BASIC REACTION STEPS IN THE SULFIDATION OF CRYSTALLINE MOO3 TO MOS2 AS STUDIED BY X-RAY PHOTOELECTRON AND INFRARED-EMISSION SPECTROSCOPY

The sulfidation of crystalline MoO3 and the thermal decomposition of ( NH4)(2)MoO2S2 to MoS2 via an {MoOS2} oxysulfide intermediate have been studied by means of monochromatic X-ray photoelectron spectroscopy (X PS) and infrared emission spectroscopy (IRES). Several basic steps of the sulfidation reaction could be resolved and explained in terms of t he structure of crystalline MoO3. The sulfidation reaction starts at l ow temperatures with an exchange of terminal O-2(-) ligands of the oxi de for S2- by reaction with H2S from the sulfiding atmosphere. In subs equent Mo-S redox reactions, bridging S-2(2-) ligands and Mo5+ centers are formed. Lattice relaxation and further sulfur uptake are the main processes before, at temperatures above 200 degrees C, direct reactio ns with H-2 occur, during which the Mo5+ centers are converted into th e 4+ oxidation state. The decomposition experiments with (NH4)(2)MoO2S 2 show that terminal O2- ligands serve as the reactive sites, The Conv ersion of terminal Mo=O-t to Mo=S entities and the subsequent generati on of Mo=O-t from mu(2) and mu(3) oxygen atoms in the MoO3 lattice app ear as the general principle of the sulfidation reaction.