Thermokinetic and Spectroscopic Mapping of Carbon Monoxide Adsorption on Highly Dispersed Pt/γ-Al 2 O 3

Alexis Sangnier (1, 2) , Eric Genty (3) , Mathilde Iachella (4) , Philippe Sautet (5, 4) , Pascal Raybaud (2) , Mickaël Matrat (1, 2) , Christophe Dujardin (3) , Céline Chizallet (2)

1 Institut Carnot IFPEN Transports Energie
2 IFPEN - IFP Energies nouvelles
3 UCCS - Unité de Catalyse et Chimie du Solide - UMR 8181
4 ENS de Lyon - École normale supérieure de Lyon
5 UC - University of California

The understanding and quantification of the CO adsorption modes and strength on ultradispersed platinum catalysts supported on γ-Al2O3 is of prominent importance for analytic and catalytic purposes. We report a multiscale experimental (AEIR, CO-TPD) and theoretical approach to provide vibrational properties, adsorption enthalpies, and desorption behaviors. First principles calculations on Pt13(CO)m/γ-Al2O3 and Pt(111) surface models (using various exchange-correlation functionals) provide a complementary view to experimental approches. Adsorption enthalpies computed with the RPBE functional appear to be the most compatible with the AEIR results. The occupation of top sites by CO dominates the behavior of supported Pt clusters. CO coverage reaches higher values in comparison to Pt(111) for similar operating conditions, and considerable cluster reconstruction is observed at high coverage. First principles calculations also confirm the IR assignment related to the various adsorption modes on top and bridge sites and demonstrate a particle size effect, lowering the frequency of linear adsorption at top sites with respect to extended Pt(111) surfaces. Finally, first principles-based microkinetic modeling of CO-TPD experiments shows that the adsorption strengths predicted on the small-size cluster by DFT are compatible with the experimental values. We discuss possible reasons for the experimental desorption pattern to be much broader than the computed pattern.

Mots clés: Density Functional Theory; Carbon monoxide adsorption; TPD; platinum subnanometric particles; AEIR

Domaines: Chimie; Catalyse

Alexis Sangnier, Eric Genty, Mathilde Iachella, Philippe Sautet, Pascal Raybaud, et al.. Thermokinetic and Spectroscopic Mapping of Carbon Monoxide Adsorption on Highly Dispersed Pt/γ-Al 2 O 3. ACS Catalysis, 2021, 11 (21), pp.13280-13293. ⟨10.1021/acscatal.1c04262⟩. ⟨hal-03500445⟩