The development of more efficient hydrotreatment catalysts, based on molybdenum (Mo), requires advanced characterization methods that allow materials to be studied in conditions that match those of their real use as closely as possible.
To produce these catalysts, a crucial activation step is necessary. This consists of hot sulfidation of the oxide phase to form the MoS2 active phase, generally promoted by cobalt or nickel. Knowing which intermediates are formed and the sulfidation kinetics of the two main players involved in activity — i.e. Mo and the promoter — are therefore major advantages when it comes to identifying the principal factors governing catalytic activity.
The SOLEIL synchrotron’s Quick-XASa ROCK beamline makes it possible to monitor the almost simultaneous chemical and structural evolution of Mo and the promotor in real activation step conditions, with a temporal resolution of just a few seconds. Processing the large amount of data generated is also facilitated by the use of chemometric methods, which have recently begun to be used in this context1.
Analysis of a CoMoP catalyst supported on alumina, has thus demonstrated a multi-step sulfidation process involving Mo (figure), with molybdenum oxysulfide as the first intermediate, followed by the development of an MoS3 phase, predominant at 200°C, which is then fully converted into MoS2 at the end of sulfidation at 400°C.
The IFPEN-SOLEIL collaboration on this line is currently continuing, with the development of a sulfidation reactor in a gas-liquid medium and under pressure.
Thanks to this equipment, continuous XAS analysis of the structural evolution around the molybdenum and cobalt during the reaction, in conditions representative of industrial processes, will make it possible to make significant advances in our understanding of the mechanisms involved.
a- X-ray absorption spectroscopy with rapid data analysis.
(1) A. Rochet, et al., Co-K and Mo-K edges Quick-XAS study of the sulphidation properties of Mo/Al2O3 and CoMo/Al2O3 catalysts, Comptes Rendus Chimie 19 (2016) 1337-1351
>> DOI: 10.1016/j.crci.2016.01.009