Promoting effects of SO42− on a NiMo/γ-Al2O3 hydrodesulfurization catalyst

Abstract

This study details the promoting effects that SO₄²⁻ has on a NiMo/γ-Al₂O₃ catalyst prepared using NiSO₄ (CAT-Sulf) as a nickel precursor, compared with the Ni(NO₃)₂ (CAT-Nit) and the industrial NiMoP-complex (CAT-NiP) after 600 °C calcination. The three catalysts were characterized by virtue of X-ray diffraction (XRD), thermogravimetry mass spectrometry (TG-MS), N₂ adsorption–desorption, hydrogen temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Hydrodesulfurization (HDS) activity was assessed using dibenzothiophene (DBT) as the feedstock. On the one hand, compared with CAT-Nit, the SO₄²⁻ anions could be anchored on the catalyst surface due to their thermal stability and strong interaction with Al₂O₃, while few NO₃⁻ anions could be found. These anchored SO₄²⁻ anions weaken the metal–support interaction and hinder the formation of NiAl₂O₄, thereby facilitating both the sulfidation of Mo species and the decoration of Ni atoms and generating more Ni–Mo–S active sites. On the other hand, compared with CAT-NiP, the residual SO₄²⁻ anions do not impair the support properties and CAT-Sulf maintains excellent textural structure, i.e. high specific surface area and a proper pore structure. Therefore, CAT-Sulf exhibits the highest dibenzothiophene hydrodesulfurization (DBT-HDS) activity out of the three catalysts. Moreover, these anchored SO₄²⁻ anions effectively hinder the aggregation and growth of the active phases, thus guaranteeing a catalyst with high metal dispersion and good stability. Finally, using the inferior residual oil as a feedstock, the stability of CAT-Sulf was also assessed compared with an industrial catalyst (CAT-Ref), and the results show that during 1500 h on stream, its HDS ratio is maintained at around 78%, while that of the industrial catalyst (CAT-Ref) declined from ca. 82% to ca. 71% after 1200 h, indicating that CAT-Sulf exhibits much better stability and shows excellent industrial potential. The anchored SO₄²⁻ anions simultaneously endow the NiSO₄-derived catalyst with excellent physical structure, high intrinsic activity and good stability, indicating that it might be a simple and effective method to balance the activity and stability of the HDS catalyst using thermostable nickel precursor salts.