Chemistry: fischer-tropsch processes; or purification or recover – Group viii metal containing catalyst utilized for the...
Reexamination Certificate
2001-12-21
2004-03-30
Parsa, J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Group viii metal containing catalyst utilized for the...
C518S700000
Reexamination Certificate
active
06713519
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to catalysts containing carbon nanotubes, methods of making catalysts containing carbon nanotubes on porous substrates, systems employing carbon-nanotube-containing catalysts, and reactions catalyzed in porous carbon nanotube-containing catalysts.
INTRODUCTION
Catalysts are crucially important in controlling chemical reactions in virtually all aspects of our lives. For example, catalysts are used to lower the temperature, increase the rate, and control the products in chemical reactions. While catalysts can be liquids or gases, solid catalysts are especially attractive for commercial applications because they are easy to store and transport, are readily separated from product streams, tend to be more environmentally benign, and can provide superior performance and greater control of a reaction.
A well-known problem with solid catalysts is slow heat and/or mass transfer. That is, with solid catalysts and systems employing solid catalysts, the speed of a chemical reaction can be limited by the time necessary for heat to travel to or from the catalyst or by the time needed for chemicals to get to and from the catalyst.
For many years, scientists and engineers have sought better catalyst materials with improved heat and/or mass transport properties. While there are probably thousands of publications and patents that address these problems, two recent patents are discussed herein.
In one approach, van Wingerden et al., in U.S. Pat. No. 6,099,965, described methods of making catalysts having desirable heat transport properties. In one example, particles of an iron-chromium alloy are placed in a steel pipe and sintered in a hydrogen atmosphere. The sintered particles are then heat treated in air and then treated with a suspension of alumina and Fe
2
O
3
/Cr
2
O
3
.
Tennet et al., in U.S. Pat. No. 6,099,965, described a catalyst comprising a rigid carbon nanotube structure and a catalytically effective amount of a catalyst supported thereon. Numerous advantages of this structure including enhanced heat and mass transfer are dicussed (see col. 16, lines 8-65).
Despite the prior work, there remains a need for novel solid catalyst materials that have superior heat and/or mass transport capabilities.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides an engineered catalyst that includes a support material having through-porosity (defined as discussed below), a layer comprising carbon nanotubes on the support material; and a surface-exposed catalytically-active composition.
In another aspect, the invention provides catalyst including a support; nanotubes dispersed over the support; and a catalytically-active composition dispersed over the nanotubes.
In yet another aspect, the invention provides a method of forming a porous carbon nanotube containing catalyst structure. In this method, a large pore support is provided having through porosity. Carbon nanotubes are formed over the large pore support, and a catalyst composition is deposited over the carbon nanotubes.
The invention also includes methods of conducting catalyzing chemical reactions in which one or more reactants are contacted with any of the carbon nanotube containing catalysts described herein. In this method, the one or more reactants react to form a product. The catalyst catalyzes the reaction relative the same reaction conducted in the absence of a catalyst. For example, the invention provides a Fischer-Tropsch process in which a gaseous composition, comprising CO and hydrogen, is passed over any of the carbon nanotube containing catalysts described herein.
The invention also provides a catalytic process for aqueous phase hydrogenations to produce higher value chemical products from biomass feedstock.
In another aspect, the invention provides a process of making a porous, carbon nanotube-containing structure, comprising: providing a support material having through-porosity; depositing seed particles on the support material to form a seeded support material; and heating the support material and simultaneously exposing the seeded support to a carbon nanotube precursor gas to grow carbon nanotubes on the surface of the seeded support material.
In another aspect, the invention provides a porous carbon-nanotube-containing structure that includes a large pore support having through porosity; and carbon nanotubes disposed over the large pore support.
In still another aspect, the invention provides a method of making a carbon-nanotube-containing structure in which a surfactant template composition (a composition containing a surfactant and silica or silica precursors) is applied onto a support. Carbon nanotubes are then grown over the layer made from the surfactant template composition.
The invention also provides processes of using carbon nanotube-containing structures. Preferably, any of the carbon nanotube-containing structures described herein can be used in processes including: adsorption, ion exchange, separation of chemical components, filtration, storage of gases (for example, hydrogen or carbon dioxide), distillation (including reactive distillation), as a support structure for chemical or biological sensors, and as a component in a heat exchanger. Features of carbon nanotube-containing structures that make these structures particularly advantageous include: high surface area, excellent thermal conductivity, capillary force for enhanced condensation, and good attractive force for certain organic species.
Thus, the invention provides a method of adsorbing a chemical component in which a chemical component is contacted with a carbon nanotube-containing structure and the chemical component is adsorbed on the surface of the carbon nanotube-containing structure. A preferred chemical species is hydrogen. In a preferred embodiment, the exterior surface of the carbon nanotube-containing structure is a palladium coating. In preferred embodiments, the adsorption is run reversibly in a process such as pressure swing or temperature swing adsorption. This method is not limited to adsorbing a single component but includes simultaneous adsorption of numerous components.
Similarly, the invention provides a method of separating a chemical component from a mixture of components. “Mixture” also includes solutions, and “separating” means changing the concentration of at least one component relative to the concentration of at least one other component in the mixture and preferably changes the concentration of at least one component by at least 50% (more preferably at least 95%) relative to at least one other component—for example reducing the concentration of a 2M feed stream to 1M or less. Particular types of separations include filtration, selective adsorption, distillation and ion exchange. Filtering can be accomplished, for example, by passing a mixture having at least two phases through a porous carbon nanotube-containing structure where at least one of the phases gets physically caught in the structure. A carbon nanotube-containing structure with surface-exposed carbon nanotubes can function efficiently for the separation of some organics because the nanotubes can be hydrophobic while organics can be adsorbed quite well. For ion exchange it is desirable to coat the surface with an ion exchange agent.
The preparation of porous materials, such as foams, coated with carbon nanotubes and a high-surface area metal oxide coating, can be difficult. The locally aligned nanotubes exhibit high surface Van der Waal forces and hydrophobic properties. Conventional wash coating of metal oxides using aqueous based solution often results in a non-uniform coating or poor adhesion onto the nanotubes. We have developed treatment methods to modify the surface properties of the nanotubes, making this new class of materials possible for application as engineered catalyst structure. We have fabricated carbon nanotube-based engineered catalyst and have demonstrated its performance for Fisher-Tropsch reaction in a microchannel reactor. Under operating conditions typical of microchannel reactors
Chin Ya-Huei
Gao Yufei
Wang Yong
Harrington Todd J.
Parsa J.
Rosenberg Frank S.
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