The effect of hydroxyl and metal synergetic structures on the FCC diesel hydrotreating performance of NiMo/Al2O3 catalysts

Abstract

Two NiMo/Al2O3 catalysts were prepared using impregnation solutions with different acid-base properties. And the effects of the surface structural differences on FCC diesel hydrotreating and desulfurization performance were investigated. XRD, Raman, H2-TPR, TEM, XPS characterization showed that NiMoO4 and polymolybdates, the mainly metal phase on the surface of NiMo/Al2O3-A, would tend to form a three bridging hydroxyl structure with the γ-Al2O3 support. The abundant NiMo alloy structures weakened the interaction between metal and oxygen atoms. While the NiMo/Al2O3-B with more developed specific surface area, pore volume and acid content tended to form double bridging hydroxyl structures, which had more active interactions with metals. The higher sulfidation degree of NiMo/Al2O3-B could be observed, exhibiting more NiMoS structures and stronger metal synergetic effects. The performance evaluation results showed that NiMo/Al2O3-A had better desulfurization and denitrification performance, and the content of S and N in the diesel decreased to 211 μg/g and 96.3 μg/g, respectively, which was attributed to the more active phases brought about by the good MoS2 dispersion. On the other hand, NiMo/Al2O3-B exhibited better hydrotreating performance, with the content of alkanes and monocyclic aromatic hydrocarbons in the product increasing from 20.5% and 24.2% to 33.6% and 48.7%, respectively. The higher content of alkanes and monocyclic aromatic hydrocarbons provided a wider range of application for FCC diesel after upgrading.