Ultradeep hydrodesulfurization of diesel fuels using highly efficient nanoalumina-supported catalysts: Impact of support, phosphorus, and/or boron on the structure and catalytic activity

Abstract In this paper, new nanocatalysts—CoMoP/nanoAl 2 O 3 , CoMoB/nanoAl 2 O 3 , CoMo/nanoAl 2 O 3 –B 2 O 3 , CoMoPB/nanoAl 2 O 3 , and CoMoP/microAl 2 O 3 —were prepared by a wet co-impregnation method on micro- and nanostructured alumina supports. The effects of physicochemical and chemical properties of the supports—new mesoporous nano-γ-Al 2 O 3 [high surface area (403.05 m 2  g −1 ), cylindrical pore size (104.59 A), large pore volume (1.69 cm 3  g −1 ), surface defects, and acidic surface] and conventional micro-γ-Al 2 O 3 [surface area (246.20 m 2  g −1 ), pore volume (0.5 cm 3  g −1 ), pore size (70.30 A), and neutral surface]—and of phosphorus (P) and boron (B) addition on the local structure and hydrodesulfurization (HDS) activity of CoMoS catalytic sites were studied in hydrodesulfurization reactions of straight-run light gas–oil (SRLGO). Porosity, morphological, and structural characterizations of the supports and nanocatalysts were done by informative techniques such as nitrogen physisorption, Mo and S X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy–energy dispersive X-ray (HRTEM–EDX), Mo- and Co-extended X-ray absorption fine structure (EXAFS), Co X-ray absorption near-edge structure (XANES), and diffuse reflectance spectroscopy–ultraviolet–visible (DRS–UV–vis). The characterization results showed that dispersion of Co and Mo to form the CoMoS II phase is improved on the nanoAl 2 O 3 support. It was found that CoMoPB/nanoAl 2 O 3 with suitable physicochemical properties—large pore size (101.26 A) and high surface area (247.97 m 2 g −1 )—was the highest active catalyst, which enabled it to decrease 13,500 ppm (1.35 wt%) sulfur of SRLGO feedstock to a sub-10 ppm transparent diesel fuel. The HDS catalytic activity of the most refractive substituted dibenzothiophene (DBT) compounds in the feed followed the sequence 4,6-dimethyl-DBT