Overview of the Fundamental Reactions and Degradation Mechanisms of NOx Storage/Reduction Catalysts William S. Epling, 1, * Larry E. Campbell, 1 Aleksey Yezerets, 2 Neal W. Currier, 2 and James E. Parks II 3 1 EmeraChem and Advanced Catalyst Systems, Maryville, Tennessee, USA 2 Cummins, Inc., Columbus, Indiana, USA 3 National Transportation Research Center, Oak Ridge National Laboratory, Knoxville, Tennessee, USA CONTENTS ABSTRACT .................................. 165 1. BACKGROUND ............................. 165 1.1 Principle of Operation ....................... 166 1.2 Methodological Difficulties .................... 168 2. FUNDAMENTALS ........................... 172 2.1 NO Oxidation ............................ 172 2.1.1 NO Oxidation Over the Noble Metal Component . . . 172 2.1.2 NO Oxidation Over the NSR Catalyst .......... 177 2.1.3 Unresolved Issues ..................... 178 2.2 NOx Sorption ............................ 179 2.2.1 Role of NO 2 in the NOx Trapping Process ....... 179 2.2.2 Effects of Gas Composition ............... 181 2.2.3 Effects of Temperature .................. 184 163 DOI: 10.1081/CR-200031932 0161-4940 (Print); 1520-5703 (Online) Copyright # 2004 by Marcel Dekker, Inc. www.dekker.com *Correspondence: William S. Epling, EmeraChem, 2375 Cherahala Blvd., Knoxville, TN 37932, USA; E-mail: bill.epling@cummins.com. CATALYSIS REVIEWS Vol. 46, No. 2, pp. 163–245, 2004