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.