High activity catalyst from exfoliated MoS 2

Abstract

By using exfoliated MoS 2 suspended as single layers in solution we have been able to prepare what appear to be unusually high activity catalysts, where hydrogenation of CO, methanation, was used as the model reaction. The process depends on three features in the preparation; first, the preparation of the single molecular layer MoS 2; second, the deposition of these as single layers onto high-surface-area Al 2O 3 (or rather deposition of Al 2O 3 onto single layers of MoS 2); and third, the deposition of monolayers of nickel onto the single layers of MoS 2. With this structure, suitably calcined and reduced to improve the interaction between the Mo, the Ni, and the Al 2O 3, we have a very high density of active sites per unit area (and per unit mass). The most active sites appear to be a form of oxysulfide. The active sites when nickel is present behave differently from Ni supported on Al 2O 3. The Ni/Mo/Al 2O 3 composition yields CO 2 as the by-product of methanation, instead of the H 2O observed with the Ni Al 2O 3 composition, and has a different activation energy. A specific formulation designed to give the maximum density of accessible Ni/Mo/Al 2O 3 sites shows an activity substantially higher than Ni Al 2O 3 . For formulation without Ni the activity of catalysts prepared by exfoliation shows substantially higher activity than those prepared by precipitation from ammonium heptamolybdate.