Morphology and Catalytic Performance of MoS2 Hydrothermally Synthesized at Various pH Values

Seung-Jae Lee,Seong-Soo Kim,Yang-Seung Son,Sung-Youl Park,Jin-Hoon Choi

doi:10.3390/catal11101229

Abstract

Although preparation conditions are known to affect the morphology and catalytic performance of hydrothermally synthesized MoS2, the influence of pH remains unclear. Herein, unsupported MoS2 was prepared from ammonium tetrathiomolybdate (ATTM) by a hydrothermal reaction at various pH values under a reaction pressure of 2 MPa. The physical and chemical properties of the MoS2 samples were characterized, and the catalytic performance for CO methanation was examined. With increasing pH, the morphology of the MoS2 particles transformed from aggregates of irregular grain-like particles to flower-like particles through the agglomeration of fine mesoporous nanoflakes. Hydrothermal synthesis at a pH of 9.5 increased the MoS2 crystallinity by enhancing the stacking of the (0 0 2) lattice plane. The MoS2 samples prepared at pH 7.0 and 9.5 showed increased CO conversion during methanation, which was associated with a low concentration of Mo5+ species and the presence of surface sulfate species. Thus, a high pH during catalyst preparation may promote the complete decomposition of ATTM to MoS2 and the formation of sulfur vacancies, which can facilitate methanation.

Highlights

MoS2 is a transition metal dichalcogenide material with a layered structure consisting of stacked S-Mo-S units in the form of a Mo atomic layer interposed between two S layers
It has been found that a nanoflake morphology can be obtained by thermally decomposing ammonium tetrathiomolybdate (ATTM) under H2 in the presence of elemental sulfur, which might play an important role in suppressing the aggregation of MoS2 nanoflakes [37]
In the hydrothermal reaction system, we suggest that the MoS2 nanoflakes were created owing to the obstruction of the growth of the (0 0 1) plane by the excess hydroxyl ions

Summary

Introduction

MoS2 is a transition metal dichalcogenide material with a layered structure consisting of stacked S-Mo-S units in the form of a Mo atomic layer interposed between two S layers. MoS2 has been applied as a catalyst for various hydrogenation reactions, including hydrodesulfurization [4,5], hydrodenitrogenation [4,6], and methanation [7,8]. It has been utilized in hydrogen storage containers [9], manganese and lithium batteries [10,11,12], and lubricants [13,14]. Several researchers have thoroughly reviewed the synthesis and structure of MoS2 [2,3] and its applications in fields such as optoelectronics [17,18]

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Results

Conclusion