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

摘要

Although there are many reports on the removal of NO x from vehicle and power plant emissions, little effort has been devot ed to the removal of NO x from cracker flue gases. Here we report a systematic investigation on the design of highly efficient NO x storage-reduction (NSR) catalysts using highly dispersed aqueous miscible organic-layered double hydroxides (AMO-LDHs) derived mixed oxides (LDOs) for NO x emission control from naphtha cracker flue gases. For a series of binary M 2+ Al 3+ LDOs, the influence of six divalent cations (Ca, Zn, Cu, Ni, Co, and Mg) on the NO x adsorption capacity, NO oxidation property, and the thermal stability of adsorbed NO x was systematically investigated. The optimal NO x storage temperature range for each binary LDO was also determined. Based on the fundamental findings of binary LDOs, a ternary LDH CoMgAl-CO 3 derived LDO CoMgAlO x with a significantly improved NO x storage capacity was designed. By tuning the Co/Mg ratio, the NO x storage capacity was greatly improved from 0.14 mmol/g for Mg 3 Al 1 O x to 0.50 mmol/g for Co 1 Mg 2 Al 1 O x at 300 °C. By further doping Pt and K 2 CO 3 , a new NSR catalyst composed of 1 wt% Pt/15 wt% K 2 CO 3 /Co 1 Mg 2 Al 1 O x was obtained, which exhibited a very high NO x storage capacity of 1.2 mmol/g. Finally, the NSR cycling performance, and the CO 2 , SO 2 and H 2 O resistance of this catalyst were also investigated. Thanks for its superior NO x storage capacity, NSR cycling performance, and CO 2 , SO 2 and H 2 O resistance, this new NSR catalyst showed great potential for the NO x control from cracker flue gases.