Study of the thermal transformation of Co- and Fe-exchanged zeolites A and X by 'in situ' XRD under reducing atmosphere

In situ'' high temperature X-ray diffraction under reducing atmosphere is used for the first time to study the thermal stability and transformations of Co- and Fe-exchanged A and X zeolites. TG-DTA and ‘‘ex situ'' XRD characterization were also carried out. The temperature of incipient crystallization of metallic phase was found to be 700 8C in Fe-zeolites and 800 8C in Co-zeolites. Moreover, ex situ X-ray experiments, after thermal treatment both under inert and reducing atmosphere, revealed the formation of ceramic phases upon the thermal collapse of the zeolitic framework. Metal nanoparticles were obtained by reduction and the size of metal clusters was found to range between 24 and 40 n