Hydrogen Activation on Zeolite Stabilized Ni-Mo Sulfide Clusters.

The activation of H₂ on NaY-encapsulated Mo sulfide clusters is significantly influenced by the presence of Ni at ion exchange positions. Ni was incorporated by partially ion exchanging the NaY zeolite with Ni²⁺ cations. Mo(CO)₆ vapors were subsequently deposited on the ion exchanged NiNaY zeolites followed by sulfidation in 10 vol % H₂S/H₂ at 673 K, leading to the formation of dimeric Mo₂S₄ clusters connected to Ni²⁺ via bridging S atoms. In contrast to the monometallic Mo sulfide clusters, which stabilize adsorbed hydrogen primarily as hydrides on Mo atoms, the bimetallic Ni-Mo sulfide clusters bind hydrogen also as sulfhydryl groups on the bridging sulfur atoms. The formation of sulfhydryl groups in Ni-Mo sulfide clusters is attributed to the lower electron density on the cluster due to coordination with more electronegative Ni²⁺. The ethene hydrogenation rate was significantly higher on the bimetallic Ni-Mo sulfide catalysts compared to monometallic Mo sulfide catalysts because the stabilization of atomic hydrogen as sulfhydryl groups opens a new hydrogenation pathway.