Raman study of supported molybdenum disulfide single layers

Owing to the increasing demand for clean transportation fuels, highly dispersed single layer transition metal sulfides such as MoS$_{2}$-based catalysts play an important role in catalytic processes for upgrading and removing sulfur from heavy petroleum feed. In its crystalline bulk form, MoS$_{2}$ is chemically rather inactive due to a strong tendency to form highly stacked layers, but, when dispersed as single-layer nanoclusters on a support, the MoS$_{2}$ becomes catalytically active in the hydrogenolysis of sulphur and nitrogen from organic compounds (hydrotreating catalysis). In the present studies alumina-supported MoS$_{2}$ samples were analyzed by confocal Raman spectroscopy. Evidence of peaks at 152 cm$^{-1}$, 234 cm$^{-1}$, and 336 cm$^{-1}$, normally not seen in the Raman spectrum of the standard bulk crystal, confirms the formation of single layers of MoS$_{2}$. Furthermore, the presence of the 383 cm$^{-1}$ Raman line suggests the trigonal prismatic coordination of the formed MoS$_{2}$ single layers. Depending on the sample preparation method, a restacking of MoS$_{2}$ layers is also observed, mainly for ex-thiomolybdate samples sulfided at 550\r{ }C.