PhD student (H/F) ME-PSD IR spectroscopy to study real industrial oxidation catalysts

The work will take place at the Solid State Chemistry and Catalysis Unit (UCCS, UMR 8181) within the Modeling and Spectroscopy team of the Heterogeneous Catalysis department. The team is based on the Cité Scientifique campus in Villeneuve d'Ascq. It develops a fundamental approach for the study of the catalytic reaction in heterogeneous catalysis combining molecular modeling (mainly DFT) and advanced spectroscopy.
The PhD is part of the MESCAT project (Dynamic behavior analysis of active species by modulation excitation spectroscopies: application in heterogeneous catalysis) funded by the National Research Agency (ANR-21-CE50-0019) which gather two teams from UCCS and a team from Synchrotron SOLEIL. The ANR project is coordinated by the scientific supervisor of the PhD.

Context. Heterogeneous catalytic reactions require synergetic interactions between reaction species and surface actives sites to promote the desirable reaction from complex manifolds of available pathways. To achieve such a high level of selectivity of the catalytic process, heterogeneous catalysts have to be tailored in a very precise way which require the monitoring of actives species. However, intermediates reaction species have a very short lifetime and are in negligible amounts compared to reactants and final products. Hence, the recorded spectroscopic signal will often be saturated by the signal of reactants and products and it is very difficult to obtain a pure spectroscopic fingerprint of intermediate reaction species. One possible approach to overcome these limitations is to apply modulation excitation (ME) conditions combined with proper spectroscopic methods. The modulation excitation spectroscopy consists in stimulating the sample with oscillatory perturbation, (e.g. rapid looping from oxidizing to reactive atmospheres) and recording spectra all along these oscillations. This rapid periodic perturbation of the system will influence only the concentration profile of the active species which will oscillate at the frequency of the periodic excitation but with a phase delay. The concentration profile of species not responding to the periodic excitation (i.e. spectator species) will remains constant making possible their removal from the global signal by a post data acquisition mathematical treatment known as PSD (phase sensitive detection).

Methodology. We propose in this PhD to apply Infrared (IR) spectroscopy under modulation excitation conditions to study the catalytic behavior of partial oxidation catalysts (Iron (III) molybdate catalyst: Fe2(MoO4)3). This catalyst is used to synthetize green platform molecules.
ME-PSD is a major advancement to monitor selectively species directly involved in a reaction. However, its use is not widespread yet and is still confined to a handful of research groups worldwide due to the fact that the state of the art of MES signal processing is still in its early stages. Indeed, the PSD treatment will convert the original spectrum signal which is function of energy (E) and time (t) into a demodulated signal (phase domain signal), a function of energy (E) and phase and the key question is how to process such a demodulated to obtain accurate information on active species. There still a need to go beyond a qualitative interpretation to obtain a quantitative analysis of the phase domain signal: (1) determination of the number of species present during the perturbation, (2) isolation of species and their sequence of apparition and (3) back-transformation to the time domain to isolate pure spectra. We will pioneer a new strategy addressing the ME-PSD signal treatment. This strategy will combine newly adopted chemometric tools to ME-PSD signal treatment, homemade algorithm to back transform the signal in time domain to isolate pure regular spectra, as well as DFT calculation to model IR spectra.