Selective catalytic reduction of NOx by methane over Co-H-MFI and Co-H-FER zeolite catalysts: characterisation and catalytic activity

Co-H-MFI and Co-H-FER were studied as catalysts for NO reduction with methane, under diluted conditions. Catalyst bulk and surface structure was characterised by chemical analysis, XRD, TG-DTA, SEM micrographs, IR studies, UV-vis spectroscopy, ammonia TPD, and TPR. Only the features due to zeolitic frameworks were observed. The UV-vis spectra showed that, after outgassing, Co ions are mainly present as Co2+. FT-IR detected residual bridging hydroxyl and silanol groups in spite of the apparent over-exchange, deduced from the chemical analysis. Co ions gave rise to Lewis acid sites of medium strength, evidenced through in situ analysis of the adsorption of a basic probe molecule. NH3-TPD measurements fully confirmed these results. TPR measurements detected easily reducible and oxidizable Co species, possibly related to nanosized Co oxide phases, together with hardly reducible Co2+ ions. Catalytic tests highlighted the Co-H-FER and Co-H-MFl activity, both in NO-selective catalytic reduction by methane and in NO oxidation to NO2, the latter being the predominant reaction at low temperatures. Some mechanistic features of the CH4-SCR reaction are discussed. (C) 2003 Elsevier Science (USA). All rights reserved.