Structure and acidity of individual Fluid Catalytic Cracking catalyst particles studied by synchrotron-based infrared micro-spectroscopy

A synchrotron-based infrared micro-spectroscopy study has been conducted to investigate the structure as well as the Brønsted and Lewis acidity of Fluid Catalytic Cracking (FCC) catalyst particles at the individual particle level. Both fresh and laboratory-deactivated catalyst particles have been studied. The applied deactivation protocols were steaming (ST), two-step cyclic deactivation (CD) and Mitchell impregnation-steam deactivation (MI). In addition, an equilibrium catalyst (Ecat) taken from a real cracking unit has been investigated. From the infrared spectra of the fresh and laboratory-deactivated samples it was clear that the zeolite component experiences partial collapse upon deactivation. Furthermore, it was found that characteristic bands, caused by the presence of clay material, are lost upon deactivation. After pyridine adsorption, the acidity of the samples could be monitored. Both Brønsted and Lewis acidity decreased in the following order: Fresh > ST > CD > MI. The Ecat sample was found to display acidity in between those of CD and MI samples. These findings are in line with earlier bulk transmission infrared as well as ammonia temperature programmed desorption measurements, which confirms the validity of acidity measurements at the single particle level. However, additional information about the distribution of Brønsted and Lewis acidity within individual catalyst particles becomes available. The developed approach reveals a larger variety in the amount of Brønsted acid sites for individual Ecat particles as compared to CD and MI particles. This observation can be attributed to the wide age distribution within industrial equilibrium catalysts and directly shows the added value of micro-spectroscopy approaches in the investigation of interparticle heterogeneities. -------------------------------------------------------------------------------