Selective hydrogenolysis of methylcyclopentane with excess methylcyclohexane over Ir-encapsulated silicalite-1

Abstract

The catalytic interconversion between methylcyclohexane (MCH) and toluene is highly promising for utilization as a liquid organic hydrogen carrier (LOHC) system. However, the inevitable isomerization of MCH promoted over the Pt/Al₂O₃ catalyst yields undesirable five-membered ring compounds such as dimethylcyclopentanes (DMCPs) and ethylcyclopentane (ECP). In this study, we developed a method for the preparation of Ir-encapsulated silicalite-1 catalyst for the selective hydrogenolysis of methylcyclopentane (MCP), a model compound of five-membered ring isomers, in the presence of excess MCH. Irⁿ⁺/silicalite-1 was synthesized hydrothermally using tetra-n-propylammonium (ⁿPr₄N⁺) hydroxide as the organic structure-directing agent. The as-prepared sample was treated under H₂ flow at 400 °C to promote the reduction of cationic Ir to highly dispersed Ir⁰ clusters in the micropores, and the Ir⁰ clusters then catalyze the hydrogenolysis of the ⁿPr₄N⁺ molecules inside the micropores, yielding Ir⁰/silicalite-1 catalyst with adequate microporosity. The diffusion coefficient of MCP in the 10-ring channels is two orders of magnitude greater than that of MCH, resulting in the molecular-sieving effect for the mixture of MCP and MCH over the silicalite-1 particles. Therefore, Ir⁰/silicalite-1 catalyst prepared in this study promoted selective hydrogenolysis of MCP even in the presence of excess MCH at 200 °C and showed lower deactivation, making it highly promising for the removal for DMCPs and ECPs from MCH to enable its use as an LOHC in hydrogen transportation.