Computational Insights into the Role of Metal and Acid Sites in Bifunctional Metal/Zeolite Catalysts: A Case Study of Acetone Hydrogenation to 2‑Propanol and Subsequent Dehydration to Propene

We
employ electronic structure calculations to elucidate the catalytic
pathways on bifunctional metal/zeolite catalysts by modeling a HZSM-5-supported
nickel tetramer cluster (Ni4-ZSM-5). Hydrogenation of acetone
to 2-propanol followed by dehydration to propene have been investigated
as model reactions. In Ni4-ZSM-5, we observe reverse hydrogen
spillover, whereby the Brønsted hydrogen migrates from the zeolite
active site to the metal cluster. Consequently, the zeolite-supported
metal cluster becomes electron-deficient, facilitating the hydrogenation
reaction. In contrast, studies conducted on the dehydration reaction
pathways indicate that the Brønsted acid catalysis in HZSM-5
is preferred over the metal catalyzed pathway in the Ni4-ZSM-5 system, again as a result of the electron-deficient nature
of the metal species.