Analysis of the Thermodynamic Feasibility of NO sub(x) Decomposition Catalysis to Meet Next Generation Vehicle NO sub(x) Emissions Standards

Scientists utilized free energy minimization calculations to establish values for the thermodynamic equilibrium concentrations of NO sub(x) and other species in stoichiometric and lean gas mixtures for a range of temperature and composition conditions. For tests implemented under lean conditions, findings indicated that NO decomposition and NO oxidation equilibria determine the lower bounds of NO sub(x) concentrations that can be realized by thermodynamic equilibration or NO sub(x) decomposition. The practical significance of these equilibrium NO sub(x) concentrations is discussed. Under the assumption of a perfect isothermal catalyst acting on a sample diesel exhaust stream collected over the federal test procedure cycle, equilibrium NO sub(x) levels were found to exceed California Low Emission Vehicle II and Tier II NO sub(x) emission standards for automobiles and trucks at temperatures over 800 K.