Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 35: Heterogeneous catalysis II
O 35.4: Vortrag
Dienstag, 23. März 2010, 15:45–16:00, H33
The Selective Catalytic Reduction (SCR) of NO with NH3 at Vanadium Oxide Catalysts: Adsorption, Diffusion, Reaction. — •Mathis Gruber and Klaus Hermann — Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin and Sfb 546, (Germany)
The Selective Catalytic Reduction (SCR) of NOx with NH3 over vanadium based metal-oxide (VOx) catalysts has been proven to be one of the most effective NOx reduction processes. Even though it is widely used in commercial applications details of the reaction mechanism are still under debate. Experiments show that adsorption, diffusion, and reactions with NO and (de)hydrogenation processes at the VOx surface contribute elementary steps. These processes are examined in theoretical studies employing density-functional theory together with gradient corrected functionals. The VOx substrate is modeled by clusters cut out from the ideal V2O5(010) surface where peripheral oxygen bonds are saturated by hydrogen. Apart from the perfect oxide surface also differently reduced surfaces are considered by introducing oxygen vacancies. NH3 is found to interact only weakly with the perfect V2O5(010) surface. In the presence of OH groups (Brønsted acid sites) NH3 can form a surface NH4+ species. NH3 can also interact with the surface near oxygen vacancies, adsorbing at vanadium centers of lower coordination (Lewis acid sites). In contrast, NO interacts much more weakly with the surface. Further, simultaneous NO, NH3 adsorption and SCR reaction scenarios at Brønsted and Lewis acid sites are examined. They result in different reaction paths and intermediates as will be discussed in detail.