Activation of the MoS2 Basal Plane to Enhance CO Hydrogenation to Methane Activity Through Increasing S Vacancies

The active site of MoS2 is usually located at the edge of crystalline MoS2, which has a lower proportion than that from the basal plane, limiting the hydrogenation activity. Therefore, activating the basal plane of MoS2 is expected to greatly enhance the hydrogenation activity. Herein, we prepared a series of MoS2 catalysts by acidolysis of ammonium tetrathiomolybdate and subsequently pyrolyzing at high temperature with different atmospheres. Through analysis, we found that the prepared MoS2 catalysts were curved, which was different from commercial MoS2. Through X-ray diffraction, transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy characterization, it was found that the MoS2 catalyst pyrolyzed under a N-2 atmosphere had a larger number of S-vacancies than the MoS2 catalysts under a H-2 atmosphere. In addition, temperature-programmed reduction results showed that the Mo-S bond energy was decreased with the increasing content of S-vacancies, which might be related to bending. Sulfur-resistant methanation results indicated that the curved MoS2 exhibited increased CO conversion with the increasing S vacancies. Furthermore, density functional theory calculation was used to simulate the generation of S vacancy and numbers of S vacancies. It was found that with the generation of S vacancy, three unsaturated coordination Mo atoms were exposed around one S vacancy and became new active sites, resulting in enhanced activity. What is more, the higher methanation activity was attributed not only from more S vacancies but also from the decreased activation energy for CO hydrogenation activation.