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Improving the reactional performance of a catalytic material (obtained by applying an active phase onto oxide grains) requires a better understanding of the mechanisms involved in the reaction. More specifically, it is necessary to be able to decorrelate the reactions taking place on the active phase from those occurring on the surface of the oxide supporting it.

This is particularly true in the case of Fischer-Tropsch catalysts, the selectivity of which can be influenced by the support’s acid-base surface properties, as well as the heterogeneity of distribution (inter and intra-grain) of the active phase (cobalt). The apparent selectivity can thus vary from one grain to another, depending on the local cobalt content and/or the surface of the support exposed.

An operando analysis method using infrared microscopy (µIR) has been developed in cooperation with teams from the SOLEIL SMIS line to describe the reactional mechanisms on oxide support grains, impregnated or otherwise with cobalt1.

The µIR analyses were performed in a reactor at 230°C and at atmospheric pressure, in the presence of CO/H2 reactive gas mixtures at different ratios. The material studied was composed of a mixture of oxide support grains alone (gs) or impregnated (gc).

 

Image optique et spectres IR de gs (bas) et gc (haut) en conditions de réaction.
Optical image and IR spectra of gs (bottom) and gc (top) in reaction conditions.

 

Comparison of the data, obtained at reactional iso-conditions on the two populations (figure), made it possible to fine-tune the spectral attributions of the surface species generated then chemisorbed (alkane, formiate, carbonyl, carbonate) and to monitor their formation rates.

Monitoring of the reaction kinetics, coupling spatial and temporal resolutions, is an asset specific to the combination of µIR with synchrotron radiation.

Being able to operate in conditions representative of processes is an additional advantage for studying and optimizing catalysts.

 


(1)  M. Rivallan, L. Lemaitre, S. Humbert, A. Berliet, S. Maury, C. Sandt, F. Borondics.  Research pending publication

 


Scientific contacts: mickael.rivallan@ifpen.fr - laurent.lemaitre@ifpen.fr

>> ISSUE 28 OF SCIENCE@IFPEN