Contribution of chemical imaging by X-ray Absorption Spectroscopy for localized monitoring of the impregnation and activation of heterogeneous catalysts

In order to reduce the energy consumption of catalytic processes, one of the levers is to optimize catalysts. This optimization is accompanied by an ever-increasing need to characterize these solids. This is particularly the case for hydrotreating catalysts that produce fuels and chemical intermediates with low environmental impact. The preparation of these catalysts is composed of a series of unit steps that will make it possible to design the future properties of the solid: from impregnation on the alumina support of metal species based on molybdenum heteropolyanions to activation in a sulfo-reducing medium to obtain the active phase, through maturation and drying. These steps of impregnation and maturation of the oxide catalysts are undergone and lead to a heterogeneous distribution of species on the support that can have a negative impact on the catalytic activity. However, the identification and quantification of these species remain a major challenge. To meet this challenge, we propose to use and optimize a spatially resolved X-ray absorption chemical imaging technique on the Quick-XAS ROCK beamline of the SOLEIL synchrotron. After the spatial and temporal optimization of the XAS analysis by chemical imaging on a catalyst impregnated with a molybdenum-based heteropolyanion solution, the PhD student will have to develop a methodology to monitor impregnation and maturation within the support. He will have to identify and quantify by XAS and Raman the different molybdenum-based compounds according to the nature of the solution and their evolution during the maturation stage. In situ monitoring of the activation step in a sulfide environment will also be studied in order to describe the activation mechanism of previously identified and localized species, in order to determine the ones most likely to generate active phases.

Keywords: Chemical imaging, spatial resolution, X-Ray Absorption, quantification, oxide catalysts

• Academic supervisor    Dr BRIOIS Valérie,  Directeur de recherche au CNRS (DR1), responsible of the  ROCK beamline of SOLEIL synchrotron
• Doctoral School    571 - Ecole Doctorale Chimie de Paris-Sud
• IFPEN supervisor    Dr LEGENS Christèle, Materials characterization department, christele.legens@ifpen.fr
• PhD location    Synchrotron SOLEIL, St Aubin, France (3/4) and  IFP Energies nouvelles, Lyon, France (1/4)
• Duration and start date    3 years, starting not earlier than September 2020
• Employer    IFP Energies nouvelles, Lyon, France
• Academic requirements    University Master degree in relevant disciplines
• Language requirements    Fluency in French and/or English, willingness to learn French