Grantee Research Project Results
2001 Progress 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 Period Covered by this Report: September 1, 2000 through August 31, 2001
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 is to develop iron oxide-based catalysts for destruction of chlorinated hydrocarbons. In the first year of the project, we studied the interaction of oxides with the highly chlorinated molecules. Carbon tetrachloride was used as a model molecule due to its simple structure to simplify the interpretation of the data. It was found that the preparation method plays an important role in this process. A mechanism of chlorine abstraction from the carbon-chlorine molecule was developed.
Our detailed study of the interaction of alumina, a common support, with carbon tetrachloride has shown that it can be consumed during the process due to formation of volatile chlorides when the process occurs at high temperatures, which leads to gradual deactivation. Bulk iron oxide was found to have very low activity.
Our recent experiments have focused on the destruction of chlorinated phenols as key intermediates in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). Our recent experiments have focused on the reactions of 2-chlorophenol.
Progress Summary:
The effect of the support on iron oxide catalytic decomposition of 2-chlorophenol: Data expressed as light-off curves clearly show that even small amounts of iron oxide supported on alumina significantly improve activity of the system. This effect is even more profound if it is taken into account that bulk iron oxide was almost inactive in the studied temperature range. With increasing iron oxide content, the light-off curves are shifted to lower temperatures with a light-off point well defined at 400oC. However, 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. No organic products were detected that indicate a complete oxidation of 2-chlorophenol to CO/CO2.
Contrary to carbon tetrachloride decomposition over alumina at high temperature, the preparation method did not significantly affect the performance of our catalysts. The light-off curves were shifted approximately 25oC towards lower temperatures for the samples prepared by the Sol-Gel method.
Based on the activity of iron oxide catalysts in 2-chlorophenol decomposition, two groups of catalysts can be distinguished: (1) iron oxide supported on silica (low activity); and (2) iron oxide supported on titania/alumina (higher activity). Significant differences between these two groups of catalysts result from the nature of the supports used. SiO2 is known to be an inert support characterized by lack of or very weak interactions between itself and the supported oxide phase. With increasing temperature, the mobility of iron oxide species increases resulting in their agglomeration and drop of activity. On the other hand, alumina and titania exhibit strong interactions with the supported, active phase, often leading to the formation of surface aluminates and titanates. Because of this, 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 showed somewhat better activity.
Modification of iron oxide/titania catalysts: There is a strong correlation between the amount of iron oxide on titania support and activity of catalysts for 2-chlorophenol decomposition. A clear maximum is visible for the catalysts loading around 2.5-3.5 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 larger crystallites that are less active in the process due to stabilization of the surface sites by the crystalline structure. Significant differences in the TPR profiles of iron oxide/titania catalysts with different iron oxide phase loading seem to support this conclusion-- low temperature reduction peaks shift to lower temperature for low iron oxide content. Additionally, there is a good correlation between the reduction peak position and light-off point for 2-chlorophenol decomposition. Taking into account the fact that most of the oxidation processes proceed according to the Mars-van Krevelen 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 due to formation of surface crystallites. This in turn leads to a decrease in reduction ability of the surface iron and a concomitant decrease in the ability of the catalyst to oxidize 2-chlorophenol.
Further improvement of iron oxide/titania catalysts for 2-chlorophenol decomposition was observed when samples were prepared by the Sol-Gel method. The TPR of these catalysts demonstrated a shift of the low temperature reduction peak towards lower temperatures.
Effect of calcium doping: The effect of calcium doping of iron oxide/titania catalysts for 1-chlorophenol decomposition also was studied. The initial data indicate that the presence of calcium has a significant impact on the 2-chlorophenol destruction. Small amounts of calcium have shifted the light-off curves of the TiFe5O sample around 50oC to lower temperature. The nature of the effect of calcium will be studied in the next phase of the project. The following hypotheses will be examined: (1) acid-base properties are changed after calcium introduction, which affects adsorption of chlorophenol (weak acid); (2) calcium enhances chlorine abstraction from the iron oxide surface and increases the rate of sites regeneration; and (3) calcium improves dispersion of the active phase.
Future Activities:
The following experiments are planned for the next phase of the project to explore the observed effects and apply the gathered information for improving the performance of iron oxide catalyst:
- XRD experiments of all samples will be performed to examine the phase of deposited iron oxide. Additionally, same experiments with "used" catalyst should provide information on the changes of the iron oxide phase during the reaction.
- IR experiments with pyridine adsorption will deliver information on the acidity of the samples. In particular, these experiments are important for the calcium doped catalyst and the influence of acid/base sites on the activity in 2-chlorophenol decomposition.
- XPS, EXAFS, and XANES experiments will be performed to gather more information on the oxidation state of iron in particular catalysts and in particular doped ones. Additionally, we will try to follow the path of chlorine on the surface of the catalysts.
- More doping materials will be introduced into the system to further improve its performance. The details on the material introduced will be decided based on the influence of acidity and reducibility of the catalyst on the activity.
Journal Articles:
No journal articles submitted with this report: View all 9 publications for this projectSupplemental Keywords:
air, atmosphere, adsorption, absorption, exposure, carcinogen, mutagen, chemicals, toxics, particulates, PAHs, dioxin, nitrogen oxides, pollution prevention, waste reduction, incineration, environmental chemistry, engineering, ecology, industry, 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.