Method of making activated carbon-supported catalysts

A method for making an activated carbon-supported catalyst involves providing an inorganic support having a continuous coating of activated carbon, activated carbon being derived from a synthetic carbon precursor, introducing a catalyst precursor into the pore structure of the activated carbon, and thermally treating the catalyst precursor to form an activated carbon-supported catalyst.

This invention relates to a method of making activated carbon-supported 
catalysts in which activated carbon derived from a synthetic carbon 
precursor is treated with a catalyst precursor. 
BACKGROUND OF THE INVENTION 
Metals such as transition metals, noble and base metals are used as 
catalysts in many chemical reactions. Catalysts generally increase the 
rate of chemical reaction which results in higher production rate in 
industry. Some catalysts are also used to drive reactions along a desired 
path, i.e., the catalysts make formation of certain chemicals 
energetically favorable over other chemicals. 
In general, catalysts are expensive, and hence it is necessary to utilize a 
given amount of catalyst to its maximum potential. This is done by 
maximizing the catalyst surface area, i.e., by increasing its dispersion. 
Catalysts can be used as solids or liquids. The solid catalysts are 
generally supported on high surface area supports. The properties of the 
support become very important in such cases. 
Activated carbon has also been used as a support for metal catalysts, e.g., 
noble metals, because of its very high surface area and other properties 
such as inertness. Such catalysts are used (powder or beads form) in 
various chemical and petrochemical reactions. These catalysts are normally 
made by dispersing noble metal particles on preformed activated carbon 
(incipient wetness technique). 
The incipient wetness technique involves dispersing the activated carbon 
powders in a solution of a metal salt. The activated carbon powder is then 
impregnated with the solution. The powder is dried, and heated to 
appropriate temperature to decompose the salt to the desired metal or 
metal oxide catalyst. Multiple impregnations are usually required to 
obtain the desired quantity of catalyst on the activated carbon. Surface 
properties of activated carbon powders play a very important part in the 
dispersion of the metal catalyst obtained. Oxygen content and surface pH 
of the carbon powder has to be carefully controlled to obtain a good 
dispersion of the metal on the activated carbon. The various steps that 
are involved in this process result in a very expensive activated carbon 
supported catalyst. Thus, it is important to maximize utilization of the 
catalyst. Although carbon supported catalysts are commercially utilized, 
performance improvements are always sought after. 
More recently, a method for producing a highly uniform dispersed catalyst 
on activated carbon is U.S. Pat. No. 5,488,023. This method involves 
combining a carbon precursor and a catalyst precursor, followed by curing, 
carbonizing, and activating the carbon precursor to produce a continuous 
uninterrupted activated carbon. The activated carbon with dispersed 
catalyst can be in the form of a coating on a substrate, granules, or a 
shaped monolithic body. 
Despite the advantages provided by this latter method of combining catalyst 
and carbon precursors, the types and amounts of catalyst precursors are 
limited because care must be taken that the carbon and catalyst precursors 
are compatible and that the carbon precursor solution is not overly 
diluted with the catalyst precursor. 
Therefore it would be advantageous to have a method of making an activated 
carbon supported catalyst that is flexible enough to accommodate a wide 
variety of metal catalysts and that produces a uniformly distributed 
catalyst. 
The present invention provides such a method. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the invention, there is provided a method 
for making an activated carbon-supported catalyst that involves providing 
an inorganic support having a continuous coating of activated carbon, the 
activated carbon being derived from a synthetic carbon precursor, 
introducing a catalyst precursor into the pore structure of the activated 
carbon, and thermally treating the catalyst precursor to form an activated 
carbon-supported catalyst.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to a catalyst and method of making it, in which a 
catalyst precursor is introduced into activated carbon that is coated onto 
an inorganic support. The activated carbon is derived from a carbon 
precursor, and therefore the activated carbon is continuous. The carbon 
precursor is synthetic. 
By carbon precursor is meant a carbon-containing substance that converts to 
continuous structure carbon on heating. The carbon precursor can include 
any liquid or liquefiable carbonaceous substance. Examples of useful 
carbon precursors include crosslinkable resins such as thermosetting 
resins, thermoplastic resins (e.g., polyvinylidene, polyvinyl chloride, 
polyvinyl alcohol, and the like), furfuryl alcohol, and coal tar pitch. 
Low viscosity carbon precursors (e.g., thermoset resins) are preferred 
especially when the precursor and catalyst are to be contacted with a 
substrate because their low viscosity allows greater penetration of the 
carbon precursor into the porosity of the substrate. Phenolic resins are 
most preferred due to their low viscosity, high carbon yield, high degree 
of cross-linking upon curing relative to other precursors, and low cost. 
Some phenolic resins that are especially suited are phenolic resole, 
plyophen (No. 43290), both supplied by Occidental Chemical Co., Niagara 
Falls, N.Y. 
The carbon precursor used In the present method can include a single 
precursor material or a mixture of two or more precursor materials. 
According to this invention, by activated carbon supported structure is 
meant that activated carbon is in contact with an inorganic material that 
supports it or gives it shape or strength. In a broad sense, the activated 
carbon can be thought of as a coating on the support or substrate. The 
resulting activated carbon coated support can take the form of powders, 
granules, or shapes such as pellets, or monoliths such as multicellular 
structures e.g. honeycombs. By monolith is meant a structure that 
functions in an application as a unitary or single body as opposed to 
multiple pieces that function in beds, such as granules, pellets, and 
powders. The activated carbon forms can be made by various techniques 
known in the art. 
For example, activated carbon coated substrates in which the activated 
carbon is derived from a carbon precursor are described in U.S. Pat. No. 
5,451,444 which is herein incorporated by reference. 
An activated carbon coating derived from a carbon precursor extends over 
the outer surface of a porous substrate in the form of a substantially 
uninterrupted layer of carbon. This continuous carbon coating is anchored 
into the porosity and, as a result, is highly adherent. If interconnecting 
porosity is present in the substrate, an interlocking network of carbon 
will be formed within the composite, resulting in an even more adherent 
carbon coating. The uninterrupted carbon provides advantages of high 
activity despite a relatively low carbon content, high strength, and high 
use temperatures. It is preferred that the coating be no greater than 
about 1 mm thick. This is in contrast to discontinuous coatings, derived 
from for example, a slurry of binder and activated carbon particles. In 
slurry-coated structures, activated carbon is bound to the binder which in 
turn is bound to the substrate. As a result, binder particles are 
necessarily interdispersed through the carbon coating, rendering it 
discontinuous. 
In general, activated carbon bodies or coatings derived from carbon 
precursors have distinct advantages over bodies and coatings made from 
activated carbon. Bodies made directly from activated carbon are made of 
discontinuous carbon which must be bound together by permanent binders; 
whereas resin-derived activated carbon bodies are made of continuous 
carbon and do not require permanent binders. This continuous carbon 
structure is strong and durable and can be used in high flow rate chemical 
processes. Such bodies also have durability in liquid streams. Bodies made 
from activated carbon particles are not durable in organic solvents and in 
many cases even in water, since the binder holding the structure together 
is water soluble. Coatings made of activated carbon particles are not as 
uniform or adherent as those derived from carbon precursors, and are more 
subject to erosion. 
It is desirable that the overall open porosity of the substrate be at least 
about 10%, preferably greater than about 25% and most preferably greater 
than about 40%. For most purposes, the desirable range of porosity is 
about 45% to about 55%. Preferably the pores of the substrate material 
create "interconnecting porosity" which is characterized by pores which 
connect into and/or intersect other pores to create a tortuous network of 
porosity within the substrate. 
The substrate must have enough strength to function in the application and 
be capable of withstanding the heat-treating temperature experienced in 
forming the activated carbon coating. 
In its most useful form, the substrate is a monolithic substrate. Typical 
monolithic substrates have means for passage of a fluid stream 
therethrough, e.g., a network of pores communicating from the outside to 
the inside, and/or through channels extending from one end of the monolith 
to the other for passage of the fluid stream into one end and out through 
the other end. 
Suitable porous substrate materials include ceramic, glass ceramic, glass, 
metal, clays, and combinations thereof. By combinations is meant physical 
or chemical combinations, eg., mixtures, compounds, or composites. 
Some materials that are especially suited to the practice of the present 
invention, although it is to be understood that the invention is not 
limited to such, are those made of cordierite, mullite, clay, magnesia, 
and metal oxides, talc, zircon, zirconia, zirconates, zirconia-spinel, 
magnesium alumino-silicates, spinel, alumina, silica, silicates, borides, 
alumino-silicates, eg., porcelains, lithium aluminosilicates, alumina 
silica, feldspar, titania, fused silica, nitrides, borides, carbides, eg., 
silicon carbide, silicon nitride or mixtures of these. Cordierite is 
preferred because its coefficient of thermal expansion is comparable to 
that of carbon, increasing the stability of the activated carbon body. 
Some typical ceramic substrates are disclosed in U.S. Pat. Nos. 4,127,691 
and 3,885,977. Those patents are W herein incorporated by reference as 
filed. 
Suitable metallic materials are any metal or alloy or intermetallic 
compound that provides durable structural service, and does not soften 
below about 600.degree. C. Particularly useful are alloys which are 
predominantly of iron group metal (i.e. Fe, Ni, and Co), either with 
carbon (e.g. steels, especially stainless or high temperature steels) or 
without carbon. Most typical of the latter alloys for higher temperature 
service are those consisting essentially of iron group metal and aluminum, 
with the preferred iron group metal being iron. Especially preferred is 
Fe, Al, and Cr. For example, Fe5-20Al5-40Cr, and Fe7-10All0-20Cr powders 
with other possible additions are especially suited. Some typical 
compositions of metal powders for forming substrates are disclosed in U.S. 
Pat. Nos. 4,992,233, 4,758,272, and 5,427,601 which are herein 
incorporated by reference as filed. U.S. Pat. Nos. 4,992,233 and 4,758,272 
relate to methods of producing porous sintered bodies made from metal 
powder compositions of Fe and Al with optional additions of Sn, Cu, and 
Cr. U.S. Pat. No. 5,427,601 relates to porous sintered bodies having a 
composition consisting essentially of in percent by weight about 5 to 40 
Cr, about 2 to 30 Al, 0 to about 5 of special metal, 0 to about 4 of rare 
earth oxide additive and the balance being iron group metal and 
unavoidable impurities, with the preferred iron group metal being iron. 
When rare earth oxide is present, the special metal is at least one of Y, 
lanthanides, Zr, Hf, Ti, Si, alkaline earth metal, B, Cu, and Sn. When no 
rare earth oxide is present, the special metal is at least one of Y, 
lanthanide, Zr, Hf, Ti, Si, and B, with optional additions of alkaline 
earths, Cu, and Sn. 
The substrate is preferably a honeycomb or matrix of thin walls forming a 
multiplicity of open ended cells extending between the ends of the 
honeycomb. 
Generally honeycomb cell densities range from 235 cells/cm.sup.2 (about 
1500 cells/in.sup.2) to 1 cell/cm.sup.2 (about 6 cells/in.sup.2). Some 
examples of commonly used honeycombs in addition to these, although it is 
to be understood that the invention is not limited to such, are about 94 
cells/cm.sup.2 (about 600 cells/in.sup.2), about 62 cells/cm.sup.2 (about 
400 cells/in.sup.2), or about 47 cells/cm.sup.2 (about 300 
cells/in.sup.2), and those having about 31 cells/cm.sup.2 (about 200 
cells/in.sup.2). Typical wall thicknesses are for example, about 0.15 mm 
for about 62 cells/cm.sup.2 (about 400 cells/in.sup.2) honeycombs. Wall 
(web) thicknesses range typically from about 0.1 to about 1.5 mm. The 
external size and shape of the body is controlled by the application. 
In another embodiment, coated monolithic substrates can be ground up to 
form granules. 
The activated carbon can be in the form of a shaped monolith. This can be 
done by known methods of shaping mixtures of carbon precursor, binders 
and/or fillers that are at least inorganic, and forming aids, such as by 
extrusion. The inorganic fillers can be considered to be the supports or 
substrates for the activated carbon. Optionally, there can be organic 
fillers, but these would not be considered to be supports or substrates 
according to this invention. 
Some fillers that are suited include both natural and synthetic, 
hydrophobic, and hydrophilic, fibrous and nonfibrous, carbonizable and 
non-carbonizable fillers. 
Some inorganic fillers that can be used are oxygen-containing minerals such 
as clays, zeolites, talc, etc., carbonates, such as calcium carbonate, 
aluminosilicates such as kaolin (an aluminosilicate clay), flyash (an 
aluminosilicate ash obtained after coal firing in power plants), 
silicates, e.g. wollastonite (calcium metasilicate), titanates, 
zirconates, zirconia, zirconia spinel, magnesium aluminum silicates, 
mullite, alumina, alumina trihydrate, spinel, feldspar, attapulgites, and 
aluminosilicate fibers, cordierite powder, etc. 
Some examples of especially suited inorganic fillers are cordierite powder, 
talcs, clays, and aluminosilicate fibers such as provided by Carborundum 
Co. Niagara Falls, N.Y. under the name of Fiberfax, and combinations of 
these. Fiberfax aluminosilicate fibers measure about 2-6 micrometers in 
diameter and about 20.degree.50 micrometers in length. 
For example some natural fillers are soft woods, e.g. pine, spruce, 
redwood, etc., hardwoods e.g. ash, beech, birch, maple, oak, etc., 
sawdust, shell fibers e.g. ground almond shell, coconut shell, apricot pit 
shell, peanut shell, pecan shell, walnut shell, etc., cotton fibers e.g. 
cotton flock, cotton fabric, cellulose fibers, cotton seed fiber, chopped 
vegetable fibers for example, hemp, coconut fiber, jute, sisal, and other 
materials such as corn cobs, citrus pulp (dried), soybean meal, peat moss, 
wheat flour, wool fibers, corn, potato, rice, tapioca, coal powder, 
activated carbon powder, etc. Some synthetic materials are regenerated 
cellulose, rayon fabric, cellophane, etc. 
Some examples of carbonizable fillers that are especially suited for liquid 
resins are cellulose, cotton, wood, and sisal, or combinations of these, 
all of which are preferably in the form of fibers. 
One especially suited carbonizable fiber filler is cellulose fiber as 
supplied by International Filler Corporation, North Tonawanda, N.Y. This 
material has the following sieve analysis: 1-2% on 40 mesh (420 
micrometers), 90-95% thru 100 mesh (149 micrometers), and 55-60% thru 200 
mesh (74 micrometer). 
Hydrophobic organic fillers provide additional support to the shaped 
structure and introduce wall porosity on carbonization because in general 
they leave very little carbon residue. Some hydrophobic organic fillers 
are polyacrylonitrile fibers, polyester fibers (flock), nylon fibers, 
polypropylene fibers (flock) or powder, acrylic fibers or powder, aramid 
fibers, polyvinyl alcohol, etc. 
Some binders that can be used are plasticizing temporary organic binders 
such as cellulose ethers. Some typical cellulose ethers are 
methylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose, 
hydroxybutyl methylcellulose, hydroxyethylcellulose, 
hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropyl 
methylcellulose, hydroxyethyl methylcellulose, sodium carboxy 
methylcellulose, and mixtures thereof. Methylcellulose and/or 
methylcellulose derivatives are especially suited as organic binders in 
the practice of the present invention with methylcellulose, hydroxypropyl 
methylcellulose, or combinations of these being preferred. 
Some binders and fillers that are especially suited are described in U.S. 
patent application Ser. No. 08/650,685, filed May 20, 1996. That 
application is herein incorporated by reference. 
Some forming e.g. extrusion aids are soaps, fatty acids such as oleic, 
linoleic acid, etc., polyoxyethylene stearate, etc. or combinations of 
these. Especially preferred is sodium stearate. Optimized amounts of 
extrusion aid(s) depend on the composition and binder 
Other additives that are useful for improving the extrusion and curing 
characteristics of the batch are phosphoric acid and oil. Phosphoric acid 
improves the cure rate and increases adsorption capacity. It is typically 
about 0.1% to 5 wt. % in the mixture. The oil addition aids in extrusion 
and results in increase in surface area and porosity. Oil is added 
typically at about 0.1 to 5 wt. % in the mixture. 
The oil must be water immiscible, so that with liquid resins it can form a 
stable emulsion. With solid resin, a suspension is formed. Some useful 
oils are petroleum oils with molecular weights from about 250 to 1000, 
containing paraffinic and/or aromatic and/or alicyclic compounds. So 
called paraffinic oils composed primarily of paraffinic and alicyclic 
structures are preferred. These can contain additives such as rust 
inhibitors or oxidation inhibitors such as are commonly present in 
commercially available oils. Some useful oil are 3 in 1 oil from 3M Co., 
or 3 in 1 household oil from Reckitt and Coleman In., Wayne, N.J. Other 
useful oils are synthetic oils based on poly alpha olefins, esters, 
polyalkylene glycols, polybutenes, silicones, polyphenyl ether, CTFE oils, 
and other commercially available oils. Vegetable oils such as sunflower 
oil, sesame oils peanut oil, etc. are also useful. Especially suited are 
oils having a viscosity of about 10 to 300 cps, and preferably about 10 to 
150 cps. 
The above ratios apply also to shaped activated carbon bodies. Generally 
the amount of activated carbon in the shaped body is about 10 to 98 wt %. 
The carbon precursor is then subjected to heat-treatments to convert the 
carbon precursor to continuous carbon (carbonize). The resulting carbon is 
then heat-treated to activate the carbon and produce an activated carbon 
structure. 
When the carbon precursor is a thermosetting resin, the carbon precursor is 
cured prior to activation and most typically prior to carbonization. The 
curing is accomplished typically by heating the precursor to temperatures 
of about 100.degree. C. to about 200.degree. C. for about 0.5 to about 5.0 
hours. Curing is generally performed in air at atmospheric pressures. When 
using certain precursors, (e.g., furfuryl alcohol) curing can be 
accomplished by adding a curing catalyst such as an acid catalyst at room 
temperature. 
Carbonization is the thermal decomposition of the carbonaceous material, 
thereby eliminating low molecular weight species (e.g., carbon dioxide, 
water, gaseous hydrocarbons, etc.) and producing a fixed carbon mass and a 
rudimentary pore structure in the carbon. 
Such conversion or carbonization of the cured carbon precursor is 
accomplished typically by heating to a temperature in the range of about 
600.degree. C. to about 1000.degree. C. for about 1 to about 10 hours in a 
reducing atmosphere (e.g. hydrogen), or inert atmosphere (e.g., nitrogen, 
argon, helium, etc.). 
Curing and carbonizing the carbon precursor results in substantially 
uninterrupted carbon. Where the carbon is in the form of a coating, the 
carbon coating is anchored into the porosity of the substrate and as a 
result is highly adherent. The top surface of the carbon coating is an 
uninterrupted layer of carbon to carbon bonds. If interconnecting porosity 
is present in the substrate, an interlocking network of carbon will be 
formed within the composition, resulting in an even more adherent carbon 
coating. The coating of uninterrupted carbon extending over the outer 
surface of the substrate provides a structure with advantages of high 
strength and high use temperatures, and high catalytic capability despite 
a relatively low carbon content. Structures can be formed which contain 
carbon in an amount less than and up to about 50% often less than and up 
to about 30% of the total weight of the substrate and carbon. 
The activating is done to substantially enhance the volume and to enlarge 
the diameter of the micropores formed during carbonization, as well as to 
create new porosity. Activation creates a high surface area and in turn 
imparts high adsorptive capability to the structure. Activation is done by 
known methods such as exposing the structure to an oxidizing agent such as 
steam, carbon dioxide, metal chloride (e.g., zinc chloride), phosphoric 
acid, at high temperatures (e.g., about 600.degree. C. to about 
1000.degree. C.). 
It has been found that fabricating the supported activated carbon from 
synthetic precursors on inorganic substrates results in a surprisingly 
different and unique nanostructure than is observed with activated carbon 
obtained from natural carbonaceous materials. This can be seen from a 
comparison of the Transmission Electron Micrographs shown as FIGS. 1 and 
3. FIG. 1 is activated carbon as a continuous coating derived from a 
synthetic carbon precursor, on an inorganic substrate. FIG. 3 is activated 
carbon derived from a natural source. The Micrograph of FIG. 1 is even 
different from that of FIG. 2 which is unsupported activated carbon 
derived from a synthetic carbon precursor. 
The TEM of the supported synthetic carbon shows a very regular structure of 
graphitic platelets with porosity in between. The pore width is uniform 
and of the order of about 0.8 nanometers, The Transmission Electron 
Micrographs of unsupported synthetic carbon and natural source based 
carbon both show random structure. The uniformity seen in the supported 
synthetic carbon is not present in this case, clearly showing the 
nanostructural differences. Such differences affect the distribution of 
catalysts on these forms and hence there functioning. Catalysts are more 
uniformly distributed on the activated carbon of FIG. 1 and hence function 
more efficiently. 
Furthermore, the method of producing the supported activated carbon 
according to this invention which requires already-formed continuous 
carbon offers greater flexibility as far as types and amounts of catalyst 
precursor, than first mixing the catalyst precursor with a carbon 
precursor (before carbonization and activation). In this latter process, 
the type and amount of catalyst precursor is somewhat dependent on the 
limits of solubility or miscibility of the catalyst precursor with the 
carbon precursor solution. If the catalyst and/or carbon precursor 
solutions are too dilute, the proper loading of carbon precursor and/or 
catalyst precursor will be limited. The method of the present invention 
removes those limitations because the amount of catalyst is not dependent 
on a carbon precursor solution but only on the available sites and surface 
chemistry on the already-formed continuous activated carbon. The 
substrates can be chemically or physically modified for the purpose of 
reaction without limitations that would be present if the catalyst were 
already present in the pores. 
The catalyst is chosen to fit the desired application, e.g., oil 
refinement, chemical synthesis, pollution abatement as automotive exhaust 
purification, etc. 
The catalyst precursor is most typically a compound e.g. organic or 
inorganic salt of a catalyst metal which decomposes to the catalyst metal 
or catalyst metal oxide on heating. Inorganic compounds can be e.g., 
oxides, salts such as chlorides, nitrates, carbonates, sulphates, complex 
ammonium salts, etc. Organic compounds can be e.g., organometallic salts 
of the appropriate type. 
Typical catalyst metals are transition metal, alkali metal, alkaline earth, 
or combinations of these. Most useful are the noble metals, base metals or 
any combination of these. Advantageously the catalyst metals are Pt, Pd, 
Rh, Zn, V, Ag, Au, Fe, Co, Cr, Ni, Mn, Cu, Li, Mg, Ba, Mo, Ru, Os, Ir, or 
combinations of these. Some examples of catalyst metals, although this 
list is not all inclusive, are V, Co, Cu, Ni or Fe oxides, for NO.sub.x 
and SO.sub.x conversion, noble metals and Cu, Zn, Co, Ni, Mn, Cr, Fe, for 
a variety of chemical reactions, etc. 
Prior to introducing the catalyst precursor into the pores of the above 
described forms of activated carbon, the surface of the activated carbon 
may need to be treated either physically to modify the surface chemistry 
of the carbon, by e.g. heat treatments, or chemically. 
Chemical treatment generates the anchor sites (chemisorption active sites) 
on the carbon surface to grasp or attract catalyst precursors in the 
liquid phase during catalyst preparation. As a result, catalyst precursors 
are chemically bonded to the carbon surface and therefore catalyst 
stability and chemically durability are improved. Typical treatments 
include oxidation such as gas phase oxidation in air or oxygen-containing 
gases and liquid phase oxidation in nitric acid, hydrogen peroxide, etc. 
to provide a highly oxygenated surface and/or other surface 
functionalities such as sulfur, nitrogen-containing groups via reaction in 
gas or liquid phase. These processes are not expected to alter the 
underlying nanostructure of the supported activated carbon. Depending upon 
the application, the surface functionality may be detrimental to catalytic 
reactions in some cases. If so, the surface functionality, particularly 
oxygen surface functional groups can be removed by thermal treatment in 
inert gases such as nitrogen, argon, helium; or hydrogen; or vacuum. 
The catalyst precursor is introduced into the pores of the above described 
forms of activated carbon treated as described above. The thin layer of 
activated carbon on the surface of the substrate results in very short 
mass transfer distance inside the pores. The catalyst precursor solutions 
thus penetrate the pores uniformly and the precursor is easily adsorbed on 
the entire internal (inside of the pores) and external surface of the 
activated carbon. In contrast, the catalyst precursors are not uniformly 
distributed on commercial microporous granular activated carbon due to 
long transport distance in each particle. 
Introducing the precursor into the pores of the activated carbon can be 
done by any one of several feasible techniques. 
One technique, for the purposes of this invention termed liquid 
infiltration, involves washing over dry activated carbon a solution of a 
metal salt dissolved in a solvent. The activated carbon is then removed 
from excess solution and placed in an oven to evaporate the solvent. The 
metal salt remains in the pore structure of the carbon and can be treated 
to form the catalyst metal. 
Another technique, termed the incipient wetness technique, which is the 
preferred method, differs from the liquid infiltration technique in a 
subtle way. The activated carbon is immersed in an appropriate amount of 
solvent, such as water. The activated carbon surface attracts the 
precursor solute from the solution into its micropores. After soaking, the 
activated carbon is dried. Thermal treatments to convert the precursor to 
the catalytically active phase completes the process. 
Sometimes hydrogen or other reducing agents are necessary to convert metal 
oxide to metallic phase if only the metallic phase is active in a 
reaction. 
The present invention has several advantages, namely, (1) when the carbon 
precursor is a liquid phase thermoset resin, such as a phenolic resin, it 
is highly amenable to making coatings on porous refractory supports, (2) 
when supported activated carbon is made as a coating on a monolithic 
substrate, it provides conductive layers that can be resistively heated to 
provide thermal energy for reactions, (3) the process is general for a 
wide range of precursors for many catalysts, (4) synthetic activated 
carbon provides unique nanostructural properties for catalytic reactions 
because of associated surface chemistry, (5) a very thin layer of 
activated carbon film, e.g. no greater than about 1 mm thick, provides not 
only efficient mass and heat transfer but also uniform distribution of 
catalyst throughout the carbon body, (6) the impurities are minimized 
because of use of a synthetic carbon precursor. 
To more fully illustrate the invention, the following non-limiting examples 
are presented. All parts, portions, and percentages are on a weight basis 
unless otherwise stated. 
A gas phase hydrogenation reaction, that of toluene hydrogenation was used 
to demonstrate the performance of the catalyst of the present invention 
because of the industrial importance of this reaction and because 
optimized commercial catalysts are available to compare the performance of 
the catalyst of the present invention with the industry standard. 
Experiments were carried out in a standard fixed bed reactor. Hydrogen is 
fed continuously, in amounts considerably in excess of stoichiometric 
amounts. Toluene is fed continuously by liquid syringe pump. The 
commercial carbon catalyst was about 40-60 mesh size. 
The reaction conditions were as follows. Temperatures are in degree Celsius 
unless otherwise stated. All the hydrogenation experiments were conducted 
in a reactor having about 1.27 cm (0.5") outside diameter and a length of 
about 45.72 cm (18"). The reactor was constructed from 316 stainless steel 
tubing, wall thickness of about 0.159 cm (0.0625"), I.D. about 0.953 cm 
(0.375"). The reactor volume was calculated based on the catalyst packed 
volume. For all the examples, the packed bed length was about 5.08 cm 
(about 2"). Void volume was filled with inert glass wool and 40-60 mesh 
cordierite. The resultant catalyst reaction volume was calculated to be 
about 3.62 cc, which is the value used for determining the contact time. 
The reactor was operated in a co-current horizontal flow mode. Liquid 
toluene and hydrogen were metered separately, and then introduced into a 
mixing tee at the base of the reactor. Intimate mixing, as well as 
preheating, was accomplished in the inert, packed bed section. Products as 
well as excess hydrogen and unreacted reactants flew into a heated 
six-port valco valve for complete composition analysis. 
The toluene was from 99.9% analytical grade toluene (Aldrich Chemical Co.). 
The hydrogen was from 99%+ purity hydrogen cylinders and then further 
purified by moisture and oxygen trap. The hydrogen feed rate was about 50 
cc/min (STP) which is equivalent to a hydrogen space-time of about 0.05 
minute at reaction conditions, i.e. 1 atm. and about 100.degree. C. 
Hydrogen space-time was about 0.05 minute. The unit in which the "Space 
Time Yield" is expressed in the examples is: Mol Product/g Pt/min. This is 
the yield of product based on equivalent weight of noble metal per unit 
time. 
Comparative Example 1 
A 1% Pt/carbon-supported commercial catalyst (1% Pt/C and about 10 mesh in 
particle size, optimized catalyst for hydrogenation) was provided in dried 
base, having a surface area of about 800 m.sup.2 /g and pore volume of 
about 0.6 c/g. After grinding into powder form (about 200 mesh) to 
increase the accessibility of the catalyst to the reactants, about 0.25 g 
of the catalyst mixed with about 2.10 g of about 40-60 mesh cordierite 
(total sample volume of about 3.62 cc) was charged to a 1.27 cm (0.5") 
diameter reactor. The sample was reduced by being first heated at about 
150.degree. C. in flowing N.sub.2 (50 cc/min) for one hour, then heated at 
about 150.degree. C. in flowing N.sub.2 /H.sub.2 (about 50:50 mole ratio, 
about 100 cc/min) for about 1 hour, and finally heated at about 
400.degree. C. in flowing N.sub.2 /H.sub.2 (about 50:50 mole ratio, about 
100 cc/min) for about 2 hours. This is the standard procedure used to 
reduce the catalyst. The sample was cooled rapidly to about 100.degree. C. 
in the N.sub.2 /H.sub.2 atmosphere. After at least 30 minutes in flowing 
N.sub.2 at about 100.degree. C., the toluene feed rate was adjusted to 
give contact time of about 6.0 hours (for example, a toluene feed rate of 
about 0.01 cc/min gives a contact time of about 6.0 hours) and the 
hydrogen flow rate adjusted to give a hydrogen space-time of about 0.05 
minute. The hydrogenation reaction was carried out at a reaction 
temperature of about 100.degree. C. The reaction product was sampled 
continuously to GC for analysis using a six-port gas phase automatic 
sampling valve. The reaction product distribution is an average of several 
measurements taken after steady-state conditions were reached. The 
conversion of toluene to methyl-cyclohexane was about 7.13%, corresponding 
to about 4.02.times.10.sup.-5 mol/g Pt/min. 
Comparative Example 2 
About 1% Pt/carbon-supported (1% Pt/C) and about 1% Pt/K-alumina supported 
commercial catalysts (both in powder form) were provided in dried base, 
having a surface area and pore volume of about 800 m.sup.2 /g of about 0.6 
cc/g (1% Pt/C) and about 230 m.sup.2 /g and about 0.5 cc/g (about 1% 
Pt/Al.sub.2 O.sub.3) respectively. About 0.25 g of tie catalyst mixed with 
about 2.10 g of about 40-60 mesh cordierite (total sample volume of about 
3.62 cc) was charged to a 1.27 cm (0.5") diameter reactor. Hydrogenation 
and catalyst pretreatment were carried out as described in Example 1. The 
result shows that the conversion of toluene to methyl-cyclohexane was 
about 3.87% and about 5.10% for 1% Pt/C and 1% Pt/Al.sub.2 O.sub.3 
respectively. They correspond to about 1.42.times.10.sup.-5 and about 
1.90.times.10.sup.-5 mol/g Pt/min in space-time yield. 
Comparative Example 3 
A 1.5% Pt/carbon-supported commercial catalyst (about 1.5% Pt/C, powder 
form) was provided in wet base, having a surface area of about 800 m.sup.2 
/g and pore volume of about 0.6 cc/g. The catalyst was dried under flowing 
N.sub.2 at about 100 ml/min at about 150.degree. C. for about 2 hours and 
cooled down to room temperature. About 0.16 g of the catalyst mixed with 
about 2.20 g of 40-60 mesh cordierite (total sample volume of about 3.62 
cc) was charged to a 1.27 cm (0.5") diameter reactor. Hydrogenation and 
catalyst pretreatment were conducted as described in Examples 1 and 2. The 
result shows that the conversion of toluene to methyl-cyclohexane was 
about 11.50% corresponding to 4.32.times.10.sup.-5 mol/g Pt/min. 
Inventive Example 1 
Carbon-impregnated honeycombs (CIH) were fabricated according to methods 
described in U.S. Pat. No. 5,451,444 by coating a thermosetting phenolic 
resole resin onto a cordierite honeycomb, which was then cured, 
carbonized, and activated at about 900.degree. C. in carbon dioxide until 
a burnoff on activation of about 19.8% was obtained. As FIG. 1 shows a 
unique regularly spaced graphitic platelet type microstructure with a 
platelet distance of about 0.7 to 1.5 nanometers as opposed to amorphous 
structures exhibited by other activated carbon forms. A comparison of 
FIGS. 1 and 3 shows the startling difference between the supported 
activated synthetic carbon of this invention and previously available 
activated carbon. The figures show the nanostructure of synthetic 
activated carbon grown on a support versus commercial carbon from natural 
sources. The carbon-impregnated honeycombs were then impregnated with Pt 
precursor using the incipient wetness impregnation method. Dihydrogen 
hexachloroplatinic acid was used as a Pt precursor. About 1% of Pt was 
loaded onto the carbon of the carbon-impregnated honeycomb, i.e., Pt to 
carbon weight ratio was about 0.01. The sample was dried in air at about 
120.degree. C. overnight. After calcination at about 400.degree. C. for 
about 2 hours in inert gases, the sample was cooled down to room 
temperature and stored in air for future use. The reason for using the 
Pt/C ratio of 0.01, which is identical to commercial Pt/C catalysts in 
Comparative Examples 1 and 2 is that the Pt/C ratio is a primary factor in 
determining Pt dispersion on carbon. 
Two pieces, about 1.20 g in total weight, of Pt-loaded carbon-impregnated 
honeycombs measuring about 9.5 mm (3/8") in diameter and about 2.54 cm 
(1") in height were charged into a 1.27 cm (0.5") diameter fixed bed 
reactor. The total amount of platinum in the two pieces of platinum-loaded 
honeycombs was equivalent to the amount of platinum charged in the reactor 
in Comparative Examples 1-3. Hydrogenation reaction with an appropriate 
pretreatment was carried out as described in Comparative Examples 1-3. The 
experimental results are given below. The carbon-impregnated honeycomb 
sample resulted in a yield of about 1.37.times.10.sup.-3 mole product/g 
Pt/min. 
It can be seen that the product yield (space time yield) over 
Pt-Carbon-impregnated honeycombs catalysts is about 5-10 times higher than 
the commercial catalysts described in Comparative Examples 1-3. The 
carbon-impregnated sample preparation parameters, in particular the 
burn-off levels, have a significant influence on their catalytic 
performance. 
Inventive Example 2 
A catalyst-impregnated CIH sample was prepared identical to Inventive 
Example 1, but with about 67.8%. burn-off on activation. This sample in 
the identical reaction carried out in Inventive Example 1 showed a 
conversion of toluene of about 3.83.times.10.sup.-4 mole product/g Pt/min, 
lower than Inventive Example 1, but significantly higher than all the 
commercial carbon supported catalysts of Comparative Examples 1-3. 
Inventive Example 3 
A catalyst sample similar to Inventive Example 2 but with about 30.3% 
activation burnoff was made and subjected to the same performance 
evaluation as in Inventive Example 1. The conversion was about 
3.08.times.10.sup.-3 mole product/g Pt/min. Again this is an order of 
magnitude greater than all the commercial catalysts of Comparative 
Examples 1-3. 
Inventive Example 4 
To evaluate the effect of catalyst physical shapes on its performance, the 
fresh catalyst sample in Inventive Example 3 was crushed into powder forms 
(about 200 mesh). Hydrogenation reaction with an appropriate pretreatment 
was carried out as described in Comparative Examples 1-3 and Inventive 
Examples 1--3. The result indicates that the conversion of toluene to 
methyl-cyclo-hexane was about 41.52%, corresponding to about 
1.66.times.10.sup.-3 mol/g Pt/min. The conversion obtained in this 
reaction with the powder form of the catalyst was about half of that 
obtained with the honeycomb form for the same conditions and weight of 
Inventive Example 3. This suggests that the monolithic shape is 
advantageous in catalytic reaction over packed bed reactor under identical 
conditions. 
This substantial improvement in performance is believed to be due to two 
factors. The first is the unusual nanostructure developed by this 
synthetic carbon as a result of deposition on a cordierite substrate. 
Another factor that causes the high performance is believed to be the thin 
layer of carbon-containing platinum that allows catalysts to be approached 
by the reactants with minimum diffusional resistance. FIGS. 1 and 3 show 
the difference between the nanostructures of the carbon utilized in this 
invention and the commercial carbon. The difference is because of the way 
the synthetic carbon is formed on the surface of a substrate versus 
commercial carbon formed from natural sources such as wood, etc. 
It should be understood that while the present invention has been described 
in detail with respect to certain illustrative and specific embodiments 
thereof, it should not be considered limited to such but may be used in 
other ways without departing from the spirit of the invention and the 
scope of the appended claims.