Examination of Tunable Edge Sites and Catalyst Deactivation in the MoS2-Catalyzed Methanation of Syngas

A simple and effective strategy based on NH4+ intercalation and thermal treatment was developed to tune the edge sites of MoS2. The catalysts were characterized by X-ray diffraction, thermogravimetric, transmission electron microscopy-energy-dispersive X-ray, scanning electron microscopy, Raman spectroscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectra, in situ Fourier-transform infrared (FT-IR) spectroscopy of NO adsorption, and CHNS elemental analysis. The intercalation of NH4+ into the interlayers of MoS2 with thermal treatment served to reduce numbers of stacking layers and generate edge-rich MoS2 with disordered structures. An increase of NH4+ intercalation resulted in a greater exposure of MoS2 edges, which enhanced the conversion rate of CO in the methanation reaction. The FT-IR study of NO adsorption demonstrated that edge sites contributed to the catalytic activity. A decrease of the activity in the long-term (100 h) stability evaluation can be attributed to the sintering of MoS2, the formation of MoO2 with a loss of active MoS2 components. This study established the intercalation of NH4+ into the MoS2 layers with subsequent heat treatment as an effective means to tune the edge sites and the catalytic activity.