The radical internal coke structure as a fingerprint of the zeolite framework

The formation and the trapping of heavy secondary products called "coke" within the pores (cages, channels) was studied during the ethanol transformation according to different topologies of zeolites: MFI, *BEA and FAU. The aim of this contribution is to (i) assess the possibilities of the electron paramagnetic resonance (EPR) spectroscopy to provide structural information on radical coke compounds and (ii) to show the relationship between the zeolite structure (pore size) and the internal coke nature (components size). In this work, EPR spectroscopy allowed to characterize quantitatively and qualitatively the radical coke molecules and give information about local chemical environment of unpaired electron and radical concentration while mass spectroscopies (MALDI-TOF and GC-MS) provide information about the molecular structure of internal soluble coke. It is shown that FAU zeolite which possesses super-cages contains in its micropores the most voluminous radical coke molecules such as coronene. While *BEA and MEI zeolites contains less heavy radical coke molecules in their micropores such as pyrene and naphthalene respectively.