Local Structure Analysis of Active Sites in NiO/γ-Al₂O₃ Catalyst for Dimethyl Sulfide Decomposition: Sulfurization Behavior of Ni Species Using X-ray Absorption Spectroscopy Analysis

Abstract

Local structures of Ni species were studied in the NiO/γ-Al₂O₃ catalyst prepared by the impregnation method for the decomposition of dimethyl sulfide (DMS). Calcination and sulfurization conditions of the prepared catalyst affected the catalytic activity for DMS decomposition. The decomposition performance was increased with sulfurization by H₂S compared to sulfurization with DMS prior to the reaction test. X-ray diffraction and X-ray photoelectron spectroscopy analyses indicated that the active sites are NiS. Furthermore, in-situ X-ray absorption spectroscopy analysis was conducted to investigate the fine structural changes of Ni species before and after the sulfurization treatment. For the catalyst calcined at 500 °C, Ni species were present as NiO and NiAl₂O₄ at a ratio of ca. 4 : 6 and only NiO was sulfurized to NiS which acts as the active sites. In contrast, for the catalyst calcined at 800 °C, Ni species were almost completely present as the Ni component in the NiAl₂O₄ structure, which is less susceptible to sulfurization than NiO. Therefore, the NiS amount in the catalyst calcined at 800 °C was significantly reduced, leading to lower decomposition activity.