Continuous De-NO_<i>x</i> under Rich/Lean Cycles by Multifunctional Catalysis of Platinum-Loaded Mordenites

Limited catalytic methods have been reported for urea-free lean NOx emission control. This study reports a continuous and cyclic de-NOx system utilizing mordenite-supported low-loading (0.3 wt %) platinum, Pt(0.3)/MOR, as a multifunctional catalytic and NH3 storage material. Under alternating feeds of rich (0.1% NO + 0.5% CO + 1% H2O) and lean (0.1% NO + 2% O2 + 1% H2O) gas mixtures, Pt(0.3)/MOR demonstrated higher de-NOx efficiency under relatively lean conditions compared to the steady-state reaction in a temperature range of 300–500 °C. The de-NOx mechanism under periodic rich/lean conditions on Pt(0.3)/MOR was investigated using operando infrared experiments. During the rich period, the Pt-catalyzed water–gas shift reaction gives H2 which reduces NO into in situ formed NH3. The generated NH3 is subsequently captured by the Brønsted acid sites of the zeolite support. In the subsequent lean period, NO is reduced by adsorbed NH3 on Pt sites. This study presents a new multifunctional material for a urea-free de-NOx system, offering a potential alternative for automotive de-NOx applications.