Abstract:
A combinatorial method is provided for the preparation and screening of heterogeneous catalysts. The method comprises the steps of: (I) providing a library of elemental catalysts; (II) reacting the catalysts with a carbon source to form product directly on the catalyst; and (III) screening the products to evaluate the catalysts.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Provisional Application No. 60/127,038 entitled “New Catalysts for Synthesis of Carbon Fibrils,” filed on Mar. 31, 1999 which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is related to a method for preparing and screening catalysts. In particular, the present invention is related to a combinatorial method for preparing and screening catalysts. 
     Combinatorial methods have been used extensively in the pharmaceutical industry. These methods can be an efficient and rapid way to synthesize and screen numerous different substances on a microscale. Combinatorial methods represent a systematic way to screen for potential drugs, catalysts and materials. Due to the miniaturization of the reaction with combinatorial chemistry, there are typically problems in translating reaction conditions and parameters from a microscale reaction to a corresponding macroscale reaction. 
     Heterogeneous catalysts have been found to be particularly useful in solid state reactions. In particular, metal alloys and elemental metals are used as heterogeneous catalysts to synthesize a variety of materials. However, most metal alloys and elemental metals are prone to oxidation. Thus, methods used to synthesize catalysts from metal alloys and elemental metals must be practiced in a controlled environment. 
     A multitude of combinations of metal alloys and elemental metals may be used to form catalysts. Therefore, the study of potential catalysts in the vast array of metal alloys and elemental metals may be a slow and tedious process. Due to the inefficiency of typical methods, new methods to discover catalysts are constantly being sought. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a combinatorial method for the preparation and screening of catalysts. In an exemplary embodiment, the method includes the steps of: 
     (I) providing a library of elemental catalysts; 
     (II) reacting the catalysts with a carbon source to form product directly on the catalyst; and 
     (III) screening the products to evaluate the catalysts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A combinatorial method has been discovered which enables rapid synthesis and screening of catalysts. The combinatorial method for the discovery of catalysts is a microscale reaction. The miniaturization of the reaction enables virtually any number of different catalysts to be screened at once making it an efficient method for discovery of new catalysts. The small scale of the reaction can have environmental benefits due to the amount of chemicals used which is usually in units of micrograms. It is both a faster and a cleaner way to do experiments in search of catalysts. “Catalysts” as used herein refer to elemental metals, metal alloys, or combinations thereof which are effective at catalytic levels for converting a reactive substrate to a product. In particular, the combinatorial method is used for discovering catalysts used for making carbon fibrils by a heterogeneously catalyzed process. 
     Carbon fibrils are microscopic fibers of carbon typically having a diameter in a range between about 1 nanometer and about 500 nanometers. In particular, it is preferable to synthesize carbon fibrils with a diameter in a range between about 10 nanometers and about 50 nanometers. The aspect ratio of length of the carbon fibril to the diameter of the carbon fibril is typically greater than about 100. 
     Combinatorial methods used for synthesizing catalysts for carbon fibril formation include a thin film catalysts library and a powder catalysts library. “Library” as used herein refers to two or more different catalysts placed on a substrate. The catalysts may be deposited on the substrate sequentially or preferably, simultaneously. “Substrate” as used herein refers to any material which supports a large collection of catalysts. There is typically a minimum interaction between the supported catalysts and substrate material during chemical reaction or synthesis. However, certain substrates which have been found to be catalytic substances may have a synergistic effect on the production of carbon fibrils. Typical substrates include ceramics, for example, alumina; glass; metals, for example, aluminum, stainless steel, copper, silver, gold, platinum, and brass; and single crystals, for example, quartz, magnesium oxide, silicon, sapphire, and lanthanum aluminate. 
     In a preferred embodiment, a thin film catalysts library is produced using a multiple gun sputtering deposition system. The multiple gun sputtering deposition system contains elemental metal or metal alloy source placed in each gun cavity. An electrical discharge can be created at each source by applying radio frequency (RF) or direct current (DC) power in a range between about 10 Watts and about 1,000 Watts through the sputter gun, which heats the elemental metal or metal alloy to form a metal plasma vapor. The metal vapor from the sputter gun is deposited onto the counter-facing substrate. The rate of the material deposition is dependent on the level of power input. The amount of material deposited can be altered by changing the amount of time the sputter gun is powered. By coupling thin film deposition from different sputter guns with different masking patterns from an array of deposition masks, a matrix library of thin film catalysts is created. Due to the multiplicity of the number of guns and hence, elemental metals and metal alloys which can be used, the possible compositions and stoichiometry of metals which are deposited on the substrate are countless thus allowing for exploration of a vast experimental space. With multiple sputtering guns, any combination of metals can be deposited on a substrate to form a thin film catalysts library. 
     In various embodiments, the thin film catalysts library is built with an in-vacuum feed-in system. This enables the metal alloy library to be made without breaking the vacuum to change sources and masks for the next deposition, which keeps the metals in an atmospherically controlled environment. In particular, the in-vacuum feed-in system is filled with a gas, for example, argon, helium, nitrogen, hydrogen, and mixtures thereof. The gas in the thin film catalysts library is hereinafter referred to as “sputtering gas”. The in-vacuum feed-in system increases the speed in the generation of libraries, and also prevents the formation of metal oxides from elemental metals and alloys which are sensitive to oxygen. Typically, the prevention of oxidation of the elemental metals and alloys is a concern but the in-vacuum feed-in system substantially inhibits the oxidation of metals and metal alloys. 
     Once the metal vapors are deposited on the substrate, the thin film catalysts library is typically thermally annealed. The library is heated to a temperature in a range between about 200° C. and about 1100° C., and preferably, to a temperature in a range between about 600° C. and about 800° C. The library is also typically in a non-organic gas environment to substantially prevent the oxidation of the elemental metals or metal alloys. Examples of typical gases include argon, helium, nitrogen, hydrogen and mixtures thereof. Although the invention is not dependent on theory, it is believed that the temperature and atmospheric conditions promote the interdiffusion of the combined metals to form catalysts. 
     An alternative manner for creating a catalysts library is through the use of a multiple channel liquid dispensing system. Each of an array of liquid dispensers can be individually controlled and programmed to dispense a liquid material. In preferred embodiments, the liquid dispensers are each filled with a soluble metal precursor such as a nitrate, acetate, or other aqueous soluble metal salt compound. An elemental metal, metal alloy or mixture thereof is carried in a soluble precursor. Once the soluble precursor or combination of soluble precursors comprising the elemental metal, metal alloy or combination thereof is deposited on the substrate as a liquid, the library is typically dried, calcined in air, and annealed in nitrogen, argon, helium, hydrogen, or combinations thereof to form an oxide-containing powder catalyst library. To synthesize metal or alloy materials from such oxide-containing powders, reducing (for example, using hydrogen, charcoal, or carbon monoxide) in a time range between about 0.5 hours and about 12 hours at a temperature in a range between about 300° C. and about 800° C. is found to be sufficient for most miniaturized samples in the library. By use of the soluble precursor, the oxidation of any elemental metal or alloy is not a problem. 
     Once the catalysts are formed, the library is placed in a suitable reactor, such as a chemical vapor deposition reactor. Typically, the catalysts on the substrate are placed in a reaction chamber, such as a fixed bed quartz tube reactor, at a temperature in a range between about 300° C. and about 1000° C., and preferably in a range between about 400° C. and about 700° C. Commonly, the reactor is initially filled with a non-organic gas in order to create a non-reactive atmosphere in the reaction chamber. In particular, the reactor is filled with a non-organic gas in order to create a non-oxidative environment such that the metal catalysts will not be oxidized. Typically, argon gas and hydrogen gas are used and are present in a volume ratio in a range between about 5.5:1 and about 1:1. A mixture of argon and hydrogen is most commonly used at a volume ratio of about 5:1 argon to hydrogen. When the organic vapor or reactant product of the organic vapor and non-organic gas under the process conditions come in contact with the catalysts, carbon fibrils may be synthesized. Due to the varying volume capacity of different reaction chambers, the flow rate can vary. Typically, the flow rate of the gas is such that it takes approximately 8 minutes to refresh the gas in the tube. 
     The reactor can be operated under a pressure in a range between about 1 torr and about 100 atmospheres. The synthesis is typically run at a pressure in a range between about 100 torr and about 10 atmospheres. 
     A carbon source (e.g., organic vapor) is released in the reactor and product, such as carbon fibrils, is formed directly on the library. Examples of organic vapors typically used in a chemical vapor deposition reactor include acetylene, ethylene, methane, benzene, carbon monoxide or mixtures thereof. Commonly, the organic vapor is mixed with one of the gases used to create a non-oxidative environment as mentioned above. Typically, a combination of ethylene gas with hydrogen gas is used at a volume ratio of 5:1. The flow rate of the vapor is such that it takes approximately 8 minutes to refresh the vapor in the tube. Carbon fibrils may also be synthesized by the reactant product of the gas and the organic vapor thereof under the process conditions. The formation of the product directly on the catalyst surface automatically accelerates the process of discovering catalysts. In addition, all the samples are integrated on the same library and may be simultaneously analyzed. 
     Screening for identity of product and efficiency of product formation can be done in several different ways. Examples include optical microscopy, electron microscopy, such as transmission electron microscopy and scanning electron microscopy, laser profilometry, X-ray diffraction, Raman scattering and high throughput x-ray diffraction. In particular, scanning electron microscopy is useful since yield and morphology may be assessed to identify promising catalysts. 
     By using combinatorial methods to discover heterogeneous catalysts, the rate of discovery compared to conventional methods may be orders of magnitude faster. Instead of examining each catalyst independently, a multitude of catalysts can be examined simultaneously. In addition, the controlled environment in which the catalysts are made ensures that the metals, metal alloys, and combinations thereof are not oxidized and the desired product can be obtained. 
    
    
     In order that those skilled in the art will be better able to practice the invention, the following examples are given by way of illustration and not by way of limitation. 
     EXAMPLE 1 
     A 128-membered thin film catalysts library was fabricated with four metals: iron, nickel, molybdenum, and chromium on a quartz substrate (2.54 centimeters×2.54 centimeters×0.5 millimeters) using an in-vacuum multiple gun sputtering deposition system with high purity (greater than 99.9%) argon as the sputtering gas. The catalysts were annealed at 200° C. for greater than 24 hours in a vacuum oven at a pressure around 10 torr. The library was then loaded into a chemical vapor deposition reactor which was free of any volatile materials, pumped to high vacuum (less than about 1 torr) and the reactor was flushed with a mixture of high purity (greater than 99.9%) hydrogen and high purity argon wherein the argon and hydrogen were in a volume ratio of about 5:1. The flow rate was such that it took about 8 minutes to refresh the gas in the tube. The temperature was slowly ramped up from room temperature to 500° C. and held at this temperature for about 12 hours before ramping up to a temperature of 600° C. at 2° C. per minute under the same gas flow. After further conditioning at 600° C. for an hour, the argon was switched off and replaced with a flow of ethylene. The volume ratio of ethylene to hydrogen was about 5:1. The library of catalysts was reacted for a half hour before the ethylene source was shut off and replaced with argon. Under a constant flow of argon and hydrogen, the furnace was then turned off and allowed to cool to room temperature before the library was taken out for analysis. 
     The thin film catalysts library was observed under a reflective optical microscope for the primary screen of catalyst candidates. Subsequently, scanning electron microscopy was used for secondary screening focusing on sample sites with adequate amount of carbon product. The following catalysts were shown to produce carbon fibrils by primary and secondary screening of the catalysts candidates: nickel and molybdenum; nickel and chromium; nickel, molybdenum and chromium; iron, nickel, and chromium; iron, nickel and molybdenum; and iron, nickel, molybdenum, and chromium. 
     EXAMPLE 2 
     A 128-membered powder catalysts library was fabricated with six metals: iron, cobalt, aluminum, zinc, chromium, and yttrium on a quartz substrate (2.54 centimeters×2.54 centimeters×0.5 millimeters) as seen in Table 1. Solutions of high purity metal nitrates (one molar in concentration) were used as metal precursors. Once the powder catalysts library was fabricated, the heterogeneous catalysts were annealed at 200° C. for greater than 24 hours in a vacuum oven (pressure about 10 torr). The library was then loaded into a chemical vapor deposition reactor which was free of any volatile materials, pumped to high vacuum (less than 1 torr), and the reactor was flushed with a mixture of high purity (greater than 99.9%) hydrogen and high purity (greater than 99.9%) argon into the tube wherein the argon to hydrogen volume ratio was about 5:1. The flow rate was such that it took about 8 minutes to refresh the gas in the tube. The temperature was slowly ramped up from room temperature to 500° C. The catalysts library was annealed for about 12 hours before ramping up the temperature to 600° C. at 2° C. per minute, under the same gas flow. After further annealing at a temperature of 600° C. for an hour, the argon was switched off and replaced with a flow of ethylene. The volume ratio of ethylene to hydrogen was about 5:1. The library of catalyst candidates was reacted for about 30 minutes before the ethylene source was shut off and replaced with argon. Under a constant flow of argon and hydrogen, the furnace was then turned off and allowed to cool to room temperature before the library was taken out for evaluation. 
     The powder library was observed under a reflective optical microscope for the primary screen of catalyst candidates. A secondary screen was made using scanning electron microscopy (SEM) focusing on sample sites with adequate amount of carbon product. The following catalysts were determined as catalysts which produced carbon fibrils: nickel and iron; cobalt and iron; chromium and cobalt; zinc and cobalt; nickel and cobalt; nickel and chromium; nickel and zinc; nickel and copper; cobalt and copper; and nickel and aluminum. 
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Fe4Fe2 
                 Co4Fe2 
                 Ni4Fe2 
                 Cr4Fe2 
                 Zn4Fe2 
                 Y4Fe2 
                 Cu4Fe2 
                 Al4Fe2 
               
               
                 Fe4Co2 
                 Co4Co2 
                 Ni4Co2 
                 Cr4Co2 
                 Zn4Co2 
                 Y4Co2 
                 Cu4Co2 
                 Al4Co2 
               
               
                 Fe4Ni2 
                 Co4Ni2 
                 Ni4Ni2 
                 Cr4Ni2 
                 Zn4Ni2 
                 Y4Ni2 
                 Cu4Ni2 
                 Al4Ni2 
               
               
                 Fe4Cr2 
                 Co4Cr2 
                 Ni4Cr2 
                 Cr4Cr2 
                 Zn4Cr2 
                 Y4Cr2 
                 Cu4Cr2 
                 Al4Cr2 
               
               
                 Fe4Zn2 
                 Co4Zn2 
                 Ni4Zn2 
                 Cr4Zn2 
                 Zn4Zn2 
                 Y4Zn2 
                 Cu4Zn2 
                 Al4Zn2 
               
               
                 Fe4Y2 
                 Co4Y2 
                 Ni4Y2 
                 Cr4Y2 
                 Zn4Y2 
                 Y4Y2 
                 Cu4Y2 
                 Al4Y2 
               
               
                 Fe4Cu2 
                 Co4Cu2 
                 Ni4Cu2 
                 Cr4Cu2 
                 Zn4Cu2 
                 Y4Cu2 
                 Cu4Cu2 
                 Al4Cu2 
               
               
                 Fe4Al2 
                 Co4Al2 
                 Ni4Al2 
                 Cr4Al2 
                 Al4Al2 
                 Y4Al2 
                 Cr4Al2 
                 Al4Al2 
               
               
                 Fe5Fe 
                 Co5Fe 
                 Ni5Fe 
                 Cr5Fe 
                 Zn5Fe 
                 Y5Fe 
                 Cu5Fe 
                 Al5Fe 
               
               
                 Fe5Co 
                 Co5Co 
                 Ni5Co 
                 Cr5Co 
                 Zn5Co 
                 Y5Co 
                 Cu5Co 
                 Al5Co 
               
               
                 Fe5Ni 
                 Co5Ni 
                 Ni5Ni 
                 Cr5Ni 
                 Zn5Ni 
                 Y5Ni 
                 Cu5Ni 
                 Al5Ni 
               
               
                 Fe5Cr 
                 Co5Cr 
                 Ni5Cr 
                 Cr5Cr 
                 Zn5Cr 
                 Y5Cr 
                 Cu5Cr 
                 Al5Cr 
               
               
                 Fe5Zn 
                 Co5Zn 
                 Ni5Zn 
                 Cr5Zn 
                 Zn5Zn 
                 Y5Zn 
                 Cu5Zn 
                 Al5Zn 
               
               
                 Fe5Y 
                 Co5Y 
                 Ni5Y 
                 Cr5Y 
                 Zn5Y 
                 Y5Y 
                 Cu5Y 
                 Al5Y 
               
               
                 Fe5Cu 
                 Co5Cu 
                 Ni5Cu 
                 Cr5Cu 
                 Zn5Cu 
                 Y5Cu 
                 Cu5Cu 
                 Al5Cu 
               
               
                 Fe5Al 
                 Co5Al 
                 Ni5Al 
                 Cr5Al 
                 Al5Al 
                 Y5Al 
                 Cu5Al 
                 Al5Al 
               
               
                   
               
               
                 The ratios of the metals are molar.  
               
             
          
         
       
     
     EXAMPLE 3 
     Using the method of Example 2, a 128-membered powder catalysts library was fabricated with eight metals: copper, iron, zinc, nickel, aluminum, cobalt, yttrium, and chromium on a quartz substrate (2.54 centimeters×2.54 centimeters×0.5 millimeters) as seen in Table 2. The following catalysts were shown to produce carbon fibrils: copper and iron; and aluminum and cobalt. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 Cu1.44Fe0.14 
                 Cu1.34Fe0.24 
                 Cu1.24Fe0.34 
                 Cu1.14Fe0.44 
               
               
                 Cu1.4Fe0.18 
                 Cu1.3Fe0.28 
                 Cu1.2Fe0.38 
                 Cu1.1Fe0.48 
               
               
                 Zn1.36Ni0.22 
                 Zn1.26Ni0.32 
                 Zn1.16Ni0.42 
                 Zn1.06Ni0.52 
               
               
                 Zn1.32Ni0.26 
                 Zn1.22Ni0.36 
                 Zn1.12Ni0.46 
                 Zn1.02Ni0.56 
               
               
                 Al1.28Co0.3 
                 Al1.18Co0.4 
                 Al1.08Co0.5 
                 Al0.98Co0.6 
               
               
                 Al1.24Co0.34 
                 Al1.14Co0.44 
                 Al1.04Co0.54 
                 Al0.94Co0.64 
               
               
                 Y1.2Cr0.38 
                 Y1.1Cr0.48 
                 Y1Cr0.58 
                 Y0.9Cr0.68 
               
               
                 Y1.16Cr0.42 
                 Y1.06Cr0.52 
                 Y0.96Cr0.62 
                 Y0.86Cr0.72 
               
               
                 Cr1.12Y0.46 
                 Cr1.02Y0.56 
                 Cr0.92Y0.66 
                 Cr0.82Y0.76 
               
               
                 Cr1.08Y0.5 
                 Cr0.98Y0.6 
                 Cr0.88Y0.7 
                 Cr0.78Y0.8 
               
               
                 Co1.04Al0.54 
                 Co0.94Al0.64 
                 Co0.84Al0.74 
                 Co0.74Al0.84 
               
               
                 Co1Al0.58 
                 Co0.9Al0.68 
                 Co0.8Al0.78 
                 Co0.7Al0.88 
               
               
                 Ni0.96Zn0.62 
                 Ni0.86Zn0.72 
                 Ni0.76Zn0.82 
                 Ni0.66Zn0.92 
               
               
                 Ni0.92Zn0.66 
                 Ni0.82Zn0.76 
                 Ni0.72Zn0.86 
                 Ni0.62Zn0.96 
               
               
                 Fe0.88Cu0.7 
                 Fe0.78Cu0.8 
                 Fe0.68Cu0.9 
                 Fe0.58Cu1 
               
               
                 Fe0.84Cu0.74 
                 Fe0.74Cu0.84 
                 Fe0.64Cu0.94 
                 Fe0.54Cu1.04 
               
               
                 Cu1.04Fe0.54 
                 Cu0.94Fe0.64 
                 Cu0.84Fe0.74 
                 Cu0.74Fe0.84 
               
               
                 Cu1Fe0.58 
                 Cu0.9Fe0.68 
                 Cu0.8Fe0.78 
                 Cu0.7Fe0.88 
               
               
                 Zn0.96Ni0.62 
                 Zn0.86Ni0.72 
                 Zn0.76Ni0.82 
                 Zn0.66Ni0.92 
               
               
                 Zn0.92Ni0.66 
                 Zn0.82Ni0.76 
                 Zr0.72Ni0.86 
                 Zn0.62Ni0.96 
               
               
                 Al0.88Co0.7 
                 Al0.78Co0.8 
                 Al0.68Co0.9 
                 Al0.58Co1 
               
               
                 Al0.84Co0.74 
                 Al0.74Co0.84 
                 Al0.64Co0.94 
                 Al0.54Co1.04 
               
               
                 Y0.8Cr0.7B 
                 Y0.7Cr0.88 
                 Y0.6Cr0.98 
                 Y0.5Cr1.08 
               
               
                 Y0.76Cr0.82 
                 Y0.66Cr0.92 
                 Y0.56Cr1.02 
                 Y0.46Cr1.12 
               
               
                 Cr0.72Y0.86 
                 Cr0.62Y0.96 
                 Cr0.52Y1.06 
                 Cr0.42Y1.16 
               
               
                 Cr0.68Y0.9 
                 Cr0.58Y1 
                 Cr0.48Y1.1 
                 Cr0.38Y1.2 
               
               
                 Co0.64Al0.94 
                 Co0.54Al1.04 
                 Co0.44Al1.14 
                 Co0.34Al1.24 
               
               
                 Co0.6Al0.98 
                 Co0.5Al1.08 
                 Co0.4Al1.18 
                 Co0.3Al1.28 
               
               
                 Ni0.56Zn1.02 
                 Ni0.46Zn1.12 
                 Ni0.36Zn1.22 
                 Ni0.26Zn1.32 
               
               
                 Ni0.52Zn1.06 
                 Ni0.42Zn1.16 
                 Ni0.32Zn1.26 
                 Ni0.22Zn1.36 
               
               
                 Fe0.48Cu1.1 
                 Fe0.3BCu1.2 
                 Fe0.28Cu1.3 
                 Fe0.18Cu1.4 
               
               
                 Fe0.44Cu1.14 
                 Fe0.34Cu1.24 
                 Fe0.24Cu1.34 
                 Fe0.14Cu1.44 
               
               
                   
               
               
                 * The ratios of the metals are molar.  
               
             
          
         
       
     
     EXAMPLE 4 
     Using the method of Example 2, a 128-membered powder library was fabricated with eight metals: copper, iron, zinc, nickel, aluminum, cobalt, yttrium, and chromium on a quartz substrate (2.54 centimeters×2.54 centimeters×0.5 millimeters) as seen in Table 3. The following catalysts produced carbon fibrils: cobalt, iron and copper; nickel, iron and yttrium; copper, iron, cobalt, and aluminum; cobalt and copper; zinc, cobalt, chromium, and copper; yttrium, cobalt, nickel, and copper; cobalt, nickel and copper; nickel, chromium, and yttrium; cobalt, zinc and copper; zinc, yttrium, chromium, and nickel; aluminum, iron, and nickel; nickel, iron, yttrium, and aluminum; nickel, cobalt, and copper; chromium and zinc; nickel and yttrium; and chromium, aluminum, and iron. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                 Fe4Fe2Al5 
                 Co4Fe2Cu5 
                 Ni4Fe2Y5 
                 Cr4Fe2Zn5 
               
               
                 Fe4Co2Al5 
                 Co4Co2Cu5 
                 Ni4Co2Y5 
                 Cr4Co2Zn5 
               
               
                 Fe4Ni2Al5 
                 Co4Ni2Cu5 
                 Ni4Ni2Y5 
                 Cr4Ni2Zn5 
               
               
                 Fe4Cr2Al5 
                 Co4Cr2Cu5 
                 Ni4Cr2Y5 
                 Cr4Cr2Zn5 
               
               
                 Fe4Zn2Al5 
                 Co4Zn2Cu5 
                 Ni4Zn2Y5 
                 Cr4Zn2Zn5 
               
               
                 Fe4Y2Al5 
                 Co4Y2Cu5 
                 Ni4Y2Y5 
                 Cr4Y2Zn5 
               
               
                 Fe4Cu2Al5 
                 Co4Cu2Cu5 
                 Ni4Cu2Y5 
                 Cr4Cu2Zn5 
               
               
                 Fe4Al2Al5 
                 Co4Al2Cu5 
                 Ni4Al2Y5 
                 Cr4Al2Al5 
               
               
                 Zn4Fe2Cr5 
                 Y4Fe2Ni5 
                 Cu4Fe2Co5 
                 Al4Fe2Fe5 
               
               
                 Zn4Co2Cr5 
                 Y4Co2Ni5 
                 Cu4Co2Co5 
                 Al4Co2Fe5 
               
               
                 Zn4Ni2Cr5 
                 Y4Ni2Ni5 
                 Cu4Ni2Co5 
                 Al4Ni2Fe5 
               
               
                 Zn4Cr2Cr5 
                 Y4Cr2Ni5 
                 Cu4Cr2Co5 
                 Al4Cr2Fe5 
               
               
                 Zn4Zn2Cr5 
                 Y4Zr2Ni5 
                 Cu4Zn2Co5 
                 Al4Zn2Fe5 
               
               
                 Zn4Y2Cr5 
                 Y4Y2Ni5 
                 Cu4Y2Co5 
                 Al4Y2Fe5 
               
               
                 Zn4Cu2Cr5 
                 Y4Cu2Ni5 
                 Cu4Cu2Co5 
                 Al4Cu2Fe5 
               
               
                 Zn5FeCr2.5Al2.5 
                 Y5FeNi2.5Al2.5 
                 Cu5FeCo2.5Al2.5 
                 Al5FeFe2.5Al2.5 
               
               
                 Zn5CoCr2.5Cu2.5 
                 Y5CoNi2.5Cu2.5 
                 Cu5CoCo2.5Cu2.5 
                 Al5CoFe2:5Cu2.5 
               
               
                 Zn5NiCr2.5Y2.5 
                 Y5NiNi2.5Y2.5 
                 Cu5NiCo2.5Y2.5 
                 Al5NiFe2.5Y2.5 
               
               
                 Zn5CrCr2.5Zn2.5 
                 Y5CrNi2.5Zn2.5 
                 Cu5CrCo2.5Zn2.5 
                 Al5CrFe2.5Zn2.5 
               
               
                 Zn5ZnCr2.5Cr2.5 
                 Y5ZnNi2.5Cr2.5 
                 Cu5ZnCo2.5Cr2.5 
                 Al5ZnFe2.5Cr2.5 
               
               
                 Zn5YCr2.5Ni2.5 
                 Y5YNi2.5Ni2.5 
                 Cu5YCo2.5Ni2.5 
                 Al5YFe2.5Ni2.5 
               
               
                 Zn5CuCr2.5Co2.5 
                 Y5CuNi2.5Co2.5 
                 Cu5CuCo2.5Co2.5 
                 Al5CuFe2.5Co2.5 
               
               
                 Al5AlCr2.5Fe2.5 
                 Y5AlNi2.5Fe2.5 
                 Cu5AlCo2.5Fe2.5 
                 Al5AlFe2.5Fe2.5 
               
               
                 Fe5FeAl2.5Al2.5 
                 Co5FeCu2.5Al2.5 
                 Ni5FeY2.5Al2.5 
                 Cr5FeZn2.5Al2.5 
               
               
                 Fe5CoAl2.5Cu2.5 
                 Co5CoCu2.5Cu2.5 
                 Ni5CoY2.5Cu2.5 
                 Cr5CoZn2.5Cu2.5 
               
               
                 Fe5NiAl2.5Y2.5 
                 Co5NiCu2.5Y2.5 
                 Ni5NiY2.5Y2.5 
                 Cr5NiZn2.5Y2.5 
               
               
                 Fe5CrAl2.5Zn2.5 
                 Co5CrCu2.5Zn2.5 
                 Ni5CrY2.5Zn2.5 
                 Cr5CrZn2.5Zn2.5 
               
               
                 Fe5ZnAl2.5Cr2.5 
                 Co5ZnCu2.5Cr2.5 
                 Ni5ZnY2.5Cr2.5 
                 Cr5ZnZn2.5Cr2.5 
               
               
                 Fe5YAl2.5Ni2.5 
                 Co5YCu2.5Ni2.5 
                 Ni5YY2.5Ni2.5 
                 Cr5YZn2.5Ni2.5 
               
               
                 Fe5CuAl2.5Co2.5 
                 Co5CuCu2.5Co2.5 
                 Ni5CuY2.5Co2.5 
                 Cr5CuZn2.5Co2.5 
               
               
                 Fe5AlAl2.5Fe2.5 
                 Co5AlCu2.5Fe2.5 
                 Ni5AlY2.5Fe2.5 
                 CrsAlAl2.5Fe2.5 
               
               
                 Al4Al2Cr5 
                 Y4Al2Ni5 
                 Co4Al2Co5 
                 Al4Al2Fe5 
               
               
                   
               
               
                 The ratios of the metals are molar.  
               
             
          
         
       
     
     It is evident that with the vast array of elemental metals and metal alloys, multiple catalysts can be fabricated and screened concurrently. The combinatorial method enables rapid discovery of the few catalysts which successfully produce carbon fibrils in an array of combinations of metals and metal alloys which do not produce carbon fibrils under the processing conditions. For instance, it was unexpectedly found that some iron combinations were ineffective catalysts for the production of carbon fibrils. Once catalysts have been determined, the catalysts can be produced on a macroscale. 
     While typical embodiments have been set forth for the purpose of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope of the invention. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present invention as defined by the following claims.