WO2008045031A2

WO2008045031A2 - Nanolayer oxidation catalysis for smoking articles

Info

Publication number: WO2008045031A2
Application number: PCT/US2006/038654
Authority: WO
Inventors: Harold B. Dellinger; Slawomir M. Lomnicki
Original assignee: Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College
Priority date: 2006-10-04
Filing date: 2006-10-04
Publication date: 2008-04-17
Also published as: WO2008045031A3; EP2086361A2

Abstract

Catalysis is used to reduce levels of radicals, other toxins, and carbon monoxide in cigarette smoke. The catalysis operates efficiently at temperatures typical of tobacco smoke, is formed from nontoxic materials, and is relatively inexpensive. The nanostructured catalyst contains titanium oxide, iron oxide, and calcium oxide. The catalyst comprises a layer of iron oxide in the y form supported on a titanium oxide core. Addition of calcium cations helps to stabilize the iron oxide in the y form. The iron oxide layer is on the order of a few nanometers thick on the surface of the titanium oxide core, in an 'egg-in-shell' structure. The nanocatalyst is highly active in promoting the oxidation of compounds such as hydroquinone, catechol, other hydrocarbons, chlorinated phenols, semiquinone radicals, and carbon monoxide, at room temperature and higher temperatures. Catalysis remains active in a pyrolytic or combustion environment for extended periods of time, and has high redox cycling potential. The efficiency of catalysis is not strongly affected by coking in a pyrolytic or combustion environment.

Description

NANOLAYER OXIDATION CATALYSIS, AND ITS USE IN REDUCING TOXIN LEVELS IN TOBACCO SMOKE

Harold B. Dellinger, Slawomir M. Lomnicki

Express Mail No. EV854031008

FiIe No. Dellinger 0314W

[0001] The development of this invention was funded in part by the United

States Government under grant number R 827719-01 -0 awarded by the Environmental Protection Agency. The United States Government has certain rights in this invention.

TECHNICAL FIELD

[0002] This invention pertains to oxidation catalysis, particularly to the catalytic oxidation of toxins in cigarette smoke and in other heated gaseous mixtures.

BACKGROUND ART

[0003] Although it may be impossible to make cigarettes and other tobacco products truly "safe," it is nevertheless a highly desirable goal to reduce the level of toxins contained in tobacco smoke. While smokers may become habituated to nicotine, meaning that it could be self-defeating to try to remove nicotine from cigarette smoke entirely, there could still be substantial public health benefits from removing other toxins from cigarette smoke, such as semiquinone radicals, other free radicals, their precursors, and carbon monoxide. Lower toxin levels could benefit not only smokers themselves, but also those who are exposed to secondhand smoke. There is an unfilled need for improved means to: (1) reduce the concentrations of free radicals and their precursors, (2) promote the decomposition of toxic organic compounds and radicals found in tobacco smoke, (3) promote the oxidation of carbon Express Mail No. EV854031008 monoxide to carbon dioxide, preferably while simultaneously decomposing toxic organic compounds and radicals, (4) operate efficiently over a temperature range from room temperature (about 25-30⁰C) to about 900⁰C, which includes temperatures typical of the generation of cigarette smoke, and temperatures within a cigarette before smoke enters the filter, (5) operate efficiently in a coking or fouling environment, (6) use nontoxic materials, and (7) be relatively inexpensive.

[0004] Semiquinone radicals and their precursors, hydroquinone and catechol, are among the most toxic components of cigarette smoke. Semiquinone radicals are unusual in that they can be stable, non-reactive, and persistent in cigarette smoke and in the environment. When introduced to biological systems, they reduce oxygen to form superoxide radicals that initiate cascade reactions that produce other reactive oxygen species, oxidative stress, and cellular damage. [0005] Prior attempts to catalyze toxins in burning cigarettes have generally not been very successful. There is an unfilled need for a technique to catalytically destroy semiquinone radicals, catechols, hydroquinones, and other toxins in burning cigarettes or other tobacco products, a technique that: (1) is selective towards the toxic species, (2) does not substantially reduce total particulate matter, which contains the taste desired by most smokers, (3) does not foul substantially upon exposure to tar formed by burning tobacco (over a time scale equal to the time it takes to burn a cigarette), (4) does not substantially clog filters on the cigarette or other tobacco product, (5) does not cause the catalyst to be aerosolized when the tobacco is burned, and (6) does not employ toxic materials. There have been prior reports of iron-oxide based catalysts for detoxifying cigarette smoke. However, these prior catalysts have not been practical, either because they lose activity rapidly as tar from the smoke clogs pores on the catalyst surface, or because the catalyst reduces the delivery of total particulate matter to the smoker (and therefore the taste associated with those particulates).

[0006] P. Li et a/., "The removal of carbon monoxide by iron oxide nanoparticles," Appl. Catal. B: Environ., vol. 43, pp. 151-162 (2003) discloses that Express Mail No. EV854031008

Fe₂O₃ nanoparticles (3 nm) were more effective than larger Fe₂O₃ particles in oxidizing carbon monoxide.

[0007] Published international patent application WO 03/086112 discloses the use of an oxyhydride such as FeOOH, AIOOH, or TiOOH in cigarettes, where the oxyhydride decomposes to form a product that acts as an oxidant or catalyst for the conversion of carbon monoxide to carbon dioxide.

[0008] Published international patent application WO 03/020058 discloses the use of nanoparticie additives in cigarettes as an oxidant or catalyst for the conversion of carbon monoxide to carbon dioxide. The nanoparticles are selected from Fe₂O₃, CuO, TiO₂, CeO₂, Ce₂O₃, AI₂O₃, Y₂O₃ doped with zirconium, and Mn₂O₃ doped with palladium.

[0009] Published international patent application WO 03/086115 discloses the use of partially reduced nanoparticie additives in cigarettes as an oxidant for the conversion of carbon monoxide to carbon dioxide, or the conversion of nitric oxide to nitrogen. The compound that is partially reduced may be selected from Fe₂O₃, CuO, TiO₂, CeO₂, Ce₂O₃, AI₂O₃, Y₂O₃ doped with zirconium, and Mn₂O₃ doped with palladium. Preferably, the partially reduced additive comprised Fe₂O₃ nanoparticles that had been treated with a reducing gas such as CO, H₂, or CH₄.

[0010] Published international patent application WO 03/086112 discloses the use of ferric oxide or zinc oxide in a tobacco product to cause the preferential combination of nitrogen with hydrogen rather than with oxygen and carbon, to form ammonia rather than pyridines, for example.

[0011] S. Lomnicki etal., "Development of a supported iron oxide catalyst for destruction of PCDD/F," Abstracts, A&WMA 96^th Annual Conference, pp. 13-14 (2003); and S. Lomnicki et al., "Development of a supported iron oxide catalyst for destruction of PCDD/F," Environ. Sci. Techno!., vol.37, pp.4254-4260 (2003) reported iron oxide catalysts for PCDD/F decomposition using 2-monochlorophenol as a test compound. Iron oxide catalysts supported on titania were prepared by two methods: impregnation and a sol-gel method. Addition of calcium oxide to the catalyst was reported to improve performance. Express Mail No. EV854031008

DISCLOSURE OF INVENTION

[0012] We have discovered that a small, microstructured particle supporting a nanostructured catalyst that contains titanium oxide, iron oxide, and calcium oxide is highly active in promoting the oxidation of various compounds, including for example semiquinone-type radicals, other free radicals, hydroquinone, substituted hydroquinones, catechol, substituted catechols, chlorinated phenols, and carbon monoxide, even at moderately elevated temperatures. The catalyst remains active in both pyrolytic and oxygen-rich environments for extended periods of time, and possesses high redox cycling potential; it is even active at room temperature and moderately elevated temperatures. Unlike highly porous catalysts whose pores are susceptible to clogging by coke, the efficiency of catalysis is not strongly affected by coking in a combustion environment. The novel process may be used, for example, to reduce levels of radicals such as semiquinone radicals, surface-stabilized organic radicals, catechols, hydroquinones, ketones, aldehydes, other toxic hydrocarbons, and carbon monoxide in tobacco smoke. The catalyst is highly reactive with these products. Catalysis operates over a temperature range from room temperature to about 900⁰C, which includes temperatures typical of tobacco smoke and in a conventional cigarette filter. The catalyst is formed from nontoxic materials, and is relatively inexpensive. [0013] The novel technique may be used, for example, to catalytically destroy semiquinone radicals, catechols, hydroquinones, and other toxins in burning cigarettes or other tobacco products. The novel technique: (1) is selective towards the toxic species, (2) does not substantially reduce total particulate matter, which contains the taste desired by most smokers, (3) does not foul substantially (over the relevant time scale) upon exposure to the tar formed by burning cigarettes, (4) does not substantially clog any filters on the cigarette or other tobacco product, (5) does not cause the catalyst to be aerosolized when the tobacco is burned, and (6) is based on nontoxic materials.

[0014] The catalyst comprises a layer of iron oxide, at least some of which is in the y form, supported on a titanium oxide core. Preferably at least 10% of the iron oxide is in the Y form. The iron oxide layer has a thickness on the order of a few Express Mail No. EV854031008 nanometers on the surface of the titanium oxide core, in an "egg-in-shell" structure. The limited addition of calcium cations helps to stabilize the iron oxide in the Y form. [0015] The catalyst comprises about 85-97% titanium oxide by weight, primarily in the core; about 1-15% by weight iron oxide, preferably about 3-10% by weight, contained primarily in a shell surrounding the titanium oxide core; calcium about 0.5-10 mole-% of the iron, preferably about 1-5 mole-% of the iron, primarily in the shell; and about 0-5% by weight other components which, if present, are in sufficiently low concentration that they do not substantially reduce the activity of the catalyst as compared to an otherwise-identical catalyst lacking such other components. The titania core preferably has a diameter between about 1 μm and about 100 μm, more preferably between about 1 μm and about 50 μm.

[0016] Our research has found that semiquinone radicals, catechol, and hydroquinone are formed at temperatures below 500⁰C in a burning cigarette, and tend to be produced in higher concentrations at higher oxygen levels. Certain components of tobacco (e.g., chlorogenic acid, lignin, cellulose) appear to be implicated in the formation of semiquinone radicals. We also found that the concentration of semiquinone radicals appears to increase as tobacco smoke ages, perhaps for as long as 120 hours. These observations imply that secondary exposure to side-stream tobacco smoke (smoke that is not inhaled by the smoker) or to environmental tobacco smoke (smoke that lingers in the air or on surfaces) can be more toxic than the mainstream smoke inhaled by the smoker, at least in some respects.

[0017] The catalyst used in the novel process may be prepared, for example, by a sol-gel preparation method. The catalyst is capable of low-temperature redox cycling between the +2 and +3 oxidation states of iron, starting at temperatures as low as ~180°C. The catalyst promotes the low-temperature (i.e., below about 500⁰C) or moderate temperature (i.e., up to about 900⁰C) oxidation of carbon monoxide to carbon dioxide, and also promotes the low-temperature or moderate-temperature oxidation of organic compounds, including for example phenols, hydrocarbons, and chlorinated hydrocarbons. Experiments have confirmed the low-temperature efficacy of the catalyst in promoting the oxidation of carbon monoxide, hydroquinone and its Express Mail No. EV854031008 derivatives, and catechol and its derivatives, all of which are found as toxins in cigarette smoke.

[0018] The catalyst will catalyze the oxidation and decomposition of a variety of compounds, such as toxic components of various combustion streams, including a variety of unsubstituted and substituted hydrocarbons, including for example acrolein, formaldehyde, acetone, benzene, halogenated benzenes, phenol, substituted phenols, halogenated phenols, other hydroxylated aromatic hydrocarbons, hydroxylated polycyclic aromatic hydrocarbons, catechol, substituted catechols, hydroquinone, substituted hydroquinones, chloroform, bromoform, furan, volatile organic compounds, halogenated volatile organic compounds, lignin, lignin decomposition products, ketones, substituted ketones, aldehydes, substituted aldehydes, radicals derived from any of these compounds, and other organic gas-phase radicals.

[0019] The catalyst is inexpensive to manufacture, it is highly efficient, and it does not readily lose activity by coking. Thus, for example, it maintains a high degree of activity in cigarette smoke. The catalyst will catalyze the destruction of free radicals and their precursors in cigarette smoke, and also inhibit the formation of the radicals upon exposure to air. Such radicals may include, for example, para-semiquinone, o/if/7o-semiquinone, substituted semiquinones, polyaromaticsemiquinones, substituted polyaromatic semquinones, phenoxyl, substituted phenoxyls, and other oxygen- containing radicals.

[0020] Standard iron oxide catalysts typically comprise the α-iron oxide crystal structure. The α-crystalline structure of iron oxide is quite stable; but it requires high temperatures to become an efficient catalyst. By contrast, the y form of iron oxide is far more reactive; but it is thermodynamically unstable, and it readily converts to the more stable α form, especially when heated. The α form of Fe₂O₃ has an octahedral structure, while the y form is a mixture of tetrahedral and octahedral structures, with unbalanced valences that contribute to its reactivity. Without wishing to be bound by this theory, we believe that our preparative approach forces a substantial fraction of the iron oxide into the more reactive Y form, and stabilizes it sufficiently to maintain it without converting to the α form upon heating. Without wishing to be bound by this Express Mail No. EV854031008 theory, we believe that in the catalyst used in this process the calcium ions assist, at least in part, by filling vacancies in the γ-form crystal structure of Fe₂O₃, vacancies that would otherwise allow the active γ-form to convert more readily to the less reactive α- form. Adding calcium ions fills some, but not all, of the unbalanced vacancies in the y crystal structure, thereby stressing bonds and maintaining catalytic activity. Excessive amounts of calcium, however, are undesirable, as excess calcium can fill too many of the vacancies. It is believed that the titanium oxide also plays a role in stabilizing the iron oxide in the y form.

[0021] Nanoparticle catalysts achieve high surface area without the need for pores, and they are therefore less susceptible to deactivation by clogging or coking. It may be more accurate, however, to describe the catalyst not as being based upon nanoparticles perse, but rather as comprising microparticles with nanolayer coatings, an "egg-in-shell" structure. The catalysts are resistant to pore clogging by coke formation. Unlike many catalysts, it is believed that these catalysts do not require pores to achieve high activity. In an "egg-in-shell" structure, a relatively nonporous titanium oxide core (diameter on the order of micrometers) is coated with a thin layer of active iron oxide catalyst (thickness on the order of nanometers). Alternatively, the catalysts may optionally be supported on a solid substrate, for example on a honeycomb-type structure, or in or on a fiber.

[0022] The catalyst is not substantially fouled, and its effectiveness is not substantially diminished by burning tobacco during the time it takes, for example, to completely burn a cigarette. The resistance to fouling is believed to result from a high surface activity that does not rely upon porosity to achieve a high surface area. [0023] By contrast, porous catalysts generally do not function well in a cigarette after the first puff. The mass transport of gases produced by the burning cigarette is high. The gases transport tar and tar precursors to the interior pores of a porous catalyst. However, heat transport to the pore interior is low. Tar forms in the pore interiors, where the temperature is too low to burn the tar out of the catalyst pore. As a consequence a porous catalyst is deactivated. Express Mail No. EV854031008

[0024] Our nonporous catalyst may be incorporated into tobacco, a cigarette filter, a separate packed bed between the tobacco and the filter, the cigarette paper, or into more than one of these locations. The catalyst does not clog conventional cigarette filters. From the smoker's perspective, the experience of smoking of a cigarette is not substantially altered by the catalyst. By contrast, placing a nanoparticle catalyst into a filter can render a cigarette virtually unsmokable, clogging the cigarette filter, reducing the air flow rate, and reducing the delivery of TPM to the smoker. The catalyst used in this invention is "nanostructured," but it is not a "nanoparticle." The catalyst used in this invention comprises a relatively large matrix material that supports a nanolayer of the active phase. In effect, it achieves the chemical properties of a nanocatalyst with a larger physical size to inhibit clogging. By not relying on porosity to achieve high surface area, fouling of the catalyst is avoided. [0025] The catalyst preferably contains only non-toxic components. In a preferred embodiment, the catalyst is formulated in a 20-80 mesh size, a size at which it should not pass through a conventional filter to any substantial extent, and thus should not be inhaled (or inhaled only minimally) by the smoker with the primary tobacco smoke. In a preferred embodiment, the placement of the catalyst in the cigarette helps to minimize both direct and second-hand exposure to the catalyst by smokers and others. Because the particles themselves are not nanosized, they generally do not enter the gas flow path of the primary smoke stream, and consequently are inhaled only minimally by the smoker. Also due to the particles' size, the particles are primarily incorporated into ash rather than into sidestream smoke. Thus, there is no exposure via sidestream smoke. Instead, the catalyst particles will be contained in the ash residue. The particles are of a size such that they will not be entrained into the air when the ash is agitated. Thus exposure to the catalyst via ash is minimal. [0026] Figure 4 depicts schematically a typical temperature distribution in a burning cigarette. Different temperature regions are conducive to forming different types of radicals. The oxidative pyrolysis 210-350⁰C zone and the RT-350°C oxidative pyrolysis zone are most conducive to forming semiquinone-type radicals. Placing the catalyst in or near these zones will therefore help to reduce the concentration of semiquinone radicals. The proximity of these zones to the periphery of the cigarettes Express Mail No. EV854031008 means that placement of the catalyst in the paper can be an effective control strategy, in lieu of, or in addition to placement in the tobacco, in front of the filter, or in the filter. [0027] Among the possible locations for the catalyst in a cigarette are the following: (1) in a packed bed between the tobacco and the filter, (2) in the tobacco, (3) in the paper, and (4) admixed with the fibers of the filter. A packed bed is perhaps the simplest approach. However, placing the catalyst in the paper or the tobacco has certain advantages. More than one option may be employed simultaneously, i.e., the catalyst may be placed in a packed bed, the tobacco, and in the paper in the same cigarette.

[0028] Option 1 , placing the catalyst in a packed bed, has the advantage that it reduces the concentration of radicals in the main stream of smoke inhaled by the smoker, regardless of the zone in which the radicals are formed. However, the temperature of the bed will be not much above room temperature, resulting in a catalytic efficiency of about 70 %.

[0029] Option 2, placing the catalyst in the tobacco itself, increases the temperature of the catalyst and therefore improves its performance. It also places the catalyst closer to the zone of formation for most of the radicals, thereby further increasing its effectiveness. After combustion the catalyst particles are incorporated primarily into the ash, with little going into either the main-stream smoke or side-stream smoke. The catalyst typically has a rusty brown color that will not substantially change the appearance of the tobacco.

[0030] Option 3, incorporation into the cigarette paper, may readily be accomplished because the catalyst is hydrophilic, and therefore compatible with other components of the paper. Like placement in the tobacco, placement of the catalyst in the paper puts the catalyst closer to where radicals are formed, and increases the temperature of the catalyst and therefore its effectiveness. Express Mail No. EV854031008

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 depicts the percentage conversion of 2-monochlorophenol over four nanocatalyst compositions in accordance with this invention, and over a standard Fe₂O₃ / TiO₂ catalyst.

[0032] Figure 2 depicts the percentage conversion of carbon monoxide over the nanocatalyst compositions, both with and without pre-exposure of the catalyst to cigarette smoke.

[0033] Figures 3(A) and 3(B) depict the oxidation of catechol and hydroquinone over the nanocatalyst compositions.

[0034] Figure 4 depicts the temperature distribution in a burning cigarette and the regions in which various radicals are formed.

MODES FOR CARRYING OUT THE INVENTION

[0035] The iron and calcium sources used in the preparation may be chosen from a variety of precursors, both organometallic and inorganic. The precursors should be soluble in the preparation solvent. Otherwise, most organometallic sources of calcium or iron are suitable, as are inorganic sources that, upon decomposition (e.g., oxidation), do not leave substantial amounts of the counter-anion in the structure of the nanoparticle. (For example, chlorides and sulfonates would generally be undesirable, as they would have a tendency to leave residues of chlorine or sulfur, respectively, in the crystal structure.) Titanium isopropoxide is the preferred titanium precursor. [0036] A preferred preparation method uses the following sequential steps:

(a) mixing a substantially anhydrous solution of titanium isopropoxide with a substantially anhydrous solution of an iron (III) salt and a substantially anhydrous solution of a calcium salt; Express Mail No. EV854031008

(b) adding to the mixture a sufficient amount of water and acid to initiate hydrolysis and gelation;

(c) allowing sufficient time for the mixture to gel;

(d) removing solvent with heat under reduced pressure; and

(e) calcining in the presence of oxygen; whereby oxides are formed having catalytic properties.

[0037] Example 1 : Preparation of catalyst

[0038] In experiments to date, our best results have been obtained when either iron (III) nitrate, or iron (III) acetylacetonate was used as the active phase precursor.

[0039] ^" The active phase precursor was dissolved in absolute ethanol in a 1 :100 molar ratio at room temperature, in the absence of substantial amounts of water. Next, calcium acetylacetonate was dissolved in the solution. (The amount of calcium is chosen to achieve the desired concentration of calcium in the final product.)

A few drops of water and hydrochloric acid were added to make the solution slightly acidic (e.g., pH around 6.0-6.9).

[0040] A titanium isopropoxide solution was prepared in absolute ethanol in a 1 :150 molar ratio at room temperature.

[0041] The two solutions were then mixed, and the mixture was left standing at room temperature for gelation (about 2 weeks). After gelation and subsequent drying at room temperature for 3 days, the samples were dried at 8O⁰C under vacuum for 24 hours. The dried samples were then calcined in air at 400⁰C for

4 hours. The samples were ground to obtain the desired mesh size, and separated into size fractions.

[0042] Scanning electron micrographs (not shown) confirmed that a thin layer (-3.5 nm) of iron oxide had formed on the exterior of the titanium oxide core.

More generally, this layer may be between about 1 nm and about 20 nm. Express Mail No. EV854031008

[0043] Examples 2-5: Oxidation of 2-monochlorophenol.

[0044] Figure 1 depicts a comparison of the degradation of a chlorinated hydrocarbon, namely 2-monochlorophenol, over unmodified iron oxide particles, versus degradation over four catalyst compositions in accordance with the present invention. These catalytic oxidation experiments were conducted over a packed bed, one-pass, gravitational quartz reactor (1/4 inch = 0.64 cm inner diameter). Onto a quartz wool bed were placed 30 mg of catalyst mixed with 30 mg of quartz powder. The reactor was placed in a high-temperature furnace, maintained at constant temperature in the range 275-45O⁰C. Prior to running an experiment, each catalyst sample was activated in 20% O₂ / He (20 ml_ / min) for 1 hour at 45O⁰C. 2-monochlorophenol (2-MCP) was introduced into the gas stream by bubbling a 20% O₂ / He stream through a saturator that was maintained at room temperature and filled with liquid 2-MCP. The catalytic reactor was connected in-line with an HP5890 Series Il gas chromatograph equipped with a flame ionization detector. Reaction products and bypass reagent were sampled with a six-port valve equipped with a 2 ml_ stainless steel loop. The products were separated from one another with a Chrompack CP-SiI 8 CB capillary column (30 m long, 0.32 mm inner diameter).

[0045] Control tests of the empty reactor without catalyst, and of the reactor containing the quartz wool bed and quartz powder but without catalyst, showed no significant destruction of 2-MCP over the studied temperature range. [0046] Four different catalyst compositions were tested. The "standard"

5% Fe₂O₃ / TiO₂ composition (i.e., a more conventional catalyst) was prepared by impregnating TiO₂ with an aqueous solution of iron (III) nitrate. Modified catalysts 1-4 were sol-gel samples prepared as described above. These four catalysts had the following compositions:

Modified catalyst 1 : 5% Fe₂O₃/ Titania

Modified catalyst 2: 5% Fe₂O₃/ Titania + 1 % Ca

Modified catalyst 3: 5% Fe₂O₃/ Titania + 3% Ca

Modified catalyst 4: 5% Fe₂O₃/ Titania + 5% Ca Express Mail No. EV854031008

[0047] These modified catalysts had substantially improved properties, with the high conversion regime shifted about 100-150⁰C lower than with the conventional catalyst.

[0048] Examples 6 and 7: Oxidation of carbon monoxide.

[0049] In this experiment we compared the oxidation of carbon monoxide as a function of temperature over Modified Catalyst 3 (as described above.) The reaction feed comprised 0.75% CO mixed with air (i.e., -20% O₂). Total gas flow was 100 cm³ per minute over 30 mg catalyst.

[0050] These catalytic oxidation experiments were conducted over a packed bed, one-pass, gravitational quartz reactor (1/4 inch = 0.64 cm inner diameter). Onto a quartz wool bed were placed 30 mg of catalyst mixed with 30 mg of quartz powder. The reactor was placed in a high-temperature furnace, maintained at constant temperature in the range 50-600⁰C. Prior to running an experiment, each catalyst sample was conditioned in 20% O₂ / He (20 ml_ / min) for 1 hour at 450°C. (Likewise, cigarettes are typically conditioned by the manufacturer by being held in air at an elevated temperature for an extended time, e.g., 150⁰C for 24 hours. This conditioning should serve the same function; or the catalyst may be separately activated before being placed in the cigarette or other tobacco product.) For samples that are denoted as "smoked," the smoke from one whole commercial Marlboro cigarette, whose filter had previously been cut off, was pulled in "puff mode" through the catalyst bed, which was maintained at 200°C. The temperature was then set to the desired value, and a mixture of 0.75% CO and 20% O₂ (by weight) in He was pulled through the catalyst bed at a total flow rate of 10O mL / min. (without prior conditioning). The gases exiting the catalyst bed (particularly CO) were analyzed on a MIDAC 2000 FTIR spectrometer in real time.

[0051] Control tests of the empty reactor without catalyst, and of the reactor containing the quartz wool bed and quartz powder but without catalyst, showed no significant destruction of CO over the studied temperature range. Express Mail No. EV854031008

[0052] Modified Catalyst 3 was superior to the conventional iron oxide catalyst for CO oxidation. We also found that the catalyst retained most of its activity for CO oxidation even following exposure to cigarette smoke. [0053] Similar results are expected when the experiment is repeated for oxidation of CO (and other compounds) directly in a stream of cigarette smoke or other tobacco smoke.

[0054] Examples 8 and 9: Oxidation of catechol and hydroquinone.

[0055] We have also tested the activity of the catalyst in promoting the oxidation of two radical precursors that occur in cigarette smoke, catechol and hydroquinone. The results of these experiments are shown in Figs. 3(A) and (B), respectively. The catalytic oxidation experiments were conducted over a packed bed, one-pass, gravitational quartz reactor (1/4 inch = 0.64 cm inner diameter). Onto a quartz wool bed were placed 30 mg of catalyst mixed with 30 mg of quartz powder. The reactor was positioned in a high-temperature furnace, maintained at constant temperature of 120⁰C. Prior to running an experiment, each catalyst sample was activated in 20% O₂ / He (20 ml_ / min) for 1 hour at 450⁰C. Either catechol or hydroquinone was introduced into the gas stream using a Varian Chromatoprobe at an injection port held at 90°C for catechol or 12O⁰C for hydroquinone, at a rate to maintain a constant 20 ppm concentration of the reactant in the input stream. The outlet of the heated injection port connected directly to the reactor. Helium (with no oxygen) was used as the carrier gas for both reagents at a flow rate of 100 ml_ / min. The catalytic reactor was connected in-line with an HP5890 Series Il gas chromatograph equipped with a flame ionization detector. Reaction products and by-pass reagent were sampled with a six-port valve equipped with a 2 ml_ stainless steel loop. The products were separated from one another with a Chrompack CP-SiI 8 CB capillary column (30 m long, 0.32 mm inner diameter).

[0056] Control tests of the empty reactor without catalyst, and of the reactor containing the quartz wool bed and quartz powder but without catalyst, showed no significant destruction of either catechol or hydroquinone overthe temperature range studied. Express Mail No. EV854031008

[0057] In both cases, 20 ppm of catechol or 20 ppm of hydroquinone, as appropriate, were passed over 30 mg of the catalyst, under pyrolytic conditions. Both catechol and hydroquinone readily decomposed over the catalyst at the relatively low temperature of 120⁰C. Fig. 3B depicts the total conversion of hydroquinone to CO₂, as well as the appearance of organic decomposition products after 5 hours of reaction. (These organic decomposition products were notfurther analyzed.) High efficiency was maintained for several hours, after which the conversion rate started to decline. It appears that there was sufficient structural oxygen in the active phase (i.e., in the nanostructured component of the catalyst, rather than in the gas phase) to sustain complete oxidation of both catechol and hydroquinone for about 4 hours. No other organic products were detected during the first 4 hours of either reaction, suggesting efficient oxidation to CO₂.

[0058] Example 10: Removal of semiquinone radicals from cigarette smoke.

[0059] We have also tested the activity of the catalyst in removing semiquinone radicals from cigarette smoke. Marlboro™ Red cigarettes were purchased from a local retail outlet. The filter of each cigarette was removed, and replaced with 30 mg of modified catalyst 4, placed between two quartz wool stoppers. Downstream of the catalyst an acetate filter was placed to remove particulate matter from the smoke stream. As a control, otherwise identical experimental cigarettes were prepared, but without the catalyst. The cigarettes were lit, and experimental "puffs" of 180 ml_ each were pulled through each cigarette. Thus each "puff" corresponded to approximately two "real puffs" by ordinary human smokers, and each cigarette was consumed after 4 such experimental puffs. The acetate filter was replaced after each puff, and each of the acetate filters with deposited total particulate matter (TPM) was left in air for 96 hours and then analyzed for semiquinone radical content. The total EPR radical signal per gram of total particulate matter decreased by 58%, from 168 x 10⁶ for the control cigarettes to 72 x 10⁶ spins per gram of TPM for the cigarettes with the incorporated catalyst. As shown in Table 1 , radical removal was greatest in the middle of the Express Mail No. EV854031008 cigarette (puffs 3+4 and 5+6), although not inconsiderable at the beginning of the cigarette (puffs 1 +2), and still significant at the end (puffs 7+8).

Table 1 - Semiquinone radical destruction

[0060] Example 11 : Effect on Total Particulate Matter.

[0061] We measured the effect of the catalyst on Total Particulate Matter

(TPM) in cigarette smoke. Because TPM carries much of the flavor of cigarette smoke, in order to be acceptable to smokers the catalyst should have minimal effect on TPM. This experiment was performed as otherwise described for Example 10, except that an acetate filter was placed behind the catalyst bed to collect TPM. TPM was determined by weighing the filter before and after the puffs. (The acetate filter, intended to trap TPM, was fundamentally different from typical cigarette filters, which allow much TPM to pass through.) As shown in Table 2, the catalyst had minimal effect on TPM, even while destroying semiquinone radicals, as shown in Table 1 above. Express Mail No. EV854031008

Table 2 - Total Particulate Matter (in mg)

[0062] Definitions. As used in the specification and claims, the

"diameter" of an object refers to the longest distance between any two points that both lie on the surface of the object. Thus the use of the term "diameter" should not be construed as implying that an object is necessarily spherical, nor that it necessarily has a circular cross-section.

[0063] The "thickness" of a layer refers to the mean thickness of the layer, averaged over the entire layer. Thus the use of the term "thickness" should not be construed as implying that a layer necessarily has a uniform thickness.

[0064] Miscellaneous. The complete disclosures of all references cited in this specification are hereby incorporated by reference. Also incorporated by reference are the complete disclosures of the following two patent applications, both of which are unpublished as of the international filing date of the present application: United States provisional patent application 60/589,239, filed 20 July 2004; and United States patent application 11/180,290, filed 13 July 2005. In the event of an otherwise irreconcilable conflict, however, the present specification shall control.

Claims

Express Mail No. EV854031008What is claimed:

1. An article of manufacture comprising tobacco and a plurality of particles; wherein said particles comprise a core and a shell, and wherein:

(a) said shell adheres to said core;

(b) said core comprises titanium oxide, and the diameter of said core is between about 1 μm and about 100 μm;

(c) said shell comprises iron oxide and calcium oxide, and the thickness of said shell is between about 1 nm and about 20 nm;

(d) the fraction of iron oxide in the particle is between about 1 % and about 15% by weight; and the ratio of calcium to iron is between about 0.5 mole-% and about 10 mole-%.

2. An article of manufacture as recited in Claim 1 , wherein said tobacco and said particles are admixed with one another.

3. An article of manufacture as recited in Claim 1 , wherein said article of manufacture is a cigarette.

4. An article of manufacture as recited in Claim 3, wherein said cigarette comprises tobacco and a filter, wherein said filter comprises a plurality of said particles.

5. An article of manufacture as recited in Claim 3, wherein said cigarette comprises tobacco, a filter, and a bed comprising a plurality of said particles, said bed being positioned between said tobacco and said filter. Express Mail No. EV854031008

6. An article of manufacture as recited in Claim 3, wherein said cigarette comprises tobacco admixed with a plurality of said particles.

7. An article of manufacture as recited in Claim 3, wherein said cigarette comprises tobacco and paper encasing said tobacco, wherein said paper comprises a plurality of said particles.

8. An article of manufacture as recited in Claim 1 , wherein: said core consists essentially of titanium oxide, the diameter of said core is between about 1 μm and about 50 μm, and said shell consists essentially of iron oxide and calcium oxide.

9. An article of manufacture as recited in Claim 1 , wherein at least some of the iron oxide has a γ-form crystal structure.

10. An article of manufacture as recited in Claim 1 , wherein at least about 10% of the iron oxide has a γ-form crystal structure.

11. An article of manufacture as recited in Claim 1 , wherein said particles are nonporous.

Express Mail No. EV854031008

12. A method for catalytically oxidizing or catalytically destroying at least one compound selected from the group consisting of carbon monoxide, acrolein, formaldehyde, acetone, benzene, halogenated benzenes, phenol, halogenated phenols, other substituted phenols, other hydroxylated aromatic hydrocarbons, hydroxylated polycyclic aromatic hydrocarbons, catechol, substituted catechols, hydroquinone, substituted hydroquinones, semiquinone radicals, chloroform, bromoform, furan, dioxane, substituted dioxanes, lignin, lignin decomposition products, ketones, substituted ketones, other aldehydes, substituted aldehydes, volatile organic compounds, halogenated volatile organic compounds, radicals derived from any of the above compounds, and other organic gas-phase radicals; said method comprising reacting the compound with oxygen at a temperature between about 25⁰C and about 900⁰C in the presence of a plurality of particles; wherein the compound is oxidized at a rate that is substantially greater than the rate at which the same compound would be oxidized under conditions that are otherwise identical, except that the particles are absent; wherein the particles comprise a core and a shell, and wherein:

(a) the shell adheres to the core;

(b) the core comprises titanium oxide, and the diameter of the core is between about 1 μm and about 100 μm;

(c) the shell comprises iron oxide and calcium oxide, and the thickness of the shell is between about 1 nm and about 20 nm;

13. A method as recited in Claim 12, wherein both carbon monoxide, and at least one further compound as recited, in addition to carbon monoxide, are catalytically oxidized or catalytically destroyed simultaneously. Express Mail No. EV854031008

14. A method as recited in Claim 12, wherein the particles are admixed with tobacco prior to combustion of the tobacco, wherein the compound is a component of smoke produced by combustion of the tobacco, and wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco.

15. A method as recited in Claim 14, wherein the tobacco is a component of a cigarette.

16. A method as recited in Claim 14, wherein the particles are contained in a filter for a tobacco cigarette, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke passes through the filter.

17. A method as recited in Claim 14, wherein the particles are contained in paper encasing tobacco in a cigarette, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke contacts the paper.

18. A method as recited in Claim 14, wherein the particles are contained in a packed bed in a cigarette, intermediate tobacco and a filter, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke passes through the packed bed.

19. A method as recited in Claim 12, wherein the compound is carbon monoxide.

20. A method as recited in Claim 12, wherein the compound is a catechol or a catechol derivative. Express Mail No. EV854031008

21. A method as recited in Claim 12, wherein the compound is a quinone or a quinone derivative.

22. A method as recited in Claim 12, wherein the compound is a hydroquinone or a hydroquinone derivative.

23. A method as recited in Claim 12, wherein the compound is phenol or a halogenated phenol.

24. A method as recited in Claim 12, wherein the compound is benzene or a halogenated benzene.

25. A method as recited in Claim 12, wherein the compound is a semiquinone radical, a substituted semiquinone radical, a phenoxyl radical, a substituted phenoxyl radical, a polycyclic aromatic semiquinone radical, or a substituted polycyclic aromatic semiquinone radical.

26. A method as recited in Claim 12, wherein the compound is an aldehyde or a ketone.

Express Mail No. EV854031008

27. An article of manufacture comprising tobacco and a plurality of particles; wherein said particles are the product of the sequential steps of:

(a) mixing a substantially anhydrous solution of titanium isopropoxide with a substantially anhydrous solution of an iron (III) salt and a substantially anhydrous solution of a calcium salt;

(c) allowing sufficient time for the mixture to gel;

(d) removing the solvent with heat under reduced pressure; and

(e) calcining in the presence of oxygen; whereby oxide particles are formed having catalytic properties.

28. An article of manufacture as recited in Claim 27, wherein said tobacco and said particles are admixed with one another.

29. An article of manufacture as recited in Claim 27, wherein said article of manufacture is a cigarette.

30. An article of manufacture as recited in Claim 29, wherein said cigarette comprises tobacco and a filter, wherein said filter comprises a plurality of said particles.

31. An article of manufacture as recited in Claim 29, wherein said cigarette comprises tobacco, a filter, and a bed comprising a plurality of said particles, said bed being intermediate said tobacco and said filter. Express Mail No. EV854031008

32. An article of manufacture as recited in Claim 29, wherein said cigarette comprises tobacco admixed with a plurality of said particles.

33. An article of manufacture as recited in Claim 29, wherein said cigarette comprises tobacco and paper encasing said tobacco, wherein said paper comprises a plurality of said particles.

34. An article of manufacture as recited in Claim 27, wherein said particles are nonporous.

35. A method for catalytically oxidizing or catalytically destroying at least one compound selected from the group consisting of carbon monoxide, acrolein, formaldehyde, acetone, benzene, halogenated benzenes, phenol, halogenated phenols, other substituted phenols, other hydroxylated aromatic hydrocarbons, hydroxylated polycyclic aromatic hydrocarbons, catechol, substituted catechols, hydroquinone, substituted hydroquinones, semiquinone radicals, chloroform, bromoform, furan, dioxane, substituted dioxanes, lignin, lignin decomposition products, ketones, substituted ketones, other aldehydes, substituted aldehydes, volatile organic compounds, halogenated volatile organic compounds, radicals derived from any of the above compounds, and other organic gas-phase radicals;

said method comprising producing a plurality of particles by the following sequential steps (a) through (e):

(b) adding to the mixture a sufficient amount of water and acid to initiate hydrolysis and gelation; Express Mail No. EV854031008

(c) allowing sufficient time for the mixture to gel;

(d) removing the solvent with heat under reduced pressure; and

(e) calcining in the presence of oxygen; whereby oxide particles are formed having catalytic properties;

and reacting the compound with oxygen at a temperature between about 25°C and about 900⁰C in the presence of a plurality of the particles; wherein the compound is oxidized at a rate that is substantially greater than the rate at which the same compound would be oxidized under conditions that are otherwise identical, except that the particles are absent.

36. A method as recited in Claim 35, wherein both carbon monoxide, and at least one further compound as recited, in addition to carbon monoxide, are catalytically oxidized or catalytically destroyed simultaneously.

37. A method as recited in Claim 35, wherein the particles are admixed with tobacco prior to combustion of the tobacco, wherein the compound is a component of smoke produced by combustion of the tobacco, and wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco.

38. A method as recited in Claim 37, wherein the tobacco is a component of a cigarette.

39. A method as recited in Claim 37, wherein the particles are contained in a filter for a tobacco cigarette, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke passes through the filter. Express Mail No. EV854031008

40. A method as recited in Claim 37, wherein the particles are contained in paper encasing tobacco in a cigarette, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke contacts the paper.

41. A method as recited in Claim 37, wherein the particles are contained in a packed bed in a cigarette, intermediate tobacco and a filter, wherein the compound is a component of smoke produced by combustion of tobacco, wherein a temperature sufficient for the catalytic oxidation is produced by the combustion of the tobacco, and wherein the catalytic oxidation occurs as cigarette smoke passes through the packed bed.

42. A method as recited in Claim 35, wherein the compound is carbon monoxide.

43. A method as recited in Claim 35, wherein the compound is a catechol or a catechol derivative.

44. A method as recited in Claim 35 wherein the compound is a quinone or a quinone derivative.

45. A method as recited in Claim 35 wherein the compound is a hydroquinone or a hydroquinone derivative.

46. A method as recited in Claim 35, wherein the compound is phenol or a halogenated phenol.

47. A method as recited in Claim 35, wherein the compound is benzene or a halogenated benzene. Express Mail No. EV854031008

48. A method as recited in Claim 35, wherein the compound is a semiquinone radical, a substituted semiquinone radical, a phenoxyl radical, a substituted phenoxyl radical, a polycyclic aromatic semiquinone radical, or a substituted polycyclic aromatic semiquinone radicals.

49. A method as recited in Claim 35, wherein the compound is an aldehyde or a ketone.