Evolution of nickel species in reactive adsorption desulfurization of benzothiophene

Reactive adsorption desulfurization (RADS) is one of the main means for the ultra-deep desulfurization of gasoline. Metallic Ni is normally assumed as the main RADS active site, and NiSx is the intermediate phase during RADS process. In this work, the evolution of nickel species, especially NiSx, were examined over NiO/ZnO-Al2O3-SiO2 and NiSO4/ZnO-Al2O3-SiO2 adsorbents. Results showed that both of the adsorbents performed high desulfurization efficiency. However, differences of the activation mechanism were observed. For the NiO adsorbent, BT (benzothiophene) can be adsorbed onto the reduced Ni sites, then the C-S bond ruptures to form NiSx. For the NiSO4 adsorbent, NiSO4 phase are firstly self-sulfied to NiSx in the presence of hydrogen or n-heptane. XRD and XPS results presented that NiO and NiSx could be found after the RADS reaction in two spent adsorbents. As same as the sulfurization of NiO into NiSx is a primary condition for the RADS reaction, NiSO4 can be partly in situ self-sulfied to NiSx. To verify the self-sulfidation of NiSO4, H2 pretreatment showed that there were NiO and NiSx species on the pretreated NiSO4/ZnO-Al2O3-SiO2 adsorbent, and the desulfurization performance of the adsorbent was obviously improved, indicating that the formation and accumulations of NiSx could promote the RADS activity. At last, the RADS mechanism of BT on two kinds of adsorbents are presented and discussed based on the assumption of NiO and NiSx as the main active components.