Dalibor Kaucký

Co2+ ions as probes of Al distribution in the framework of zeolites. ZSM-5 study

The occurrence of “Al pairs” in the framework of ZSM-5 and their spatial distribution in zeolites was estimated by using exchanged Co2+ ions as probes for “Al pairs”. The visible spectra of Co2+ ions were employed to monitor the distribution of Co2+ ions, and thus “Al pairs”, among the individual cationic sites, i.e. local framework arrangements at defined positions in the zeolite channels. The effects of concentration of aluminum in the framework and conditions of zeolite synthesis on the presence of “Al pairs” and their spatial distribution in the ZSM-5 framework were investigated. It has been shown that the distribution of Al atoms in the framework is not controlled by statistic rules, but depends on the conditions of zeolite synthesis and aluminum concentration in the framework.

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 α-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 β-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 Coα>ZSM-5 Coβ>BEA Coβ≈ZSM-5 Coα≫FER Coβ≈MOR Coα≫CHA Co≈MOR Coβ. A correlation between the activity of the individual Co ions in CH4-SCR of NO and a distance between the cationic sites was observed.

Al distribution in ZSM-5 zeolites: an experimentalstudy

Al atoms are not randomly distributed in ZSM-5 zeolites but their distribution is affected by the Si/Al composition and the synthesis procedure.