IR spectroscopy evidence of MoS2 morphology change by citric acid addition on MoS2/Al2O3 catalysts – A step forward to differentiate the reactivity of M-edge and S-edge

Abstract

Citric acid was used as chelating agent to prepare a series of MoS2/Al2O3 catalysts. CO adsorption followed by infrared spectroscopy characterization (IR/CO) was employed to probe the M-edge and S-edge of MoS2 slabs on these catalysts. Addition of citric acid promotes the growth of S-edge, whereas it inhibits that of M-edge: The morphology of MoS2 is progressively modified from a slightly truncated triangle with predominately M-edge to a hexagon with both M-edge and S-edge with increasing citric acid amount. Such morphology change is of great importance to the catalytic performance as M-edge and S-edge demonstrate different reactivity in hydrodesulfurization (HDS) reactions. Indeed, IR/CO data reveal that sulfur vacancy creation occurs more easily on M-edge, whereas at room temperature, thiophene tends to adsorb more strongly on S-edge. Moreover, parallel between IR/CO study and HDS test shows that S-edge has a higher intrinsic activity than M-edge in thiophene HDS reaction.