The simultaneous selective catalytic reduction of N2O and NOX with CH4 on Co- and Ni-exchanged mordenite

Abstract

Co- or Ni-exchanged Na-MOR (Si/Al=9.2) prepared by ion-exchange method were characterized by in situ UV–vis DRS and FTIR. We studied the selective catalytic reduction with CH4 in the presence of O2 (CH4-SCR) for the simultaneous abatement of NO and N2O (CH4-SCRsim) and the related reactions: (i) abatement of N2O (CH4−SCRN2O), (ii) abatement of NO (CH4-SCRNO), (iii) N2O decomposition, and (iv) CH4 combustion. The catalytic measurements were performed in a flow apparatus with GC analysis of reactants and products.FTIR characterization with CO of Ni-MOR identified isolated Ni2+ and [Ni2+ONi2+] dimers, both mainly located in α-sites. In Ni-MOR, the amount of isolated Ni2+ and of dimers was comparable, whereas in Co-MOR isolated Co2+ were more abundant than [Co2+OCo2+]. Transition metal ion (tmi) dimers were easily reduced by CO to [tmi+□tmi+] yielding CO2. In situ UV–vis DRS characterization indicated that by heating in N2O, Co2+ oxidized to Co3+O−, whereas Ni2+ did not.Catalytic results for CH4-SCRsim showed that Co-MOR was active, whereas Ni-MOR was ineffective, because it did not abate N2O. Both catalysts were active for CH4−SCRN2O and for CH4-SCRNO. Whereas Co-MOR was highly active for N2O decomposition and poorly active for CH4 combustion, Ni-MOR was inactive for N2O decomposition and active for CH4 combustion.The NO abatement in CH4-SCRsim on both Co-MOR and Ni-MOR occurred via CH4-SCRNO, and the active sites were isolated tmi2+ in α-sites. The N2O abatement in CH4-SCRsim on Co-MOR occurred in β-sites via N2O decomposition, and the active sites were isolated Co2+, that formed Co3+O− intermediate (UV–vis DRS evidence). The N2O abatement in CH4-SCRsim on Ni-MOR did not occur, because Ni2+, that formed no Ni3+O−, were inactive in N2O decomposition. Redox behavior of [Ni2+ONi2+] accounted for Ni-MOR activity in CH4−SCRN2O and CH4 combustion.