Novel NiW hydrodesulfurization catalysts supported on Sol-Gel Mn-Al2O3

- Mn effects on calcination and activation of NiW/MnO-Al2O3 catalysts were analyzed.
- Ni-polyoxotungstate formation depends on Mn oxidation state.
- Addition of Mn favors formation of fully WS2 phase and a highly active NiWS phase.
- NiW/MnO-Al2O3 catalysts present high TOF for dibenzothiophene hydrodesulfurization.

A series of new NiW catalysts supported on manganese-containing sol-gel alumina for dibenzothiophene hydrodesulfurization (HDS) application was evaluated in the present study. The manganese amount was varied in the support in a 0.1-2.0 mol% range (as MnO). After impregnation, the catalysts were dried at 120 °C for 4 h, calcined at 400 °C for 4 h, and finally sulfided using a 10 mol% H2S in H2 mixture at 400 °C for 4 h. The resulting sulfided NiW/Mn-Al2O3 catalysts were evaluated in the hydrodesulfurization of dibenzothiophene (DBT) at T = 300 °C and P = 30 bars.During the preparation process, catalysts were characterized after each important step: after drying, after calcination, and finally after sulfidation. Results show that the manganese concentration influences the type of supported Ni-polyoxotungstate deposited on the support. For NiW catalysts supported on 0.1 and 0.5 mol% of MnO, the main tungsten oxide species present are WO42− and W12O408− species, respectively. Increasing the Mn content to 1 mol% of MnO leads to a mixture of polyoxotungstates that favors the formation of an intrinsically highly active promoted NiWS phase after sulfidation. Increasing further the Mn amount to 2 mol% of MnO results in the formation of WO3 clusters and of Mn3+ species reacting with Ni to form a NiMnO spinel phase. This leads to deleted HDS activity for the corresponding NiW catalyst after sulfidation. Finally, results emphasize the beneficial role of manganese since its addition allows to synthetize higher active NiW catalysts for dibenzothiophene hydrodesulfurization than when using the alumina support only.

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