WO2018098493A1

WO2018098493A1 - Bodies comprising fibrous carbon nanoparticles, exhaust systems, and related methods

Info

Publication number: WO2018098493A1
Application number: PCT/US2017/063522
Authority: WO
Inventors: Dallas B. Noyes
Original assignee: Seerstone Llc
Priority date: 2016-11-28
Filing date: 2017-11-28
Publication date: 2018-05-31

Abstract

This application discloses a body having an inlet, an outlet, and at least one outer wall, and a porous network of fibrous carbon nanoparticles formed within the body. The porous network of fibrous carbon nanoparticles defines a plurality of gas paths between the inlet and the outlet. The body may be used as part of an exhaust system. Methods of forming such bodies are also disclosed.

Description

BODIES COMPRISING FIBROUS CARBON NANOPARTICLES, EXHAUST SYSTEMS, AND RELATED METHODS

PRIORITY CLAIM

This application claims the benefit of the filing date of United States Provisional

Patent Application Serial No. 62/427,038, filed November 28, 2016, for "Carbon Nanotubes in Exhaust System and Related Materials and Methods."

TECHNICAL FIELD

Embodiments of this disclosure relate generally to nanofiber structures including catalytically active materials thereon, and to related methods.

BACKGROUND

The subject matter of this application builds upon the subject matter of U.S. Patent 8,679,444, issued March 25, 2014, and titled "Method for Producing Solid Carbon by Reducing Carbon Oxides," the entire disclosure of which is incorporated herein by reference.

Nanoparticles are effective catalysts because of their high specific surface area. Many compositions of nanoparticles are suitable for use as nanocatalysts for a wide variety of reactions. The development of nanoparticle catalysts is a promising route for improvements in a wide variety of reactions. The widespread use of nanocatalysts has been hindered by many factors, including high cost of manufacture; clumping, agglomeration, and merging of nanocatalysts into large particles under reactor conditions; increased pressure drop caused by the nanocatalysts; and removal of the nanocatalyst from reactors by elutriation and entrainment in reactor process streams.

Catalytic converters are used in combustion engines to reduce emissions by converting carbon monoxide, unburned hydrocarbons, and oxides of nitrogen into carbon dioxide, water, and nitrogen prior to exhausting gases into the atmosphere. Typical catalytic converters are lined with expensive catalyst materials to catalyze the reactions within the catalytic converter. Various forms of equipment may be equipped with catalytic converters such as automobiles, electric generators, transportation vehicles, airplanes, and other devices with internal- combustion engines. Generally, a catalytic converter may be used with any set of equipment to reduce emissions of undesirable pollutants. It would be desirable to form a catalytic converter with nanoparticle catalysts to reduce undesired pollutants while reducing the overall cost of manufacture of the catalytic converter.

DISCLOSURE

An exhaust system of an internal-combustion engine includes a body with at least one inlet, at least one outlet, and at least one outer wall. A porous network of fibrous carbon nanoparticles is formed within the body and assists in defining a plurality of gas paths between the inlet and the outlet of the body of the exhaust system. The fibrous carbon nanoparticles disposed within the exhaust system may promote oxidation of carbon oxides and hydrocarbons and also reduction of nitrous oxides. The fibrous carbon nanoparticles include nanocatalyst particles attached thereto.

In certain embodiments, a metal material suitable for growing fibrous carbon nanoparticles and suitable for oxidizing or reducing the emissions from an internal- combustion engine is integrated within a body. Fibrous carbon nanoparticles are secured to and attached to the metal material. The fibrous carbon nanoparticles assist in forming a plurality of gas paths between the inlet and the outlet of the exhaust system.

A method of forming an exhaust system includes forming the body with at least one inlet, at least one outlet, and at least one outer wall. A porous network of fibrous carbon nanoparticles is formed on at least a portion of the internal walls of the exhaust system. The porous network of fibrous carbon nanoparticles defines a plurality of gas paths between the inlet and the outlet of the exhaust system.

A method of forming an exhaust system includes forming fibrous carbon nanoparticles with embedded nanocatalysts within the exhaust system. A metal material suitable for growing fibrous carbon nanoparticles and for oxidizing or for otherwise reducing the emissions from an internal-combustion engine is incorporated within the body. A porous network of fibrous carbon nanoparticles may be formed from the incorporated metal material and from at least one wall of the exhaust system.

In certain embodiments, the exhaust system includes an inlet for distributing a gaseous flow into a catalytic converter. The system includes a chamber sized and configured to receive the catalytic converter. The catalytic converter includes a porous network of fibrous carbon nanoparticles disposed on a body defined by a plurality of channels. A plurality of metal particles selected from the group consisting of palladium, platinum, ruthenium, vanadium, and rhodium is disposed on the porous network of fibrous carbon nanoparticles. The system includes an outlet for directing exhaust that is substantially free of nitrous oxides, carbon monoxide, and unburned hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified schematic of a nanofiber according to an embodiment disclosed herein;

FIG. 2 is a simplified diagram of an exhaust system, including a catalytic converter;

FIG. 3 is a cross-sectional stylized view of a honeycomb monolithic structure;

FIG. 4 is a simplified schematic of an internal-combustion engine with each cylinder including its own catalytic converter;

FIG. 5 is a simplified cross-sectional stylized view of a portion of piping of a system lined with nanofibers according to an embodiment disclosed herein;

FIG. 6 is a simplified cross-sectional stylized view of a portion of piping of an exhaust system lined with a network of nanofibers according to an embodiment disclosed herein;

FIG. 7 is a simplified schematic of an internal-combustion engine with a mounted catalyst material according to an embodiment disclosed herein; and

FIG. 8 is a simplified block-flow diagram of a system including a stationary internal- combustion system according to an embodiment disclosed herein. MODE(S) FOR CARRYING OUT THE INVENTION

The following description provides specific details, such as catalyst types, stream compositions, and processing conditions (e.g., temperatures, pressures, flow rates, reaction gas mixtures, etc.) to provide a thorough description of embodiments of the disclosure. However, a person of ordinary skill in the art will understand that the embodiments of the disclosure may be practiced without employing these specific details. Indeed, the embodiments hereof may be practiced in conjunction with conventional systems and methods employed in the industry. In addition, only those process components and acts necessary to understand the embodiments of the disclosure are described in detail below. A person of ordinary skill in the art will understand that some process components (e.g., pipelines, line filters, valves, temperature detectors, flow detectors, pressure detectors, and the like) are inherently disclosed herein as being in common practice in the chemical and automotive industry and that adding various conventional process components and acts would be in accord with the disclosure. The drawings accompanying the disclosure are for illustrative purposes only, and are not meant to be actual views of any particular material, reactor, or system. Additionally, elements common between figures may retain the same numerical designation.

As used herein, the term "configured" refers to a shape, material composition, and/or arrangement of a structure or an apparatus facilitating operation of the structure or the apparatus in a pre-determined or intended way. As used herein, the term "substantially," in reference to a given parameter, property, or condition, means to a degree that one of ordinary skill in the art would understand that the given parameter, property, or condition is met with a small degree of variance. As used herein, relational terms, such as "first," "second," "top," "bottom," "upper," "lower," "over," "under," etc., are used for clarity and convenience in understanding the disclosure and accompanying drawings and do not connote or depend on any specific preference, orientation, or order, except where the context indicates otherwise. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context indicates otherwise.

Nanotubes and nanofibers generally grow from a nanocatalyst nucleating site on the surface of a bulk catalyst material, or from particles in an aerosol (see, e.g., the incorporated U.S. Patent 8,679,444). During the growth of the nanofibers, nanocatalyst particles from the surface of the bulk catalyst material are raised from the surface of the bulk catalyst and become at least part of the growth tip of the nanofibers. The nanocatalyst particles become embedded in or attached to the growth tips of the nanofibers, and are supported by the resulting nanofibers. The mounted nanocatalyst particles that catalyze the formation of nanofibers are typically catalyst particles for catalyzing another reaction and may be suitable for many industrial reactions. By way of non-limiting example, during the reduction of carbon oxides to form carbon nanotubes, each nanotube formed may raise at least a particle of catalyst material from a surface of bulk catalyst material. Thus, a carbon nanotube formed from an iron catalyst may contain an iron particle on the tip of the carbon nanotube. Similarly, a carbon nanotube formed from nickel, chromium, ruthenium, rhodium, platinum, palladium, associated alloys thereof, or other catalyst material may have the respective metals embedded at the tips of the nanotubes.

Without being bound by any particular theory, it appears that the catalyst surface is slowly consumed by the formation of fibrous carbon nanoparticles due to embedding a particle of the catalyst material into growth tips of the fibrous carbon nanoparticles. Because of this consumption, the material on which a fibrous carbon nanoparticle grows may not be considered a catalyst in the classical sense, but is nonetheless referred to herein and in the art as a "catalyst," because the carbon is not believed to react with the material. Furthermore, fibrous carbon nanoparticles may not form at all absent the catalyst.

As an alternative theory, the reactions forming solid carbon may occur because of the presence of carbon in the catalyst material. Without being bound by any particular theory, carbon may act as a nucleating site for the reactions to proceed. Thus, the carbon in the catalyst material may promote reactions to reduce carbon oxides to solid carbon. As layers of solid carbon are formed, the newly formed carbon material may operate as nucleating sites for subsequent layers of solid carbon.

Nanotubes or nanofibers may be formed from various materials. By way of non- limiting example, silicon nanofibers may be formed from a gold catalyst or from a nickel- based or zinc-based catalyst, thereby embedding the catalyst particle on the growth tip of the grown silicon nanofiber. As another example, a plurality of boron nitride nanofibers may be formed from an iron catalyst supported on a S1O2 and/or AI2O3 support material, resulting in a boron nitride nanofiber with embedded iron nanocatalysts at the nanofiber growth tip. Boron carbide nanofibers may be formed with porous alumina templates wherein a precursor (such as 6,6'-(CH₂)6-(BioHi₃)₂) is placed in the alumina template as described in Mark J. Pender et al., Molecular and Polymeric Precursors to Boron Carbide Nanofibers, Nanocylinders, and Nanoporous Ceramics, (Pure Appl. Chem. , Vol. 75, No. 9, pp. 1287-1294, 2003), the entire contents of which is incorporated herein by this reference. The template is heated to approximately 140°C and then subsequently dissolved with, for example, a hydrofluoric acid solution, leaving boron carbide nanofibers. Alternatively, boron carbide nanofibers may be formed by reacting fibrous carbon nanoparticles with boron powder at approximately 1150°C. Alumina nanofibers may be formed by various methods such as the internal crystallization method and extrusion, electrospraying, electrospinning, chemical vapor deposition (CVD), and sol-gel methods, as known in the art, and as described in Mohamad Ridzuan Noordin & Kong Yong Liew, "Synthesis of Alumina Nanofibers and Composites," (Ashok Kumar ed., 2010), 405-418, the entire contents of which is incorporated herein by this reference. As another non-limiting example, carbon nitride nanofibers may be formed by pyrolysis of melamine over a catalyst material such as nickel or iron. Cadmium sulfide nanofibers may be formed by electro-deposition or by electrospinning. Titania nanofibers may be formed by a direct sol-gel process or electrospinning. Carbon nanotubes or nanofibers may be formed by reacting a carbon oxide (CO, CO2, etc.) with a reducing agent (H₂, CH₄, etc.) in a reaction zone including a catalytic metal such as iron, nickel chromium, platinum, palladium, etc., at a temperature between about 500°C and 800°C. As used herein, the term "carbon nanofiber" or "CNF" means and includes a carbon-containing material comprising a solid cylindrical shape substantially free of any voids (e.g., without a hollow central portion). A carbon nanofiber may be similar to a carbon nanotube (CNT), but may include a solid core rather than a hollow central portion. As used herein, the term "fibrous nanoparticles" includes both nanofibers and nanotubes. The above-mentioned products may be formed using methods known in the art or subsequently developed.

Fibrous nanoparticles may be formed using a variety of bulk catalyst materials. For example, fibrous nanoparticles may be formed from elements of Groups 1-15 of the periodic table (e.g., Groups 2-11), lanthanides, actinides, oxides of such elements, alloys of such elements, and combinations thereof. Non-limiting examples of suitable catalyst materials for the formation of carbon nanoparticles include vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, oxides thereof, and alloys thereof. Note that the periodic table may have various group numbering systems. As used herein, group 2 is the group including Be, group 3 is the group including Sc, group 4 is the group including Ti, group 5 is the group including V, group 6 is the group including Cr, group 7 is the group including Mn, group 8 is the group including Fe, group 9 is the group including Co, group 10 is the group including Ni, group 11 is the group including Cu, group 12 is the group including Zn, group 13 is the group including B, group 14 is the group including C, and group 15 is the group including N. Various grades of the catalyst material may be used. For example, the catalyst material may be a grade of an iron-, chromium-, molybdenum-, cobalt-, tungsten-, or nickel-containing alloy or superalloy. Such materials are commercially available from numerous sources, such as from Special Metals Corp., of New Hartford, New York, under the trade name INCONEL®, or from Haynes, Int'l, Inc., of Kokomo, Indiana, under the trade name HASTELLOY® (e.g., HASTELLOY® B-2, HASTELLOY® B-3, HASTELLOY® C-4, HASTELLOY® C-2000, HASTELLOY® C-22, HASTELLOY® C-276, HASTELLOY® G-30, HASTELLOY® N, or HASTELLOY® W). In some embodiments, the catalyst material is steel of a low-chromium grade. Metals subject to metal dusting may also be used as the catalyst material.

The catalyst nanoparticles on the growth tip of each of the fibrous nanoparticles may be substantially the same size or may have a range of sizes. In addition, the catalyst nanoparticles may each have substantially the same shape, or at least some of the catalyst nanoparticles may have a substantially different shape.

Fibrous nanoparticle structures with nanocatalyst particles in the growth tips, may be an efficient method for catalyzing the reactions that take place in a typical catalytic converter. Emissions from an internal-combustion engine may be controlled by flowing exhaust through a catalytic converter. An emission control system may include a steel housing that contains a metal or ceramic structure that acts as a catalyst support and/or substrate. The catalyst may have a high overall surface area (e.g., relative to conventional catalytic converters) to transform pollutants in the exhaust gas into relatively harmless gases. Catalyst materials supported on fibrous nanoparticle structures may be an effective method of increasing the specific surface area within an exhaust manifold or catalytic converter without significantly increasing the pressure drop within the emission control system.

In one embodiment, fibrous nanoparticles with embedded nanocatalyst particles are disposed within a catalytic converter. The fibrous nanoparticles may be created through any method known to the art, including arc discharge, laser ablation, hydrocarbon pyrolysis, the Boudouard reaction, the Bosch reaction and related carbon oxide reduction reactions, or wet chemistry methods (e.g., the Diels-Alder reaction). The methods described herein are applicable to fibrous nanoparticles regardless of the method of manufacture or synthesis. In one embodiment, fibrous nanoparticles are formed by reacting a carbon-containing gas (CO, C0₂, etc.) with a reducing agent (H₂, CH₄, etc.) in a reaction zone including a catalytic metal such as iron, nickel, chromium, platinum, palladium, ruthenium, etc., at a temperature between about 500°C and 800°C. In one embodiment, carbon dioxide is reacted with a reducing agent to form fibrous nanoparticles. In one embodiment, the reducing agent is H₂. In another embodiment, the reducing agent is a hydrocarbon (e.g., CH₄, C₂H₅, etc.) or an alcohol (e.g., methanol, etc.). In some embodiments, the reducing agent includes a mixture of one or more of these materials.

In some embodiments, the fibrous nanoparticles may contain at least 50%, at least 75%, at least 90%, or even at least 95% of the total mass of the element(s) of which the fibrous nanoparticles are formed in the catalytic converter. For example, if the fibrous nanoparticles are carbon-based (e.g., CNTs or CNFs), the fibrous nanoparticles may contain at least 50% of all the solid carbon within the catalytic converter. Thus, though there may be other forms of solid carbon formed incidentally, the fibrous carbon nanotubes may be the majority of the solid carbon. In one embodiment, the catalytic converter may include fibrous nanoparticles with additional mounted nanocatalyst particles as described in U.S. Patent Application Publication 2016/0030926, published February 4, 2016, and titled "Compositions of Matter Comprising Nanocatalyst Structures, Systems Comprising Nanocatalyst Structures, and Related Methods," the disclosure of which is incorporated herein by reference in its entirety. Fibrous nanoparticles used in the catalytic converters described herein may include a nanocatalyst particle embedded in the growth tip of substantially all of the fibrous nanoparticles and may include additional mounted nanocatalyst particles on the surface of substantially all of, or a plurality of, the fibrous nanoparticles. The additional catalyst materials may be deposited on the fibrous nanoparticles by any suitable method, such as by electro-chemical deposition, atomic layer deposition (ALD), CVD, sputtering, or deposition of an organometallic compound with carbonyl groups.

Referring to FIG. 1, a fibrous nanoparticle 100 is attached to a bulk catalyst material 110. The fibrous nanoparticle 100 may include a particle 120 separated from the bulk catalyst material 110 proximal the growth tip of the fibrous nanoparticle 100. As described above, additional catalyst material 130 may be deposited on the fibrous nanoparticle 100. The additional catalyst material 130 may include any element from Groups 1-15 of the periodic table, and may include combinations of such elements. By way of non-limiting example, the additional catalyst material 130 may include vanadium, titanium, platinum, palladium, ruthenium, rhodium, oxides thereof, and combinations thereof.

In an internal-combustion engine, the combustion of hydrocarbons results in the formation of carbon dioxide and water. However, unburned hydrocarbons and carbon monoxide may be present in the exhaust of the engine. In addition, oxides of nitrogen (NO_x) are typically formed at the elevated operating temperatures of internal-combustion engines. Catalytic converters may be used to reduce the emissions of CO, NO_x, and unburned hydrocarbons in the exhaust of internal-combustion engines. In many embodiments, a three- way catalytic converter is desired, meaning that the catalytic converter contains catalyst that converts three reactants into less harmful pollutants. Specifically a three-way catalytic converter includes catalysts that oxidize unburned hydrocarbons and CO into CO2 and water, and catalysts that reduce NO_x to N₂ and O2. The oxidation of CO is shown in Equation 1 below and the reduction of NO_x is shown in Equation 2 below:

2 CO + 0₂→ 2C0₂ Equation 1

2 NO_x→ N₂ + x0₂ Equation 2 A catalytic converter may include catalyst materials for the oxidation of various constituents in the exhaust gas and may also include catalyst material for the reduction of various constituents in the exhaust gas. Oxidation reactions within a catalytic converter may be catalyzed by catalysts such as platinum and palladium. In other embodiments, oxidation catalysts may include combinations of platinum, palladium, rhenium, ruthenium, silver, osmium, iridium, gold, nickel, cerium, iron, copper, or manganese. Reduction catalysts may include platinum, rhodium, vanadium, molybdenum, titanium, catalysts known to be useful for selective catalytic reduction, and combinations thereof. Because platinum may act as both an oxidizing catalyst and a reduction catalyst, platinum catalyst may be advantageously disposed within an exhaust system to optimize oxidation and reduction of unwanted pollutants.

Many catalytic converters include a combination of catalysts such as platinum, rhodium, and/or palladium. One problem with catalytic converters is their high cost of manufacture, due largely to, e.g., the cost of the catalysts. Increasing the surface area of active catalyst sites may have the effect of increasing the efficiency of the catalytic converter while also decreasing the amount (i.e., mass) of catalyst material required, thus reducing the overall cost of the catalytic converter. Fibrous nanoparticle structures may be implemented within an exhaust system to increase the conversion efficiency of the catalytic converter by increasing the active surface area of the catalyst material, and decreasing the total amount of catalyst required. By way of non-limiting example, fibrous nanoparticles may be used in a catalytic converter or may line portions of the piping within an exhaust system.

In one embodiment, fibrous nanoparticles are formed from a catalyst that may include both oxidation catalysts and reduction catalysts suitable for catalytic converters. By way of non-limiting example, the fibrous nanoparticles may be formed from a bulk catalyst including platinum, rhodium, palladium, ruthenium, vanadium, and combinations thereof. The resulting fibrous nanoparticles may include a plurality of catalytically active materials embedded within the nanoparticle structures. By way of non-limiting example, fibrous nanoparticles may be grown from a substrate including a plurality of catalyst materials, such as platinum, palladium, ruthenium, rhodium, and vanadium. In another embodiment, fibrous nanoparticles may be formed from individual bulk catalysts and then combined in a selected ratio. For example, fibrous nanoparticles may be formed from a rhodium catalyst, a palladium catalyst, and a platinum catalyst, and fibrous nanoparticles from each may be collected individually. A mixture of fibrous nanoparticles with a selected ratio of rhodium: palladium: platinum may be formed by mixing appropriate amounts of each of the types of fibrous nanoparticles. In another embodiment, the bulk catalyst from which the fibrous nanoparticles are grown may be selected to have the selected ratio of metals such that the resulting fibrous nanoparticles include the selected ratio of particular types of embedded nanocatalyst within the fibrous nanoparticles.

An exhaust manifold typically comprises cast iron, steel, stainless steel, aluminum, or another metal. Referring to FIG. 2, an exhaust system 200 may include an exhaust manifold 210 mounted to a cylinder head 205 of an internal-combustion engine. Exhaust gases from the cylinder head 205 enter the exhaust manifold 210.

The exhaust manifold 210 may include a body shaped and configured to be secured to the cylinder head 205, may contain an exhaust port for each cylinder of the engine, and may have at least as many inlets as there are combustion cylinders of the intemal-combustion engine to which it is attached. The exhaust manifold 210 may include at least one outer wall made of steel, stainless steel, aluminum, a superalloy, a ceramic material, or a combination thereof. The exhaust manifold 210 may be shaped and configured to be adapted to and secured to an intemal-combustion engine.

An exhaust pipe 212 may connect the exhaust manifold 210 to the catalytic converter 220. The individual ports from the exhaust manifold 210 may combine into a single exhaust pipe 212 through which all of the exhaust gases flow into a chamber sized and configured to contain catalytic converter 220. Alternatively, each port from the exhaust manifold 210 may connect to a separate exhaust pipe 212. Some exhaust systems 200 may include elements of a catalytic converter within the exhaust system 200. For example, the exhaust manifold 210 or other piping within the exhaust system 200 may include fibrous nanoparticles with particles of oxidation catalyst and particles of reduction catalyst attached thereto. Although the cylinder head 205 in FIG. 2 shows four cylinders, the cylinder head 205 may include any number of cylinders, depending on the size and configuration of the associated engine.

In the depicted embodiment, exhaust gases flow from the cylinder head 205 of an intemal-combustion engine through the exhaust manifold 210. The outlet of each portion of the exhaust manifold 210 may unite prior to entering the catalytic converter 220. After passing through the catalytic converter 220, the exhaust gases pass through the remaining portions of the exhaust system 200 and exit as purified gas 230. Purified gas is substantially free of nitrous oxides, carbon monoxide, and unburned hydrocarbons. In each embodiment, the diameter of the exhaust piping within the exhaust system 200 may be modified or increased to reduce the backpressure within the exhaust system 200. For the same exhaust gas flow, an increased cross-sectional area decreases the flow velocity, reduces backpressure, and reduces the likelihood of entrainment of any nanofibers within the exhaust system 200.

Catalytic converters may include honeycomb-type converters or converters including a bed of pellet-type catalysts. The honeycomb-type converters or the pellet-type catalyst beds may be formed from fibrous nanoparticles with mounted nanocatalysts, as shown in FIG. 1. In one embodiment, the fibrous nanoparticles are placed into a slurry and extruded into a monolithic honeycomb structure with active catalyst sites. In another embodiment, the fibrous nanoparticles are incorporated within an existing monolithic structure. In another embodiment, catalytically active fibrous nanoparticles may be placed in pellet, tablet, or granular form and form a portion of the catalytic converter.

Honeycomb-type catalytic converters generally have a high active surface area and a high void fraction, resulting in a low pressure drop as combustion gases travel through the converter. Honeycomb-type catalytic converters are frequently coated with a washcoat material that increases the internal surface areas of the honeycomb structure. Fibrous nanoparticles with active nanocatalysts may be placed in honeycomb monolith structures. Such monolithic structures may be formed by full-body extrusion or as a coating on cordierite or other honeycomb substrates.

A monolithic honeycomb structure is shown in FIG. 3. The monolithic structure may include passages of various shapes, such as triangular, square, hexagonal, circular, oval, or any other shape. The honeycomb may have between about 300 cells per square inch (csi) (46 cells/cm²) and about 1600 csi (248 cells/cm²), such as between about 400 csi (62 cells/cm²) and about 600 csi (93 cells/cm²), between about 900 csi (139 cells/cm²) and about 1200 csi (186 cells/cm²) or between about 1200 csi (186 cells/cm²) and about 1600 csi (248 cells/cm²). The monolith may have a wall thickness between about 0.002 inch (0.0051 cm) and about 0.012 inch (0.0304 cm), such as between about 0.002 inch (0.0051 cm) and about 0.004 inch (0.0101 cm), between about 0.004 inch (0.0101 cm) and about 0.008 inch (0.0203 cm), and between about 0.008 inch (0.0203 cm) and about 0.012 inch (0.0304 cm).

In one embodiment, the monolithic structure is formed from a slurry including fibrous nanoparticles with catalyst particles embedded therein. In another embodiment, the monolithic structure is formed from a base structure of monolithic material, and catalytically active fibrous nanoparticles are disposed (e.g., placed, formed, etc.) within the structure and on surfaces of the structure. Typical honeycomb monoliths include a base material of cordierite, a magnesium aluminosilicate (Mg₂Al₄Si50i8) that has a low coefficient of thermal expansion. Typically, because cordierite contains only macropores, the cordierite material may be coated with an alumina washcoat that increases the porosity of the cordierite. A typical washcoat material may include aluminum oxide that coats the walls of the honeycomb. The washcoat is porous and increases the surface area, which allows for more reactions to take place. By way of non-limiting example, rather than depositing precious metals onto the washcoat, fibrous nanoparticles with embedded nanocatalysts including the precious metals may be deposited onto the washcoat. In one embodiment, the washcoat may be unnecessary because fibrous nanoparticles with attached nanocatalysts may provide sufficient surface area and porosity to efficiently reduce the emissions from an internal-combustion engine.

The fibrous nanoparticles may be formed into a solution or suspension such as in water, hexane, acetone, etc. In one embodiment, the fibrous nanoparticles are formed into a mixture that includes nanotubes and a resin including a binder material. The binder material may hold the mixture together and bind the fibrous nanoparticle structures into a matrix. Various binder materials may include phenolic binders, epoxy binders, polyester binders, vinyl ester binders, and super-, ultra-high molecular weight polyethylene (UHMWPE) powder as described in Ramesh Thiruvenkatachari et al., "Post Combustion CO2 Capture by Carbon Fibre Monolithic Adsorbents," {Progress in Energy and Combustion Science, vol. 35, No. 5 pp. 438-455, 2009), the entire contents of which are incorporated herein by this reference.

The binder may include an agglomerating agent such as polyethylene oxide, cellulose, methylcellulose, sepiolite, mixtures thereof, and other agglomerating agents as known in the art. The mixture may include a plasticizer to control the plasticity of the solution and to aid in extrusion of the mixture. A slurry may be formed by combining the nanostructures with the resin material and mixing with water or another solvent. In another embodiment, the fibrous nanoparticles may be mixed with water to form a paste or slurry by slowly removing the water from the solution. The catalytic activity of the end product may be varied by altering the ratio and type of fibrous nanoparticles added to the slurry. For example, by altering the weight percent of fibrous nanoparticles grown from various bulk catalysts, the weight percent of particular nanocatalysts may be controlled in the final monolithic structure. By way of non- limiting example, the weight percent of platinum, palladium, rhodium, ruthenium, chromium, iron, and nickel may be controlled by controlling the weight percent of such fibrous nanoparticles in the slurry. In one embodiment, powdered metal particles may be added to the slurry to effectively add such metal particles to the monolithic structure. By way of non- limiting example, powdered vanadium, titanium, nickel, stainless steel alloys, ruthenium, palladium, platinum, and combinations thereof may be added to the slurry.

The slurry may be shaped into any desired shape by pouring into a mold and allowing the slurry to dry as it adapts to the shape of the mold. The monolithic structure may be dried at a temperature between about 30°C and about 150°C. Following drying, the molded structure may be cured by heating the structure to between about 300°C and about 800°C, such as between about 300°C and about 400°C, about 400°C and about 600°C, or between about 600°C and about 800°C. The molded structure may be pyrolized to create a pore structure throughout the honeycomb mold and to pyrolize the resin binder within the molded structure.

In another embodiment, the monolithic structure is calcined at temperatures between about 400°C and about 900°C to create additional porosity in the monolithic structure. The monolithic structure may be further activated by subjecting the monolith to an activating agent for an extended period of time. For example, the monolithic structure may be subjected to CO2 at a temperature between about 700°C and about 1000°C for a specified time. The resulting structure is a monolithic structure formed from various nanotubes. The monolithic structure includes catalytically active sites which derive from the bulk material from which the fibrous nanoparticles were grown.

In another embodiment, the molded shape may be subjected to a sintering atmosphere. As used herein, the term "sintering" means and includes annealing or pyrolizing at temperatures and pressures sufficient to induce chemical or physical bonding. For example, the fibrous nanoparticles may be heated to elevated temperatures to form covalent bonds between adjacent fibrous nanoparticles. The fibrous nanoparticles may be heated to a temperature of at least 1500°C, 1800°C, 2100°C, 2400°C, 2500°C, 2700°C, or even to just below the sublimation temperature of carbon (approximately 3600°C). The heating may be performed in an inert environment, such as one containing argon, helium, or nitrogen. After heating the fibrous nanoparticles in a non-reactive environment, the fibrous nanoparticles may be allowed to cool to a temperature at which the carbon of the fibrous nanoparticles does not react with oxygen. Such heating of the fibrous nanoparticles may result in cross-linking of adjacent fibrous nanoparticles or may result in the partial or complete sintering of the fibrous nanoparticles. The sintering typically occurs in a non-oxidizing environment, such as a vacuum or an inert atmosphere so that the fibrous nanoparticles are not oxidized during the sintering. In another embodiment, the sintering is performed by spark plasma sintering. In another embodiment, a honeycomb structure may be formed by extruding a slurry or paste including fibrous nanoparticles into a desired shape. The slurry may be extruded through, e.g., a die press, extruder, or roller press to form the desired honeycomb structure. An extrusion die may include an opening with the cross-sectional shape of the monolithic honeycomb to be formed. After the structure is extruded through the opening, the resulting monolithic structure may be heated, carbonized, cured, calcined, or partially or fully sintered as described above with respect to a molded monolithic structure.

In one embodiment, after the honeycomb structure is formed from a slurry, additional fibrous nanoparticles may be formed on and within the honeycomb structure. For example, additional fibrous nanoparticles may be formed within the honeycomb structure by reducing a carbon oxide in the presence of the catalysts within the honeycomb structure. The additional fibrous nanoparticles maybe heated, calcined, pyrolized, or partially or fully sintered.

In another embodiment, a base honeycomb monolithic structure, such as a ceramic, cordierite, or other monolith structure is provided. A slurry or paste containing the mounted nanocatalysts may be prepared as described above. For example, the slurry may include fibrous nanoparticles with mounted nanocatalysts in a solvent such as water, hexane, acetone, etc. The monolithic structure may be loaded with catalytically active fibrous nanoparticles contained within the slurry or paste by contacting the monolithic structure with the slurry for a predetermined time and then drying and washing the structure. In one embodiment, the monolithic structure is dipped or immersed into the slurry containing the fibrous nanoparticles to coat the entire structure with fibrous nanoparticles.

The process of dipping and drying may be repeated any number of times to provide adequate contact and sufficient deposition of the fibrous nanoparticles on the monolithic structure. After drying and washing, the monolith may include several active catalytic sites that include catalyst materials embedded on the fibrous nanoparticles. After each cycle of dipping or immersing, the monolithic structure may be dried, cured, carbonized, calcined, or partially or fully sintered as described above.

The catalytic sites in the monolith may include catalytic structures present in the slurry from which the monolith was coated. By way of non-limiting example, if the slurry includes carbon nanofibers formed from a stainless steel material, the active catalyst sites of the monolith may include iron, nickel, and chromium. In another example, a monolithic structure including nanofibers with active platinum, rhodium, and palladium sites is formed from fibrous nanoparticles including such metals. In another embodiment, a base monolithic structure is provided, such as a cordierite structure. Suitable catalyst materials are deposited on or otherwise associated with the monolithic structure, such as any metal that may catalyze the reduction and oxidation reactions in a catalytic converter. The catalyst materials may be deposited by at least one of by electro-chemical deposition, ALD, CVD, sputtering, or deposition of an organometallic compound with carbonyl groups. In one embodiment, the structure is coated with a washcoat prior to depositing the catalyst materials on the structure. Fibrous nanoparticles may be grown from the deposited catalytic materials by reducing a carbon oxide with a reducing agent, as described above. The fibrous nanoparticles may be fully or partially sintered within the honeycomb structure.

In another embodiment, the fibrous nanoparticles may be compacted into pellet or bead forms. Beads of nanocatalyst materials may be formed by pressing the fibrous nanoparticles into a desired shape and then heating, such as by partially or completely sintering. In another embodiment, a slurry of fibrous nanoparticles as described above may be extruded into desired shapes such as pellets, tablets, or other shapes and then heat treated or fully or partially sintered. High internal porosity is achieved by carefully burning off the organic additives and by incomplete sintering, as described above. The pellets are porous beads and may have various diameters, such as between about 0.1 millimeter (mm) and about 5 mm, between about 0.1 mm and about 1 mm, between about 1 mm and about 3 mm, or between about 3 mm and about 5 mm.

Referring again to FIG. 2, the monolithic honeycomb structures with embedded catalysts or the formed beads/pellets may be placed within the catalytic converter 220 of the exhaust system 200. The exhaust system 200 may include one or more exhaust manifolds 210 depending on the size and configuration of the internal-combustion engine. The catalytic converter 220 may include a monolithic honeycomb structure or a plurality of pellets or beads as described herein. In one embodiment, an optional supplemental converter 215 is included in the exhaust system 200. The supplemental converter 215 may include a small honeycomb monolithic structure, a small bed of beads or pellets, or a portion of the exhaust piping lined with fibrous nanoparticles with active nanocatalysts through which the exhaust gases must pass. The supplemental converter 215 may be configured to increase the conversion and efficiency of the exhaust system 200 during start up when the exhaust system 200 is cold.

In any of the embodiments, drying, curing, calcining, pyrolizing, or partially or fully sintering the fibrous nanoparticles may result in forming a porous network of nanomaterials. In one embodiment, the fibrous nanoparticles are carbon nanotubes formed into a continuous and porous network. The porous network of carbon nanotubes may have a mean pore size between about 1 nm and about 10 nm, such as between about 1 nm and about 3 nm, between about 3 nm and about 6 nm, or between about 6 nm and about 10 nm. The carbon nanotubes may be formed into a porous network of cross-linked carbon nanotubes.

FIG. 4 shows a simplified diagram of an internal-combustion engine 400 having a cylinder head 405 and an exhaust system 415. The cylinder head 405 contains multiple cylinders 410 (four shown in FIG. 4). Exhaust generated in each cylinder 410 may remain separate from the exhaust from the other cylinders 410. Thus, each cylinder 410 may be connected to separate exhaust piping of the exhaust system 415, and the exhaust from each cylinder 410 may pass through a separate catalytic converter 420a, 420b, 420c, or 420d. This may be an effective method of reducing backpressure within the internal-combustion engine 400 and the exhaust system 415. After passing through the catalytic converters 420a, 420b, 420c, and 420d, the exhaust may combine into a single pipe or may exit the exhaust system 415 as separate purified gas 430a, 430b, 430c, and 430d.

The exhaust manifold and exhaust piping may be formed from various materials, such as cast-iron, stainless steel, a ceramic base material coated with a metal or a plurality of metals, or combinations thereof. The ceramic material may be coated with metals such as any of the metals that catalyze the oxidation or reduction reactions in a catalytic converter. In one embodiment, all of, or portions of, the exhaust piping may be formed of fibrous nanoparticles that have been compressed and sintered to hold a desired shape. In another embodiment, fibrous nanoparticles are grown on an inner wall of the exhaust piping. The fibrous nanoparticles may be partially or fully sintered, pyrolized, calcined, or otherwise heat treated after formation within the exhaust system piping.

In another embodiment, the exhaust gases from, e.g., an internal-combustion engine may be converted to less-harmful pollutants by lining the exhaust manifold and exhaust piping with catalytically active fibrous nanoparticles. A catalyst material may be deposited on at least portions of the exhaust piping by impregnation, adsorption and ion exchange, precipitation or coprecipitation, a sol-gel process, or spray coating. The exhaust piping may be lined with fibrous nanoparticles grown from and attached to the inner walls of the exhaust manifold. For example, fibrous nanoparticles may grow from the inner walls or surfaces of the exhaust piping by passing a reactive gas including a carbon oxide and a reducing agent through the exhaust piping. By way of non-limiting example, CO or CO2 may be mixed with H₂ in the exhaust piping at temperatures above approximately 600° C to form carbon nanotubes such as described in U.S. Patent 8,679,444.

Referring to FIG. 5, a simplified cross-sectional stylized view of a portion of exhaust piping 500 is shown with fibrous nanoparticles 510 attached to an inner wall of the exhaust piping 500. The fibrous nanoparticles 510 are depicted as being formed into a porous network defining a plurality of gas paths. The portion of the exhaust piping 500 may be inside an exhaust manifold or within other portions of an exhaust system mounted to an internal- combustion engine. In one embodiment, the exhaust piping 500 is subjected to conditions suitable for forming fibrous nanoparticles within the exhaust piping 500, and the resulting fibrous nanoparticles 510 may be partially or fully sintered into a porous network of fibrous nanoparticles 510. The fibrous nanoparticles 510 typically include nanocatalyst 520 embedded in the growth tips of the fibrous nanoparticles 510. The fibrous nanoparticles 510 may also include additional catalyst of various metals on the surface of the fibrous nanoparticles 510 and dispersed throughout the network. The fibrous nanoparticles 510 may be substantially similar to fibrous nanoparticle 100 shown in FIG. 1. The network of fibrous nanoparticles 510 may be cross-linked by fully or partially sintering to form stable and interconnected fibrous nanoparticles within the exhaust manifold. The network of fibrous nanoparticles 510 may include a plurality of discrete fibrous nanoparticles secured to the body of the exhaust piping 500.

The network of fibrous nanoparticles 510 may be formed in situ within the exhaust piping 500, such as by passing a reactive gas through the exhaust piping 500. By way of non- limiting example, the fibrous nanoparticles 510 may be formed by passing a reactive gas including a carbon oxide and a reducing agent through the exhaust piping 500 at temperatures and pressures suitable for forming carbon nanotubes. By way of non-limiting example, carbon nanotubes may be formed by maintaining a temperature of at least about 600°C in the exhaust piping 500 and by maintaining a pressure of at least about 30 psi (207 kPa) within the exhaust piping 500 during nanotube formation.

Referring to FIG. 6, a cross-sectional stylized view of exhaust piping 600 is shown. Previously formed fibrous nanoparticles may be inserted into the exhaust piping 600 and adhered to the surfaces thereof. In one embodiment, a slurry or paste including the fibrous nanoparticles may be formed as described above. The slurry or paste may be flowed through portions of the exhaust system and may line the interior walls of the exhaust piping 600. The slurry may be dried, cured, and calcined, or partially or fully sintered as described above. After the slurry or paste is dried, a network of fibrous nanoparticles 610 lines interior surfaces of the exhaust piping 600. The process may be repeated to form a desired thickness of the network of fibrous nanoparticles 610 within the exhaust piping 600.

Referring to FIG. 7, suitable catalyst material for growing fibrous nanoparticles may be inserted into an exhaust system 700 of a combustion engine. A catalyst insert 715 may be incorporated into the exhaust system 700 of the combustion engine. An exhaust manifold may include a plurality of pipes 710 attached to a cylinder head 705. Each pipe 710 may include its own catalyst insert 715, or the catalyst insert 715 may extend throughout the pipes 710 of the exhaust system 700. The catalyst insert 715 may include a metal mesh, a metal wire, a metal sheet, a metal foil, a plurality of each, or combinations thereof. By way of non- limiting example, the catalyst insert 715 may include any catalyst suitable for catalyzing oxidation or reduction reactions that take place in a catalytic converter, such as, for example, platinum, rhodium, palladium, ruthenium, vanadium, titanium, etc.

Fibrous nanoparticles may be grown on the catalyst insert 715 within the exhaust system 700. The fibrous nanoparticles may form a continuous network of interlocking nanoparticles by forming covalent bonds between adjacent nanoparticles, such as by partially or fully sintering the fibrous nanoparticles, pyrolizing, or otherwise heat treating the fibrous nanoparticles. Downstream of the catalyst insert 715, the exhaust system 700 may include a catalytic converter or a plurality of catalytic converters as described above with respect to FIGS. 2 and 4. In one embodiment, the exhaust system 700 is made of a steel material, the catalyst insert 715 is incorporated within the exhaust system 700, and the catalyst insert 715 includes a combination of a platinum material, a palladium material, and a rhodium material.

In another embodiment, the exhaust system of an internal-combustion engine may incorporate fibrous nanoparticles spun into a nanofiber fabric. By way of non-limiting example, carbon nanotubes or nanofibers may be formed on activated carbon sheets. In another embodiment fibrous nanoparticles are spun into sheets of nanoparticles. The sheets of fibrous nanoparticles may be up to several meters in length. The fabric may be formed from fibrous nanoparticles by any method known in the art. The fabric may be formed from and include fibrous nanoparticles with embedded nanocatalysts. Additional nanocatalysts may be deposited onto the surfaces, such as by electro-chemical deposition, ALD, CVD, sputtering, or deposition of an organometallic compound with carbonyl groups on the nanotube surfaces, either before or after forming the nanotubes into a fabric material. FIG. 8 shows a simplified block-flow diagram of a system 800 including a stationary internal-combustion engine 830. The stationary internal-combustion engine 830 may include an air intake 810 and fuel supply 820. Exhaust 840 may exit the stationary internal- combustion engine 830 and enter an exhaust system 850. The exhaust system 850 may include a catalytic converter or piping lined with fibrous nanoparticles, as described in the embodiments above. By way of non-limiting example, the exhaust system 850 may include a monolithic honeycomb structure with mounted nanocatalysts, a bed of beads made of nanofibers, a plurality of fibrous nanoparticles lined within portions of the exhaust system 850, metal insert materials on which fibrous nanoparticles are grown, or a fabric wound and integrated within the exhaust system 850. At least a portion of internal walls of the piping of the exhaust system 850 may be coated with fibrous nanoparticles as described above with respect to FIG. 5 and FIG. 6.

The system 800 may include a collection system 860 for collecting any loose nanoparticles and collecting them into solids 870. The collection system 860 may be partially or fully bypassed and the system 800 may include suitable piping and valves to bypass collection system 860. Collection system 860 may include any device for solid/gas separation, such as a particulate filter, a cyclone separator, an electrostatic precipitator, or any device known in the art of solid/gas separation. Collection system 860 may be sized and configured to minimize backpressure within the stationary internal-combustion engine 830.

Purified exhaust 865 exits the system 800 without harmful pollutants such as NO_x,

CO, and unburned hydrocarbons. A portion of the solids 870 may be recycled to the exhaust system 850 in recycle 890. Purge 880 may remove a portion of collected materials from the system 800. The system 800 may include piping and valves suitable to control the amount that is purged in purge 880.

Claims

What is claimed is: 1. An apparatus, comprising:

a body having an inlet, an outlet, and at least one outer wall; and

a porous network of fibrous carbon nanoparticles formed within the body, wherein the porous network of fibrous carbon nanoparticles defines a plurality of gas paths between the inlet and the outlet.

2. The apparatus of claim 1, wherein the fibrous carbon nanoparticles comprise carbon nanotubes.

3. The apparatus of claim 1, wherein the fibrous carbon nanoparticles comprise carbon nanofibers.

4. The apparatus of any of claims 1 through 3, wherein the body comprises at least one of steel, stainless steel, a superalloy, or a ceramic material.

5. The apparatus of any of claims 1 through 3, wherein the body is shaped and configured to be secured to an internal-combustion engine having at least one combustion cylinder.

6. The apparatus of claim 5, wherein the body defines a plurality of inlets equal to at least a number of combustion cylinders of the internal-combustion engine.

7. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon nanoparticles comprises a plurality of cross-linked fibrous carbon nanoparticles.

8. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon nanoparticles comprises a plurality of discrete fibrous carbon nanoparticles secured to the body.

9. The apparatus of claim 8, wherein substantially all of the discrete fibrous carbon nanoparticles comprise at least one particle of nanocatalyst embedded in at least one end of the fibrous carbon nanoparticle.

10. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon nanoparticles comprises a plurality of sintered fibrous carbon nanoparticles.

11. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon nanoparticles comprises a monolithic honeycomb structure comprising the fibrous carbon nanoparticles.

12. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon nanoparticles comprises fibrous carbon nanoparticles attached to at least one of a metal wire, a metal mesh, a metal sheet, a metal foil, and a carbon nanofabric material secured within the body.

13. The apparatus of any of claims 1 through 3, further comprising a plurality of metal particles secured to the porous network of fibrous carbon nanoparticles.

14. The apparatus of claim 13, wherein the plurality of metal particles comprises at least one material selected from the group consisting of palladium, platinum, ruthenium, vanadium, and rhodium.

15. The apparatus of any of claims 1 through 3, wherein the porous network of fibrous carbon comprises solid carbon, and wherein at least 50% of the solid carbon is in the form of fibrous carbon nanoparticles.

16. A method, comprising:

forming a body having an inlet, an outlet, and at least one outer wall; and

forming a porous network of fibrous carbon nanoparticles within the body, wherein the porous network defines a plurality of gas paths between the inlet and the outlet.

17. The method of claim 16, wherein forming a porous network of fibrous carbon nanoparticles within the body comprises forming carbon nanotubes.

18. The method of claim 16, wherein forming a porous network of fibrous carbon nanoparticles within the body comprises forming carbon nanofibers.

19. The method of any of claims 16 through 18, wherein forming the body comprises forming the body to comprise at least one of steel, stainless steel, a superalloy, or a ceramic material.

20. The method of any of claims 16 through 18, wherein forming the body comprises securing at least one of a metal wire, a metal mesh, a metal sheet, a metal foil, and a carbon nanofabric material to at least one interior wall of the body.

21. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles comprises forming a plurality of cross-linked fibrous carbon nanoparticles.

22. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles comprises sintering the fibrous carbon nanoparticles.

23. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles comprises forming a monolithic honeycomb structure comprising a plurality of fibrous carbon nanoparticles.

24. The method of any of claims 16 through 18, further comprising securing a plurality of metal particles selected from the group consisting of palladium, platinum, ruthenium, vanadium, and rhodium to the porous network of fibrous carbon nanoparticles.

25. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles within the body comprises forming a porous network of fibrous carbon nanoparticles grown from a catalyst comprising at least one of platinum, palladium, ruthenium, vanadium, and rhodium.

26. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles comprises passing a reactive gas into the body.

27. The method of any of claims 16 through 18, wherein forming a porous network of fibrous carbon nanoparticles comprises forming solid carbon, and wherein at least 50% of the solid carbon is in the form of fibrous carbon nanoparticles.

28. An exhaust system, comprising:

an inlet for distributing a gaseous flow into a catalytic converter;

a chamber sized and configured to receive the catalytic converter, the catalytic converter comprising:

a porous network of fibrous carbon nanoparticles disposed on a body defined by a plurality of channels; and

a plurality of metal particles selected from the group consisting of palladium, platinum, ruthenium, vanadium, and rhodium disposed on the porous network of fibrous carbon nanoparticles; and

an outlet for directing exhaust from the catalytic converter, the exhaust being substantially free of nitrous oxides, carbon monoxide, and unburned hydrocarbons.