Selective catalytic reduction of N2O with CH4 on Ni-MOR: A comparison with Co-MOR and Fe-MOR catalysts

Abstract

The selective catalytic reduction of N2O with CH4 in the presence of excess O2 (CH4-SCRN2O) and CH4+O2 reaction were studied on Ni-MOR, Co-MOR and Fe-MOR, prepared from H-MOR or Na-MOR, by ion-exchange or CVD.FTIR showed that transition metal ions (tmi) were well dispersed, mainly isolated with at least two coordinative vacancies. For CH4-SCRN2O, irrespective of Brønsted acid site and Na+ amount, catalysts were active in the order Fe-MOR>Ni-MOR>Co-MOR. Using a methane-poor mixture, on all samples CH4-SCRN2O consisted of two nearly independent reactions: CH4+N2O and CH4+O2. Using a methane-rich mixture, CH4-SCRN2O consisted of a CH4+N2O+O2 reaction, whose stoichiometric ratios depended on the tmi. Whereas on Ni-MOR methane combustion occurred as side reaction, on Co-MOR and Fe-MOR no side reactions occurred. Accordingly, for CH4+O2 Co-MOR and Fe-MOR were poorly active, whereas Ni-MOR were highly active.We conclude that in CH4-SCRN2O a monoatomic oxygen form activates methane on Co-MOR and Fe-MOR catalysts, whereas both a monoatomic oxygen form and a molecular oxygen form activate methane on Ni-MOR. Being active for the CH4-SCRN2O and CH4-SCRNOx and forming CO only in traces, Ni-MOR are promising catalysts for the simultaneous SCR of N2O and NOx using CH4 as reducing agent.