Investigation of Reverse-Hydrogen Spillover on Zeolite-Supported Palladium Tetramer by ONIOM Method

The present study explores favorable chemical state of zeolite-supported Pd-4 clusters using the ONIOM (our-own-N-layered integrated molecular orbital + molecular mechanics) approach, as implemented in the Gaussian03 code. Lowest-energy structures of Pd-4 in the gas phase as well as on a zeolite support are found to be in the triplet state. The calculations reveal that reverse hydrogen spillover from bridging OH groups of zeolite support onto Pd-4 results in a hydrogenated Pd4H/Zeo((m - 1)H), m = 1-3 species, which are energetically preferable over the bare zeolite-supported form of Pd-4/Zeo(mH). The process of single hydrogen transfer from the zeolite support to the Pd-4 Cluster is found to be exothermic and more favorable than two- and three-proton transfer processes.