Nature and structure of tungsten surface species present on NiO-WO3/Al2O3 hydrotreating catalysts

Superficial characterization and hydroconversion of tetralin over NiW sulfide catalysts supported on zirconium doped mesoporous silica

“…The relative intensities were calculated as a ratio of the peak heights. In the first case, an important increase in this intensity ratio is only observed for the Ni(7.5)W precursor, revealing the presence of a majority of W-O-W bridged bonds, in good agreement with the results found by XPS analysis (vide supra), thus confirming that the presence of nickel favors the formation of poly-tungstate species [23,36]. The intensity ratio also depends on the P 2 O 5 percentage in the precursors.…”

“…Since the surface area of this support is very high (503 m 2 g −1 ), the theoretical dispersion attained for WO 3 with loading of 20 wt.% should be very good, 1.3 W nm −2 , this being very far from the value established by Ouafi et al [36] as necessary to form a monolayer of tungsten on the surface of the support (7 W at. nm −2 ).…”

Hydrodesulfurization of sulfur refractory compounds: Effect of gallium as an additive in NiWS/γ-Al2O3 catalysts

“…4 the presence of vibrations between 350 cm −1 and 675 cm −1 can be observed for Ni/Ga(0.0)-␥-Al 2 O 3 and Ni/Ga(1.2)-␥-Al 2 O 3 samples. These peaks can be clearly assigned; the vibration between 350 and 500 cm −1 corresponding probably to tetrahedral NiO and the second one between 500 and 675 cm −1 centered at 560 cm −1 can be related with octahedral NiO [36,37]. Vibrations corresponding to the crystalline NiAl 2 O 4 were not detected.…”

“…These Ni species could be assigned to crystalline NiAl 2 O 4 with vibrations peaks approximately at 840, 620, 375 and 200 cm −1 . Signals at 460 and 500 cm −1 have been related to tetrahedral NiO species and those between 500 and 600 centered approximately at 555 cm −1 correlated to NiO octahedral species [36,37]. In order to get more insight about Ni species, Raman spectroscopy and temperature programmed reduction (TPR-H 2 ) analyses for Ni/Ga(x)-␥-Al 2 O 3 calcined materials were carried out.…”

Structure and Quantification of Edge Sites of WS2/Al2O3 Catalysts Coupling IR/CO Spectroscopy and DFT Calculations

“…At higher CO uptake appears a shoulder at 2141 cm −1 , corresponding to physisorbed CO. The two bands at 2121 cm −1 and 2066 cm −1 were observed since the very first introduced CO doses and were attributed to CO in interaction with coordinatively unsaturated W sites (CUS) of low oxidation state . Early work of Duchet on W/Al 2 O 3 catalysts already reported the presence of two bands at 2110 cm −1 and 2060 cm −1 on sulfided phase, called W 1 and W 2 , respectively.…”