Abstract
Hydrodesulfurization catalysis ensures upgrading and purification of fossil fuels to comply with increasingly strict regulations on S emissions. The future shift toward more diverse and lower-quality crude oil supplies, high in S content, requires attention to improvements of the complex sulfided CoMo catalyst based on a fundamental understanding of its working principles. In this study, we use scanning tunneling microscopy to directly visualize and quantify how reducing conditions transforms both cluster shapes and edge terminations in MoS2 and promoted CoMoS-type hydrodesulfurization catalysts. The reduced catalyst clusters are shown to be terminated with a fractional coverage of sulfur, representative of the catalyst in its active state. By adsorption of a proton-accepting molecular marker, we can furthermore directly evidence the presence of catalytically relevant S–H groups on the Co-promoted edge. The experimentally observed cluster structure is predicted by theory to be identical to the structure present under catalytic working conditions.
Highlights
Hydrodesulfurization catalysis ensures upgrading and purification of fossil fuels to comply with increasingly strict regulations on S emissions
The promotional effect is within the Co-promoted MoS2 (CoMoS) structural model attributed to formation of new edge sites formed by preferential substitution of Co at Mo spuopsiptoiornt4s–6a.loTnhgethaetoemdgisetsicofdseisncgrliep-tliaoyneroMf othSe2 nanoclusters morphology on a and edge structures of MoS2 and CoMoS-type structures has previously been investigated by scanning tunneling microscopy (STM)[7,8] and scanning transmission electron microscopy[9,10]
We use experimental STM studies of a goldsupported model system to directly reveal the sensitivity of both the cluster shape and edge structures of MoS2 and promoted CoMoS nanoclusters toward reductive conditions induced by H2 gas dosing at elevated temperature
Summary
Hydrodesulfurization catalysis ensures upgrading and purification of fossil fuels to comply with increasingly strict regulations on S emissions. Previous studies have shown how metallic catalyst clusters expose dynamic morphology in response to changes in its environmental gaseous composition[22,23], but similar effects are not as well understood for compounds such as oxides and sulfides Such information is crucially important for the understanding of the catalytic pathways of HDS since the elementary steps are strongly influenced by the state of the edge sites[15,24,25]. We use experimental STM studies of a goldsupported model system to directly reveal the sensitivity of both the cluster shape and edge structures of MoS2 and promoted CoMoS nanoclusters toward reductive conditions induced by H2 gas dosing at elevated temperature.
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