Does Density of Cationic Sites Affect Catalytic Activity of Co Zeolites in Selective Catalytic Reduction of NO with Methane?

Selective catalytic reduction of NO with methane (CH₄-SCR) in an excess of oxygen over Co ions located in ZSM-5 of various Si/Al composition and in ferrierite, mordenite, chabazite and beta zeolite was investigated. From the comparison of the dependence of the TOF values per Co ion for NO conversion to N₂ and Co ions distribution among the cationic sites on total Co ion concentration, the catalytic activity of the individual Co ions was estimated. The -type Co²⁺ ions, located in the main channel of mordenite and ferrierite and coordinated above the rectangle of four framework oxygens of the channel wall exhibit the highest activity in these zeolites. On the other hand, the -type Co²⁺ ions coordinated in the plane of four oxygens of the deformed six-member ring located in the channel intersection of ZSM-5 and in channels of beta zeolite control the activity of these Co zeolites. The sequence of activity of Co²⁺ ions in CH₄-SCR of NO was FER Co>ZSM-5 Co>BEA CoZSM-5 CoFER CoMOR CoCHA CoMOR Co. A correlation between the activity of the individual Co ions in CH₄-SCR of NO and a distance between the cationic sites was observed.