Catalytic activity of Co-ZSM-5 for the abatement of NOx with methane in the presence of oxygen

Mechanism of NO-SCR by methane over Co,H-ZSM-5 and Co,H-mordenite catalysts

“…Therefore, not the zeolite cations but small Co-oxide microaggregates in the zeolite pores were suggested to be the real active sites [29,30]. The found correlation between the catalytic activity and the Co 2+ concentration and the absence of evidence for the presence of oxide microaggregates at low cobalt loadings strongly questions this notion [33,41,51,53]. Intrapore Co-oxo species were observed only at higher Co loadings.…”

“…As it was reported earlier [11,22,26,29,33], the Co-oxide clusters promote the NO 2 -generating NO-COX reaction (Fig. 5), but not the N 2 -forming CH 4 /NO-SCR reaction step of the NO-SCR process ( Fig.…”

“…However, the participation and the particular role of these Co-species in the NO-SCR reaction are not fully clarified yet. It is generally accepted that the Co-oxide or oxide like Co species can enhance NO 2 formation [3,22,25,26,31] and also initiate methane combustion [24,26,29,32,33]. However, contradictory opinions were expressed about the role of Co 2+ cations.…”

“…It should be noted that the Co 3 O 4 , which was the main Co species in our catalysts, promote also the undesired methane combustion [3,24,27,29,33]. This reaction can decrease the selectivity of NO reduction by consuming the reducing agent methane.…”

“…3A and 4A) [3,11,22,26,33,41,51,53] but do not contribute to the NO-COX activity of the catalyst (Fig. 5) The role of zeolite Co 2+ ions in the NO-SCR is still matter of debate.…”