Crystal Structure and Transformation of Ammonium Oxo- and Thiomolybdates Characterized by Solid-State ¹⁴N and ³³S MAS NMR Spectroscopy

Beskrivelse

Cobalt-molybdenum and nickel-molybdenum hydrotreating catalysts are used extensively at oil refineries to improve the environmental quality of liquid fuels by e.g. hydrodesulfurization (HDS). Ammonium molybdate (NH₄)₂MoO₄, dimolybdate (NH₄)₂Mo₂O₇, heptamolybdate (NH₄)₆Mo₇O₂₄·4H₂O, tetrathiomolybdate (NH₄)₂MoS₄, and tetrathiotungstate (NH₄)₂WS₄ are all important precursors for the preparation of catalytically active molybdenum and tungsten sulfide nanoparticles. Alumina-supported nanoparticles may be formed by sulfidation of oxidic precursors while non-supported MeS_2+x (Me = Mo, W) may be formed by thermal decomposition of (NH₄)₂MeS₄. Employing the experience gained from our continuous advancements in solid-state ¹⁴N (I = 1) and natural-abundance ³³S (I = 3/2) MAS NMR, this presentation reports on applications of these techniques for characterization of the abovementioned precursors. ¹⁴N MAS NMR is used to characterize the crystal structures of all precursors including the two polymorphs of (NH₄)₂MoO₄, mS60 and mP60, recently distinguished by synthesis and structure determination. Their unique and characteristic ¹⁴N MAS NMR spectra allows the transformation reactions of (NH₄)₂MoO₄ to be followed both qualitatively and quantitatively while fingerprint ¹⁴N MAS NMR spectra for the polymolybdates allow product identification. Natural-abundance ³³S MAS NMR spectra for the central and satellite transitions are obtained for (NH₄)₂MoS₄ and (NH₄)₂WS₄. Analysis of these spectra allows determination of the principal elements for both the quadrupole coupling and chemical shift tensors as well as the relative orientation of the tensors for these isostructural (P_nma) tetrathiometallates.

Periode	24 jul. 2006 → 29 jul. 2006
Begivenhedstitel	48th Rocky Mountain Conference on Analytical Chemistry, Solid-State NMR Section
Begivenhedstype	Konference
Konferencenummer	48th
Arrangør	www.rockychem.com
Placering	Breckenridge, Colorado, USAVis på kort