In situ tracking of the impact of atomic-scale fragment structures on MoS2 nanocrystals for high-stability industrial NiMo/γ-Al2O3 hydrodesulfurization catalysts

Abstract

Despite the significant global interest in removing S heteroatoms from fossil fuels to meet ever-tougher S emission rules, the single metal atoms and metal atom clusters (henceforth referred to as “fragment structures”) present in industrial hydrodesulfurization (HDS) catalysts are rarely addressed. Herein, atomic-scale and in situ techniques were used to address the above gap and shed light on the structural evolution of these catalysts during their applications. The morphologies of fresh and post-diesel-reaction catalysts were examined using aberration-corrected scanning transmission electron microscopy and X-ray absorption fine structure. For the post-diesel-reaction catalysts, the MoS2 nanocrystals grew with greater Mo coordination and fewer S vacancies, and the fragment structures were gradually reduced. The impact of fragment structures on MoS2 during catalyst application was tracked using in situ techniques, and multiple MoS2 growth mechanisms were proposed based on experimental and theoretical (density functional theory) data. Given the high structural sensitivity of hydrotreatment reactions, this study provides important insights into the previously debated issues related to the structure–activity relationships of industrial HDS catalysts.