Effect of citric acid addition on the hydrodesulfurization activity of MoO 3/Al 2O 3 catalysts

Abstract

A series of MoO 3/Al 2O 3 catalysts was prepared using citric acid (CA) as a chelating agent by a simultaneous impregnation method or by a post-treatment method. The catalyst was tested for the HDS of thiophene. The catalysts were characterized by means of LRS, XRD, Mo K-edge EXAFS and XANES, NO adsorption capacity, and surface area measurements. The catalysts were also subjected to a chemical vapor deposition (CVD) technique using Co(CO) 3NO as a precursor of Co to prepare CVD-Co/MoS 2 catalysts. The addition of citric acid to 8.7 wt% Mo/Al 2O 3 increased neither the HDS activity nor the edge dispersion of MoS 2 particles. On the other hand, the addition of citric acid by the post-treatment to MoO 3/Al 2O 3 catalysts having a higher Mo content (>20 wt% Mo) significantly enhanced the edge dispersion of MoS 2 particles and thus the catalytic activity of MoS 2/Al 2O 3 and CVD-Co/MoS 2/Al 2O 3. The addition of citric acid by the post-treatment resulted in the formation of well-dispersed Mo species on the catalyst surface at the expense of crystalline MoO 3. The Mo K-edge XAFS and XANES showed that the sulfidation degree of Mo is greatly improved by the addition of citric acid at a high Mo content regardless of the addition procedure.