Note: Descriptions are shown in the official language in which they were submitted.
~3~z383
NOVEL TRANSITION METAL DICHALCOGENIDE CATALYSTS
FIELD OF ~HE INVENTIO~
This invention is directed to novel catalysts,
and more particularly novel flocculated supported
single-layered transition metal dichalcogenide cata-
lysts.
BACKGROVND OF THE INV~NTION
The preparation of high surface area catalysts
for use in oil refining, gasification of coal, or for
other reactions requiring catalytic surfaces, has been a
developing field for many years. Catalysts are pre-
sently prepared in many different ways. Hydrodesulfuri-
zation catalysts, for example, are usually prepared by
co-impregnating a suitable support (e.g. alumina) with a
salt (e.g. ammonium heptamolybdate) and a promoter (e.g.
a nickel or cobalt salt) followed by calcination. The
catalysts are then sulfided immediately prior to use.
There are several drawbacks and limitations to the
catalyst preparation processes which are presently
employed, one of which is high cost. Also, the number
of active sites per gram of catalyst is generally low,
thereby resulting in lo~ catalyst activity.
Another method for making catalysts involves
the exfoliation of a layered transition metal dichalco-
genide (e.g. molybdenum disulfide) containing an alkali
metal. Alkali metals can be introduced into transition
metal dichalcogenides in a number of ways. For example,
lithium can be introduced or "intercalated" by soaking
the layered compound in a solution of n-butyllithium in
hexane, as described by M.B. Dines in Materials Research
Bulletin, Vol. 10, pages 287-291 (1975) and in U.S.
Patent No. 3,933,688, issued in 1976. Other methods of
ff
13(~Z~3
obtaining a layered compolln~ with alkali metal between
the layers are, for example, intercalation of the
transition metal dichalcogenide with the alkali metal
from solution in liquid ammonia as described by W.
Rudorff in Chimia, Vol. 19, page 4~39 (1965), or by
electrointercalation in an electrochemical cell as
described by M.S. Whittingham in U.S. Patent No.
4,009,052, issued 1977, or R.R. Haering, J.A.R. Stiles
and K. Brandt in U.S. Patent No. 4,224,390, issued 1980,
or by exposing the layered compound to hot alkali metal
vapors as mentioned on page 308 of Intercalated Layered
Materials, edited by F. Levy (1979).
United States Patents Nos. 4,299,892, Dines et
al., November, 1981, and 4,323,480, Dines et al., April,
1982, are also of interest in this area.
SUMMARY OF THE INVENTION
A novel method of catalyst preparation which
is different from present techniques, and which can
produce extremely high active catalytic site densities,
is disclosed. The method utilizes a powder of a layered
transition metal dichalcogenide where the chalcogenide
is a sulfide which contains an al~ali metal between the
layers (e.g. molybdenum disulfide which contains
lithium)-
The powder is rapidly mixed with water orother suitable hydrogen generating liquid, sometimes
with A12O3 suspended in it. The layered material
exfoliates in the liquid. Vigorous agitation such as
ultrasonication or high-speed stirring may assist in
separating the layers. During exfoliation, a rapid
reaction of the alkali metal (e.g. lithium) with water
leads to hydrogen evolution between the planes of the
disulfide. The crystallites (grains of the powder) are
thereby "blown apart", that is, they "exfoliate" into
~3V;~ 3
"single layer" platelets comprised of one-layer units of
tlle original metal dichalcogenide. The particles of
exfoliated layered material and the particles of the
support substance adhere together, provided that the pH
of the solution is appropriately adjusted. Promoters
can also be added at this point. The material is washed
in water or other suitable liquid, and a dry powder is
recovered. This powder, consisting of an exfoliated
layered material on a support, is, with appropriate heat
treatments for activation, the equivalent of a sulfided
catalyst prepared by conventional means, but offers
equal or better surface area per gram of disulfide using
a procedure that is better understood and amenable to
variations.
lS The invention is directed to a process of
preparing a substance of the form:
MS2:Z
wherein MS2 is a single layer of a transition metal
disulfide (M being the transition metal and S being
sulfur) selected from the group consisting of MoS2,
TaS2, WS2; and Z is a suitable support substance
interspersed in the layers of MS2, which comprises:
(a) introducing an al~ali metal into MS2 in multi-
layer form in a dry environment such that the alkali
metal is substantially intercalated between the layers
of the MS2; (b) immersing the intercalated MS2 in a
reducible hydrogen generating solution to thereby cause
the layers of MS2 to separate; and (c) depositing the
exfoliated layers of MS2 on the support substance Z.
We also disclose a process of preparing a
substance of the form MS2:Y:Z wherein MS2 is a
single layer transition metal layered dichalcogenide
such as MoS2, TaS2, WS2; Y is a promoter sub-
stance; and Z is a support substance; which comprises:
(a) intercalating the MS2 in multi-layer form with an
-- 3
13(~Z~3~33
alkali metal in a dry environment such that the alkali
metal is substantially intercaLated between the layers
of the MS2; (b) immersing the intercalated MS2 in a
reducible hydrogen generating solution to thereby cause
the layers of MS2 to separate; and (c) mixing the
support su~stance and the promoter material in a first
solution; (d) subsequently mixing the first and second
solutions so as to simultaneously flocculate the MS2,
promoter material and support solution to form the
MS2:Y:Z compound.
We also disclose a process where the support
material Z is introduced by precipitation or aasorption
from solution using a technique similar to the inclusion
of Y above, which comprises: (a) intercalating the
MS2 in multi-layer form with an alkali metal in a dry
environment such that the alkali metal is substantially
intercalated between the layers of the MS2; (b)
immersing the intercalated MS2 in a reducible hydrogen
generating solution to thereby cause the layers of MS2
to separate; (c) mixing soluble salts of the support
material and (if desired) the promoter material in
separate solutions; and (d) subsequently mixing the
three solutions to flocculate the disulfide single
layers, the support material and (if desired) the
promoter material.
In all cases above, if the starting material
is a transition metal dichalcogenide w'nich already
contains an alkali metal, step (a) in the processes
described is omitted. In all cases above, the solids
are separated from the supernatant liquids, dried, and
activated by suitable high temperature treatments.
D~AWINGS
In the drawings:
Figure 1 illustrates a chart o~ temperature
~302~133
proc~rammed desorption (TPD) of various catalyst species
vs. catalytic activity of the catalyst in methanation.
Figure ~ illustrates the cross-sectional
configuration of a flocculated molybdenum disulfide-
alumina-promoter structure; and
Figure 3 illustrates the cross-sectional
configuration of a dried, calcined molybdenum
~oxysulfide)-nickel, alumina structure.
DETAILED DESCRIPTIO~ OF SPECIFIC
EMBODIMENTS OF THE INVENTIO~
We have developed a new form of single layer
transition metal dichalcogenide, particularly, molyb-
denum disulfide, MoS2, in the form of single molecular
layers suspended in aqueous solution. We have been able
to deposit these single layers onto aluminum oxide
(A1203) in several ways. Using semi-empirical
techniques and ideas based on models of what should be
useful confi~urations, we have been able to prepare
catalysts for the hydrogenation of CO (methanation
catalysts) which are three to ten times more active than
catalysts prepared by classical precipitation tech-
niques. Our invention has similar application to hydro-
desulfurization catalysts and catalysts for hydrogena-
tion of heavy oils, etc.
In the important application of MoS2 as a
hydrodesulfurization catalyst for the oil and coalindustries, it has been suggested in the literature that
the active sites for hydrodesulfurization are associated
with single layers of molybdenum disulfide on alumina
with cobalt atoms closely associated with each site.
With our new form of molybdenum disulfide, prepared
initially as single layers, it is possible to make a
highly concentrated, homogeneous array of such active
sites. ~le concentration of active sites per gram of
-- 5 --
13V2~3
cataLyst is much greater than is possible by the "acci-
dental" generation of such sites during the classical
precipitation methods of catalyst preparation now
followed.
Exfoliated MoS2 has been deposited on alu-
mina particles in aqueous suspension, enabling recovery
of dry exfoliated MoS2 supported on the alumina. With
no surfactant, it was found by experimentation that if
exfoliation tooX place in water in the presence of a
sufficient quantity of alumina powder, or if sufficient
alumina powder was introduced following exfoliation, the
suspension would clear in a few minutes, thereby imply-
ing deposition of the flakes of MoS2 nto the alumina
under conditions when the MoS2 Would not adhere to
itself ~flocculate). Deposition on alumina thus pro-
vides a method of removing the exfoliated MoS2 from
suspension without re-stacking by flocculation. Such
"supported" samples were washed to remove lithium
hydroxide, then dried.
The amount of alumina (1 ~icron diameter
powder) necessary to clear a suspension of exfoliated
MoS2 was such that the total area of the alumina was
approximately matched to half the total area of the
MoS2 (as calculated knowing the mass of MoS2 and
assuming single-layer dispersion). The suspension did
not clear if insufficient alumina was present, in~i-
cating that the alumina particles became covered with
monolayers of MoS2, and additional MoS2 particles
remained in suspension without adhering to the MoS2-
coated aLumina, or to other MoS2 Particles. Deposi-
tion of multilayers, if desired, was achieved at this
point in the process by lowering the pH to below 3 to
cause flocculation. Numerous samples of alumina-
supported MoS2 were prepared and varying amounts of
coverage were achieved using MoS2 monolayers and
~3(~2~3
multilayers. Typical proportions of MoS~ to alumina
were in the range 0.5% to 10~ MoS2 by mass.
As an initial step in the preparation of our
supported single-layer transition metal dichalcogenides,
and as a specific example, we have developed a new form
of exfoliated MoS2. In using the expression, "exfoli-
ated Mo52", we mean MoS2 suspended in aqueous solu-
tion in the form of single molecular layers, ready to
process in various configurations, including those most
suitable for a supported catalyst.
In the preparation of exfoliated MoS2, there
are several steps to perform. First, a commercial fine
MoS2 powder ttypically 1 micron size~ is intercalated
with lithium. In this step, the MoS2 powder is
suspended in a solution of n-butyllithium in hexane, in
an inert atmosphere (e.g., argon) in a dry box. After
soaking for a few hours to a day in this solution, the
lithium has penetrated between the layers of the layer
compound MoS2, that is, the lithium has "inter-
calated". The intercalated MoS2:Li is removed fromthe dry box while still protected from air and from
moisture and is then immersed in an a~ueous solution.
The intercalated lithium reacts with the water and
generates hydrogen. The ~enerated hydrogen gas pushes
the layers of the MoS2 apart such that the powder
essentially is "blown apart" by the hydrogen. Vigorous
agitation such as by ultrasonication or high-speed
stirring may assist in separating the layers. If the pH
is maintained at a value above about 3 the suspension
will not flocculate but will stay for days or more
suspended in water.
The next step is to process the exfoliated
MoS2, and several techniques have been developed. The
exact optimum procedures depend on the application of
interest in each case. For example, if the objective is
13~2;~3
to prepare a catalyst, then at this point the required
catalytic promoter can be added to the molybdenum
disulfide.
We have made extensive studies of the adsorp-
S tion of various hydroxylated cations on the surace of
the exfoliated MoS2 including the important promoters
cobalt (Co) and nickel (Ni) that are used in hydrodesul-
furization catalysis. If we adjust the p~ correctly, we
can induce adsorption of the cobalt or the nickel in the
form of a partial monolayer on the surface of the
molybdenum disulfide single layers, an arrangement that
should be close to ideal for catalytic activity. The
fact that the cobalt and nickel, presumably in the form
of hydroxides, are adsorbed as a partial monolayer is
simply demonstrated by restacking the MoS2 with the
monolayer still adsorbed ~this is done simply b~
centrifuging out the material and drying) upon which it
is determined by X-ray diffraction that the spacing
between the layers has decreased by 8 to 10 percent.
We have termed such structures "inclusion compounds`'~
The cobalt or the nickel monolayer acts to bind the
MoS2 layers more tightly than they would be bound with
just the normal van der Waals attraction of the
crystal.
Alternatively, if the solution reaches a pH at
which precipitation of the hydroxide normally occurs, we
can deposit clusters of Co(OH)2 Or Ni(OH)2 On the
MoS2 layers. It has been -Eound that the inclusion of
some heavy atoms or precipitate particles increases the
surface area of the MoS2 Substantially. This is
attributed to the separation of the layers (sometimes
observed by X-ray diEfraction) allowing gases (in
particular, nitrogen ~as for the BET measurements) to
penetrate and measure the entire surface area of the
MoS2 plus clusters.
~3~2~B3
The include~ material can alternative~y be
aluminum hydroxide introduced as aluminum nitrate, with
the 10cculation of MoS2 onto monolayers of aluminum
hydroxide or clusters of aluminum hydroxide. In such a
case, the aluminum compounds so introduced can be used
as the "support".
- In the preparation of this new MoS2 form as
a catalyst, the MoS2 is interspersed with alumina that
is suspended in the solution or added to the solution.
We have discovered that in an intermediate p~ region,
that is a region where neither the MoS2 nor the
A1203 alone will ~locculate, a mixture of MoS2 and
A1203 Will flocculate. This is entirely unexpected.
We have concluded that the MoS2 adsorbs on the alumina
as a single layer, or (with fine A1203 of particle
size less than the diameter of the MoS2 layers) the
A1203 deposits on the monolayers of ~10S2, forming
aggregates as indicated by Figure 2. There are two
pieces of evidence for this conclusion. First, because
the MoS2 will not adhere to itself (will not floccu-
late), then when the alumina becomes covered by a single
layer of MoS2 a second layer of MoS2 is not expected
to deposit on the first. When another particle of
alumina deposits on the flocculate, then another layer
of MoS2 can deposit. Second, the suspension clears
(everything settles out) with one micron alumina parti-
cles when the MoS2 percentage by weight is less than
2%, but the suspension does not clear if the MoS2
percentage by weig~t is greater than 5%. This percent-
age is essentially the amount of MoS2 necessary toform a monolayer on the alumina particles, and confir~s
the fact that if there is too much MoS2 to form a
monolayer (greater than a few percent) the excess MoS2
stays in suspension.
~3~2~83
This ability to form monolayers of MoS~ on
alumina (or monolayers of MoS2 separated by fine
alumina particles) is considered extremely important in
the preparation of catalysts, both because (as discussed
below) we have made exceptionally active catalysts using
monolayexs on A1203 or NiO, or both, and because
models of hydrodesulfurization catalysis suggest mono-
layer MoS2 is exceptionally active.
Preparation of Catalyst
We have studied the preparation of the new
catalyst ta optimize the hydrogenation of CO (the
methanation reaction). Using the techniques described
above, we have studied the reactivity of MoS2 without
alumina and as single layers on alumina and in many
intermediate forms. We have introduced promoters in the
form of inclusion compounds.
We have compared the catalytic activity for
methanation using exfoliated MoS2 with various formu-
2~ lations including flocculated MoS2, precipitated (fromammonium heptamolybdate) MoS2. precipitated or
adsorbed nickel, or combinations of flocculated or
precipitated MoS2 and nickel on alumina. Figure 1
shows results that summarize many of the measurements.
Figure 1 represents a plot of the active surface area
determined from temperature programmed desorption (TPD)
of various species from the catalyst vs. the catalytic
activity of the catalyst in methanation. The type of
preparation for each of the points is indicated on the
curve. The most important result of Figure 1 from the
point of view of the present disclosure is the fact that
the catalytic activity changes dramatically with the
various forms of preparation and the catalytic activity
can be compared for these various forms of preparation.
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13~1Z3~;~
As a basic reference point, the catalytic
activity for various ~ormulations without nickeL present
as a promoter can be seen in Figure 1. From this we can
compare the best exfoliated MoS2 sample (supported on
alumina) which is Sample #2, where 30~ MoS2 is exfoli-
ated on 500 A A1203. Sample #2 can be com-
pared to Samples #10 or #11, where the 30% molybdenum
disulfide is prepared by precipitation from ammonium
heptamolybdate, Sample ~10 giving the catalytic activity
in the oxide form, Sample #11 the catalytic activity in
sulfided form. A factor of ten improvement in catalytic
activity for the catalyst based on exfoliated MoS2 can
be observed.
Further, we can compare the activity of cata-
lysts that include nickel. For example, Sample ~8,which is a commercial catalyst with nickel and MoO3
supported on alumina to give a high activity in hydro-
genation catalysis, can be compared to Samples #13 or
#14 using the exfoliated ~oS2 with nickel. Again, we
find a factor of five or more increase in catalytic
activity for the catalysts based on exfoliated MoS2.
In this case it may be due to an improvement in the
dispersion of the nickel.
It is clear from the foregoing results that by
using exfoliated MoS2 as the starting material and
suitably preparing the catalyst one can obtain a supe-
rior catalyst over that prepared by the standard preci-
pitated MoS2 from ammonium heptamolybdate, both in the
case of promoted and non- promoted catalysts. We fully
expect that novel superior catalysts for hydrodesulfuri-
zation can be prepared using similar techniques.
From the literature on hydrodesulfurization
catalysts, the claim is that monolayer deposits of
MoS2 on alumina with a promoter present provide the
most active sites. Of course, with the normal way of
13(~Z~3
preparing the catalysts (co-precipitation of Mo and the
promoter), there is little control over such sites, for
the materials deposit as crystallites. Chemists have
concluded that where there happens to be a single atom
of Mo on the Al of the A12O3, the site is specially
active. With our process of exfoliation and floccula-
tion in the form of single MoS2 layers, we have
developed the ability in principle to make every site on
the A1203 a "single atom" site. To obtain the
greatest number of such sites, one wants ultra-fine
alumina (the alumina we have used for our experiments is
of the order of 300A to 500A diameter). We
concluded that the optimum configuration of the material
after flocculation should be the form shown in Figure 2.
To achieve this form, we have combined two processes
such that they will occur simultaneously, namely,
adsorption of the promoter (nickel from the nitrate,
depositing as Ni(O~1)2), ~nd deposition of the fine
alumina particles on the single layers of MoS2.
Either of these processes could cause flocculation if
the pH level is correctly adjusted. The requirement is
that both occur simultaneously and the whole mass
flocculate together.
We have found by experiment that at pH 6.2, a
mixture of the MoS2 and the alumina will flocculate,
although neither will settle out by itself. The alumina
particles bind the MoS2 layers together until the mass
reaches a few thousand angstroms in diameter and is
large enough to flocculate. Also at pH 6.2, the mixture
Of Ni(N03)2 and MoS2 will flocculate; again it is
presumed that the monolayer of ~i(OH)2 binds the
MoS2 single layers together. At this particular pH,
both flocculations occur at about the same rate, w'nich
is desirable in order to achieve the configuration s'nown
in Figure 2.
~3~Z~t5 3
To induce "simultaneous flocculation", we have
prepared the alumina suspension in a nickel nitrate
solution and have care~ully adjusted the pH to 6.2. In
a separate container, we have exfoliated the MoS2, and
adjusted its pH to 6.2. The two suspensions were then
mixed and flocculation followed.
After flocculation, the sample was dried and
calcined at 500C (heated in oxygen), a process that
converts much of the sulfide to an oxide. We believe
this leads to a much stronger interaction between the
Al, the Mo, and the Ni. We believe the configuration is
that shown in Figure 3, especially after a final hydro-
gen treatment at 5S0C. The configuration shown in
Figure 3 gives complete coverage on the A1203 of the
favoured Al/Mo/Ni sites and at the same time breaks up
the MoS2 layers so that there is rapid access for the
gases to be reacted (in the present case CO and H2 to
make CH4).
Experimentally, we have found that our proce-
dure provides five to ten times the catalytic activity -
of any of the other treatments tested at temperatures
between 300 to 400~C, as indicated in Figure 1. The
samples under discussion are those marXed #15 in Figure
1. Examples of experimental procedure and the resulting
improvements are discussed below.
Example 1
Layers Deposited on Alumina
We have found that adding 0.3 g
gamma-A12O3 from Cabot Corporation (Alon
gamma-alumina) of 300-500 A diameter to 100 ml H2O
yields a suspension that is acidic with a pH of about
3.9. The pH of this suspension was raised to pH 6.4 by
adding droplets of a 0.1 molar solution of NaOH and
stirring well. The pH was maintained well below pH 9 to
- 13 -
~3C~Z~3
avo;d rapid flocculation. Intercalated MoS2 with Li,
MoS2:Li, was formed by adding 1 g MoS2 powder to 50
ml of 2.5 molar solution n-butyllithium dissolved in
hexane, the procedure being performed in an argon
S atmosphere (in a dry box). After soaking for two days,
the supernatant hexane was poured off, the vial of
- MoS2:Li was washed twice with hexane, and the vial was
stoppered. The powder, removed from the dry box,
stoppered to preclude attack by air or water vapour, was
inserted in 100 ml H2O, resulting in copious gas
evolution and resulting in exfoliation of the MoS2
into a single-layer suspension of MoS2 (as determined
by X-rays, P. Joensen, R.F. Frindt and S.R. Morrison,
Mat. Res. Bull. 21 457 (1986)) in a solution of LioH at
a pH of the order of 12. The pH of the suspension was
lowered to 6.4 by adding dilute HN03 as required.
This suspension was then mixed with the suspension of
A12O3.
The procedure for mixing the two suspensions
was as follows. About 50 ml of deionized water in a
container was stirred with a magnetic stirrer. The two
100 ml suspensions prepared as above at pH 6.4 in two
different containers were simultaneously poured into the
stirred ~2 After a few minutes, when the liquids
were well mixed, the stirring was stopped. Within one
to two minutes, the solution began to clear, an indica-
tion of the completeness of the attraction between the
MoS2 and the alumina and the beginning of floccula-
tion. In about five to ten ~intues, the whole mixture
totally flocculated. The clear supernatant solution was
then removed and the flocculated precipitate was re-
covered and washed twice in deionized water. The sample
was dried at 60C in air, then inserted into an appara-
tus designed to measure the catalytic activity, calcined
at 500C and reduced in forming gas at 550C. The
- 14 -
1 3~I Zr ~
sample was then tested for catalytic activity, with the
result indicated in Figure 1, Sample #1.
Example 2
MoS? with Included Nickel (No Alumina)
As a second example, we describe the prepara-
tion of Sample #13 of Figure 1. A 10 ml 0.1 molar
solution of Ni(NO3)2-6E~2O (29 g/l~ was prepared.
The solution was acidic with a pH of 4.2. This pH was
raised to 6.2 by adding a 0.1 molar solution of NaOH.
At a pH of 6.6, the solution was found to become cloudy
and a further increase in pH caused the Ni(OH)2 to
precipitate. Because we wanted a solution, not a
suspension, we stopped at a pH of 6.2 + 2 percent.
1 g MoS2 as a suspension of single layers in 100 ml
H2O, prepared as in Example 1, with an adjusted pH of
6.2, was mixed with the above nickel solution in the
same manner as described in Example 1. The suspension
cleared and the Ni-included MoS2 precipitate was
recovered and washed twice with deionized water. The
presence of the nickel was confirmed by an electron
microprobe measurement. As in Example 1, the material
was calcined at 500~C in air, reduced at 550C in E12,
and tested for catalytic activity with the results given
in Figure 1, Sample #13.
Example 3
Promoter ~i Included with MoS~
Single Layers on Alumina
This method was used to prepare the highly
active Sample #15 of Figure 1. A hydroxylated nickel
solution (30 ml) was prepared as in Example 2 with a pH
of 6.2. The pH of the alumina suspension (0.3 g in 100
ml), prepared as in ~.xample 1, was adjusted to 6.2. The
two liquids were mixed. A suspension of single layer
MoS2 (1 g in 100 ml) was prepared as in Example 1.
~3(~231~3
The A12O3/Ni suspensiorl and the MoS2 suspension
were then mixed as described in Example 1 and the solu-
tion cleared in about five minutes. The sample was
dried, calcined, and reduced as in Example 1. The
sample was tested for catalytic activity with the
results shown for Sample #15 of Figure 1.
Example 4
Precipitated Alumina on Single-Layer MoS~
10100 ml of 0.1 molar Al(~03)3 gH2O was
prepared (3.75 g aluminum nitrate in 100 ml ~2) The
solution was acidic with a pH value of 3.1. The pH was
raised slowly with a 0.5 molar ~aOH solution at a rate
of one drop per hour while stirring thoroughly with a
magnetic stirrer. After several days at a pH value of
about 4.8, we found that the Al(OH)3 precipitated, so
to prevent this, the pH was allowed to rise only to 4.4
2 percent. It was then mixed with the MoS2 single
layer suspension (1 g in 100 ml) as described in Example
2, but with the pH of the MoS2 only lowered to a p~ of
8.5. The pH of the mixture remained at 4.4. The
mixture flocculated in ten to twenty hours. The preci-
pitates were washed, dried and further processed. In
this case, the calcining step was omitted. The sample
was exposed to forming gas at 530C. Two samples were
made, one with an Al:Mo ratio of 0.7 (as measured by
electron microprobe) and one with an Al:Mo ratio of 1.1.
In the former case, the TP~ of CO was enhanced by a
factor of 10 over Sample #4 in Figure 1, and in the
latter case, the TPD of 2 was enhanced by a factor of
30 over Sample ~4 in Figure 1. Thus the samples
provided large adsorption of the gases of interest in
catalysis. With the sample where the CO adsorption was
enhanced, the catalytic activity for methanation was
increased a factor of 100 over that of Sample ~4, Figure
Z;~83
1, where the MoS2/A12O3 (atomic percent) is the
same.
As will be apparent to those skilled in the
art in the light of the foregoing disclosure, many
alterations and modifications are possible in the
practice of this invention without departing from the
spirit or scope thereof. Accordingly, the scope of the
invention is to be construed in accordance with the
substance defined by the following claims.
