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.