Regulating the Fe/Mo ratio of FeMoOx/LaTiOy to boost aerobic oxidative desulfurization of diesel

Catalytic oxidation desulfurization (CODS) technology has shown great promise for diesel desulfurization by virtue of its low cost, mild reaction conditions, and superior desulfurization performance. Herein, a series of FeMoO_x/LaTiO_y-z samples with diverse Fe/Mo ratios were prepared via a facile citric acid-assisted method. The impact of Fe incorporation on the dispersion and surface elemental states of Mo species, as well as oxygen species content of the synthesized FeMoO_x/LaTiO_y-z catalysts were systematically characterized using TEM, BET, UV-vis DRS, XPS, XANES, and reaction kinetics, and their CODS performances were examined for 4,6-DMDBT removal. Experimental results demonstrated that Fe/Mo ratio significantly affected the Ti−O bond strength, surface dispersion and electronic structure of Mo species on FeMoO_x/LaTiO_y-z catalysts. FeMoO_x/LaTiO_y-2 catalyst showed outstanding cycling durability and the best CODS performance with almost 100% removal of 4,6-DMDBT from model oil within 75 min due to its proper MoO₃ dispersion, optimal redox property, and the most oxygen vacancy concentration. Nevertheless, further enhancing Fe content led to the increased dispersion of Mo species, while the decrease active Mo species as well as the increase of steric effect for 4,6-DMDBT accessing to the catalytic reactive sites considerably increase the apparent activation energy of FeMoO_x/LaTiO_y-z (z> 2) catalysts during the CODS process, thereby seriously suppressing their CODS performances. Moreover, Radical trapping experiments reveal that the ·, generated by the activation of O₂ at the active sites, catalytic oxidized 4,6-DMDBT to the product of 4,6-DMDBTO₂, thereby enabling both deep desulfurization and recovery of high-value 4,6-DMDBTO₂. These findings offer an alternative strategy to achieve ultra deep desulfurization as well as separate and recover high economic value sulfone substances from diesel.