thesis by Leonor Catita*
In order to obtain cleaner fuels, hydrotreatment (HDT) processes require new, more active and more selective catalysts. In turn, this necessitates a better understanding of a key step in the preparation of catalysts: impregnation of the support by an aqueous or organic solution of the metallic precursors, future active sites in catalysis.
In this research, an analytical methodology based on MRIa and Ramanb techniques was developed to characterize the impregnation step. The objective is to be able to describe the physical and chemical phenomena involved in the transport of the metallic precursor
within the support porosity.
This study marked the first in situ use of MRI in real systems such as HDT catalysts to monitor the impregnation step with a complex aqueous solutionc, in the presence or otherwise of citric acid(1). Thanks to Raman imaging, we confirmed the identification of the
chemical characteristics of the molybdenum species deposited on the support. We thus highlighted a preferential affinity between citric acid and the surface of the γ alumina (figure), as well as the significant impact of the local pH and the presence of phosphorus on the characteristics of the species deposited(2).
These results were used as the foundations for developing a mathematical model aimed at rationalizing the monometallic catalyst impregnation step. The model is used to estimate, for a given solution, the impregnation time within new supports and to evaluate active phase accessibility.
The method developed can be applied to numerous other catalyst systems, in order to make them more efficient via the improved distribution of the active phase.
a - NMR (Nuclear Magnetic Resonance) Imaging.
b - Spectroscopic method providing information about chemical structure and compounds present.
c - Composed of molybdenum (Mo), cobalt (Co) and phosphorus (P).
*Thesis entitled "Contribution of NMR and Raman imaging for modeling and rationalization of the impregnation process of metallic precursors in porous media"
(1) L. Catita, A-A. Quoineaud, D. Espinat, C. Pichon, O. Delpoux, Application of Magnetic Resonance Imaging and Raman Imaging to study the impact of phosphorus in impregnation of hydrotreatment catalysts , Applied Catalysis A:General Vol. 547 (2017), 164-175
>> DOI: 10.1016/j.apcata.2017.08.039
(2) L. Catita, A-A. Quoineaud, M. Moreaud, D. Espinat, C. Pichon, O. Delpoux, Impact of Citric Acid on the Impregnation of CoMoP/γ-Al2O3 Catalysts: Time and Spatially Resolved MRI and Raman Imaging Study, Topics in Catalysis, Sept. 2018, Volume 61, Issue 14, pp 1474–1484
>> DOI: 10.1007/s11244-018-1038-7
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