Design of highly efficient NOx storage-reduction catalysts from layered double hydroxides for NOx emission control from naphtha cracker flue gases

Abstract

Although there are many reports on the removal of NOx from vehicle and power plant emissions, little effort has been devoted to the removal of NOx from cracker flue gases. Here we report a systematic investigation on the design of highly efficient NOx storage-reduction (NSR) catalysts using highly dispersed aqueous miscible organic-layered double hydroxides (AMO-LDHs) derived mixed oxides (LDOs) for NOx emission control from naphtha cracker flue gases. For a series of binary M2+Al3+ LDOs, the influence of six divalent cations (Ca, Zn, Cu, Ni, Co, and Mg) on the NOx adsorption capacity, NO oxidation property, and the thermal stability of adsorbed NOx was systematically investigated. The optimal NOx storage temperature range for each binary LDO was also determined. Based on the fundamental findings of binary LDOs, a ternary LDH CoMgAl-CO3 derived LDO CoMgAlOx with a significantly improved NOx storage capacity was designed. By tuning the Co/Mg ratio, the NOx storage capacity was greatly improved from 0.14mmol/g for Mg3Al1Ox to 0.50mmol/g for Co1Mg2Al1Ox at 300°C. By further doping Pt and K2CO3, a new NSR catalyst composed of 1wt% Pt/15wt% K2CO3/Co1Mg2Al1Ox was obtained, which exhibited a very high NOx storage capacity of 1.2mmol/g. Finally, the NSR cycling performance, and the CO2, SO2 and H2O resistance of this catalyst were also investigated. Thanks for its superior NOx storage capacity, NSR cycling performance, and CO2, SO2 and H2O resistance, this new NSR catalyst showed great potential for the NOx control from cracker flue gases.