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 P2Mo5O236− 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 PMo12O403− heteropolymolybdate species, but no P2Mo5O236− was detected. The use of paramagnetic cobalt instead of zinc cations had a paramagnetic effect on the 31P-NMR signal of the PMo12O403−, indicating that the PMo12O403− 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.