Molybdenum(VI) speciation in sulfidic waters; stability and lability of thiomolybdates

The sulfidation of crystalline MoO3 and the thermal decomposition of (NH4)2MoO2S2 to MoS2 via an {MoOS2} oxysulfide intermediate have been studied by means of monochromatic X-ray photoelectron spectroscopy (XPS) and infrared emission spectroscopy (IRES) Several basic steps of the sulfidation reaction could be resolved and explained in terms of the structure of crystalline MoO3 The sulfidation reaction starts at low temperatures with an exchange of terminal O2- ligands of the oxide for S2- by reaction with H2S from the sulfiding atmosphere In subsequent Mo−S redox reactions, bridging S22- ligands and Mo5+ centers are formed Lattice relaxation and further sulfur uptake are the main processes before, at temperatures above 200 °C, direct reactions with H2 occur, during which the Mo5+ centers are converted into the 4+ oxidation state The decomposition experiments with (NH4)2MoO2S2 show that terminal O2- ligands serve as the reactive sites The conversion of terminal MoOt to MoS entities and the subsequent

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Basic reaction steps in the sulfidation of crystalline MoO3 to MoS2, as studied by X-ray photoelectron and infrared emission spectroscopy

Three- and low-dimensional inorganic semiconductors

Three alkyltrimethylammonium thiomolybdates, [R–N(CH3)3]2MoS4 (where R = lauryl, myristyl or cetyl) were synthesized in aqueous solution, and characterized by 1H-NMR spectroscopy. These alkyltrimethylammonium thiomolybdates were used (the lauryl and myristyl thiomolybdates for the first time) as precursors for in situ prepared MoS2 catalysts, activated during the hydrodesulfurization of dibenzothiophene. The catalysts were analyzed by EDX, showing large voids and a S/Mo ratio around 2. High surface areas up to 443 m2/g and type IV adsorption–desorption nitrogen isotherms were obtained. X-ray diffraction showed that the catalysts are poorly crystalline, with a very weak (002) peak intensity for all samples except the MoS2 catalyst prepared from pure ammonium tetrathiomolybdate precursor. A high dibenzothiophene conversion (74%) was observed with the catalyst obtained from the lauryltrimethylammonium thiomolybdate precursor, attributed mainly to its high specific surface area. Selectivity results showed that all the prepared catalysts strongly favored the hydrogenation pathway.

Laurence D. Rosenhein

Papers

Syntheses and characterization of ammonium and tetraalkylammonium thiomolybdates and thiotungstates

Synthesis, characterization and electrochemistry of the mixed metal species (RNC)4Mo(μ-t-BuS)2FeX2 (R = cylohexyl, t-butyl;X = Cl,Br)

Synthesis amd characterization of [Et4,N]2[Mo(CO)4(SR)2] (R = Ph, Bz): New, potentially chelating bis-thiolate species