Methods for preparing catalysts supported on carbon nanotube networks

Abstract

A new method for preparing a supported catalyst is herein provided. The supported catalyst comprises a carbon nanotube network structure containing metal catalysts. The metal catalyst may be loaded onto functionalized carbon nanotubes before forming the carbon nanotube network structure. Alternatively, the metal catalyst may be loaded onto the carbon nanotube network structures themselves.

Description

CROSS REFERENCE INFORMATION [0001] This application claims benefit to and priority of U.S. Provisional Application No. 60 / 628,469, filed Nov. 16, 2004, which is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION [0002] The invention relates to a composition of supported catalyst comprising networks of carbon nanotubes. The catalysts or catalyst precursor may be predeposited onto the carbon nanotube followed by formation of the carbon nanotube network structure with the predeposited or metal loaded carbon nanotube. Alternatively, the catalysts or catalyst precursor may be deposited onto the carbon nanotube after the formation of the carbon nanotube network structure. Whether the catalyst is deposited prior to or after the formation of the carbon nanotube network structure, the result of the present invention is a supported catalyst comprising a carbon nanotube network structure with metal catalysts more evenly and thoroughly dispersed in the structure. As such, t...

AI Technical Summary

Benefits of technology

[0033] Catalysts or catalyst precursors useful in the methods of the present invention include, but are not limited to, metals such as ruthenium, osmium, rhodium, iridium, palladium, platinum or a mixture thereof, as well as metal oxides, metal halides, metal carbides, metal nitrides, metal phosphides and metal sulfides of other transition metals including but not limited to Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, W or combinations thereof. The metal catalysts or metal catalyst precursors may be loaded onto the nanotubes by any known method, such as ion exchange, impregnation, or incipient wetness, precipitation, physical or chemical adsorption or co-precipitation. In an exemplary embodiment, the metal catalysts are predeposited or loaded onto the functionalized carbon nanotubes by ion exchange, i.e. mixing a solution containing salts of said metal catalysts with the functionalized carbon nanotubes, allowing the salts to react with the functional groups of the functionalized nanotubes and evaporating the remaining solution (e.g., the excess solvent from the solution ). Alternatively, the metal catalysts are predeposited or loaded onto carbon nanotubes by impregnation, or incipient wetness, i.e. wetting a mass of carbon nanotubes with a solution of metal salts and evaporating the solvent. Alternatively, metal salts may be caused to precipitate from solution in the presence of a mass of carbon nanotubes causing said precipitated metal salts to physically or chemically adsorb on said nanotubes, followed by evaporation of the solvent.

Problems solved by technology

Because heterogeneous reactions are normally carried out at elevated temperatures (and sometimes at elevated pressures as well) and in a reactive atmosphere, the exact chemical nature of the active catalyst component within the reaction zone can be difficult to determine.

These pores can be inaccessible because of diffusion limitations.

The cost of replacing attritted catalyst, the cost of separating it from the reaction mixture and the risk of contaminating the product are all burdens upon the process.

In slurry phase, e.g., where the solid supported catalyst is filtered from the process stream and recycled to the reaction zone, the attritted fines may plug the filters and disrupt the process.

In the case of a catalyst support, this is even more important since the support is a potential source of contamination both to the catalyst it supports and to the chemical process.

Further, some catalysts are particularly sensitive to contamination that can either promote unwanted competing reactions, i.e., affect its selectivity, or render the catalyst ineffective, i.e., “poison” it.

Carbons of agricultural origin may contain these contaminants as well as metals common to biological systems and may be undesirable for that reason.

Furthermore, supported catalysts which have catalytic materials more evenly dispersed throughout or within the support generally have higher yield and catalytic activity than supported catalysts which have poor distribution of the catalytic material in or on the support.

These differences, among others, make graphite and carbon black poor predictors of carbon nanotube chemistry.

While activated charcoals and other materials have been used as catalysts and catalyst supports, none have heretofore had all of the requisite qualities of high surface area, porosity, pore size distribution, resistance to attrition and purity for the conduct of a variety of selected petrochemical and refining processes as compared to carbon nanotube structures.

Furthermore, unlike carbon nanotube structures, much of the surface area in activated charcoals and other materials is in the form of inaccessible micropores.

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