Desilicated zeolite BEA for the catalytic cracking of LDPE: the interplay between acidic sites' strength and accessibility

Abstract

Catalytic cracking of low-density polyethylene by BEA zeolites evidenced the mutual dependence of speciation and accessibility of the acidic sites, which are either inherent to the microporous structure or reachable from the newly developed mesoporous surface. FT-IR spectroscopic evaluation coupled with GC-MS product analysis in combination with thermogravimetric analysis allows the acidic function of the sites to be related to the catalytic performance. Results show that the enhanced number of acidic sites available for LDPE is not as important as the number of highly acidic Si(OH)Al groups hosted in the internal voids of the microporous environment. Microporous beta zeolite is more catalytically active towards cracking since it provides a high number of Si(OH)Al zeolite-type groups of high strength. The mesoporosity benefitted in the LDPE cracking when the strength of the protonic acid sites remained above the level of 80% of the original one. The reduced acidic strength by further mesoporosity development is not compensated by the high amount of easily accessible sites; thus, the mesoporosity effect fails.