Selective hydrodesulfurization of FCC naphtha over CoMo catalysts supported on synthesized γ-alumina composites with one-dimensional molecular sieves

The design of advanced hydrodesulfurization (HDS) catalysts with optimal support acidity and shape selectivity is crucial for producing high-quality fuels. In this study, SAPO-11, ZSM-22, and γ-Al₂O₃ were initially synthesized separately. Composite supports were then prepared by physically mixing each molecular sieve (SAPO-11 or ZSM-22) with γ-alumina in a ratio of 10 to 90 wt%. CoMo/composite catalysts were subsequently prepared through incipient wetness impregnation onto these supports. The synthesized catalysts were examined in the hydroupgrading of a model feed consisting of thiophene (1000 ppm S), 1-hexene (20 vol%), and n-heptane (80 vol%). Hydrotreating reactions were carried out in T = 220–280 °C, LHSV = 5 and 10 h −1 , P = 2 MPa, and H 2 /feed = 120 NL/L. The supports and catalysts were characterized using X-ray diffraction (XRD), N 2 adsorption−desorption, scanning electron microscopy (SEM), temperature-programmed desorption of NH 3 (TPD), H 2 temperature-programmed reduction (TPR), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). It was found that the incorporation of molecular sieves into γ-Al 2 O 3 significantly altered the acid properties of catalyst leading to a marked improvement in the selectivity factor from 1.41 for CoMo/γ-Al 2 O 3 to 5.46 for CoMo/AS11 and 2.93 for CoMo/AZ22 at 220 °C and an LHSV of 10 h −1 . Among the catalysts, CoMo/AZ22 exhibited the highest isomerization percentage under both LHSV conditions, ascribed to the suitable one dimentional pore structure and a balanced proportion of weak and medium acid sites provided by ZSM-22, which favor isomerization pathways.