Carbon-stabilized mesoporous MoS2 — Structural and surface characterization with spectroscopic and catalytic tools

Structural and surface properties of carbon-containing mesoporous MoS2 and of a reference MoS2 were studied with various techniques including XRD, elemental analysis, TEM, XPS, EXAFS, nitrogen physisorption, oxygen chemisorption (OCS), determination of exchangeable surface hydrogen, and kinetic study of test reactions like ethene hydrogenation and H2/D2 exchange. The study was made before and after use of these catalysts in the hydrodesulfurization of dibenzothiophene. The microstructure of carbon-stabilized MoS2 is characterized by nanoslabs of ≈ 2 nm average stacking height embedded in an amorphous matrix with a very broad pore-size distribution. Thermal stress induced a collapse of the microporous structure leading to the formation of mainly mesopores. The carbon is well-distributed over the bulk, without any signature of carbide species detected neither in XPS nor in EXAFS measurements. The activity patterns of both materials (related to the OCS capacity) were similar despite the differing sulfur content, with the carbon-stabilized MoS2 being more sulfur deficient. This suggests that the catalytic properties of the latter material were caused by near-stoichiometric MoS2 apparently present in the nanoslabs, whereas the sulfur vacancies in the sulfur-deficient amorphous phase were blocked by strongly adsorbed carbon residues. Interestingly, the HDS reaction did not cause significant changes of the properties of the carbon-stabilized MoS2. Conversely, the reference MoS2 was strongly activated, in particular with respect to ethene hydrogenation, which can be explained by a pronounced sulfur loss during the HDS reaction, without significant site blockage by the coke deposited.

Mesoporous, carbon-containing MoS2 made by thermolysis of tetrapropylammonium thiomolybdate, and reference MoS2 prepared by thermolysis of ammonium tetrathiomolybdate were studied by various methods including well-characterized test reactions, prior and after application in the hydrodesulfurization of dibenzothiophene. The use of test reactions permitted to extend the scope of conclusions significantly.Figure optionsDownload as PowerPoint slideResearch Highlights
► C-stabilized MoS2 consisting of MoS»2 nanoslabs in S-deficient amorphous structure with vacancies blocked by C.
► No ordered Mo-C relation from XAFS, no indication for carbides by XAFS and XPS.
► HDS hardly changed C-stabilized MoS2 while reference MoS2 from ammonium thiomolybdate was strongly altered.