Redispersion effects of citric acid on CoMo/γ-Al2O3 hydrodesulfurization catalysts

•Redisperse the Mo oxides by weakening the MoO3-Al2O3 interaction.•Transform MoO42 − or β-CoMoO4 into polymolybdate species.•Promote bulk MoO3 to form well-dispersed MoO3 species.•Remove the CoAl2O4-like species to form more Co-Mo-S active sites.•The sulfidation and morphology of active species were significantly improved.

Calcined CoMo/γ-Al2O3 catalysts were modified by citric acid (CA) with different CA/Co ratios and the corresponding structure evolutions were systematically characterized. Then combined with HDS activity results, potential redispersion effects of CA were suggested: (i) weaken the MoO3-Al2O3 interaction via competitive interacting with the OH groups of alumina surface to realize the redispersion of Mo oxides; (ii) transform tetrahedral MoO42 − or β-CoMoO4 into octahedral polymolybdate species and promote bulk MoO3 to form well-dispersed MoO3; (iii) remove the CoAl2O4-like species. These effects probably together promote the resulting sulfided catalysts with more type II CoMoS active sites, thus enhancing the HDS activity.

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