Grantee Research Project Results
Final Report: Ferric Oxide/Alkali Metal Oxide Induced Oxidation of CHCs in Polluted Gas Streams
EPA Grant Number: R827719Title: Ferric Oxide/Alkali Metal Oxide Induced Oxidation of CHCs in Polluted Gas Streams
Investigators: Dellinger, Barry , Lomnicki, Slawomir
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 1999 through August 31, 2002
Project Amount: $358,396
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Water , Land and Waste Management , Air
Objective:
The objective of this research project was to develop an iron oxide-based catalyst for destruction of chlorinated hydrocarbons. Carbon tetrachloride (CCl4) was used as a model molecule because of its simple structure that would simplify the interpretation of the data. It was found that the preparation method plays an important role in this process. Additionally, the mechanism of chlorine abstraction from the carbon-chlorine molecule was developed.
Summary/Accomplishments (Outputs/Outcomes):
A detailed study of the interaction of the common support such as alumina with CCl4 have shown that it can be consumed during the process as a result of formation of volatile chlorides when the process occurs at high temperatures, which leads to gradual deactivation. Bulk iron oxide has been found to show very low activity.
Research on the supported iron oxide over the titanium dioxide led to development of a highly active catalyst capable of low-temperature destruction of chlorinated hydrocarbons. Data expressed as light-off curves clearly showed that even a small amount of iron oxide supported on alumina significantly improves activity of the system. In particular, the Sol-Gel synthesis method and doping of iron oxide active phase with calcium resulted in a catalyst of unique oxidation properties with respect to the destruction of organic pollutants. The latter preparation method resulted in better dispersion of iron oxide on the surface and the formation of γ-Fe2O3. This is in contrast to the impregnated samples where α-Fe2O3 crystallites were formed. Formation of γ-Fe2O3 resulted in improved reducibility of the active phase that favorably affected the catalytic oxidation properties of the catalyst (i.e., the light-off curves for the Sol-Gel samples were shifted toward lower temperatures). Addition of calcium oxide to iron oxide catalyst further improved the performance of the system through stabilization and increase in the concentration of γ-Fe2O3 in the Sol-Gel prepared samples. Addition of calcium oxide has a dual effect on the performance of the catalyst: (1) it creates oxygen vacancies in the reduction-resistant Fe2O3 octahedral structures, thereby improving the reducibility of the active phase; and (2) iron oxide can transform during decomposition of chlorinated hydrocarbons into iron chloride. Calcium oxide also improved the chlorine transfer from the surface iron oxide species thereby providing a relatively fresh surface for further catalytic oxidation.
Results
Catalyst Preparation. To compare the activity of supported iron oxide catalysts and to choose the support that gives the best results for chlorophenol decomposition three different series of catalysts were prepared: supported on alumina, silica, and titania. Additionally, the preparation method was discriminated in each of the series of the samples: impregnated catalysts and Sol-Gel catalysts.
For impregnated catalysts, the incipient wetness method of preparation was applied. Iron nitrate (Aldrich) was dissolved in the amount of water sufficient to obtain the volume of the solution for incipient wetness of the support to occur. The amount of iron nitrate was chosen to obtain the catalysts containing 2.5, 3.5, 5.0, and 10.0 weight percent of Fe2O3 with respect to the mass of the support. Next, the support was introduced into the solution (titania, silica gel, and alumina-activated, all Aldrich reagents). After that, the samples were evaporated, dried for 12 hours at 80ºC and finally calcined for 12 hours at 450ºC.
For Sol-Gel catalysts the appropriate amount of iron acetyl acetonate was dissolved in ethyl alcohol and added to the solution of support precursor. Support precursor solution was prepared by mixing tetraethoxysilane (Aldrich) for silica, aluminum sec-butoxide (Aldrich) for alumina, or titanium isopropoxide (Acros Organics) for titania with equal volumetric amount of solvent (isopropyl alcohol). Next, both precursor solutions (active phase and support) were mixed together and a few drops of HCl solution (1:1) were added to start the gelation process. The solution was left to gellify for 10 days, and gelation samples were dried under vacuum at 100ºC for 12 hours and then calcined at 450ºC for 12 hours.
For the catalysts doped with calcium oxide, calcium acetyl acetonate was added to active phase precursor solution. Calcined catalysts were grinded and sieved and 100- to 120-mesh size grain was collected for catalytic experiments. Fine powder was collected for use with various spectroscopic and characterization experiments.
Table 1 presents the composition of obtained catalysts, their preparation method, and their annotated symbols used throughout this report.
Table 1. Composition of Prepared Catalysts
Symbol | Preparation method | Support | Iron Oxide content | Doping Material, | |
TiFe25 | Impreg. | Titania | 2.5 | -- | -- |
TiFe35 | Impreg. | Titania | 3.5 | -- | -- |
TiFe50 | Impreg. | Titania | 5.0 | -- | -- |
TiFe100 | Impreg. | Titania | 10.0 | -- | -- |
SG-TiFe25 | Sol-Gel | Titania | 2.5 | -- | -- |
SG-TiFe35 | Sol-Gel | Titania | 3.5 | -- | -- |
SG-TiFe50 | Sol-Gel | Titania | 5.0 | -- | -- |
AlFe10 | Impreg. | Alumina | 1.0 | -- | -- |
AlFe50 | Impreg. | Alumina | 2.5 | -- | -- |
AlFe25 | Impreg. | Alumina | 5.0 | -- | -- |
SG-AlFe25 | Sol-Gel | Alumina | 2.5 | -- | -- |
SG-AlFe50 | Sol-Gel | Alumina | 5.0 | -- | -- |
SiFe25 | Impreg. | Silica | 2.5 | -- | -- |
SiFe50 | Impreg. | Silica | 5.0 | -- | -- |
SiFe100 | Impreg. | Silica | 10.0 | -- | -- |
SG-SiFe25 | Sol-Gel | Silica | 2.5 | -- | -- |
SG-SiFe50 | Sol-Gel | Silica | 5.0 | -- | -- |
TiFe50Ca1 | Impreg. | Titania | 5.0 | Ca | 1 |
TiFe50Ca3 | Impreg. | Titania | 5.0 | Ca | 3 |
TiFe50Ca10 | Impreg. | Titania | 5.0 | Ca | 10 |
SG-TiFe25Ca1 | Sol-Gel | Titania | 2.5 | Ca | 1 |
SG-TiFe25Ca3 | Sol-Gel | Titania | 2.5 | Ca | 3 |
SG-TiFe25Ca5 | Sol-Gel | Titania | 2.5 | Ca | 5 |
SG-TiFe50Ca1 | Sol-Gel | Titania | 5.0 | Ca | 1 |
SG-TiFe50Ca3 | Sol-Gel | Titania | 5.0 | Ca | 3 |
SG-TiFe50Ca5 | Sol-Gel | Titania | 5.0 | Ca | 5 |
* Percent with respect to iron oxide mass |
Catalyst Efficacy. Data obtained in an earlier phase of the project have indicated that alumina can be active in the decomposition of chlorinated organics, in particular at temperatures above 500ºC. Application of such a high temperature, however, resulted in sublimation of formed surface aluminum chloride that led to gradual loss of active material and deactivation of the catalyst. Deposition of the active material on the surface of alumina can shift the operating temperature range to lower values and consequently prevent the sublimation of aluminum chloride. Alternatively, the transfer of chlorine from the active phase to the alumina (or other support) will maintain the activity. At the same time both oxygen and water formed during the decomposition process can slowly remove chlorine from support surface by oxidation reaction or surface hydrolysis.
Data expressed as light-off curves clearly show that even a small amount of iron oxide supported on alumina significantly improves activity of the system. This effect is even more profound when taking into account that bulk iron oxide was inactive in the presented temperature range. With increasing iron oxide content, the light-off curves were shifting to lower temperatures with a light-off point well defined at 400ºC. Because the differences between the activity of the catalysts containing 2.5 and 5 percent of iron oxide supported on alumina are in the range of error, it can be concluded that further increase of iron oxide content would not result in improved performance in 2-chlorophenol decomposition. It is worth noting at this point that no organic products of the reaction were detected, which indicates a total oxidation of 2-chlorophenol to CO/CO2.
Application of Sol-Gel preparation method for iron oxide/alumina catalysts affected the activity of the catalyst only to some extent: the light-off curves were shifted approximately 25ºC towards lower temperatures for the samples prepared by Sol-Gel method. This result is surprising when compared to the results obtained for CCl4 decomposition over different prepared aluminas, where the preparation method affected the activity significantly. This indicates that all the activity results from the deposited iron oxide phase. As the bulk iron oxide was found to be inactive, the interaction of alumina surface with iron oxide resulted in formation of surface active species. Also, the fact that iron oxide is in a dispersed form on the support contributes to the improved activity compared to bulk iron oxide. Because alumina by itself appeared to be not very active at the studied temperature range, higher activity of Sol-Gel samples may result from much bigger surface area of Sol-Gel alumina (as presented in the most recent annual report) and as a result, higher dispersion of iron oxide. The dispersion of iron oxide has not been studied and there are plans to do so in the future.
The comparison of activity of impregnated iron oxide catalysts supported on various supports in 2-chlorophenol decomposition shows that the iron oxide catalyst can be divided into two groups: those supported on silica and those supported on titania and alumina. The catalysts supported on titania and alumina show typical S-shaped light-off curves and reach 90 percent conversion around 430ºC. Iron oxide/silica catalysts, however, exhibit a maximum conversion of approximately 30 percent between 400 and 425ºC and then the activity drops. The significant differences between these two groups of catalysts result from the nature of the supports used. Silicon dioxide is known to be an inert support characterized by lack of or very weak interactions between itself and supported active phase. With increasing temperature, the mobility of iron oxide species increases, resulting in their agglomeration and drop of activity.
Alumina and titania exhibit strong interactions with supported active phase often leading to the formation of surface aluminates and titanates. Therefore, iron oxide is stabilized on the surface, which prevents its migration and agglomeration. Additionally, electronic interactions with the support are possible that can result in stabilization of some particular oxidation states of supported metal ions.
Among the two supports in the second group of catalysts, those supported on titania seem to affect iron oxide properties more distinctly, particularly at lower temperatures. Based on this observation, we decided to focus further experiments on the development of iron oxide/titania based catalysts for chlorinated hydrocarbon (CHC) decomposition.
Examination of the activity of impregnated iron oxide/titania catalysts as a function of iron content revealed a strong dependence between the amount of introduced iron oxide and activity of catalysts for 2-chlorophenol decomposition. Interestingly, a clear maximum is visible for the catalysts loading around 2.5-3.0 percent of iron oxide; above this loading, the light-off curves for 2-chlorophenol destruction shift to higher temperatures. Such behavior can result from the decrease of the dispersion of active phase with increasing loading and formation of bigger crystallites that are less active in the process as a result of stabilization of the surface sites by crystalline structure.
The results of BET surface area measurements, presented in Table 2, indicate only small differences in the surface area for the impregnated samples, and cannot explain the different behavior of the samples with different iron oxide content.
Table 2. Surface Area of Iron Oxide/Titania Catalysts
Catalyst Symbol | BET surface area (m2/g) |
TiO2 | 10.8 |
TiFe25 | 10.3 |
TiFe35 | 15.4 |
Tife50 | 11.8 |
SG-TiFe25 | 41.5 |
SG-TiFe35 | 58.9 |
SG-TiFe50 | 36.5 |
TiFe50Ca1 | 12.5 |
TiFe50Ca3 | 30.9 |
TiFe50Ca10 | 14 |
To improve the dispersion of the titania supported iron oxide, we attempted to prepare the catalysts with the Sol-Gel method. The Sol-Gel preparation method sometimes can be used to obtain a higher content of active phase without formation of crystalline domains. The SGTiFe catalyst samples were characterized by an increase in surface area (see Table 2). The surface area of the SGTiFe catalysts with various iron oxide loadings ranged from 36-59 m2/g, with the highest surface area detected for SGTiFe35 (58.9 m2/g).
In addition to the surface area, the activity of the catalyst candidates was affected by the preparation method. The greatest improvement of 2-MCP destruction was observed for the catalysts containing 5 percent of iron oxide (i.e., the light-off curve shifted about 75ºC lower in temperature for the samples prepared by the Sol-Gel method with respect to a similar impregnated sample). The effect of the preparation method on the activity of the samples with low iron oxide content (2.5-3.5%) was less significant; the performance of SGTiFe25 only slightly improved in the temperature range of 375-400ºC, whereas the performance of the SGTiFe35 sample did not change compared to TiFe35.
Although the magnitude of improvement is somewhat surprising, it is not entirely unexpected. For lower concentration iron oxide impregnated samples, the dispersion of active phase was good and no crystallites of hematite were detected. Consequently, the increase of the surface area for the Sol-Gel samples did not significantly affect the dispersion. In contrast, for the TiFe50 impregnated catalyst, low dispersion and formation of crystallites of Fe2O3 were detected and an increase in surface area for the Sol-Gel prepared samples should result in improved dispersion of iron oxide species. In fact, the X-ray diffraction (XRD) spectrum of the SGTiFe50 catalyst confirms this hypothesis. Application of Sol-Gel preparation method resulted in disappearance of the peaks characteristic of α-Fe2O3 crystallites from the samples containing 5 percent of iron oxide, indicating the lack of larger crystallites with hematite structure.
The differences in the preparation procedure in the Sol-Gel and impregnation methods also may result in different active phase-support interactions. In the impregnation method, the active phase precursor is deposited on already calcined and formed supports. In contrast for the Sol-Gel method, precursors of both support and active phase are well mixed prior to the calcination process and are formed at the same time. This can result in incorporation of the active phase cations in the support structure, which results in a new phase with different properties. XRD spectra of the Sol-Gel samples did not show the presence of any iron titanates, and the only new peaks detected were those originating from small amounts of rutile titania. The formation of the latter is caused by higher stability of the rutile form than the anatase form of titania, with the latter tending to transform during calcination into the more thermodynamically stable rutile structure. As the Sol-Gel preparation method did not significantly affect samples other than those containing 5 percent of iron oxide, it seems reasonable to conclude that the improvement of the catalytic properties of SGTiFe50 catalyst over TiFe50 is attributed to improved dispersion of iron oxide phase.
The combination of both Sol-Gel preparation methods as well as calcium oxide doping resulted in further improvement of the 2-MCP destruction properties of the iron oxide/titania catalyst. For the SGTiFe25Ca series, the best results were achieved for a very small amount of CaO admixture (1 percent of the active phase). Above this concentration, the light-off curves shifted towards higher temperatures, SGTiFe25Ca3 demonstrating the same activity as SGTiFe25. Further increase in calcium oxide concentration to 5 percent, resulted in the light-off curve being pushed up to the temperature of the non-modified TiFe25 catalyst. Nevertheless, the combined effect of preparation method and CaO doping (1%) resulted in significant improvement of the 2-MCP destruction compared to the TiFe25 sample, with a 75ºC shift of activity towards lower temperatures.
The effect of calcium doping together with the Sol-Gel preparation method is even more profound in the case of the TiFe50 catalyst. The Sol-Gel preparation method by itself resulted in significant improvement of the 2-MCP decomposition. Addition of calcium oxide allowed further improvement of the activity, with the maximum improvement reached for the SGTiFe50Ca3 sample. The samples with both higher and lower calcium oxide content appeared to have lower activity, though much better than SGTiFe50.
The temperature programmed reduction (TPR) results show significant differences between particular catalysts. Usually, iron oxide TPR spectra consist of three peaks, originating from three phase/oxidation transformations: Fe3+ (α-Fe2O3) to Fe3O4 to Fe2+ (FeO) to Fe0. For TiFe25 catalysts the first reduction step is visible at 331ºC, and, the TiFe35 catalyst shows a very distinct peak for the same transformation at 372ºC. Comparing these results with experimental data of 2-chlorophnol decomposition, they are in good correlation with the fact that the TiFe25 catalyst shows higher activity at lower temperatures; however, between 375 and 400ºC the activity of TiFe35 “jumps” significantly, and 2-chlorophenol decomposition conversion is 10 percent higher for this catalyst than that of TiFe25. Accordingly, TiFe50 starts to show high activity at temperatures above 425ºC, which also agrees with the TPR profile. Taking into account the fact that most of the oxidation processes proceed according to a reaction mechanism, the above observations indicate, that for low loading of iron oxide on titania, the active phase is finely dispersed and characterized by high reduction ability. This reducibility of surface iron is playing a crucial role in oxidation processes. With increasing loading above a certain level, dispersion decreases, probably because of the formation of surface crystallites. This, in turn, leads to a decrease in the reduction ability of the surface iron and the oxidation process activity.
The XRD spectrum of the SGTiFe samples did not exhibit peaks characteristic of any crystalline iron oxide structure, which suggests that the surface species are two-dimensional. Crystallites of α-Fe2O3 are very difficult to reduce to coordinatively unsaturated ions because of their high geometrical stability of [FeO6] octahedral units, and the titania surface forces the formation of octahedral structures. It also has been previously reported, however, that the Sol-Gel preparation method may favor formation of γ-Fe2O3 (maghemite) that will not be visible in XRD spectrum if the crystallites are smaller than 5 nm. γ-Fe2O3 has a cubic, spinel structure with the cationic vacancies and iron cations in a tetrahedral coordination and is more readily reducible compared to α-Fe2O3. Although this can explain the much lower reduction temperature of Fe2O3 in the Sol-Gel prepared samples, more research is needed concerning the nature of surface iron oxide species in this catalyst. The application of both calcium doping and the Sol-Gel preparation method affected the structure of the catalyst. The XRD spectrum of the SGTiFe50Ca samples did not show the presence of hematite crystallites, which indicates a good dispersion of iron oxide. Furthermore, in contrast to the SGTiFe50 sample, the presence of the small amounts of calcium oxide prevented the formation of the rutile structure of titania. Moreover, the peaks originating from the anatase form of TiO2 are much broader compared to other samples, indicating a less ordered material.
The effect of calcium doping on the catalyst seems to be of a nature that is very different than a modification of the oxidation state or crystalline structure of iron oxide. As the best improvement of oxidation properties of 2-MCP is obtained for the samples containing only up to 3 percent of calcium with respect to the active phase content, it is reasonable to assume a synergistic effect of calcium and iron oxides. TPR profiles of TiFe50Ca3 samples indicate small reducibility changes compared to the TiFe50 sample (i.e., the first peak at 450ºC is shifted slightly towards lower temperature and better developed than the one at 465ºC for the TiFe50 sample). Although the changes are visible, they only partially account for the significant improvement of the catalytic properties of the TiFeCa series in 2-MCP decomposition.
The small shift in reduction peak in TiFeCa may result from incorporation of the calcium cation in α-Fe2O3 oxide crystallites. In such a case, as calcium in CaO has a lower oxidation state than iron in Fe2O3, to sustain neutrality of the crystal lattice, oxygen vacancies are created. Oxygen vacancies are electron acceptor sites and can have a localized effect on host cations to be more electron accepting.
This explanation of Ca effect on TiFe samples is in agreement with the XRD results that indicated the presence of α-Fe2O3 crystallites in both TiFe50 and TiFe50Ca samples. If the concentration of calcium increases above some point, phase separation of CaO and Fe2O3 will occur, decreasing the synergistic effect of calcium and iron oxides. As a result the decrease of catalytic activity of the TiFeCa samples will be observed above certain calcium levels. Such negative effect of calcium content above 5 percent has been detected.
Another phenomenon of calcium effect has to be taken into consideration. In our system, calcium ions are likely to be incorporated into iron oxide crystallites, which may further improve the ion exchange between the iron and calcium. Once chloride ions are withdrawn from iron by calcium, to maintain the ion exchange efficiency, calcium chloride needs to be re-oxidized to CaO. The activation energy for CaCl2 oxidation by molecular oxygen is low (23 kcal/mole) and even lower in the presence of water vapor (12 kcal/mole), which is a product of oxidation reaction of hydrocarbons. Thus CaO is readily regenerated to continue catalyst activity. The stoichiometric interaction between the calcium oxide and iron chloride can be described as follow:
2FeCl3+3CaO= Fe2O3 + 3CaCl2
CaCl2+H2O=CaO +2HCl or CaCl2+O2=CaO + Cl2
At higher calcium oxide concentrations, however, phase separation of CaO and Fe2O3 may occur resulting in lesser contact. Consequently, iron oxide regeneration would have to be completed by gas phase oxygen. This helps to explain the retardation of the catalyst efficiency with increasing calcium content. Because improvement in catalyst efficiency is only observed at low levels of calcium doping and higher calcium doping results in decreased catalyst efficiency, dechlorination of CHCs by CaO itself is an unlikely explanation for the improved efficiency for 2-MCP destruction observed in our system.
Addition of calcium oxide also can affect the stability of adsorbed species. Alkali dopants have been reported to influence the behavior of oxide catalysts through the stabilization of enolic forms of the ketones on the surface, which increases the total oxidation yield. Similarly, addition of calcium into a palladium catalyst resulted in stabilization of methoxy species during methanol reaction. Generally, as CaO is a basic oxide, it can enhance the adsorption of weak acids such as phenols and contribute to their catalytic destruction.
The best performance of our catalyst was observed for the samples prepared by the Sol-Gel method doped with small amounts of calcium. The Sol-Gel method favors the formation of γ-Fe2O3 on the surface, which is more readily reduced and thus more active in the Mars-van Krevelen process. The admission of calcium in Sol-Gel samples further increases the amount of γ-Fe2O3 formed. TPR profiles reveal a significant increase of the low temperature reduction peaks attributed to the conversion γ-Fe2O3→Fe3O4 and Fe3O4→FeO after introduction of calcium into Sol-Gel prepared samples. Additionally, after introduction of calcium, the lower temperature peak shifted 40º higher, whereas the higher temperature peak shifted to a lower temperature by 10º. These shifts, together with the distinct increase of the intensity of the peaks, indicate structural impacts of calcium doping on iron oxide species.
γ-Fe2O3 has a spinel structure with some of the iron ions residing in tetrahedral positions and cationic vacancies. This structure is similar to γ-Al2O3 and as such it can be compared to γ-Al2O3 transformations. Admission of calcium can result in stabilization of the structure by incorporation of Ca2+ ions into cationic vacancies of the oxide, as has been similarly observed for MgAl2O4. As a result, more iron oxide surface species will exist in the form of γ-Fe2O3 than in the more thermodynamically stable α form.
Concomitantly, incorporation of calcium ions into cationic vacancies results in the γ-Fe2O3 spinel becoming more resistant to reduction. This causes the shift in the TPR reduction peak attributed to the transformation of γ-Fe2O3 to Fe3O4. Calcium ions may still be present in the crystallites after the transformation into Fe3O4 (both oxides have a very similar geometry, with iron in both tetrahedral and octahedral interstitials). Thus, the reduction is simplified to removal of some oxygen ligands, without rearrangement of the structure, creating vacancies and perturbation of the lattice. As a result, further reduction to FeO is enhanced.
Oxidation of hydrocarbons according to the Mars-van Krevelen mechanism requires involvement of surface lattice oxygen of the active phase as well as the redox cycle of the cations involved in the oxygen transfer process. In a previous manuscript on the formation of polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/PCDF) over a copper oxide/silica surface, we demonstrated that electron transfer occurs between the adsorbed molecule and surface cation resulting in the reduction of the latter (Lomnicki, et al., 2003). We believe that this also is occurring in the iron oxide based catalyst.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 9 publications | 4 publications in selected types | All 4 journal articles |
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Khachatryan L, Dellinger B. Formation of chlorinated hydrocarbons from the reaction of chlorine atoms and activated carbon. Chemosphere 2003;52(4):709-716. |
R827719 (Final) |
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Lomnicki S, Dellinger B. A detailed mechanism of the surface-mediated formation of PCDD/F from the oxidation of 2-chlorophenol on CuO/silica surface. Journal of Physical Chemistry A 2003;107(22):4387-4395. |
R827719 (Final) R828191 (Final) |
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Lomnicki S, Dellinger B. Development of supported iron oxide catalyst for destruction of PCDD/F. Environmental Science & Technology 2003;37(18):4254-4260. |
R827719 (Final) R828191 (Final) |
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Supplemental Keywords:
oxide-based catalyst, chlorinated hydrocarbons, chlorine abstraction, chlorine abstraction, volatiles chlorides, catalyst, doping, catalytic oxidation, TPR experiments, Sol-Gel preparation, chemical transport modeling,, RFA, Scientific Discipline, Air, Toxics, particulate matter, Environmental Chemistry, HAPS, Atmospheric Sciences, Ecological Risk Assessment, Engineering, Chemistry, & Physics, Environmental Engineering, Fourier Transform Infrared measurement, particulates, catalytic oxidation, emission control technologies, hydrocarbon, MACT standards, chemical transport modeling, alkali metal oxide, chlorinated hydrocarbons, pollutant transport, ferric oxide, toxic contaminants, cost effectiveProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.