Atomic‐scale visualization of the growth and structure of
M
o
S
2‐based hydrodesulfurization catalysts
Authors: Pilsgaard Hansen Lars , Zhu Yuanyuan , Ramasse Quentin M. , Kisielowski Christian , Dahl‐Petersen Christian , Brorson Michael , Helveg Stig 
Published: December 2016

Atomic‐scale visualization of the growth and structure of MoS
2
‐based hydrodesulfurization catalysts

Lars P. Hansen
*1
, Yuanyuan Zhu
2
, Quentin M. Ramasse
3
, Christian Kisielowski
4
, Christian Dahl‐Petersen
1
, Michael Brorson
1
and Stig Helveg
1

1
Haldor Topsoe A/S, Haldor Topsøes Allé 1, DK‐2800 Kgs. Lyngby, Denmark.

2
Pacific Northwest National Laboratory, Richland, WA, United States

3
SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Daresbury WA4 4AD, United Kingdom

4
Lawrence Berkeley National Laboratory, National Center for Electron Microscopy and Joint Center for Artificial Photosynthesis, Berkeley CA 94708, United States of America.

*email: lpha@topsoe.dk

Current environmental legislation calls for the production of clean fuels with ultra‐low sulfur contents. To produce such fuels, oil refineries have to process mineral oil by catalytic hydrodesulfurization reactions. The state‐of‐the‐art hydrodesulfurization catalysts are based on highly anisotropic MoS
2
nanocrystals as the active component [1,2]. The MoS
2
structure consists of two‐dimensional S–Mo–S slabs which may be stacked to various degrees. The catalytic reactivity of the MoS
2
nanocrystals has been associated with their exposed edges and the catalysis can be further boosted by attaching promoter metals such as Co or Ni to the edges [1,2]. However, a detailed understanding of how these Co‐promoted MoS
2
catalysts functions has been lacking, reflecting that information about the abundance and structure of the edge sites on MoS
2
‐based catalysts has not been accessible.

Recent advancements have made (scanning) transmission electron microscopy (S)TEM a powerful technique for studying industrial‐style catalysts at the atomic‐level [3‐7]. This presentation will outline the benefit of these advancements for the study of MoS
2
‐based hydrodesulfurization catalysts. First, a differentially pumped electron microscope, dedicated entirely to corrosive sulfur‐containing gas reaction environments, was used for time‐resolved TEM imaging of the growth of MoS
2
nanocrystals during the sulfidation reaction that transforms a molybdenum oxide precursor into highly dispersed MoS
2
nanocrystals (Figure 1). Specifically, these time‐resolved image series provide new information about the evolution of MoS
2
nanocrystals with different size, morphology and stacking and thus uncover mechanisms responsible for the nucleation and growth of the MoS
2
nanocrystals. These
in situ
observations are beneficially combined with STEM imaging and electron energy loss spectroscopy (EELS) enabling the detection of the catalytic active edge structures and the location of promoter atoms at the single atom level (Figure 2). Thus, the combined use of
in situ
and single‐atom sensitive (S)TEM observations provides new insight into the formation of MoS
2
nanocrystals at the atomic‐level that can help to develop the understanding of structure‐sensitive properties in industrial‐style hydrodesulfurization catalysts.