WO2004110190A2

WO2004110190A2 - Nanoscale composite catalyst to reduce carbon monoxide in the mainstream smoke of a cigarette

Info

Publication number: WO2004110190A2
Application number: PCT/IB2004/002188
Authority: WO
Inventors: Kent B. Koller; Sarojini Deevi
Original assignee: Philip Morris Products SA
Current assignee: Philip Morris Products SA
Priority date: 2003-06-13
Filing date: 2004-06-10
Publication date: 2004-12-23
Anticipated expiration: 2005-12-13
Also published as: WO2004110190A3; US20040250825A1; US7243658B2

Abstract

Cut filler compositions, cigarette paper, cigarette filters, cigarettes, methods for making cigarettes and methods for smoking cigarettes are provided, which involve the use of nanoscale particle composite catalysts capable of acting as a catalyst for the conversion of carbon monoxide to carbon dioxide. The nanoscale composite catalyst comprises metal and/or metal oxide particles supported on nanoscale support particles. The nanoscale composite catalyst can be prepared by forming a mixture by combining nanoscale particles with a colloidal solution, a metal precursor solution with nanoscale particles, or a metal precursor solution with a colloidal solution, and then heat-treating the mixture.

Description

Nanoscale Composite Catalyst to Reduce Carbon Monoxide in the Mainstream Smoke of a Cigarette

Field of the Invention

0001 The invention relates generally to methods for reducing constituents such

as carbon monoxide in the mainstream smoke of a cigarette during smoking. More

specifically, the invention relates to cut filler compositions, cigarettes, methods for making cigarettes and methods for smoking cigarettes, which involve the use of nanoparticle additives capable of reducing the amounts of various constituents in

tobacco smoke.

Background of the Invention

0002 In the description that follows reference is made to certain structures and

methods, however, such references should not necessarily be construed as an

admission that these structures and methods qualify as prior art under the applicable

statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art.

0003 Smoking articles, such as cigarettes or cigars, produce both mainstream

smoke during a puff and sidestream smoke during static burning. One constituent of

both mainstream smoke and sidestream smoke is carbon monoxide (CO). The

reduction of carbon monoxide in smoke is desirable.

0004 Catalysts, sorbents, and/or oxidants for smoking articles are disclosed in

the following: U.S. Patent No. 6,371,127 issued to Snider et al., U.S. Patent No. 6,286,516 issued to Bowen et al., U.S. Patent No. 6,138,684 issued to Yamazaki et al., U.S. Patent No. 5,671,758 issued to Rongved, U.S. Patent No. 5,386,838 issued to Quincy, III et al., U.S. Patent No. 5,211,684 issued to Shannon et al., U.S. Patent

No. 4,744,374 issued to Deffeves et al., U. S. Patent No. 4,453,553 issued to Cohn, U.S. Patent No. 4,450,847 issued to Owens, U.S. Patent No. 4,182,348 issued to

Seehofer et al., U.S. Patent No. 4,108,151 issued to Martin et al., U.S. Patent No.

3,807,416, and U.S. Patent No. 3,720,214. Published applications WO 02/24005,

WO 87/06104, WO 00/40104 and U.S. Patent Application Publication Nos.

2002/0002979 Al, 2003/0037792 Al and 2002/0062834 Al also refer to catalysts,

sorbents, and/or oxidants.

0005 Iron and/or iron oxide has been described for use in tobacco products (see

e.g., U.S. Patent No. 4,197,861; 4,489,739 and 5,728,462). Iron oxide has been

described as a coloring agent (e.g. U.S. Patent Nos. 4,119,104; 4,195,645;

5,284,166) and as a burn regulator (e.g. U.S. Patent Nos. 3,931,824; 4,109,663 and

4,195,645) and has been used to improve taste, color and/or appearance (e.g. U.S.

Patent Nos. 6,095,152; 5,598,868; 5,129,408; 5,105,836 and 5,101,839).

0006 Despite the developments to date, there remains a need for improved and

more efficient methods and compositions for reducing the amount of carbon

monoxide in the mainstream smoke of a smoking article during smoking. Summary

0007 Tobacco cut filler compositions, cigarette paper, cigarette filter material,

cigarettes, methods for making cigarettes and methods for smoking cigarettes that involve the use of nanoscale composite catalysts capable of converting carbon

monoxide to carbon dioxide are provided.

0008 One embodiment provides a tobacco cut filler composition comprising

tobacco and a nanoscale composite catalyst for the conversion of carbon monoxide

to carbon dioxide, wherein the nanoscale composite catalyst comprises nanoscale

metal particles and/or nanoscale metal oxide particles supported on nanoscale

support particles.

0009 Another embodiment provides a cigarette comprising tobacco cut filler,

wherein the cut filler comprises a catalyst capable of converting carbon monoxide to

carbon dioxide, wherein the catalyst is in the form of a nanoscale composite catalyst

comprising nanoscale metal particles and/or metal oxide particles supported on

nanoscale support particles. The cigarette can further comprise cigarette paper and

optionally a cigarette filter, wherein the cigarette paper and/or the filter comprises a

nanoscale composite catalyst.

0010 Provided are cigarettes that preferably comprise up to about 200 mg of the

catalyst per cigarette, and more preferably from about 10 mg to about 100 mg of the

catalyst per cigarette. Preferably the nanoscale composite catalyst is added to the

tobacco cut filler, cigarette paper, cigarette filter, cigarette and/or cigarette filter material in a catalytically effective amount, i.e., an amount effective to convert at

least about 10%, preferably at least about 25% of the carbon monoxide to carbon dioxide.

0011 A further embodiment provides a method of making a cigarette,

comprising (i) adding a nanoscale composite catalyst to a tobacco cut filler; (ii)

providing the cut filler to a cigarette making machine to form a tobacco column; and (iii) placing a paper wrapper around the tobacco column to form the cigarette.

0012 In a preferred embodiment the nanoscale metal particles and/or metal

oxide particles comprise transition, refractory and precious metals such as B, Mg,

Al, Si, Ti, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Ce, Hf, Ta, W,

Re, Os, Ir, Pt, Au and mixtures thereof, and the nanoscale support comprises

nanoscale particles of aluminum oxide, silicon oxide, titanium oxide, iron oxide,

cobalt oxide, copper oxide, zirconium oxide cerium oxide, yttrium oxide optionally

doped with zirconium, manganese oxide optionally doped with palladium, and mixtures thereof.

0013 According to another preferred embodiment, the nanoscale metal particles

and/or nanoscale metal oxide particles comprise Au and the nanoscale support

particles comprise silicon oxide, titanium oxide, iron oxide and/or copper oxide. For

example, the nanoscale composite catalyst can comprise from about 0.1 to 25 wt.%

gold nanoscale particles supported on iron oxide nanoscale particles. 0014 Also provided are methods of forming a cigarette containing a nanoscale composite catalyst. According to one embodiment, the method comprises combining nanoscale metal and/or metal oxide particles and nanoscale support

particles in a colloidal solution, increasing the viscosity of the colloidal solution to

form an intimate mixture of the nanoscale particles and the colloidal solution, and

drying the mixture. According to a further embodiment, the method comprises

combining a metal precursor and a solvent to form a metal precursor solution,

combining the metal precursor solution with support particles to form a mixture, heating the mixture to a temperature effective to thermally decompose the metal

precursor into nanoscale particles, and drying the mixture.

0015 The nanoscale particles and the nanoscale support particles can have an

average particle size less than about 100 nm, preferably less than about 50 nm, more

preferably less than about 10 nm, and most preferably less than about 7 nm. The

nanoscale composite catalyst is preferably carbon free.

0016 The nanoscale support particles can be derived from a colloidal solution

and can comprise silicon oxide, titanium oxide, iron oxide and/or copper oxide,

where the concentration of colloids in the colloidal solution can be from about 10 to

60 weight percent. The viscosity of the colloidal solution can be increased by

changing the pH of the colloidal solution. The step of increasing the viscosity of the

colloidal solution can comprise adding a dilute acid or a dilute base to the colloidal

solution, such as dilute HCl. According to a preferred method, the viscosity of the colloidal solution is increased to form a gel before the step of heating the mixture.

The step of drying the mixture can comprise air-drying or super-critical drying.

0017 According to a further method, the metal precursor is one or more of

dionates, oxalates and hydroxides and the metal comprises at least one element selected from B, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag,

Sn, Ce, Hf, Ta, W, Re, Os, Ir, Pt and Au. The solvent can comprise at least one of

distilled water, alcohol, aldehydes, ketones and aromatic hydrocarbons. Preferably,

the mixture is heated to a temperature of from about 200 to 400EC. The nanoscale

particles are preferably intimately mixed with, or are coated on the nanoscale

support particles.

0018 Yet another embodiment provides a method of smoking the cigarette described above, which involves lighting the cigarette to form smoke and drawing

the smoke through the cigarette, wherein during the smoking of the cigarette, the

catalyst acts as a catalyst for the conversion of carbon monoxide to carbon dioxide.

Brief Description of the Drawings

0019 Figures 1-4 show TEM images of a nanoscale composite catalyst. The

images show nanoscale gold particles supported on a nanoscale iron oxide support. Detailed Description of Preferred Embodiments

0020 Provided are tobacco cut filler compositions, cigarette paper, cigarette

filter material, cigarettes, methods for making cigarettes and methods for smoking

cigarettes that involve the use of nanoscale composite catalysts capable of

converting carbon monoxide to carbon dioxide.

0021 "Smoking" of a cigarette means the heating or combustion of the cigarette

to form smoke, which can be inhaled. Generally, smoking of a cigarette involves lighting one end of the cigarette and, while the tobacco contained therein undergoes

a combustion reaction, drawing the cigarette smoke through the mouth end of the

cigarette. The cigarette may also be smoked by other means. For example, the

cigarette may be smoked by heating the cigarette and/or heating using electrical

heater means, as described in commonly-assigned U.S. Patent Nos. 6,053,176;

5,934,289; 5,591,368 or 5,322,075.

0022 The term "mainstream" smoke refers to the mixture of gases passing down the tobacco rod and issuing through the filter end, i.e. the amount of smoke issuing

or drawn from the mouth end of a cigarette during smoking of the cigarette.

0023 In addition to the constituents in the tobacco, the temperature and the

oxygen concentration are factors affecting the formation and reaction of carbon

monoxide and carbon dioxide. The total amount of carbon monoxide formed during

smoking comes from a combination of three main sources: thermal decomposition

(about 30%), combustion (about 36%) and reduction of carbon dioxide with carbonized tobacco (at least 23%). Formation of carbon monoxide from thermal

decomposition, which is largely controlled by chemical kinetics, starts at a temperature of about 180D C and finishes at about 1050D C. Formation of carbon

monoxide and carbon dioxide during combustion is controlled largely by the

diffusion of oxygen to the surface (k_a) and via a surface reaction (k_b). At 250D C, k_a

and k_b, are about the same. At 400D C, the reaction becomes diffusion controlled.

Finally, the reduction of carbon dioxide with carbonized tobacco or charcoal occurs

at temperatures around 390D C and above.

0024 During smoking there are three distinct regions in a cigarette: the

combustion zone, the pyrolysis/distillation zone, and the condensation/filtration zone. While not wishing to be bound by theory, it is believed that the nanoscale

composite catalyst can target the various reactions that occur in different regions of

the cigarette during smoking.

0025 First, the combustion zone is the burning zone of the cigarette produced

during smoking of the cigarette, usually at the lighted end of the cigarette. The

temperature in the combustion zone ranges from about 700D C to about 950D C, and

the heating rate can be as high as 500D C/second. Because oxygen is being

consumed in the combustion of tobacco to produce carbon monoxide, carbon

dioxide, water vapor, and various organics, the concentration of oxygen is low in the

combustion zone. The low oxygen concentrations coupled with the high

temperature leads to the reduction of carbon dioxide to carbon monoxide by the carbonized tobacco. In this region, the nanoscale composite catalyst can convert carbon monoxide to carbon dioxide via both catalysis and oxidation mechanism.

The combustion zone is highly exothermic and the heat generated is carried to the pyrolysis/distillation zone.

0026 The pyrolysis zone is the region behind the combustion zone, where the

temperatures range from about 200D C to about 600D C. The pyrolysis zone is where

most of the carbon monoxide is produced. The major reaction is the pyrolysis (i.e.

the thermal degradation) of the tobacco that produces carbon monoxide, carbon

dioxide, smoke components, and charcoal using the heat generated in the

combustion zone. There is some oxygen present in this region, and thus the

nanoscale composite catalyst may act as a catalyst for the oxidation of carbon

monoxide to carbon dioxide. The catalytic reaction begins at 150D C and reaches

maximum activity around 300D C.

0027 In the condensation/filtration zone the temperature ranges from ambient to

about 150D C. The major process in this zone is the condensation/filtration of the

smoke components. Some amount of carbon monoxide and carbon dioxide diffuse

out of the cigarette and some oxygen diffuses into the cigarette. The partial pressure

of oxygen in the condensation/filtration zone does not generally recover to the

atmospheric level.

0028 The nanoscale composite catalyst comprises metal and/or metal oxide

nanoscale particles supported on nanoscale support particles. Nanoscale particles are a novel class of materials whose distinguishing feature is that their average grain or other structural domain size is below 100 nanometers. The nanoscale particles can have an average particle size less than about 100 nm, preferably less than about

50 nm, more preferably less than about 10 nm, and most preferably less than about 7 nm. Nanoscale particles have very high surface area to volume ratios, which makes

them attractive for catalytic applications. The nanoscale particle size can be

measured using transmission electron microscopy (TEM).

0029 The support can comprise inorganic oxide materials such as silica gel, iron

oxide, titanium oxide, aluminum oxide or other material. The synergistic

combination of catalytically active nanoscale particles with a catalytically active

(nanoscale) support can produce a more efficient catalyst. Thus, nanoscale particles

advantageously allow for the use of smaller quantities of material as compared with

conventional catalysts to catalyze, for example, the oxidation of CO to CO₂.

0030 The nanoscale composite catalyst comprises metal and/or metal oxide

particles and a support that may be made using any suitable technique, or the

constituents can be purchased from a commercial supplier. For instance, MACH I,

Inc., King of Prussia, PA sells Fe₂O₃ nanoscale particles under the trade names

NANOCATϋ Superfine Iron Oxide (SFIO) and NANOCATD Magnetic Iron Oxide.

The NANOCATO Superfine Iron Oxide (SFIO) is amorphous ferric oxide in the

form of a free flowing powder, with a particle size of about 3 nm, a specific surface

area of about 250 m²/g, and a bulk density of about 0.05 g/ml. The NANOCATQ Superfine Iron Oxide (SFIO) is synthesized by a vapor-phase process, which renders

it free of impurities that may be present in conventional catalysts, and is suitable for use in food, drugs, and cosmetics. The NANOCATD Magnetic Iron Oxide is a free

flowing powder with a particle size of about 25 nm and a surface area of about 40 m²/g. According to a preferred embodiment, nanoscale metal particles, such as

nanoscale noble metal particles, can be supported on nanoscale iron oxide particles.

0031 According to one method, commercially available metal and/or metal

oxide nanoscale particles such as nanoscale gold, copper, copper-zinc and/or silver

particles can be intimately mixed with a dispersion of a support material such as

colloidal silica, which can be gelled in the presence of an acid or base and allowed to

dry such as by drying in air. Acids and bases that can be used to gel the colloidal

mixture include hydrochloric acid, acetic acid, formic acid, nitric acid, ammonium

hydroxide, and the like. The colloidal support can be any suitable concentration

such as, for example, 10 to 60 wt.%, e.g., a 15 wt.% dispersion or a 40 wt.%

dispersion. When an acid containing chlorine is used, preferably the gel is washed

in de-ionized water before drying in order to reduce the concentration of chloride

ions in the gel.

0032 According to a second method, nanoscale particles can be formed in situ

upon heating a mixture of a suitable metal precursor compound and support. By

way of example, metal and/or metal oxide precursor compounds such as gold

hydroxide, silver pentane dionate, copper (II) pentane dionate, copper oxalate-zinc oxalate, or iron pentane dionate can be dissolved in a suitable solvent such as alcohol and mixed with a support material such as colloidal silica. During or after

gelation, the metal precursor-colloidal silica mixture can be heated to a relatively

low temperature, for example 200-400EC, wherein thermal decomposition of the

metal precursor results in the formation of nanoscale metal and/or metal oxide

particles supported on the silica support. In place of colloidal silica, colloidal titania or a colloidal silica-titania mixture can be used as a support.

0033 Alternatively, both the nanoscale support particles and the metal and/or

metal oxide nanoscale particles can be formed in situ upon heating a mixture of

suitable metal precursor compounds. For example, a metal precursor such as gold

hydroxide, silver pentane dionate, copper (II) pentane dionate, copper oxalate-zinc

oxalate, or iron pentane dionate can be dissolved in a suitable solvent such as

alcohol and mixed with a second metal precursor (e.g., a support precursor) such as

titanium pentane dionate, iron pentane dionate, iron oxalate or other oxide precursor.

The metal precursor mixture can be heated to a relatively low temperature, for

example 200-400EC, wherein thermal decomposition of the metal precursors results

in the formation of nanoscale metal and/or metal oxide particles supported on

nanoscale oxide support particles.

0034 Molecular organic decomposition (MOD) can be used to prepare nanoscale

particles. The MOD process starts with a metal precursor containing the desired

metallic element dissolved in a suitable solvent. The process can involve a single metal precursor bearing one or more metallic atoms or the process can involve

multiple single metallic precursors that are combined in solution to form a solution mixture. As described above, MOD can be used to prepare nanoscale metal particles and/or nanoscale metal oxide particles, including the support.

0035 The decomposition temperature of the metal precursor is the temperature

at which the ligands substantially dissociate (or volatilize) from the metal atoms.

During this process the bonds between the ligands and the metal atoms are broken

such that the ligands are vaporized or otherwise separated from the metal.

Preferably all of the ligand(s) decompose. However, nanoscale particles may also

contain carbon obtained from partial decomposition of the organic or inorganic

components present in the metal precursor and/or solvent. Preferably the nanoscale

particles are essentially carbon free.

0036 The metal precursors used in MOD processing preferably are high purity,

non-toxic, and easy to handle and store (with long shelf lives). Desirable physical

properties include solubility in solvent systems, compatibility with other precursors

for multi-component synthesis, and volatility for low temperature processing.

0037 Nanoscale particles can be obtained from mixtures of metal precursors or

from single-source metal precursor molecules in which one or more metallic

elements are chemically associated. The desired stoichiometry of the resultant

particles can match the stoichiometry of the metal precursor solution. 0038 An aspect of the method described herein for making a nanoscale

composite catalyst is that a commercially desirable stoichiometry can be obtained. For example, the desired atomic ratio in the catalyst can be achieved by selecting a metal precursor or mixture of metal precursors having a ratio of first metal atoms to

second metal atoms that is equal to the desired atomic ratio.

0039 The metal precursor compounds are preferably metal organic compounds, which have a central main group, transition, lanthanide, or actinide metal atom or

atoms bonded to a bridging atom (e.g., N, O, P or S) that is in turn bonded to an

organic radical. Examples of the main group metal atom include, but are not limited

to, B, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Ce,

Hf, Ta, W, Re, Os, Ir, Pt and Au. Such compounds may include metal alkoxides, β-

diketonates, carboxylates, oxalates, citrates, metal hydrides, thiolates, amides,

nitrates, carbonates, cyanates, sulfates, bromides, chlorides, and hydrates thereof.

The metal precursor can also be a so-called organometallic compound, wherein a

central metal atom is bonded to one or more carbon atoms of an organic group.

Aspects of processing with these metal precursors are discussed below.

0040 Precursors for the synthesis of nanoscale oxides are molecules having pre¬

existing metal-oxygen bonds such as metal alkoxides M(OR)_n or oxoalkoxides

MO(OR)_n , R = saturated or unsaturated organic group, alkyl or aryl, β-diketonates

M(β-diketonate)_n (β-diketonate = RCOCHCOR¹) and metal carboxylates M(O₂CR)_n.

Metal alkoxides have both good solubility and volatility and are readily applicable to MOD processing. Generally, however, these compounds are highly hygroscopic and require storage under inert atmosphere. In contrast to silicon alkoxides, which are liquids and monomeric, the alkoxides based on most metals are solids. On the

other hand, the high reactivity of the metal-alkoxide bond can make these metal

precursor materials useful as starting compounds for a variety of heteroleptic species

(i.e., species with different types of ligands) such as M(0R)_n-xZχ (Z = β-diketonate

or O₂CR).

0041 Metal alkoxides M(OR)_n react easily with the protons of a large variety of

molecules. This allows easy chemical modification and thus control of stoichiometry by using, for example, organic hydroxy compounds such as alcohols,

silanols (R₃SiOH), glycols OH(CH₂)_nOH, carboxylic and hydroxycarboxylic acids,

hydroxyl surfactants, etc.

0042 Fluorinated alkoxides M(ORp)_n (R_F = CH(CF₃)₂, C₆F₅, ...) are readily

soluble in organic solvents and less susceptible to hydrolysis than classical

alkoxides. These materials can be used as precursors for fluorides, oxides or

fluoride-doped oxides such as F-doped tin oxide, which can be used as metal oxide

nanoscale particles and/or as a nanoscale support.

0043 Modification of metal alkoxides reduces the number of M-OR bonds

available for hydrolysis and thus hydrolytic susceptibility. Thus, it is possible to

control the solution chemistry in situ by using, for example, β-diketonates (e.g. acetylacetone) or carboxylic acids (e.g. acetic acid) as modifiers for, or in lieu of, the alkoxide.

0044 Metal β-diketonates [M(RCOCHCOR')_n]_m are attractive precursors for

MOD processing because of their volatility and high solubility. Their volatility is governed largely by the bulk of the R and R¹ groups as well as the nature of the

metal, which will determine the degree of association, m, represented in the formula

above. Acetylacetonates (R=R=CH₃) are advantageous because they can provide

good yields.

0045 Metal β-diketonates are prone to a chelating behavior that can lead to a

decrease in the nuclearity of these precursors. These ligands can act as surface

capping reagents and polymerization inhibitors. Thus, small particles can be

obtained after hydrolysis of M(OR)_n-x(β-diketonate)_x. Acetylacetone can, for

instance, stabilize nanoscale colloids. Thus, metal β-diketonate precursors are

preferred for preparing nanoscale particles.

0046 Metal carboxylates such as acetates (M(O₂CMe)_n) are commercially

available as hydrates, which can be rendered anhydrous by heating with acetic

anhydride or with 2-methoxyethanol. Many metal carboxylates generally have poor

solubility in organic solvents and, because carboxylate ligands act mostly as

bridging-chelating ligands, readily form oligomers or polymers. However,

2-ethylhexanoates (M(O₂CCHEt_nBu)_n), which are the carboxylates with the smallest

number of carbon atoms, are generally soluble in most organic solvents. A large number of carboxylate derivatives are available for aluminum. Nanoscale aluminum-

oxygen macromolecules and clusters (alumoxanes) can be used as catalyst materials. For

example, formate Al(O₂CH)₃(H₂O) and carboxylate-alumoxanes

[AlO_x(OH)_y(O₂CR)_z]_m can be prepared from the inexpensive minerals gibsite or

boehmite.

0047 Multicomponent materials can be prepared from mixed metal (hetero- metallic) precursors or, alternatively, from a mixture of single metal (homo-metallic) precursors.

0048 The use of multiple single-metal precursors has the advantage of

flexibility in designing precursor rheology as well as product stoichiometry.

Hetero-metallic precursors, on the other hand, may offer access to metal systems

whose single metal precursors have undesirable solubility, volatility or compatibility.

0049 Mixed-metal species can be obtained via Lewis acid-base reactions or

substitution reactions by mixing alkoxides and/or other metal precursors such as

acetates, β-diketonates or nitrates. Because the combination reactions are controlled

by thermodynamics, however, the stoichiometry of the hetero-compound once

isolated may not reflect the composition ratios in the mixture from which it was

prepared. On the other hand, most metal alkoxides can be combined to produce

hetero-metallic species that are often more soluble than the starting materials. 0050 The solvent(s) used in MOD processing are selected based on a number of criteria including high solubility for the metal precursor compounds; chemical inertness to the metal precursor compounds; rheological compatibility with the deposition technique being used (e.g. the desired viscosity, wettability and/or

compatibility with other rheology adjusters); boiling point; vapor pressure and rate

of vaporization; and economic factors (e.g. cost, recoverability, toxicity, etc.).

0051 Solvents that may be used in MOD processing include pentanes,

hexanes, cyclohexanes, xylenes, ethyl acetates, toluene, benzenes, tetrahydrofuran,

acetone, carbon disulfide, dichlorobenzenes, nitrobenzenes, pyridine, methyl

alcohol, ethyl alcohol, butyl alcohol, and mineral spirits.

0052 According to another method, nanoscale particles of metals and/or

metal oxides can be formed on a nanoscale support, such as an iron oxide support.

Suitable precursor compounds for the metal, metal oxide and iron oxide are those

that thermally decompose at relatively low temperatures, such as discussed above.

According to an embodiment, a metal precursor solution can be combined with an

iron oxide support. The support can be commercially available nanoscale particles,

such as nanoscale iron oxide particles, or the support can be prepared from a

colloidal solution or metal precursor solution as described above.

0053 A metal precursor solution may be contacted with a support in a

number of ways. For example, the metal precursor may be dissolved or suspended

in a liquid, and the support may be mixed with the liquid having the dispersed or suspended metal precursor. The dissolved or suspended metal precursor can be adsorbed onto a surface of the support or absorbed into the support. The metal

precursor may also be deposited onto a surface of the support by removing the

liquid, such as by evaporation so that the metal precursor remains on the support. The liquid may be substantially removed from the support during or prior to thermally treating the metal precursor, such as by heating the support at a

temperature higher than the boiling point of the liquid or by reducing the pressure of

the atmosphere surrounding the support.

0054 Thermal treatment causes decomposition of the metal precursor to

dissociate the constituent metal atoms, whereby the metal atoms may combine to

form metal and/or metal oxide particles having an atomic ratio approximately equal

to the stoichiometric ratio of the metal(s) in the metal precursor solution.

0055 The support or support precursor can be contacted with a metal

precursor solution and the contacted support can be heated in the substantial absence

of an oxidizing atmosphere. Alternatively, the support or support precursor can be

contacted with a metal precursor solution and the contacted support can be heated in

the presence of an oxidizing atmosphere and then heated in the substantial absence

of an oxidizing atmosphere.

0056 The metal precursor-contacted support is preferably heated to a

temperature equal to or greater than the decomposition temperature of the metal

precursor. The preferred heating temperature will depend on the particular ligands used as well as on the degradation temperature of the metal(s) and any other desired

groups which are to remain. However, the preferred temperature is from about

200EC to 400EC, for example 300EC or 350EC. The heating of the metal

precursor-contacted support can occur in an oxidizing and/or reducing atmosphere.

0057 Iron oxide nanoscale particles smaller than about 100 nm can be used

as a support for nanoscale gold particles. As an example, iron oxide nanoscale

particles having a size as small as 3 nm can be used as the support material. The

Au-Fe₂O₃ nanoscale composite catalyst can be produced from gold hydroxide that is

dissolved in alcohol and mixed with the iron oxide. Decomposition of the hydroxide

into nanoscale gold particles, which can be intimately coated/mixed with the iron

oxide nanoscale particles, can be caused by heating the mixture to 300 or 400EC.

TEM images of nanometer scale gold particles supported on nanometer scale iron

oxide are shown in Figures 1-4.

0058 In general, a metal precursor and a support can be combined in any

suitable ratio to give a desired loading of metal particles on the support. Gold

hydroxide and iron oxide can be combined, for example, to produce from about 1%

to 25% wt.%, e.g., 2 wt.%, 5 wt.% or 15 wt.%, gold on iron oxide.

0059 Other preferred support materials include Cu₂O, CuO, SiO₂, TiO₂,

CoO, ZrO, CeO₂, Ce₂O₃, or Al₂O₃, or doped metal oxides such as Y₂O₃ optionally

doped with zirconium, Mn₂O₃ optionally doped with palladium, and mixtures

thereof. The support may include substantially any material which, when heated to a temperature at which a metal precursor is converted to a metal and/or metal oxide on the surface thereof, does not melt, vaporize completely, or otherwise become incapable of supporting nanoscale particles.

0060 During the conversion of CO to CO₂, the nanoscale composite

catalyst may become reduced. For example, Fe₂O_3j which may comprise the support

or particles dispersed on a support, may be reduced to Fe₃O₄ or FeO during the

reaction of CO to CO₂.

0061 Iron oxide is a preferred constituent in the composite because it has a

dual function as a CO catalyst in the presence of oxygen and as a CO oxidant for the

direct oxidation of CO in the absence of oxygen. A catalyst that can also be used as

an oxidant is especially useful for certain applications, such as within a burning

cigarette where the partial pressure of oxygen can be very low.

0062 A catalyst is capable of affecting the rate of a chemical reaction, e.g. ,

increasing the rate of oxidation of carbon monoxide to carbon dioxide and/or

increasing the rate of reduction of nitric oxide to nitrogen without participating as a

reactant or product of the reaction. An oxidant is capable of oxidizing a reactant,

e.g., by donating oxygen to the reactant, such that the oxidant itself is reduced.

0063 The nanoscale composite catalysts will preferably be distributed

throughout the tobacco rod portion of a cigarette. By providing the nanoscale

composite catalysts throughout the tobacco rod, it is possible to reduce the amount of carbon monoxide drawn through the cigarette, and particularly at both the

combustion region and in the pyrolysis zone.

0064 The nanoscale composite catalysts, as described above, may be

provided along the length of a tobacco rod by distributing the nanoscale composite catalysts on the tobacco or incorporating them into the cut filler tobacco using any

suitable method. The nanoscale composite catalysts can also be incorporated in

cigarette filter material that is used to make a cigarette filter. The nanoscale

composite catalysts may be provided in the form of a powder or in a solvent in the

form of a dispersion. Nanoscale composite catalysts in the form of a dry powder can

be dusted on cut filler tobacco and/or cigarette filter material. Nanoscale composite

catalysts may also be present in the form of a dispersion and sprayed on the cut filler

tobacco, cigarette paper and/or cigarette filter material. The nanoscale composite

catalyst may also be added to the cut filler tobacco stock supplied to the cigarette

making machine or added to a tobacco column prior to wrapping cigarette paper

around the tobacco column. The catalysts may be added to paper stock of a cigarette

papermaking machine or to cigarette filter material during or after processing of the

cigarette filter material (e.g., during the manufacture of the cigarette filter material or

during the manufacture of a cigarette filter comprising the cigarette filter material).

0065 The step of heating a mixture comprising a metal precursor solution

to a temperature effective to thermally decompose the metal precursor into nanoscale particles is preferably performed prior to adding the nanoscale composite catalyst to

the cigarette.

0066 The amount of the nanoscale composite catalyst can be selected such

that the amount of carbon monoxide in mainstream smoke is reduced during

smoking of a cigarette. Preferably, the amount of the nanoscale composite catalyst

will be a catalytically effective amount, e.g., from about a few milligrams, for example, 5 mg/cigarette, to about 200 mg/cigarette. More preferably, the amount of

nanoscale composite catalyst will be from about 10 mg/cigarette to about 100

mg/cigarette. The nanoscale composite catalyst can be added to the tobacco cut

filler and/or cigarette filter in an amount effective to convert at least about 10%,

preferably at least about 25% of the carbon monoxide to carbon dioxide.

0067 One embodiment provides a cut filler composition comprising

tobacco and at least one catalyst that is capable of converting carbon monoxide to

carbon dioxide, where the catalyst is in the form of a nanoscale composite catalyst.

0068 Any suitable tobacco mixture may be used for the cut filler.

Examples of suitable types of tobacco materials include flue-cured, Burley,

Maryland or Oriental tobaccos, the rare or specialty tobaccos, and blends thereof.

The tobacco material can be provided in the form of tobacco lamina, processed

tobacco materials such as volume expanded or puffed tobacco, processed tobacco

stems such as cut-rolled or cut-puffed stems, reconstituted tobacco materials, or

blends thereof. The tobacco can also include tobacco substitutes. 0069 In cigarette manufacture, the tobacco is normally employed in the form of cut filler, i.e. in the form of shreds or strands cut into widths ranging from about 1/10 inch to about 1/20 inch or even 1/40 inch. The lengths of the strands

range from between about 0.25 inches to about 3.0 inches. The cigarettes may

further comprise one or more flavorants or other additives (e.g. burn additives,

combustion modifying agents, coloring agents, binders, etc.) known in the art.

0070 Another embodiment provides a cigarette comprising a tobacco rod,

wherein the tobacco rod comprises tobacco cut filler having at least one nanoscale

composite catalyst, as described above, which is capable of acting as a catalyst for

the conversion of carbon monoxide to carbon dioxide. A further embodiment

provides a method of making a cigarette, comprising (i) adding a nanoscale

composite catalyst to a tobacco cut filler; (ii) providing the cut filler to a cigarette

making machine to form a tobacco column; and (iii) placing a paper wrapper around

the tobacco column to form the cigarette.

0071 Techniques for cigarette manufacture are known in the art. Any

conventional or modified cigarette making technique may be used to incorporate the

nanoscale composite catalysts. The resulting cigarettes can be manufactured to any

known specifications using standard or modified cigarette making techniques and

equipment. Typically, the cut filler composition is optionally combined with other

cigarette additives, and provided to a cigarette making machine to produce a tobacco

rod, which is then wrapped in cigarette paper, and optionally tipped with filters. 0072 Cigarettes may range from about 50 mm to about 120 mm in length. Generally, a regular cigarette is about 70 mm long, a "King Size" is about 85 mm

long, a "Super King Size" is about 100 mm long, and a "Long" is usually about 120

mm in length. The circumference is from about 15 mm to about 30 mm, and preferably around 25 mm. The tobacco packing density is typically between the range of about 100 mg/cm³ to about 300 mg/cm³, and preferably 150 mg/cm³ to

about 275 mg/cm³.

0073 Yet another embodiment provides a method of smoking the cigarette

described above, which involves lighting the cigarette to form smoke and drawing

0074 While the invention has been described with reference to preferred

embodiments, it is to be understood that variations and modifications may be

resorted to as will be apparent to those skilled in the art. Such variations and

modifications are to be considered within the purview and scope of the invention as

defined by the claims appended hereto.

Claims

What is claimed is:

1. A cut filler composition comprising tobacco and a nanoscale

composite catalyst for the conversion of carbon monoxide to carbon dioxide,

wherein the nanoscale composite catalyst comprises nanoscale metal particles and/or

nanoscale metal oxide particles supported on nanoscale support particles.

2. The cut filler composition of Claim 1 , wherein the nanoscale metal

particles and/or nanoscale metal oxide particles comprise an element selected from

the group consisting of B, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru,

Rh, Pd, Ag, Sn, Ce, Hf, Ta, W, Re, Os, Ir, Pt, Au and mixtures thereof.

3. The cut filler composition of Claim 1, wherein the nanoscale support

particles comprise an oxide selected from the group consisting of aluminum oxide,

silicon oxide, titanium oxide, iron oxide, cobalt oxide, copper oxide, zirconium

oxide, cerium oxide, yttrium oxide optionally doped with zirconium, manganese

oxide optionally doped with palladium, and mixtures thereof.

4. The cut filler composition of Claim 1 , wherein the nanoscale support

particles are derived from a colloidal solution.

5. The cut filler composition of Claim 1 , wherein the nanoscale metal

particles and/or nanoscale metal oxide particles comprise gold and the nanoscale support particles comprise an oxide selected from the group consisting of silicon

oxide, titanium oxide, iron oxide, copper oxide and mixtures thereof.

6. The cut filler composition of Claim 1 , wherein the nanoscale metal

particles and/or nanoscale metal oxide particles comprise gold and the nanoscale

support particles comprise iron oxide.

7. The cut filler composition of Claim 1 , wherein the nanoscale

composite catalyst comprises from about 0.1 to 25 wt.% gold nanoscale particles

supported on iron oxide nanoscale support particles.

8. The cut filler composition of Claim 1 , wherein the nanoscale support

particles and the nanoscale metal and/or metal oxide particles have an average

particle size less than about 50 nm.

9. The cut filler composition of Claim 1 , wherein the nanoscale support

particles and the nanoscale metal and/or metal oxide particles have an average

particle size less than about 10 nm.

10. The cut filler composition of Claim 1, wherein the nanoscale

composite catalyst is essentially carbon free.

11. The cut filler composition of Claim 1 , wherein the cut filler

comprises the nanoscale composite catalyst in an amount effective to convert at least

about 10% of the carbon monoxide to carbon dioxide.

12. A cigarette comprising cut tobacco filler, cigarette paper and cigarette filter, wherein the cut filler, cigarette paper and/or cigarette filter comprise a catalyst

capable of converting carbon monoxide to carbon dioxide, wherein the catalyst is in

the form of a nanoscale composite catalyst comprising nanoscale metal particles

and/or nanoscale metal oxide particles supported on nanoscale support particles.

13. The cigarette of Claim 12, wherein the nanoscale metal particles

and/or nanoscale metal oxide particles comprise an element selected from the group

consisting of B, Mg, Al, Si, Ti, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag,

Sn, Ce, Hf, Ta, W, Re, Os, Ir, Pt, Au and mixtures thereof.

14. The cigarette of Claim 12, wherein the nanoscale support particles

comprise an oxide selected from the group consisting of aluminum oxide, silicon

oxide, titanium oxide, iron oxide, cobalt oxide, copper oxide, zirconium oxide,

cerium oxide, yttrium oxide optionally doped with zirconium, manganese oxide

optionally doped with palladium, and mixtures thereof.

15. The cigarette of Claim 12, wherein the nanoscale support particles are derived from a colloidal solution.

16. The cigarette of Claim 12, wherein the nanoscale metal particles

and/or nanoscale metal oxide particles comprise gold and the nanoscale support

particles comprise an oxide selected from the group consisting of silicon oxide,

titanium oxide, iron oxide, copper oxide and mixtures thereof.

17. The cigarette of Claim 12, wherein the nanoscale metal particles

and/or nanoscale metal oxide particles comprise gold and the nanoscale support

particles comprise iron oxide.

18. The cigarette of Claim 12, wherein the nanoscale composite catalyst

comprises from about 0.1 to 25 wt.% gold nanoscale particles supported on iron

oxide nanoscale support particles.

19. The cigarette of Claim 12, wherein the nanoscale support particles

and the nanoscale metal and/or metal oxide particles have an average particle size

less than about 50 nm.

20. The cigarette of Claim 12, wherein the nanoscale support particles and the nanoscale metal and/or metal oxide particles have an average particle size less than about 10 nm.

21. The cigarette of Claim 12, wherein the nanoscale composite catalyst

is essentially carbon free.

22. The cigarette of Claim 12, wherein the cut filler comprises the

nanoscale composite catalyst in an amount effective to convert at least about 10% of

the carbon monoxide to carbon dioxide.

23. The cigarette of Claim 12, wherein the cigarette comprises from

about 5 mg of the nanoscale composite catalyst per cigarette to about 200 mg of the

nanoscale composite catalyst per cigarette.

24. The cigarette of Claim 12, wherein the cigarette comprises from

about 10 mg of the nanoscale composite catalyst per cigarette to about 100 mg of the

nanoscale composite catalyst per cigarette.

25. The cigarette of Claim 12, wherein the catalyst comprises gold

nanoscale particles supported on nanoscale iron oxide support particles and the catalyst is incorporated in the cigarette filter.

26. A method of making a cigarette, comprising:

(i) incorporating a nanoscale composite catalyst in tobacco cut filler, cigarette paper and/or cigarette filter;

(ii) providing the cut filler to a cigarette making machine to form a

tobacco column;

(iii) placing a paper wrapper around the tobacco column to form a tobacco

rod; and

(iv) attaching the cigarette filter to the tobacco rod to form the cigarette.

27. The method of Claim 26, comprising combining nanoscale metal

and/or metal oxide particles that comprise an element selected from the group

Sn, Ce, Hf, Ta, W, Re, Os, Ir, Pt and Au and mixtures thereof, and

nanoscale support particles comprising an oxide selected from the group consisting

of aluminum oxide, silicon oxide, titanium oxide, iron oxide, cobalt oxide, copper

oxide, zirconium oxide, cerium oxide, yttrium oxide optionally doped with

zirconium, manganese oxide optionally doped with palladium, and mixtures thereof

to form the nanoscale composite catalyst.

28. The method of Claim 26, comprising combining nanoscale metal particles and/or nanoscale metal oxide particles comprising gold and nanoscale

support particles comprising an oxide selected from the group consisting of silicon

oxide, titanium oxide, iron oxide, copper oxide and mixtures thereof to form the

nanoscale composite catalyst.

29. The method of Claim 26, comprising combining nanoscale metal

particles and/or nanoscale metal oxide particles comprising gold and nanoscale

support particles comprising iron oxide to form a nanoscale composite catalyst

comprising from about 0.1 to 25 wt.% gold.

30. The method of Claim 26, comprising adding the nanoscale composite

catalyst to the cut filler to give from about 5 mg to 200 mg of the nanoscale

composite catalyst per cigarette.

31. The method of Claim 26, comprising adding the nanoscale composite

catalyst to the cut filler to give from about 10 mg to 100 mg of the nanoscale

composite catalyst per cigarette.

32. The method of Claim 26, further comprising forming the nanoscale

composite catalyst by: combining nanoscale metal and/or metal oxide particles with a colloidal

solution, increasing the viscosity of the colloidal solution to form an intimate mixture of the metal and/or metal oxide nanoscale particles and the colloidal solution, and

drying the mixture to form the nanoscale composite catalyst.

33. The method of Claim 32, comprising combining nanoscale particles

having an average particle size of less than about 7 nm with the colloidal solution.

34. The method of Claim 32, comprising combining a colloidal solution

having a concentration of colloids of from about 10 to 60 weight percent with the

nanoscale particles.

35. The method of Claim 32, wherein the increasing the viscosity of the

colloidal solution comprises changing the pH of the colloidal solution.

36. The method of Claim 32, wherein the increasing the viscosity of the

colloidal solution comprises adding a dilute acid or a dilute base to the colloidal

solution.

37. The method of Claim 32, further comprising adding dilute HCl to the colloidal solution.

38. The method of Claim 32, wherein the drying comprises air-drying or super-critical drying.

39. The method of Claim 32, further comprising washing the mixture in

de-ionized water before the drying.

40. The method of Claim 27, further comprising forming the nanoscale

composite catalyst by:

combining a metal precursor and a solvent to form a metal precursor solution,

combining the metal precursor solution with nanoscale support particles to form a mixture,

heating the mixture to a temperature effective to thermally decompose the

metal precursor into nanoscale particles, and

drying the mixture.

41. The method of Claim 40, comprising combining the metal precursor

solution with nanoscale support particles that are in a colloidal solution.

42. The method of Claim 40, comprising combining nanoscale support

particles that comprise and oxide selected from the group consisting of aluminum

oxide, silicon oxide, titanium oxide, iron oxide, cobalt oxide, copper oxide,

zirconium oxide, cerium oxide, yttrium oxide, manganese oxide and mixtures thereof with the metal precursor solution.

43. The method of Claim 40, comprising combining a metal precursor comprising a dionate, oxalate and/or a hydroxide with the solvent.

44. The method of Claim 40, comprising combining a metal precursor

comprising an element selected from the group consisting of B, Mg, Al, Si, Ti, Fe,

Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Ce, Hf, Ta, W, Re, Os, Ir, Pt,

Au and mixtures thereof with the solvent.

45. The method of Claim 40, comprising combining a solvent comprising

at least one of distilled water, alcohol, aldehydes, ketones and aromatic

hydrocarbons with the metal precursor.

46. The method of Claim 40, wherein the mixture is heated to a

temperature of from about 200 to 400EC.

47. The method of Claim 40, comprising combining nanoscale support particles having an average diameter of less than about 50 nm with the metal

precursor solution.

48. The method of Claim 41 , wherein the viscosity of the colloidal

solution is increased to form a gel before heating the mixture.

49. The method of Claim 48, wherein the gel is washed before heating

the mixture.

50. The method of Claim 41 , comprising combining a colloidal solution

metal precursor solution.

51. The method of Claim 41 , comprising combining a metal precursor

solution comprising gold with a colloidal solution comprising an oxide selected

from the group consisting of silicon oxide, titanium oxide, iron oxide, copper oxide

and mixtures thereof.

52. The method of Claim 41 , comprising combining a metal precursor

solution comprising gold with a colloidal solution comprising iron oxide at a ratio of

about 0.1 to 25 wt.% gold to iron oxide.

53. The method of Claim 41 , wherein the increasing the viscosity of the colloidal solution comprises varying the pH of the mixture.

54. The method of Claim 41 , wherein the step of increasing the viscosity

of the colloidal solution comprises adding a dilute acid to the mixture.

55. The method of Claim 54, wherein dilute HCl is added to the mixture.

56. The method of smoking the cigarette of Claim 12, comprising

lighting the cigarette to form smoke and drawing the smoke through the cigarette,

wherein during the smoking of the cigarette, the catalyst acts as a catalyst for the

conversion of carbon monoxide to carbon dioxide.