In the way towards non carboneous energy, Hydrogen appears as an optimal energy vector. One option for its green production (green hydrogen) is to use biomass, a carbon-neutral and naturally abundant sustainable energy resource. The treatment of biomass either thermic or biologic leads to formation of syngas (CO, H2).
The water gas shift (WGS) reaction, which transforms CO and H2O in CO2 and H2, has then attracted renewed interest as the key process of maximum hydrogen production from the biomass-derived syngas. However, conventional metal oxide catalysts for WGS reaction are easily deactivated by sulfur-containing impurities, which are ubiquitous in biomass feedstocks. Establishing an energy-efficient and economical WGS catalytic process requires the development of high-performance and stable catalysts capable of adapting to the diversified qualities biomass feedstocks, especially for the issue of sulfur poisoning.
Sulfides are considered good candidates for the sulfur-tolerant WGS catalysts. Up to now, most of the studies were focused on the activity and stability of the catalysts playing with the composition of the catalysts, but only a few works aim to rationalize the obtained results. Indeed, the characterization of sulfide catalysts is not straightforward due to their sensitivity to air. Recently, the LCS has applied the adsorption of CO followed by IR spectroscopy methodology on sulfide catalysts for WGS [1,2] . It was shown for the first time that the two different edges exposed by MoS2 slabs, M-edge and S-edge sites, present different activities and stabilities with time on stream for WGS. In particular, it appears that the M-edge sites are deactivating during time on stream.
To enhance both the activity and stability of M-edge sites for WGS, we propose the addition of decoration metals such as Co [2] or Ni and even Pt as already used for hydrotreating reactions [3]. The characterization of the edge decoration at the atomic scale is thus required. We have shown in previous works that Z contrast imaging by HR STEM HAADF is a relevant technique for the characterization of the slab shape (directly linked to the proportion of exposed sites) and partially for the edge chemical composition [4–6].
Indeed, the chemical mapping at the atomic scale is incomplete with this approach since Z contrast is exploitable only if the Z values are quite different. Sulfide catalysts being sensitive to the electron beam, the mapping can be obtained by EELS spectroscopy but only if coupled with a very sensitive detection technology (CMOS) that allows reducing the exposure time (by a factor of 10). Such rare equipment has just been acquired by the CIMAP laboratory. The use of this new characterization technique at the atomic scale is a very interesting opportunity for the PhD student.
The PhD subject will be divided into two parts :
Part 1 at LCS
Preparation of promoted sulfide catalysts – Characterization of sulfide catalysts by IR/CO – Water Gas Shift activity test – Operando characterization.
Part 2 at CIMAP
High resolution transmission electron microscopy – High Angular Annular Dark Field mode – Electron Energy Loss Spectroscopy mode –
The PhD will allow the candidate to acquire expertise in both sulfide catalyst preparation/characterization by IR spectroscopy and Advanced Microscopy characterization. Note that the student will be formed to be autonomous on the microscope equipped with cutting-edge detectors. The objective of the study is to acquire fundamental knowledge for application in sustainable development. Hence, at the end of PhD, the candidate will have obtained experiences that will fit both with the academic and industrial worlds.
[1] W. Zhao, Sulfide Catalysts for Water Gas Shift: mechanism study and role of K and Co in promoting MoS2 edge sites, Normandie Université, n.d.
[2] J. Chen, J. Zhang, J. Mi, E.D. Garcia, Y. Cao, L. Jiang, L. Oliviero, F. Maugé, Hydrogen production by water-gas shift reaction over Co-promoted MoS2/Al2O3 catalyst: The intrinsic activities of Co-promoted and unprompted sites, Int. J. Hydrogen Energy. (2018). https://doi.org/https://doi.org/10.1016/j.ijhydene.2018.02.194.
[3] J. Kibsgaard, A. Tuxen, K.G. Knudsen, M. Brorson, H. Topsøe, E. Laegsgaard, J. V Lauritsen, F. Besenbacher, Comparative atomic-scale analysis of promotional effects by late 3d-transition metals in MoS2 hydrotreating catalysts, J. Catal. 272 (2010) 195–203. https://doi.org/10.1016/j.jcat.2010.03.018.
[4] L. Zavala-Sanchez, X. Portier, F. Maugé, L. Oliviero, High-resolution STEM-HAADF microscopy on a γ-Al2O3 supported MoS2 catalyst – Proof of the changes in dispersion and morphology of the slabs with the addition of citric acid, Nanotechnology. 31 (2020) 35706. https://doi.org/10.1088/1361-6528/ab483c.
[5] L.A. Zavala-Sanchez, X. Portier, F. Maugé, L. Oliviero, Promoter Location on NiW/Al2O3Sulfide Catalysts: Parallel Study by IR/CO Spectroscopy and High-Resolution STEM-HAADF Microscopy, ACS Catal. 10 (2020) 6568–6578. https://doi.org/10.1021/acscatal.0c01092.
[6] L. Zavala-Sanchez, X. Portier, F. Maugé, L. Oliviero, Formation and stability of CoMoS nanoclusters by the addition of citric acid: A study by high resolution STEM-HAADF microscopy, Catal. Today. 377 (2021) 127–134. https://doi.org/10.1016/j.cattod.2020.10.039.
Ideally, the student with physical chemistry background should apply for both M2 training period (4-6 months from January to July 2022) and PhD thesis (from September/October 2022 to September/October 2025). However, good candidate for PhD thesis only will be considered. The application with an excellent CV is mandatory (cursus in 4 years to get M1 and mentions required). The deadline for M2 + PhD application is on Januray 15th 2022.
Lieu de travail : CAEN
Date de publication : 24/11/2021
Niveau d’études souhaité : M2
Financial support
grant from LABEX EMC3.
Contact
laetitia.oliviero[at]ensicaen.fr (LCS)
xavier.portier[at]ensicaen.fr (CIMAP)
