Influence of Ligands on the Surface Characteristics of CoMo/γ-Al2O3 and Hydrodesulfurization Catalytic Activity on Dibenzothiophene-Type Compounds.

Abstract

Refractory sulfur compounds in fuel oils combust, releasing sulfur oxides (SOx) into the atmosphere, which is a significant source of pollution. In this study, we focused on comparing the surface properties and hydrodesulfurization (HDS) activity of CoMo-(L)/γ-Al₂O₃ containing chelating ligands (L), specifically acetic acid (AA), with those of ethylenediaminetetraacetic acid (EDTA), citric acid (CA). CoMo/γ-Al₂O₃, CoMo-AA/γ-Al₂O₃, CoMo-EDTA/γ-Al₂O₃ and CoMo/γ-Al₂O₃ were prepared by hydrothermal treatment of the mixtures of Co(NO₃)₂.6H₂O and (NH₄)₆Mo₇O₂₄.4H₂O with stoichiometric Co/Mo ratios and enriched with chelating ligands (L=AA, CA and EDTA). Based on the product distributions of the hydrodesulfurization (HDS) of dibenzothiophene (DBT), a reaction pathway of dibenzothiophene (DBT) HDS was proposed to follow hydrogenation (HYD) and direct desulfurization (DDS) routes. In addition, the ligand modification of CoMo/γ-Al₂O₃ catalysts resulted in enhancement of surface properties and HDS activity which is in the order of CoMo-CA/γ-Al₂O₃ (98 %)> CoMo-AA/γ-Al₂O₃ (94 %) > CoMo-EDTA/γ-Al₂O₃ (90 %) > CoMo/γ-Al₂O₃ (43 %). CoMo-AA/γ-Al₂O₃ presented a higher HYD/DDS ratio compared to CoMo-CA/γ-Al₂O₃, CoMo-EDTA/γ-Al₂O₃, and CoMo/γ-Al₂O₃, respectively which makes it a promising HDS catalyst.