A Detailed Speciation of Iron on FCC Catalysts Based on an Integrated Use of Advanced Characterisation Methods and Thermodynamic Equilibrium Simulation

Abstract This paper aims to characterise six spent and equilibrated catalysts (Ecats) collected from two different fluid catalytic cracking (FCC) units. Apart from bench-scale facilities including Mӧssbauer spectroscopy, XPS, XRD and SEM–EDS, synchrotron X-ray Adsorption Spectroscopy (XAS) was used to investigate the speciation of iron (Fe), vanadium (V) and sulphur (S), their spatial distribution across each single catalyst and variation between the two refineries. Additionally, thermodynamic equilibrium calculations were performed to elaborate the probable formation mechanisms. As have been confirmed, the oxidation state of iron varies greatly between top surface and bulk of each catalyst, and between the samples collected from different refineries. Fe2+ is predominant in the catalysts collected from the refinery with a partial combustion regenerator. It is also in higher concentration inside a catalyst than on the surface, and preferentially combined with other metallic contaminants on the Al3+-centred active sites, causing the deactivation of the catalysts.