Contrast-matching small-angle neutron scattering to monitor the accessibility of solvents to the porosity of coked FCC catalysts

Small-angle neutron scattering (SANS) has been performed on fresh and deactivated fluid catalytic cracking (FCC) equilibrium catalysts. The catalysts were coked using a vacuum gas oil feed and stripped for varying periods of time in standard microactivity test (MAT) and fluidized-bed reactors. BET surface areas and contrast-matching SANS were measured on these samples to elucidate the influence of coke on the catalyst porosity. It was found that significant contrast matching could be obtained by mixing the catalyst with deuterated methanol, and there was good agreement between the gas adsorption and SANS results in terms of the mesoporosity. SANS indicated that the level of closed porosity is negligible in the fresh catalyst but significant in the deactivated catalysts and that the level decreases as the total coke content is reduced during stripping. Furthermore, the use of d-dodecane demonstrated that SANS can also provide information about sieving effects caused by the catalyst structure.