Patent Application
20080023016
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.
A preferred method for preparing uses the following sequential steps:
(a) mixing a substantially anhydrous solution of titanium isopropoxide with a substantially anhydrous solution of an iron (Ill) salt and a substantially anhydrous solution of a calcium salt;
(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 the solvent with heat under reduced pressure to make a sol; and
(e) calcining the sol in the presence of oxygen; whereby oxides are formed having catalytic properties.
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.
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).
A titanium isopropoxide solution was prepared in absolute ethanol in a 1:150 molar ratio at room temperature.
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 80° C. under vacuum for 24 hours. The dried samples were then calcined in air at 400° C. for 4 hours. The samples were ground to obtain the desired mesh size, and separated into size fractions. Preferred size is 100-120 mesh, but the size can vary depending on the particular use to which the catalyst will be put.
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.
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.
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 14 were sol-gel samples prepared as described above. These four catalysts had the following compositions:
The novel catalysts had substantially improved properties, with the high conversion regime shifted about 100-150° C. lower than with the conventional catalyst.
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.
These catalytic oxidation experiments were conducted over a packed bed, one-pass, gravitational quartz reactor (¼ 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 reactorwas positioned in a high-temperature furnace, maintained at constant temperature in the range 50-600° C. Prior to running an experiment, each catalyst sample was activated in 20% O2/He (20 mL/min) for 1 hour at 450° C. 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 100 mL/min. The gasses exiting the catalyst bed (particularly CO) were analyzed on a MIDAC 2000 FTIR spectrometer in real time.
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.
The novel catalyst 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 following exposure to cigarette smoke. The activity of the catalyst remained high despite its contact with the coke and tar from cigarette smoke.
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.
We have also tested the activity of the novel iron oxide catalyst in promoting the oxidation of two known radical precursors in cigarette smoke, namely catechol and hydroquinone. The results of these experiments are shown in
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 over the studied temperature range.
In both cases, 20 ppm of catechol or 20 ppm of hydroquinone, as appropriate, were passed over 30 mg of the novel catalyst, under pyrolytic conditions. Both cathecol and hydroquinone readily decomposed over the novel catalyst at the relatively low temperature of 120° C.
We have also tested the activity of the novel iron oxide catalyst to 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 168×106 for the control cigarettes to 72×106 spins per gram of TPM for the cigarettes with the incorporated catalyst. As shown in the table below, radical removal was greatest in the middle of the cigarette (puffs 2 and 3), although not inconsiderable at the beginning of the cigarette (puff 1), and still significant at the end (puff 4).
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.
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.
Miscellaneous. The complete disclosures of all references cited in this specification are hereby incorporated by reference. Also incorporated by reference is the entire disclosure of the following publication by the inventors, a publication that is not prior art to the present application: S. Lomnicki et al., “Development of a supported iron oxide catalyst for destruction of PCDD/F,” Environ. Sci. Technol., vol. 37, pp. 4254-4260 (2003). In the event of an otherwise irreconcilable conflict, however, the present specification shall control.
The benefit of the Jul. 20, 2004 filing date of provisional application Ser. No. 60/589,239 is claimed under 35 U.S.C. § 119(e).
The development of this invention was funded in part by the Government under grant number R827719-01-0 awarded by the Environmental Protection Agency. The Government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 60589239 | Jul 2004 | US |
