Self-sulfidation adsorbent for reactive adsorption desulfurization

The Ni/ZnO-Al2O3-SiO2 adsorbent is a widely used industrial adsorbent for reactive adsorption desulfurization (RADS) process. Metallic Ni and NiO are assumed as the main RADS active sites, and NiSx is the intermediate phase to transfer sulfur to ZnO. However, NiSx could also be the active center for RADS process. In this work, to conduct the desulfurization activity of NiSx, a novel NiSO4/ZnO-Al2O3-SiO2 adsorbent was prepared and examined through a serious experimental and theoretical study over the conventional adsorbents. Results showed that NiSO4 based adsorbents could first self-sulfide to NiSx phases, and then NiSx plays as main active sites for RADS. The NiSO4 phases improved the direct desulfurization selectivity of dibenzothiophene (DBT). By adjusting the content of nickel, the sulfur removal rate of adsorbent with 3 wt% Ni from NiSO4 could achieve the same level of adsorbent prepared with 18 wt% Ni from NiO. Moreover, NiSO4 based adsorbent performs excellent desulfurization activity, and its breakthrough sulfur capacity achieves 122.0 mgS/g. The evolution of Ni species on NiSO4 adsorbent has been studied, and a desulfurization mechanism that takes both NiO and NiSx as active phases has been carried out. NiO phase mainly promotes the hydrodesulfurization pathway, while NiSx phase prefers the direct desulfurization pathway. Finally, the mechanism of RADS on NiSx and the reaction pathways of DBT are also presented.