The use of solid state nuclear magnetic resonance (NMR) to study the effect of composition on the properties of equilibrium fluid cracking catalysts (FCCs) Original Research Article

Solid state nuclear magnetic resonance (NMR) spectroscopy together with microactivity testing have been used to characterize the changes that occur in a fluid cracking catalyst (FCC) during gas oil cracking in a refinery fluid catalytic cracking unit (FCCU). The 29Si NMR spectra of fresh FCCs show the well known five peaks pattern attributed to the presence of HY-type crystals. However, after aging, equilibrium FCCs are generated in which the 29Si NMR spectrum of the zeolitic component is reduced to one main dominant resonance near −107 ppm representative of T[4Si,0Al] sites. Thus, irrespective of composition, extensive dealumination of the cracking component in FCCs occurs during recirculation in a FCCU yielding 29Si NMR spectra in which the presence of framework Al is no longer visible. Similar conclusions have been obtained from the corresponding 27Al MAS NMR spectra showing that the dealuminated faujasite structure in equilibrium FCCs contains only extra-framework Al(IV), Al(V), and Al(VI) species. In the presence of tin, vanadium effects on the coordination of Al and Si in equilibrium FCCs, could not be observed by 29Si or 27Al NMR spectroscopy.