Monitoring cobalt ions siting in BEA and FER zeolites by in-situ UV–Vis spectroscopy: A DRS study

Two series of cobalt exchanged BEA and FER zeolites were obtained by using two distinct preparation methods to introduce the metal through ion-exchange, the conventional method and a microwave (MW)-assisted method. The different Co-based zeolites were characterized by the means of spectroscopic UV–Vis technique and chemical analyses and compared in terms of efficiency in cobalt introduction and cobalt siting within the pores of BEA and FER structures. A first concluding result relates with the implementation of a quantitative Co UV–Vis analysis, a simple method that can easily substitute time consuming and expensive chemical analyses. From the analysis of DRS UV–Vis spectra obtained for materials with cobalt contents from 0.01 to 3 wt.%, and assuming different Al framework distributions, it was possible to identify the siting of Co cations or the occurrence of oxidic Co species. For both zeolites, conventional and microwave-assisted ion exchange led to similar Co distributions over sites α, β and γ, although in the latter case the final amount of Co is substantially lower. Moreover, microwave radiation seems to be an interesting tool to prepare metal-based zeolites with interesting catalytic oxo-cations and/or cobalt oxide.