; ' , , , ~ ~ '
.. , ,- .' . :: ', , '.,: ';; , ;, :`
