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Pollution from hydrofluorocarbons (HFC) poses a serious challenge to the environmental community. Released from industrial operations, they have contaminated both the atmosphere and groundwater and are considered persistent in both media.1 For over the past 20 years, the practice of synthesizing hydrofluorocarbons as alternatives to chlorofluorocarbons (CFC) has been conducted in an effort to reverse the effects of stratospheric ozone layer depletion. 2,3 However, in doing so these new fluorinated compounds exhibited an unexpected property as a potent global warming greenhouse gas (GHG) with radiative forcing potentials in the range of 100 to 10,000 equivalents greater than carbon dioxide.4 Conversely, HFCs exhibit desirable properties as precision cleaning solvents due to their low surface energy but that use has lead to releases contaminating groundwater resulting in recalcitrant pollution in the form of dense nonaqueous phase liquids (DNAPL).5 The Environmental Protection Agency (EPA) has recently requested studies on the environmental impact of HFCs with respect to a number of petitions received from various environmental action groups imploring the use of the Montreal Protocol as the vehicle by which to achieve elimination of the compounds from industrial operations.6,7 Additionally, results from studies requested by the international community have shown HFCs to exhibit developmental and neurological damage in animal life along with their impact to humans remaining not completely understood.8,9,10 Therefore, the potential hazards of HFCs to human health and the environment necessitates the development of an effective and environmentally responsible technology for their remediation from groundwater. The National Aeronautics and Space Administration (NASA) has employed the use of various halogenated solvents in its spacecraft cleaning operations at its facilities for many years iv and in that time experienced accidental releases which eventually resulted in environmental contamination.11,12,13 Many of the organic solvents employed in these operations consisted of halogenated compounds with most being partially chlorinated and fluorinated hydrocarbons. Through normal use and operation, releases of these materials found their way into the environs of atmosphere, soil and groundwater. Remediation of fluorinated compounds has not followed the successful path laid by clean-up technologies developed for their chlorinated counterparts.14,15,16,17 Fluorinated compounds are resistant however to those methods due to their unreactive nature stemming from the properties of the strong carbon-fluorine bond. 18 This unique bonding property also ensures that their environmental persistence endures. 19 One particular fluorinated groundwater contaminant, the HFC 1,1,1,2,2,3,4,5,5,5-decafluoropentane (DFP), which serves as an excellent cleaning agent and has been used by NASA since the late 1990’s and still remains in use today, was selected as the focus of this study. 20 For this study, various reductive metal systems were evaluated for their capability towards effective degradation of DFP. These included the metals: iron, magnesium, aluminum and zinc and several bimetallic alloys as well as attempts employing some on carbon support. Variations in protic solvent reaction media and acidic metal activation were also explored. The bimetallic reductive catalytic alloy, magnesium with palladium on carbon support Mg(Pd/C) in aqueous media, proved to be the successful candidate with 100% conversion to simple hydrocarbons. Mechanistic evaluation for degradation is proposed via a series of stepwise catalytic reduction reactions. Kinetic studies revealed degradation to obey second order reaction kinetics. Further study should be conducted optimizing an in situ groundwater delivery method for field application. Additionally, the developed technology should be assessed against other v groundwater fluorocarbon pollutants; either as a method for remediating multiple fluorinated polluted sites or as a polishing agent where all other non-fluorinated halogen pollutants have been abated.

Due to increasingly stringent regulations limiting the emissions of nitrogen oxides worldwide from lean exhaust mobile and other sources, there is great technological need for catalytic reduction of NOx. There is great interest in developing catalysts capable of reducing NOx species in this chemically complex exhaust environment. Currently, no such commercial catalyst is available using hydrocarbon selective catalytic reduction of NO x (HC SCR NOx) technology that will enable manufacturers to comply with future worldwide NOx emissions standards. HC SCR NOx would be the most attractive solution given that hydrocarbon fuel is already on-board. The objectives of this work were to develop a highly active catalyst for reformate assisted HC SCR NOx, determine the effects of the exhaust environment on NOx conversion activity, and develop a mechanism and kinetic model to predict the performance of the active catalyst. A series of Al2O3 supported catalysts with either Pd, Ag, An, or Pd-Ag were made using various catalyst synthesis methods. The catalysts were characterized and their activity evaluated at steady state conditions for NOx conversion under a surrogate diesel exhaust environment with varied reformate and propylene feed conditions. The evaluation procedure was developed using a factorial design method containing four factors: temperature, H2/CO ratio, HC1/NOx ratio, and total reductant composition (H2, CO, and propylene). Temperature had 8 levels in the temperature range of 200-550°C evenly spaced while the other factors each had three. The factor values were chosen using envisioned typical diesel exhaust aftertreatement conditions as the basis including the concept of secondary reductant injection. Silver supported on gamma alumina (Ag/gamma-Al2O3) catalysts showed the highest NOx conversion at all conditions. The factorial design results showed that one main factor, HC1/NO x ratio, and interactions such as H2/CO with HC1/NOx, H2/CO with temperature, and HC 1/NOx with temperature most significantly effected NO x conversion. For all scenarios investigated, the higher inlet propylene concentrations (1000 and 1400 ppm) reformate widened the NOx conversion activity window in the case of higher H2/CO ratios (1 and 2). For the CO dominant H2/CO ratio (0.6) the activity window was narrower than for the H2 dominant conditions at propylene conditions evaluated.

Silver and platinum alumina catalysts prepared by a single-step sol-gel procedure, sol-gel alumina samples modified by an acid or base, and H 3PO4 modified sol-gel alumina impregnated with platinum were studied on a laboratory flow reactor system for the lean NOx reduction in the presence of excess oxygen. An optimal loading of 5 wt% for silver alumina was determined to achieve the best lean NOx reduction by propylene. Different hydrocarbon species significantly altered the NOx activity. Among the reductant types tested, n-octane achieved the best performance followed by propylene, ethylene, propane, and finally toluene. Using n-octane as the reductant, 100% NOx conversion was achieved from 350°C to 460°C. At equivalent moles of hydrogen, the 5% platinum alumina achieved 95% NOx conversion at 100°C with hydrogen as compared to 48% NOx conversion at 250°C for propylene. For the NOx/O2/H2 reaction, the N2O selectivity has a strong inverse relationship to temperature yielding the highest N2O selectivity at the lowest temperature. Increasing the individual reactant concentrations (O2, H2 , or NOx) on the reaction showed a negative order relationship with respect to O2, a positive first order with H2, and a zero order with NO. The thermal stability of acid or base modified alumina was characterized in terms of pore morphology and surface area during sintering experiments. The addition of H3PO4 to the boehmite sol during the pepitzation stage of alumina preparation significantly increased the thermal stability. In fact, after calcination at 1100°C for 16 hours, the H 3PO4-alumina sample retained a surface area of 125M 2/g with no indication of alpha-alumina. The best NOx activity was observed with NH4OH and H2O modified alumina samples exhibiting large pore volumes and pore-size distributions. By exposure to 1000°C for 16 hours, severely sintered platinum impregnated on HNO3 and H3PO4 modified sol-gel alumina modestly affected the NOx reduction by hydrogen whereas the use of propylene significantly degraded the NOx performance. Furthermore, compared to HNO 3-alumina, platinum supported on H3PO4-alumina exhibited lower N2O selectivity and higher net NOx conversion regardless of the type of reductant, calcination temperature, platinum dispersion, and platinum loading.