Effect of citric acid addition on the hydrodesulfurization activity of MoO3/Al2O3 catalysts

Hydrodesulfurization Activity of Co–Mo/Al₂O₃ Catalysts Prepared with Citric Acid: Post-treatment of Calcined Catalysts with High Mo Loading

“…1). In agreement with the HDS of thiophene, the activity of CA/ Mo/Al was about twice as high as that of Mo _ CA/Al for the HDS of DBT 17) . With the promotional effect of Co, the activity for the HDS of DBT was increased much more by the addition of Co with respect to Mo Table 2.…”

“…4 nm pores by the presence of citric acid 17), 18) . The adsorption isotherm of Mo/Al (dried) (Mo _ CA/Al with CA/Mo 0) did not show any large change in the pore structure of the sup- port, whereas 10% citric acid/Al2O3 17) showed the formation of a specific pore structure. This suggests that carbonaceous deposits produced by the decomposition of citric acid during the sulfidation process forms a specific structure with 4-nm diameter pores.…”

“…We suggest that the unchanged dispersion of Mo in the simultaneous impregnation catalysts (Fig. 3) is due to the formation of large agglomerated Mo _ CA complexes outside the pores of Al2O3 during the drying process, whereas with the post-treatment method, citric acid redisperses the Mo species by reaction with Mo oxide particles dispersed in the pores of the support to form in-situ well dispersed Mo _ CA complexes inside of the pores 17) . This surface model is consistent with the insitu XAFS observations for Co _ Mo/B2O3/Al2O3 with 8.7 wt% Mo, showing that the sulfidation of Mo _ CA in CA/Mo/Al takes place at a lower temperature than in Mo _ CA/Al 27) .…”

“…The hydrogenation activity of calcined Co _ Mo catalysts was improved by treatment with ethylenediaminetetraacetate 19) . More recently, we showed that welldispersed Mo _ CA complexes are formed on the support at high Mo content during the preparation of Mo/Al2O3 catalysts by a post-treatment method with citric acid 17) . Therefore, addition of citric acid by the post-treatment method improves the edge dispersion of MoS2 particles on the catalyst surface, resulting in significant increases in the catalytic activity for the HDS of thiophene and the sulfidation of Mo for Mo/Al2O3 sulfide catalysts at high Mo content 17) .…”

“…X-ray photoelectron spectroscopy (XPS) showed that the sulfidation of Mo is improved by the addition of citric acid 11), 16) . X-ray absorption fine structure (XAFS) showed that the formation of surface Mo _ citrate complexes results in increased sulfidation of Mo at a high Mo content for unpromoted Mo catalysts 17) . Our previous study found that the activity of Co _ Mo/ B2O3/Al2O3 calcined catalysts with 8.7 wt% Mo for the HDS of thiophene was greatly improved by treatment with citric acid (post-treatment method) 18) .…”