Morphology, microstructure, coordinative unsaturation, and hydrogenation activity of unsupported MoS2: How idealized models fail to describe a real sulfide material

Bekx-Schürmann, S. and Mangelsen, S. and Breuninger, P. and Antoni, H. and Schürmann, U. and Kienle, L. and Muhler, M. and Bensch, W. and Grünert, W.

Volume: 266 Pages:
DOI: 10.1016/j.apcatb.2020.118623
Published: 2020

Polycrystalline MoS2 from (NH4)2MoS4 thermolysis was activated in dilute H2 at 523 K < TR < 873 K and studied by XRD, total scattering analysis, XPS, HRTEM, and chemisorption to explain, why coordinative unsaturation decreases with growing TR contrary to expectations from the MoS2 structure. Hydrogenation rates were measured for identifying active sites. With increasing TR, activity and chemisorption peaked at different TR,peak. Below TR,peak, increasing activity was not paralleled by changes in MoS2 microstructure. Decreasing chemisorption above TR,peak was assigned to saturation of vacancies by sulfide from internal defects and to inclusion of vacancies in the interior of aggregates. Upon high-temperature reduction, stacks grew anisotropically (basal planes extended), retaining defects like bending, turbostratic disorder. Preferential exposure of stack bases in aggregate surfaces resulted in enhanced decrease of chemisorption. Correlations between activity, edge area and (b)rim length estimated from a morphological model localized active sites in the (b)rim region. © 2020 Elsevier B.V.

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