Single-step flame-made Pt/MgAl2O4 – A NOx storage-reduction catalyst with unprecedented dynamic behavior and high thermal stability

One weight percentage of Pt/MgAl2O4, without any additional classical storage component (Ba or K), was synthesized by single-step flame spray pyrolysis. The catalyst consisting of nano-sized Pt dispersed on MgAl2O4 spinel showed superior dynamic performance in NOx storage-reduction at short regeneration times (<30 s) compared to a standard 1%Pt–20%Ba/Al2O3 reference catalyst. The better NSR performance at short regeneration times of Pt/MgAl2O4 is limited to the use of hydrogen and H2–CO mixtures as reductants, whereas with other reductants, CO or C3H6, the NSR performance was similar for both catalysts. The efficiency of the reduction agents decreased in the order H2 > H2 + CO > CO > C3H6. XRD and time-resolved in-situ DRIFT investigations indicate that bulk nitrate species are formed on Pt–Ba/Al2O3, whereas on the spinel-based Pt/MgAl2O4 catalyst predominantly surface species were formed. The superior dynamic performance of the spinel-based Pt/MgAl2O4 is attributed to the different adsorbed NOx species and their different stability under regeneration conditions. Pt/MgAl2O4 also showed higher thermal stability up to 800 °C and lower stability of sulfur-containing species.