AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM6
Photo-stimulated NO Adsorption on Metal Oxides

Thursday, November 5, 1998, 10:00 am, Room 309

Session: Oxide Surface Chemistry
Presenter: E.R. Blomiley, University of Illinois, Urbana
Authors: E.R. Blomiley, University of Illinois, Urbana
E.G. Seebauer, University of Illinois, Urbana
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Coal combustors generate large quantities of NO@sub x@ compounds that face increasingly stringent regulation. Current NO removal technologies depend in part on selective catalytic reduction (SCR) processes that react NO with reductants like CO or NH@sub 3@ at high temperature. The high costs of reheating the flue gas over the catalyst and problems with slip of the reductant past the reactor have stimulated searches for alternative technologies. Here we examine the surface photochemistry underlying one particularly novel alternative: injection of an inexpensive semiconducting metal oxide (like Fe@sub 2@O@sub 3@) in an illuminated flue geometry in order to stimulate photoadsorption. The NO-laden particulates are then removed in an electrostatic precipitator. We have shown in high and low-pressure experiments that while pure iron and titanium oxides are inactive for NO removal, iron oxides supporting adsorbed Cl display significant activity even at room temperature. The presence of such activity is surprising, and appears to result from a complex interaction between the underlying semiconductor, the adsorbed Cl, weakly adsorbed water, and the photogenerated charge carriers. The activity remains surprisingly robust even in the presence of active gaseous species like SO@sub 2@. Temperature-programmed desorption reveals that some of the NO desorbs essentially reversibly, some forms NO@sub 2@, and the remainder desorbs intact while the substrate decomposes by volatilization of iron chlorides. The potential for such reactions to influence tropospheric NO@sub x@ chemistry in urban areas will be discussed.