Catalyst selectivity: spectral investigations

ThESIS BY Fabien Caron*

The environmental constraints associated with the production of high-octane sulfur-free gasolines require improvements to the selectivity of the catalysts used for the hydrodesulfurization (HDS) of sulfur-containing molecules^a. Given the scale of this industrial challenge, it is vital to improve the understanding of the reaction mechanisms governing this selectivity on an atomic scale.

Thanks to kinetic studies via high-throughput experimentation, the hypothesis of a support effect on the function of active phase^b sites was confirmed: the selectivity of the CoMoS catalyst is different depending on the nature of its support (alumina-gamma, alumina-delta or silica).

A multi-technical approach combining high-resolution microscopy, infrared spectroscopy (figure) and ab initio modeling^c, was used to explain this fact. It is due to the impact of the support on the nanostructure of the active CoMoS phase and on speciation^d of the promoted sites..

Science 35 — IR spectroscopy techniques employed:
a) IR spectra of CoMoS/silica and /γ-alumina saturated in NO(1).
b) In situ ATR-IR monitoring of the interaction of 3-methylthiophene on CoMoS/γ-alumina(2).

The design of a dedicated unit, combining gas chromatography and in situ IR, then made it possible to explore, for the first time, the formation of intermediates on the catalyst in conditions similar to those of the industrial process.

This research, conducted in partnership with Turin University, paved the way to the development of an innovative and promising methodology for innovative operando catalyst characterization.

^{a - While limiting the hydrogenation of alkenes (unsaturated hydrocarbons with formula CnH2), to maintain the octane number.

b - In this case molybdenum disulfide, promoted by cobalt (CoMoS).

c - Based on basic laws of physics.

d - Chemical and structural form in which an element is found.}

*Thesis entitled "Bridging the gap between spectroscopic and catalytic properties of supported CoMoS catalysts"

⁽¹⁾ F. Caron, M. Rivallan, S. Humbert, A. Daudin, S. Bordiga, P. Raybaud. Active sites speciation of supported CoMoS phase probed by NO molecule: A combined IR and DFT study, J. Catal. 361 (2018) 62.
>> DOI : 10.1016/j.jcat.2018.02.017

⁽²⁾ F. Caron, M. Rivallan, A. Daudin, S. Bordiga, P. Raybaud (in progress)

Scientific contacts: antoine.daudin@ifpen.fr - mickael.rivallan@ifpen.fr

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