Thesis by Ana Teresa Fialho Batista*

Platinum nanoparticles supported on chlorinated γ-alumina are used in bifunctional heterogeneous catalystsa, which are central to numerous industrial processes. An atomic-scale study, for which different physicochemical parameters were varied, allowed the location of the two types of active sites present in these catalysts and the distance between them to be determined. Both are critical parameters for catalyst performance.

To do so, a multi-technique approach combining synthesis, advanced characterization and modeling (figure) was implemented, with contributions from several IFPEN research divisions and partner laboratories: IPCMS, CRMN, ESRFb and Institut Néel. The HR-HAADF-STEMc analyses revealed that sub-nanometric Pt particles and Pt single atoms are present on the alumina(1).

Moreover, electronic tomography showed that the majority of Pt nanoparticles are located on the edges of alumina support platelets. This original result is coherent with the NMR and DFTd analyses that showed that chlorine is also stabilized on the edges(2). Finally, a mathematical analysis and a geometric catalyst model were used to estimate average inter-site distances.

Illustration of study means: STEM image, tomographic volume and molecular model of a Pt nanoparticle on a chlorinated alumina edge.

This improved understanding opens up new catalyst performance improvement routes based on preparation methods targeting active site location tuning on an atomic scale.

*Thesis entitled "Atomic scale insight into platinum based catalysts supported on chlorinated gamma-alumina"

a - Comprising active metal sites and acid sites
b - Strasbourg Institute of Materials Physics and Chemistry; High-Field Nuclear Magnetic Resonance Spectroscopy Center in Lyon; European Synchrotron Radiation Facility
c - High Resolution – High Annular Angle Dark Field – Scanning Transmission Electron Microscopy
d - Nuclear Magnetic Resonance and Density Functional Theory

(1) A.T.F. Batista, W. Baaziz, A.-L. Taleb, J. Chaniot, M. Moreaud, C. Legens, A. Aguilar-Tapia, O. Proux, J.-L. Hazemann, F. Diehl, C. Chizallet, A.-S. Gay, O. Ersen, P. Raybaud, ACS Catal. 2020, 10, 7, 4193-4204.

(2) A.T.F. Batista, D. Wisser, T. Pigeon, D. Gajan, F. Diehl, M. Rivallan, L. Catita, A.-S. Gay, A. Lesage, C. Chizallet, P. Raybaud, J. Catal. Priority Communication 2019, 378, 140-143.

Scientific contact: Ana Teresa Fialho Batista