Single-step flame-made Pt/MgAl_2O_4 - A NO_x storage-reduction catalyst with unprecedented dynamic behavior and high thermal stability

摘要

One weight percentage of Pt/MgAl_2O_4, 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 MgAl_2O_4 spinel showed superior dynamic performance in NO_x storage-reduction at short regeneration times (<30 s) compared to a standard 1%Pt-20%Ba/Al_2O_3 reference catalyst. The better NSR performance at short regeneration times of Pt/MgAl_2O_4 is limited to the use of hydrogen and H_2-CO mixtures as reductants, whereas with other reductants, CO or C_3H_6, the NSR performance was similar for both catalysts. The efficiency of the reduction agents decreased in the order H_2 > H_2 + CO > CO > C_3H_6. XRD and time-resolved in-situ DRIFT investigations indicate that bulk nitrate species are formed on Pt-Ba/Al_2O_3, whereas on the spinel-based Pt/MgAl_2O_4 catalyst predominantly surface species were formed. The superior dynamic performance of the spinel-based Pt/MgAl_2O_4 is attributed to the different adsorbed NO_x species and their different stability under regeneration conditions. Pt/MgAl_2O_4 also showed higher thermal stability up to 800 °C and lower stability of sulfur-containing species.