NiMo catalysts supported on Mn-Al2O3 for dibenzothiophene hydrodesulfurization application

Modification of the traditional Al2O3 support through addition of manganese to Al2O3 mixed Mn-Al oxides was herein envisaged to obtain highly active NiMo catalysts for hydrodesulfurization application. The effect of adding manganese was determined considering different Mn-Al2O3 supports synthetized using a sol?gel approach. The manganese-containing supports were furthermore impregnated with Ni(NO3)2 + (NH4)6Mo7O24 aqueous solutions at pH = 9 and characterized at their oxide state using UV?vis diffuse reflectance and Raman spectroscopies after drying and calcination steps. NiMo/Mn-Al2O3 catalysts were also characterized at the sulfide state mainly by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Finally, the sulfide catalysts were evaluated in the hydrodesulfurization of dibenzothiophene. Results show that the oxidation state of manganese species directly influences the nature of the Mo oxide species and their interaction with the Al2O3 support. At low Mn content (up to 0.5 mol% Mn as MnO), Mn2+ species leads to weaker interaction with the support and a higher intrinsic activity of the NiMoS species. However, these promoted sites are also formed in a lower amount than without adding Mn to the support. At too high manganese content (?2 mol% Mn as MnO), Mn3+ species are formed and react with Ni to form a spinel phase decreasing the proportion of promoted phase to be formed after sulfidation. The highest activity is therefore observed at an intermediate Mn content of 1 mol% for which a higher intrinsic activity resulting from weaker support interaction and higher sulfidation rate combine together to achieve highly active NiMo HDS catalysts.