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

摘要

The selective catalytic reduction of N2O with CH4 in the presence of excess O2 (CH4-SCR_(N2O)) 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-SCR_(N2O), irrespective of Bronsted 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-SCR_(N2O) consisted of two nearly independent reactions: CH4 + N2O and CH4 + O2. Using a methane-rich mixture, CH4-SCR_(N2O) 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-SCR_(N2O) 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-SCR_(N2O) and CH4-SCR_(NOx) and forming CO only in traces, Ni-MOR are promising catalysts for the simultaneous SCR of N2O and NO_x using CH4 as reducing agent.