(403d) Density Functional Theory Study of NOx Storage Reduction Catalysts

The NOx storage reduction (NSR) catalysts have emerged as the most successful approach to combat this problem of lean burn NOx reduction. However, these systems are required to operate under two distinct regimes: a lean condition in which NO is oxidized over a noble metal component (usually Pt) to form NO2 which can subsequently adsorb on the storage agent (usually barium oxide) and a reducing atmosphere during which a reducing agent (e.g. H2, CO, C3H6) reacts with NOx released by the catalyst reacts to produce N2. Surface science studies of epitaxially grown metal layers on top of a different metal single crystal have revealed that these pseudomorphic monolayers have novel adsorption properties and therefore could potentially serve as a whole new class of catalysts. Specifically, using density functional theory we propose to examine pseudomorphic monolayers of Pt and Pd over other transition metals for their ability to perform in demanding task of operating both reducing and oxidizing environments in the NSR system. From these calculations, it is hoped that suitable candidates are identified for replacement of monometallic Pt catalysts thereby simultaneously improving performance and reducing cost. As a starting point, the oxidation of NO to NO2 and dissociative adsorption of O2 were examined for a variety of potential candidate catalysts. It is important to recognize that the stable surfaces in the oxidizing environment may in fact be surface oxides.