Effects of Citric Acid Addition Method on the Activity of NiMo/γ-Al2O3 Catalysts in Simultaneous Hydrodesulfurization and Hydrodenitrogenation Reactions

Two NiMo catalysts were prepared by different methods using citric acid to assess the effects of preparation method on dibenzothiophene hydrodesulfurization (HDS) and simultaneous HDS and hydrodenitrogenation: co-impregnation and post-treatment. Characterization of oxide catalysts was performed by nitrogen physisorption, X-ray diffraction, and temperature-programmed sulfidation, while sulfided samples were characterized by temperature-programmed reduction (TPR-S) and NO chemisorption. The catalytic evaluation for HDS reaction was performed in a three-phase reactor, with and without quinoline. The direct desulfurization is the preferred route for the HDS of dibenzothiophene. The post-treatment method was more efficient in achieving higher catalytic activity than co-impregnation. Furthermore, TPR-S and NO chemisorption results show an enhancement in the density of active sites on the catalyst prepared by post-treatment, being more hydrogenating than the one synthesized by co-impregnation. Although the catalyst prepared by post-treatment was more inhibited by quinoline, it remained more active than the one synthesized by co-impregnation.