Effect of trimesic acid as chelating agent in sulfided CoMoP/γ-Al₂O₃ catalyst for hydrodesulfurization of straight-run gas oil

The effect of trimesic acid (TA) on the surface of γ-Al₂O₃ for CoMoP catalysts has been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The γ-Al₂O₃ support was modified by surface impregnation of a solution of TA to afford TA/Co molar ratios (0.5, 1.0 and 2.0) in the final composition. The CoMoP material with atomic ratio of TA/Co = 1.0 displayed the highest HDS activity. FT-IR results suggest that the carboxylic acid moieties (AA) of the TA deposited on the γ-Al₂O₃ interact with the Mo and Co species. The DRS UV vis revealed the presence of Co species in distorted octahedral symmetry. The Mo^Oh/Mo^Th ratio varied depending on the amount of the organic additive. TGA results indicated that the TA on the catalyst with TA/Co ratio = 1.0 often decomposes at lower temperature in comparison with the other samples. Thus, a lower temperature decomposition favors the surface concentration of metals species for the sulfurization degree. The interaction of the TA induces moderate metal-support interaction. Raman spectroscopy showed that the presence of TA influenced significantly on the ratio Mo[dbnd]O/(Mo[dbnd]O + Mo–O–Mo + Mo–O) on the catalyst surface. Raman results also evidenced the highest ratio Mo[dbnd]O/(Mo[dbnd]O + Mo–O–Mo + Mo–O) for the CoMoP (1.0) sample. Apparently, the augment of the Mo[dbnd]O species is related to a major availability of Mo species for the formation of MoS₂ for HDS reaction. The XPS and HRTEM results showed higher formation and more dispersed MoS₂ and CoMoS species for the catalysts modified by TA compared to that of the reference sample. The CoMoP (1.0) showed higher Mo_e/Mo_t ratio in comparison with CoMoP (0.0), which resulted in a higher gas oil HDS activity.