Location of Co and Ni promoter atoms in multi-layer MoS2 nanocrystals for hydrotreating catalysis
•Industrial-style hydrotreating catalysts are examined by STEM-EEL spectrum imaging.•Element maps resolve Co and Ni atoms at edges of multi-layer MoS2 nanocrystals.•The edge-located Co and Ni atoms are proposed to promote hydrotreating reactions differently.
The location of Co and Ni promoter atoms in industrial-style hydrotreating catalysts is examined by combining aberration-corrected scanning transmission electron microscopy and electron energy loss spectrum imaging. The observations unambiguously demonstrate that both Co and Ni promoter atoms occupy sites at all low-indexed edge terminations of hexagonally shaped multi-layer MoS2 nanocrystals. In contrast, similar observations for single-layer MoS2 nanocrystals show that Co-promoter atoms preferentially attach at the (−1 0 0) S-edge termination and are absent at the (1 0 0) Mo-edge termination. The apparent discrepancy between single- and multi-layer MoS2 nanocrystals can be explained by the 2H-MoS2 crystal structure, for which successive MoS2 layers alternatingly expose Mo- and S-edge terminations in any of the low-indexed directions. Thus, the multi-layer Co–Mo–S and Ni–Mo–S nanocrystals, formed in the present type of industrial-style hydrotreating catalyst, are consistently described as a superposition of single-layer Co–Mo–S and Ni–Mo–S structures, and in turn, provide promoted edge sites with different steric accessibility for the organic compounds in mineral oil distillates.
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Journal: Catalysis Today - Volume 261, 1 March 2016, Pages 75–81