Hydrogen Activation on Zeolite Stabilized Ni–Mo Sulfide Clusters

Abstract

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.