ASAXS study of the influence of sulfidation conditions and organic additives on sulfide slabs multiscale organization

One of the ways to improve the activity of the sulfide catalysts is to increase the quantity of molybdenum up to contents greater than 15 wt%. For such high Mo contents, the distribution of MoS2 particles is suspected to play an important role in the catalytic activity. A complete description of the active phase is thus required and implies measuring i) the size and stacking distribution of the isolated slabs, ii) the proportion of Mo involved in aggregates or individual slabs, iii) the size of the aggregates. These steps are essential to deeply explain the intrinsic activity of the catalysts. To address this challenge, Anomalous Small-Angle X-ray Scattering (ASAXS) analyses have been performed on different sets of catalysts, prepared with various organic additives and activated either by a gas sulfidation (1 bar, 350 degrees C,15%H2S/H-2) or by real industrial liquid sulfidation (30 bar, 350 degrees C, H-2/gas oil/DMDS). Furthermore, the spent catalysts were also characterized after HDS catalytic test on a real feedstock. The aim of this study was not to elucidate in detail the chemical mechanisms involved when using additives or different sulfidation conditions, but rather to better understand the impact of the microstructural organization on catalytic performances and demonstrate the potential of the ASAXS technique to give new insights on the multi-scale organization of the molybdenum active phase. We thus demonstrate that ASAXS allows to obtain a more detailed description of the slabs compared to TEM and, simultaneously, to identify and quantify the aggregation state of the particles which occurs on high loaded catalysts. The role of the additives is clearly highlighted after liquid sulfidation, as we demonstrate the dispersive effect of triethylene glycol and thioglycolic acid and to a lower extent of citric acid. The slab length and stacking are decreased, as well as the aggregate amount and size. The analysis of the spent catalysts have also revealed the significant evolution of the active phase under HDS reaction conditions. Among other parameters, the aggregate amount appears as a relevant descriptor since a correlation is found with the intrinsic catalytic performances, which suggests an issue of active sites accessibility. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

Increasing the molybdenum content in sulfide catalysts can improve their activity, with the distribution of MoS2 particles playing a crucial role. Anomalous Small-Angle X-ray Scattering (ASAXS) has been used to analyze the microstructural organization of the molybdenum active phase, revealing the impact of additives and sulfidation conditions on catalytic performance. The study demonstrates the potential of ASAXS in providing detailed insights on the multi-scale organization of the active phase.