Thermally Induced Structure and Functionality Evolution of a Pt–based Lean NOx Trap Catalyst

Abstract

AbstractApplying a NOx trap catalyst to effectively remove NOx contaminants from the oxygen–rich exhaust is still very challenging, due to the lack of use guidance based on deactivation mechanisms. The temperature–dependent Pt sintering rate constant was described using Pt dispersion determined by pulse CO chemisorption. It was found that 700–850 °C was the determining temperature regions for the significant Pt sintering, according to the sintering kinetics and the evolution of active Ptδ+ sites. The weak basicity plays a critical role in trapping NOx at low–temperature (≤300 °C), and the NOx trap efficiency decreases because of the loss of catalytic activity and medium basicity caused by forming BaAl2O4 phase. The reduction of NOx towards N2 on the Pt crystallites smaller than 18 nm is structure sensitive and decreases with losing the reducibility of catalysts. The security for long–time use of a NOx trap catalyst should be exposed to the exhaust gas within 750 °C, and effectively removing NOx contaminants requires it to be worked in the 350–500 °C regions. These findings can guide engineers and applied chemists how to efficiently use a NOx trap catalyst in the automotive exhaust purification system.