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

摘要

In this paper, new nanocatalysts - CoMoPanoAl_2O_3, CoMoBanoAl_2O_3, CoMoanoAl_2O _3-B_2O_3, CoMoPBanoAl_2O_3, and CoMoP/microAl_2O_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_2O_3 [high surface area (403.05 m~2 g~(-1)), cylindrical pore size (104.59 ?), large pore volume (1.69 cm~3 g~(-1)), surface defects, and acidic surface] and conventional micro-γ-Al_2O_3 [surface area (246.20 m~2 g~(-1)), pore volume (0.5 cm~3 g~(-1)), pore size (70.30 ?), 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_2O _3 support. It was found that CoMoPBanoAl_2O_3 with suitable physicochemical properties - large pore size (101.26 ?) and high surface area (247.97 m~2g~(-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 < 2,4-dimethyl-6-ethyl-DBT < 4,6-diethyl-DBT < 2,4,6,8-tetramethyl-DBT < 4-methyl-DBT determined by comprehensive two-dimensional gas chromatography (GC × GC-SCD) analysis. It was confirmed that the HDS reaction and catalytic activity of the CoMoS sites is controlled particularly by pore size, surface area, acidity, and the surface properties of the support.