Pelletization effects on intermetallic Pt-rare earth catalysts supported on mesoporous zeolite for propane dehydrogenation

Abstract

The growing global importance of direct propylene production has increased interest in propane dehydrogenation (PDH) technologies over the recent years. A recent investigation has demonstrated unprecedented catalytic longevity of the intermetallic alloys of Pt-Y particles supported on a powder form of multi-ammonium surfactant- derived mesoporous zeolite. Unfortunately, catalysts designed from the laboratories must be shaped into industrially relevant forms, often assisted by additives that might significantly impact their original catalytic performances. Therefore, the thesis employs three conventional types of binders (20 wt% in each case, pseudoboehmite, fumed silica, and synthetic hydrotalcite) to investigate pelletization effects on intermetallic Pt-Y catalysts supported on mesoporous MFI zeolite. The use of pseudoboehmite (later phase-transitioned to alumina) exhibited the highest mechanical strength without losing the zeolite mesoporosity or structural crystallinities. Upon metal loading, a successful formation of highly dispersed intermetallic Pt-Y alloys was observed on the pelletized mesoporous zeolites. Since a quarter of catalytically active Pt elements was shown to reside on the binder portions, decreased catalytic performances in PDH were expected. However, the resulting catalytic properties of these intermetallic catalysts formed on the pseudoboehmite-bound pellets significantly deviate from our initial expectations. Considerable increases in propane conversion and decreases in propylene selectivity were observed, attributed to a generation of Brønsted acid sites at the zeolite-binder interface. In the case of pseudoboehmite- bound pellets, the study further suggests that the acid sites were formed due to the migration of extra-framework aluminum species during the pelletization process.