Note: Descriptions are shown in the official language in which they were submitted.
~ 2809 C~
The lnvention relates to a process to be used ln heterogeneously-
catalyzed or electrochemical-catalyzed processes for preparlng supported
catalysts by exchanging protons oi acid groups ot actlve carbon with cations
irom a ~olutlon oi a compound oY a catalytlcally actlve metal and separatlng
the treated mass lrom the solutlon.
Furuoya and collaborators descrlbed a method ior prep~rlng pa11ad~um-
on-carbon catalysts, in whlch the palladlum 19 depo~lted ag J-al1 metal
crystallites (Intern. Chemlcal Englneerlng 10, no 21, Aprll 1970,
pp. 333-338) This method provides ior oxidl$ing the actlve carbon with nitric
acid, lmpregnatlng the oxidlzed oarbon ior 48 hours with an aqueous solution
oi a palladlum-ammlne complex, during which operation protons iorm the carbon
suriace are exchanged agalnst posltlvQ palladium-ammine complex ions,
isolating the lmpregnated solid mass by rlltration, and subsequently washlng
and drying lt. Following this, the catalyst is actlvated by treating lt in
succes~icn wlth hydrogen at 300 & ior 3 hours, wlth alr at 150 C ior 1 hour
and, iinally, once more with hydrogen at 150 C ior 10 minutes, ffl ls method
has the drawback Or being laborlous. Moreover, carbon oxidized with nitric
acid in extremely diiiicult to iilter. The low activlty suggests that coarse
metal crystallites may have iormed.
Catalysts ln whlch the catalytlcally active metal is deposlted a9
small crysatllltes can also be prepared by the method described in Applicant's
Canadia~ patent application 247~496 This procedure yields a catalyst oi high
~atalytlc activity, by start~ng ~rom an active aarbon with a given ~avourable pore
distrlbution to which a salt oi a catalytically active metal is adsorbed in
an aqueous medlum and by periorming the hydrolysls and reduction oi' the
resulting oxide or hydroxide in one single step with a mixture oi liquld
hydrolyzlng and reduclng agent9.
It has been iound that Furuoya'~ process can be carried out in a ~ -
much simpler way, whilst yielding a catalyst oi equivalent quallty but oi
improved iiltration bebavlour, whloh, moreover, can be direotly applied
without requiring the ~airly oomplioated reduclng treatment.
- 2 -
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10~850~
The present invention is directed to preparing an active metal-on-
carbon catalyst in which the metal particles are deposited as small
crystallites, whilst avoiding the cumbersome preparation method of Furuoya.
According to the invention, there is provided a process for
preparing supported catalysts to be used in heterogeneous-catalytical or
electro-catalytical processes, by exchanging protons of acid groups on acti~e
carbon with cations from solutions of one or more of the salts or complex
compounds of the metals of Groups I B and YIII of the Periodic System of
Elements and Zn and separating the treated catalyst mass from the solution,
the catalyst being reduced in the medium of the reaction catalyzed by the
catalyst, without separate reduction of said catalyst. The cations may e.g.
originate from one or several salts or complex compounds of notably of Ag,
Au, Co, Cu, Fe, Ir, Ni, Os, Pd, Pt, Rh, Ru as well as Zn.
For the supporting material use must be made of carbon containing
acid surface groups. Some active carbons that can be used for the purpose
are commercially available, ant are known as hydrophilic active carbon, or
as active carbon suited for treatment of liquids. The acidity of these
carbons and the number of acid groups on their surfaces can be determined
titrimetrically, as is stated by B.R. Puri in "Chemistry and Physics of
Carbon", published by Marcel Dekker, New York, 1970, Chapter 6, pp 229 ff.
It is possible to increase the number of acid groups on the -~
supporting surface, if a high degree of loading should be desirable, by
subjectlng the carbon to a known oxidative treatment with oxygen, ozone,
hydrogen peroxide, potassium persulphate, potassium nitrate, nitrogen
monoxide or nitrogen dioxide. In the preparation of the present catalyst,
increasing the number of acid groups can be performed the most adequately by
treating the carbon with hydrogen peroxide. Application of this compound,
combined with an appropriate choice of the duration of the treatment and the
temperature at which it is carried out, enables the number of acid groups to
be controlled at discretion and ensures that the coal will retain good
fil~ration properties. The treatment is all the more important in those
3 -
~0~8s02
cases where it is desired to deposit larger quantities of metal on the
support by means of ion-exchange.
In the manner described above, metals forming positive ions in
solution can be deposited on a support carrying acid groups. Also complex
,.:, - 1,
' : .
: ~ :` ` `
.
- 3a -
1~ "
10~8S~
lons, lr carrylng a po~ltive ohargo, can`th~ be oxehang~d galnse aold grou
on the ~uriace ot the ~upport.
The process o~ the lnvention can also be u~ed ior preparing
alloyed catalysts, starting ~rom solutions oi mixtures Or salts or co~ples
compounds of the catalytically actlve metals. Ion exchange with the cld
surrace groups results in a statistlc dlstrlbutlon oi tho alloy-tor~lng lon~
on the suriace Or the support, and i'ormatlon oi homo~cneous alloy partlol-~.
Ii the compound to be exchanged, tor example a complox lo,n, 19 ~se-ptlbl-
to the aotlon of acid, and is llable to decompose under the iniluenes oi the
acld surtace o~ the support, one can ~lrst exchange the acld group~ agalnst
alkall metal lons, and subsequently exchsnge the alkali metal lons agaln-~t
the posltlve lons Or the catalytlcally actlve compound.
m e amount ot metal that can be deposlted on the suriace oi the
support by exchanging aeld groups agalnst posltlve metal lons mar be varled
wlthln wlde llmlts, lor example irom 0.1 to approxlmately 10% wt ealeulated
to the weieht oi the ultlmate catslyst. ~he rlgure shows the tltratlon curve
lor several actlve carbon types as a measure o~ the number Or acld groups.
e number Or meq ~a(OH)2 needed ior neutrallzlng a slurry o~ 100 g ac~tlve
carbon ln distllled water 19 plotted on the absclssa, and the ~H value
~20 on the ordlnate. It can be derlved ~rom thls plot tbat type CX aetlve
carbon msde by CECA, Frsnce, possesses a large numbei Or acld groups.
Practlce has shown that up to a ralrly degree Or loadlng thls sctlve
earbon type 19 a su~ted support ior preparing catalysts accordlng to
the invention. However, arter this active carbon type has been troated
~25 with H202 at 40 & ror 20 hours, more aeld groups appear to he present,
wlth the eonsequenee that exchango wlth a Pd(NH3)4 C12-solution and
, ~:
~ reduction yields a cataly~t whlch contalns approximately 5% wt o~
~ :
psllsdium; lnstead Or 2X wt wlth the untreatod aetlvo earbon. ~`
The qusntity Or catalytlcally actlve materlal to be deposlted by exchange
~30 ¢an be determlned by mean~ ~f the abovenentloned titratlon curve~ m e
degree o~ loadlng wlth catalytlcally aetlve metal eorresponds with the
nu~ber Or ~urrace proton~, ~hlch 1~ detenslned ~ro~ the nu ber Or ~q.
8h(0H)2~100 B carbon durlng neutrallzatlon to a pH Or approxi ately 7.
Uslng the process oi the lnventlon, skin-t~pe cataly~tq osn al-~o
be prepared ln an eriiclent manner irom granules, pellets or other
S arte~acts conslstlng oi actlve carbon or materlal containlng actlve carbon,
by cub~ectlng sald granules, pellets or other arteiacts to the exchsnge and
sub~equent reductlon treatments descrlbed above. 8y the 'ter~ actlve oarbon'
19 to be understood all CU-QtOmary actlve carbon type-~, such a~ carbon
prepared irom peat, coal, bone etc, but al~o grsphlte and osrbon blaok,
provided all these type-~ carry acid group~ on thelr quriaoe. ~ ;
me catalysts acoordlng to the lnventlon can be employed ln
hydrogenatlon processes, ln whlch case the treatment ior reduclng the metal -~
lon to the iree metal may be carrled out ln ~ltu. Palladium-on-c~rbon,
platlnum-on-carbon or platlnum-pallad~um-on-carbon cataly-~ts made aacordlng
~5 to the invention are very sulted ior catalyzlng the preparatlon Or hydroxyl-
a~ine by reductlon or nltrate lons or nltrogen monoxlde with hydrogen ln
.
a strongly acid medium. m e carbon treated ~lth the noble-metal complex can
be immedlately employed ln the reaction medlum. Previous reduction 1~ no
.
;i longer nece-~sary. ``
Accordlng to the lnventlon electrodes ior iuel cells can be prepared,
notably noble metal-on-carbon electrodes.
ffl e invention will be rurther elucldated with reierence to the
; ~ollowing example without, however, belng restrlcted thereto.
~' ` `
20 B 0~ active carbon, make CECA, France, type CX, with an
acc-#~ble suriace area (EET area) o~ lOS5 m /g wa~ ~tlrred with 120 ml oi ~`
dlstllled water ior V2 hour ln order to expel atr and other ad~orbed ga5e~.
Next, 105 ml oi a palladlum a nine chloride, Pd(NH3)4C12, solutlon contalning
2.2 g o~ palladlum (calculated as metal) were added, whereupon the solutlon
~ ..
30~ wa3 stlrred ior 20 h at room temperature to exchange suriace protons agalnst
_ 5 _
1~85~
Pd(NI13)~ lons Sub~oquently, t~e solld m-99 was separated by iiltr-tlon,
and drled ior 6 hours at 60-70 C. One ~l$th Or the palladluo ln the
solutlon deposlted on the active carbon. ~ecause there is only exchange
on ~he suriace oi the active coal, no adsorption occurs.
The solutlon may have thereiore a highe- concentration oi Pd(NH3)4 -ionY
than that i9 necessary i'or the exchange.
With the aid oi the catalyst prepared ln thls way several experl ents
were carried out:
a. A minor portion oi the catalyst was sub~ected to basic
hydrolysis and reduction with alkallne methanol. m ls experlment dld not
yleld a sultable catalyst because the dissolved palladium particles were
present ln colloidal iorm.
~ b. Another portlon oi the catalyst was used, without iurther previous
; treatment, ior the catalyzed preparation oi hydroxylamlne irom nitrate lons
at 30 &. To thls end hydrogen gas (80 l/h) was ied lnto one lltre oi an
aqueous buiier solution which contalned 207 cm o$ phosphorlc acid (85%-
conoentration), 82 g oi sodlum hydroxide and 198 g Or NaN03, whereupon
750 mg oi the catalyst was added and dlspersed by sti~rrlng. The activity
oi the catalyst was measured and expressed in g oi hydroxylamine per g oi
metal/hour. m e result o$ the measurements is given in the table, exp. no. 1.
c. A small portion oi the catalyst was reduced with hydrogen gas prior
to appllcation. To this end, nitrogen gss containing 1 vol-% Or hydrogen gas
was passed over it at the rate Or 20 l/h in a pyrex~glass tube at 300 &
ior 1 hour. m e ~eduction was then continued ior 1 hour at 300 C with a
mixture oi 50% vol. oi nitrogen gas and 50% vol. oi hydrogen gas, supplied
at the rate di 20 l/h, aiter which coolin~ was eiiected to room temperature
in a stream o$ pure nitrogen. The meAsurlng results are shown in the table,
Exp no. 2.
For the purpose Or ¢omparison catalysts were prepared according
to the process oi the Canadia~ patent application 247,496, stArting
rrom the iollowing aotlve carbons. CECA type CX, Carbopuron type 4N, '
:
~ Trade mark
10~8502
Carbopouron type 4N without basic hydrolysis and reduction, and Norit type
SX 2 in which latter case the reduction was carried out with hydrogen
(experiments 4, 5, 6 and ~ Likewise for comparison, a catalyst was prepared
according to the method described by Furuoya. The result obtained with this
catalyst is shown in the Table, exp. no. 3.
i
Table
xp.
no. Catalyst preparationBET surface Acidity Activity
g NH20H/g
area (m2/g) Pd/h
1. 1.9% wt Pd as Pd(NH3)4 1055 strongly acid 24.5
present on CECA CX, prepared
according to the invention
2 1.9~ wt Pd on CECA CX* pre-1055 strongly acid 20.5
pared by ion exchange and
i separate reduction with H2
i at 300C
3 10.7% wt Pd on CECA CX* prepared -
according to the method described 1055 strongly acid 2.6
by Furuoya `
~, ,
4 7% wt Pd on CECA CX* prepared 1055 strongly acid 18.9
according to Neth. patent
application 7,502,968
9.4% wt Pd on Carbopuron 4N* 895 weakly acid 19.9
prepared according to Neth.
patent application 7,502,968
6. 9.4% wt Pd on Carbopuron 4N* 895 weakly acid 6.3 - prepared according to Neth.
patent application 7,502,968
but with omission of the basic
hydrolysis and reduction
7 10.6% wt Pd on Norit SX-2* 1090 weakly acid 6.7
prepared according to Neth.
~ patent application 7,502,968
d ~ but with H2-reduction at 300C
~- Comparison of the results of experiment 1 (accordlng to the invention) with
~ :.
~-~; those of the other experiments ~accorting to known processes) shows that
; the process of the invention yields the most catalyst.
* Trade Mark
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I~ ~
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