Investigation of Ag-based low temperature NOx adsorbers

Abstract

Future emission standards are becoming increasingly stringent as California will phase in LEV III regulations starting in 2015 and EPA will implement Tier 3 regulations starting in 2017. Current vehicles emit greater than 50% of targeted tailpipe emissions during the first minute or two following “cold-start” mainly due to the ineffectiveness of existing catalytic converters at low temperatures (<180°C). Thus, developing low temperature emission control technologies has become a top priority of automobile manufacturers and their suppliers. In this article, Ag-based catalysts (Ag/Al2O3) were evaluated as a low temperature NOx adsorber using a laboratory fixed-bed flow reactor system. For the first time superior low temperature NO to NO2 conversion efficiencies and NOx storage capacity in the presence of hydrogen were demonstrated. Sulfation and desulfation experiments were conducted to examine the impact of sulfur on the low temperature NOx storage. Several supplier catalysts, including two diesel oxidation catalysts (DOC) and a passive NOx adsorber (PNA), were also tested to provide comparisons to the Ag-based catalysts.