Review Paper: Sol–gel and hybrid materials for catalytic, photoelectrochemical, and sensor applications
The effect of Nb as a support modifier on the NiMo6/Al2O3–Nb2O5(x) (x = 0, 1, 4, and 8 wt% Nb) catalysts was studied. The supports were prepared by one-pot coprecipitation from soluble precursors. The XRF analysis of the catalysts showed that the contents of Mo and Ni increased slightly with the presence of Nb. Micropore area and pore volume augmented importantly with Nb content, resulting in pore diameters between 5.3 and 9.3 nm. XPS analysis showed that the presence of Nb decreases the active metal–support interaction, improving the Mo and Ni sulfidation degree. The Raman spectra of sulfided catalysts suggested an increase in the number of layers of MoS2 in the presence of Nb. Generally, the thiophene HDS activity at normal pressure of sulfided NiMo6/Al2O3–Nb2O5(8) was greater than that of the sulfided catalysts with x = 0, 1, and 4 wt% Nb, which can be attributed to the Nb promotion that would have an effect on the type of active site (Brønsted or Lewis acidic sites), since the number of sites by CO chemisorption for sulfided NiMo6/Al2O3–Nb2O5(x) did not show correlation with the catalytic activity. The high-pressure HDS activity of dibenzothiophene was also greater in the presence of Nb, and the hydrogenation route was preferred for the Nb-promoted solid, while the unpromoted one showed a larger yield of direct desulfurization products.
The niobium-containing catalyst presented the best catalytic activity.
Niobium promotion influenced the type of active site.
The presence of Nb improves the sulfidation degree of Mo and Ni.
Nb increases the number of Lewis acid sites related to HDS activity.
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The authors would like to acknowledge financial support to Universidad del Atlántico-Colombia (through Project CB21-FGI2016 “7ma Convocatoria 2016”). E.P.P. dedicates this work to Ofelia Polo (R.I.P.).
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Conflict of Interest
The authors declare that they have no conflicts of interest.