Density functional theory studies of nitrogen oxide storage reduction catalysts

Lean NOx traps or NOx storage reduction (NSR) catalyst have been subject of considerable attention recently to address the need for more fuel-efficient engines. First pioneered by researches at Toyota, the NOx storage catalyst operates under cycling conditions, lean and reach.;The reliance on platinum as the primary active element is not ideal due to its high cost. One strategy would be the development of bimetallic catalysts whose properties mimic that of Pt or possibly improve the performance of Pt. 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.;We have examined both the NO oxidation (and O2 dissociation) step to model oxidation chemistry and we have looked at WGS shift chemistry as a starting point in our examination of reduction chemistry in a series of Pt and Pd catalysts. We have found that we can overlay volcano plots of the two systems to find a new optimal catalyst where either Pt or Pd is in compression.;Recent studies have indicated that performance of NSR catalyst at low temperature could be possible improved by switching to palladium However, reports to deactivation due to complete oxidation of the catalyst exist leading to some controversy as to the nature of the catalytic surface. Therefore we have calculated the phase diagrams for Pd surfaces in the NO oxidation environment. Beyond, thermodynamic considerations, kinetic concerns must mitigate as well. Kinetic Monte Carlo simulations have been performed to evaluate turnover frequencies for the Pd surface (actually a surface oxide of Pd) under NO oxidation conditions. Turnover frequencies indicate performance on par with the best catalysts observed experimentally, indicating that our model for a surface oxide is valid and must be considered when discussing NO oxidation.