| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS+AS+EN-TuA |
| Session: | Mechanistic Insight of Surface Reactions: Catalysis, ALD, etc. - II |
| Presenter: | Signe Sørensen, Aarhus University, Denmark |
| Authors: | S.G. Sørensen, Aarhus University, Denmark J.V. Lauritsen, Aarhus University, Denmark |
| Correspondent: | Click to Email |
Cobalt promoted MoS2 nanoclusters (CoMoS) are the active phase of the hydrodesulfurization catalyst which enables sulfur removal from crude oil. New legislations on sulfur impurity levels in diesel in EU and US demands still lower sulfur content which increases the requirements for even more effective catalysts.
Previously catalysts were improved by costly trial-and-error experiments. To target the improvements attempts, understanding of the catalytic mechanism is crucial. In the hydrodesulfurization catalysis the main source to residual sulfur content is the sterically hindered sulfur containing molecules, as the reactivity towards these is very low. To targeted enhance the catalytic activity, atomic scale understanding of this catalytic mechanism is essential.
Scanning tunneling microscopy (STM) is an outstanding tool for real space, atomic-scale imaging of supported nano-scale systems. This makes it the optimal tool for investigating the interaction between the sulfur containing molecules and metal-supported CoMoS, as it offers the unique and powerful ability to directly observe the catalytic active site by imaging single molecules adsorbing on the nanoparticles.
In this study STM is used on a model system of Co-promoted MoS2 on a gold substrate under ultrahigh vacuum conditions. To study the adsorption of the strongly steric hindered sulfur containing molecule 4,6-dimethyl-dibenzothiophene the molecule is dosed directly onto the nanoparticles which means that their location, orientation and the dynamics of single molecules can successfully be revealed through atom-resolved STM images and films. All observed adsorption modes are either associated with a sulfur vacancy on the corner site of the nanoclusters or with the one-dimensional metallic edge state associate with the edge of the Co-promoted MoS2 nanoclusters. These observations strongly indicate that these sites are important active sites of the catalyst and enable targeting the attempts for enhanced activity to optimization of the number of these apparent active sites in the industrial catalyst.