Promoting effects of SO42- on NiMo/γ-Al2O3 hydrodesulfurization catalyst
The paper studied the promoting effects of SO42- on NiMo/γ-Al2O3 catalyst prepared using NiSO4 (CAT-Sulf) as nickel precursor compared with Ni(NO3)2 (CAT-Nit) and the industrial NiMoP-complex (CAT-NiP) after 600 oC calcination, respectively. Three catalysts were characterized by virtue of XRD, TG-MS, N2 adsorption-desorption, H2-TPR, XPS and HRTEM. The hydrodesulfurization (HDS) activity was assessed using dibenzothiophene (DBT) as the feedstock. On the 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- could be found. These anchored SO42- anions could 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 the excellent textural structure, i.e. high specific surface area, proper pore structure. Therefore, CAT-Sulf exhibits the highest DBT-HDS activity in the three catalysts. Moreover, these anchored SO42- anions could effectively hinder the aggregation and growth of active phases, thus guaranteeing catalyst with high metal dispersion and well stability. Finally, using the inferior residual oil as the feedstock the stability of CAT-Sulf was also assessed as compared with an industrial catalyst (CAT-Ref), and results show that during 1500 h on stream, the HDS ratio of maintains around 78%, while that of the industrial catalyst (CAT-Ref) declined from ca. 82% initially to ca. 71% after 1200 h, indicating CAT-Sulf exhibits much better stability and shows excellent industrial potentials. The anchored SO42- anions endow the NiSO4-derived catalyst with excellent physical structure, high intrinsic activity and well stability simultaneously, indicating it might be a simple and effective method to balance activity and stability of the HDS catalyst by using the thermostable nickel precursor salts.