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Studies of N{sub 2}0 adsorption and decomposition on Fe-ZSM-5

Description: The interactions of N2O with H-ZSM-5 and Fe-ZSM-5 have been investigated using infrared spectroscopy and temperature-programmed reaction. Fe-ZSM-5 samples with Fe/Al ratios of 0.17 and 0.33 were prepared by solid-state exchange. It was determined that most of the iron in the samples of Fe-ZSM-5 is in the form of isolated cations, which have exchanged with Bronsted acid H+ in H-ZSM-5. The infrared spectrum of N2O adsorbed on H-ZSM-5 at 298 K exhibits bands at 2226 and 1308 cm-1 associated with vibrations of the N-N and N-O bonds, respectively. The positions of these bands relative to those seen in the gas phase suggest that N2O adsorbs through the nitrogen end of the molecule. The heat of N2O adsorption in H-ZSM-5 is estimated to be 5 kcal/mol. In the case of Fe-ZSM-5, additional infrared bands are observed at 2282 and 1344 cm-1 due to the interactions of N2O with the iron cations. Here too, the directions of the shifts in the vibrational features relative to those for gas-phase N2O suggest that the molecule adsorbs through its nitrogen end. The heat of adsorption of N2O on the Fe sites is estimated to be 16 kcal/mol. The extent of N2O adsorption on Fe depends on the oxidation state of Fe. The degree of N2O adsorption is higher following pretreatment of the sample in He or CO at 773 K, than following pretreatment in O2 or N2O at the same temperature. Temperature-programmed decomposition of N2O was performed on the Fe-ZSM-5 samples and revealed that N2O decomposes stoichiometrically to N2 and O2. A higher activity was observed if the catalysts were pretreated in He than if they were pretreated in N2O. For the He-pretreated samples, the activation energy for N2O decomposition was estimated to be 42 kcal/mol and the preexponential factor of the rate coefficient for ...
Date: March 8, 2002
Creator: Wood, Benjamin R.; Reimer, Jeffrey A. & Bell, Alexis T.
Partner: UNT Libraries Government Documents Department

Investigation of the liquid/vapor composition of compressed liquid CO2 with N2 and O2 in integrated pollutant removal systems for coal combustion

Description: Accurate prediction of the processes in Integrated Pollutant Removal (IPR) using compression and condensation of coal combustion products requires an understanding of the liquid/vapor ternary CO2/O2/N2 system. At conditions close to the critical point of CO2 the existing equations of state deviate from the sparse measured results available in the literature. Building on existing data and procedures, the USDOE/Albany Research Center has designed an apparatus for examining compositions in this region. The design of the apparatus and planned initial experiments are presented.
Date: January 1, 2005
Creator: Oryshchyn, Danylo B.; Ochs, Thomas L.; Summers, Cathy A.; Penner, Larry R. & Gerdemann, Stephen J.
Partner: UNT Libraries Government Documents Department

Emissions Of Greenhouse Gases From Rice Agriculture

Description: This project produced detailed data on the processes that affect methane and nitrous oxide emissions from rice agriculture and their inter-relationships. It defines the shifting roles and potential future of these gases in causing global warming and the benefits and tradeoffs of reducing emissions. The major results include: 1). Mechanisms and Processes Leading to Methane Emissions are Delineated. Our experiments have tested the standard model of methane emissions from rice fields and found new results on the processes that control the flux. A mathematical mass balance model was used to unravel the production, oxidation and transport of methane from rice. The results suggested that when large amounts of organic matter are applied, the additional flux that is observed is due to both greater production and reduced oxidation of methane. 2). Methane Emissions From China Have Been Decreasing Over the Last Two Decades. We have calculated that methane emissions from rice fields have been falling in recent decades. This decrease is particularly large in China. While some of this is due to reduced area of rice agriculture, the bigger effect is from the reduction in the emission factor which is the annual amount of methane emitted per hectare of rice. The two most important changes that cause this decreasing emission from China are the reduced use of organic amendments which have been replaced by commercial nitrogen fertilizers, and the increased practice of intermittent flooding as greater demands are placed on water resources. 3). Global Methane Emissions Have Been Constant For More Than 20 Years. While the concentrations of methane in the atmosphere have been leveling off in recent years, our studies show that this is caused by a near constant total global source of methane for the last 20 years or more. This is probably because as some anthropogenic sources have ...
Date: July 16, 2009
Creator: Khalil, M. Aslam K.
Partner: UNT Libraries Government Documents Department