31P MAS NMR and Raman study of a Co(Zn)MoP/γ-Al2O3 HDS catalyst precursor containing triethylene glycol

The effect of triethylene glycol on phosphate-doped Co(Zn)Mo catalysts supported on γ-Al2O3 was studied by means of 31P magic angle spinning nuclear magnetic resonance (MAS NMR) and Raman spectroscopy. 31P MAS NMR experiments, carried out on ZnMo/γ-Al2O3 doped with phosphate and triethylene glycol, suggested that the image species that formed in the impregnation solution decomposed to monophosphate and an Anderson-type aluminum molybdate species on contact with the support. The presence of triethylene glycol favored the formation of polyphosphate and image heteropolymolybdate species, but no image was detected. The use of paramagnetic cobalt instead of zinc cations had a paramagnetic effect on the 31P-NMR signal of the image, indicating that the image species are bound to the promoter atoms. The close proximity of the promoter and Mo allows a better decoration of MoS2 and improves the catalytic activity.