Physicochemical characterization of the interaction between cobalt molybdenum oxide and silicon dioxide. 1. Influence of the cobalt-molybdenum ratio

Abstract

Physicochemical studies on a series of cobalt-molybdenum supported on silica catalysts containing the same amount of oxide phase with an atomic ratio r = Co/(Co + Mo) ranging from 0 to 1 and the phases obtained after reduction by hydrogen allow us a better understanding of the structure of these solids. X-ray diffraction, DRS, and XPS measurements of the oxide phase, the study of the reduction by hydrogen by use of gravimetric measurements, and ESR and DRS measurements carried out on the reduced phase show that weak interaction of the molybdenum with the silica (as compared with those on alumina) strongly modify the nature of the species presented on the support. It has been shown that cobalt and molybdenum almost stoichiometrically form C0M0O4 (a and b phases). Furthermore when Mo03 and Co304 are in excess they cover the CoMo04 crystals forming a geod structure. In conclusion, it is proposed that, when the interactions of the molybdenum with the support are weak, the CoMo "bilayer" precursor of the active sites is not easily formed. Consequently the strong interaction between cobalt and molybdenum leads to the formation of bulk CoMo04, compound which does not form, after activation, the active phase in HDS catalysts.

Influence of the support on the catalytic performance of Mo, CoMo, and NiMo catalysts supported on Al2O3 and TiO2 during the HDS of thiophene, dibenzothiophene, or 4,6-dimethyldibenzothiophene

“…The assignation is not an easy task since the possible species in the catalyst, Co 2+ Td , Co 2+ Oh and Co 3+ Oh , have bands at similar energies. The triplet with peaks at 542, 584 and 632 nm, and the wide contribution in the NIR region with maxima at 1233, 1435 and 1566 nm can be assigned to Co 2+ Td [37][38][39]. The formation of the triplet indicates that the tetrahedron is distorted [40], likely due to the presence of water molecules in the catalyst.…”

Ultra deep hydrodesulfurization of dibenzothiophene derivatives over NiMo/TiO2-Al2O3 catalysts

“…Moreover, XPS peaks broaden when the sample charges heterogeneously, because electrons are escaping the surface from regions of unequal potential. In other reports, the Mo(3d) peak broadening has been ascribed to metalsupport interactions [60,[66][67][68][69]. In order to minimize the effect of charging during the XPS analysis, we used a flood gun, which sprays low energy electrons onto the sample.…”

MoCo(Ni)/ZrO2?SiO2 hydrotreating catalysts: physico-chemical characterization and activities studies

“…As particle growth of MoO 3 on support increases the wavelength shifts from 260 to 300 nm. According to the literature [21,22], Mo tetrahedral species absorb at 220-280 nm, while Mo octahedral species present transition at 230-330 nm. In our case, the increasing of the Mo loading to higher than 8 wt.% showed absorption bands at around 330 nm, due to the presence of bulk aggregation of MoO 3 .…”