The adsorption phenomena occurring at the surface of a highly-dispersed Pt/Al2O3 catalyst for hydrogenation reactions were thoroughly investigated in the gas-phase by transmission IR spectroscopy and in the liquid-phase by ATR-IR spectroscopy. The reduction of Pt/Al2O3 in H-2 with the formation of Pt-hydrides and adsorption of CO were used as case studies for the comparison of the two different environments under otherwise similar experimental conditions. We found that compared to gas-phase, the selected solvent (cyclohexane) greatly affects the reducibility of Pt. Incomplete reduction under the adopted liquid-phase conditions was demonstrated by the formation of carbonate species at very low CO coverage. Moreover, cyclohexane competes with the adsorbates (H-2 as well as CO) for the occupancy of the available surface sites, thus affecting the shape, position and relative intensity of the infrared signals corresponding to the surface Pt-H and Pt-CO species and leading to an overall lower H and/or CO coverage. Our spectroscopic data show also that the presence of the solvent is crucial in maintaining the Pt nanoparticles in partially H-solvated state even in a H-2-free environment. This evidence might have important implications with respect to the catalyst reactivity and stability.

Gas phase vs. liquid phase: monitoring H2 and CO adsorption phenomena on Pt/Al2O3 by IR spectroscopy

Carosso, Michele
First
;
Ricchebuono, Alberto;Vottero, Eleonora;Manzoli, Maela;Morandi, Sara;Pellegrini, Riccardo;Piovano, Andrea;Ferri, Davide
;
Groppo, Elena
Last
2022

Abstract

The adsorption phenomena occurring at the surface of a highly-dispersed Pt/Al2O3 catalyst for hydrogenation reactions were thoroughly investigated in the gas-phase by transmission IR spectroscopy and in the liquid-phase by ATR-IR spectroscopy. The reduction of Pt/Al2O3 in H-2 with the formation of Pt-hydrides and adsorption of CO were used as case studies for the comparison of the two different environments under otherwise similar experimental conditions. We found that compared to gas-phase, the selected solvent (cyclohexane) greatly affects the reducibility of Pt. Incomplete reduction under the adopted liquid-phase conditions was demonstrated by the formation of carbonate species at very low CO coverage. Moreover, cyclohexane competes with the adsorbates (H-2 as well as CO) for the occupancy of the available surface sites, thus affecting the shape, position and relative intensity of the infrared signals corresponding to the surface Pt-H and Pt-CO species and leading to an overall lower H and/or CO coverage. Our spectroscopic data show also that the presence of the solvent is crucial in maintaining the Pt nanoparticles in partially H-solvated state even in a H-2-free environment. This evidence might have important implications with respect to the catalyst reactivity and stability.
12
4
1359
1367
Pt/Al2O3, operando spectroscopy, Pt hydrides, IR spectroscopy
Carosso, Michele; Fovanna, Thibault; Ricchebuono, Alberto; Vottero, Eleonora; Manzoli, Maela; Morandi, Sara; Pellegrini, Riccardo; Piovano, Andrea; Ferri, Davide; Groppo, Elena
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2318/1848096
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