NO(x) abatement by trapping/catalytic reduction and theoretical/experimental studies on new sorbents.
Huang, Helen Yaping
2002
Abstract
<italic>NO<sub>x</sub> abatement by trapping</italic>/<italic>catalytic reduction </italic>. In order to improve fuel economy, it is desirable to operate engines under lean-burn conditions. NO<sub>x</sub> trapping/reduction is a promising approach for NO<sub>x</sub> removal under such conditions. Mechanistic studies show that the role of noble metals under lean-burn conditions is to increase the reaction rates of NO oxidation to NO<sub>2</sub> and nitrite oxidation to nitrate. Nitrite and NO<sub>2</sub> are intermediates and nitrate mainly comes from oxidation of nitrite. Pt/BaO/Al<sub>2</sub>O<sub>3</sub> is known to be effective for NO<sub> x</sub> removal through lean-rich cycles, but it deactivates in the presence of SO<sub>2</sub> due to formation of stable barium sulfate. We investigate Fe-Mn based transition metal oxides as NO<sub>x</sub> sorbents. They are found to be efficient for NO<sub>x</sub> adsorption and are resistant to SO<sub> 2</sub>. We further study Pt-Rh/TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> as NO<sub>x</sub> trapping/reduction catalysts. They are highly active for NO<sub>x</sub> removal through lean-rich cycles. NO<sub>x</sub> conversion of 90% is obtained after 5 h lean-rich cyclic runs in the presence of 100 PPM SO<sub>2</sub>. These sorbents and catalysts are also characterized by BET surface area, pore size distribution, XRD, XPS, TPD and FT-IR spectroscopy. Some other NO removal techniques are also investigated in this work, such as kinetic study of NH<sub>3</sub>-SCR on Fe-ZSM-5 and the study of catalyzed carbon-NO reactions. <italic>Theoretical</italic>/<italic>experimental studies on new sorbents </italic>. Quantum chemical calculations are performed to study the gas-solid adsorption. The studies include (1) anion and cation effects on olefin adsorption on metal halides, (2) comparison of the pi-complexations of ethylene and carbon monoxide with Cu<super>+</super> and Ag<super>+</super>, (3) anion effects on the adsorption of acetylene by nickel halides, and (4) ONIOM study of hydrogen adsorption on carbon nanotubes. Quantum chemical explanations of the sorbent-sorbate bonding are explained by molecular orbital theories. Amine surface modified silica xerogel and MCM-48 are synthesized as selective sorbents for CO<sub>2</sub> and H<sub>2</sub>S removal from natural gas mixtures. Very high adsorption capacities and adsorption rates are obtained for both gases. The sorbents can be regenerated completely by pressure swing or temperature swing. The presence of water vapor in the adsorption gas enhances CO<sub> 2</sub> adsorption and barely affects the H<sub>2</sub>S adsorption.Subjects
Abatement Adsorption Catalytic Experimental Fuel Economy Lean Burn New Nitric Oxide No Reduction Sorbents Studies Theoretical Trap Trapping
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