A density functional study of the chemical differences between Type I and Type II MoS2-based structures in...

Area of Science:

• Catalysis
• Materials Science
• Surface Chemistry

Background:

• Type II MoS2-based structures exhibit higher hydrotreating catalytic activity than Type I.
• Type I structures feature Mo-O linkages to alumina supports, unlike Type II structures with weaker interactions.

Purpose of the Study:

• To investigate the origin of activity differences between Type I and Type II MoS2-based structures in hydrotreating catalysts.
• To elucidate the role of electronic and bonding differences introduced by bridging oxygen bonds.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Analysis of electronic structure, bonding, and energetics of MoS2 and Co-Mo-S systems.

Main Results:

• Mo-O linkages, likely on the (1010) S edge, significantly increase the energy for sulfur vacancy formation.
• Oxygen linkages alter one-dimensional metallic-like brim states and change hydrogen adsorption energetics.
• Reactivity of the S edge is reduced due to suppressed vacancy formation.

Conclusions:

• Electronic and bonding differences caused by bridging oxygen bonds are responsible for activity variations in MoS2 hydrotreating catalysts.
• The findings explain the observed Type I-Type II transition temperatures for Co-Mo-S structures with varying cobalt content.