Oxygen Adsorption, Subsurface Oxygen Layer Formation and Reaction with Hydrogen on Surfaces of a Pt–Rh Alloy Nanocrystal

• Published in: Topics in catalysis 2020-11, Vol.63 (15-18), p.1522-1531
• Main Authors: Owczarek, Sylwia, Lambeets, Sten V., Bryl, Robert, Barroo, Cédric, Croquet, Olivier, Markowski, Leszek, Visart de Bocarmé, Thierry
• Format: Article
• Language: English
• Subjects: Catalysis; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; FEM; field emission microscopy; Industrial Chemistry/Chemical Engineering; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; model catalysis; nanocatalysis; Original Paper; Pharmacy; Physical Chemistry; Pt; Rh; subsurface oxygen
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-020-01394-w

The oxygen adsorption and its catalytic reaction with hydrogen on Pt–Rh single crystals were studied at the nanoscale by Field Emission Microscopy (FEM) and Field Ion Microscopy (FIM) techniques at 700 K. Both FEM and FIM use samples prepared as sharp tips, apexes of which mimic a single nanoparticle of catalyst considering their similar size and morphology. Oxygen adsorption on Pt-17.4 at.%Rh samples leads to the formation of subsurface oxygen, which is manifested in the field emission (FE) patterns: for O 2 exposure of ~3 Langmuir (L), {113} planes appear bright in the emission pattern, while for higher oxygen doses, i.e. 84 L, the bright regions correspond to the high index planes between the {012} and {011} planes. Formation of subsurface oxygen is probably accompanied by a surface reconstruction of the nanocrystal. The subsurface oxygen can be effectively reacted off by subsequent exposure of the sample to hydrogen gas at 700 K. The hydrogenation reaction was observed as a sudden, eruptive change of the brightness seen on the FE pattern. This reaction resulted in the recovery of the initial field emission pattern characteristic of a clean tip, with {012} facets being the most visible. It was shown that the oxygen accumulation-reduction process is completely reversible. The obtained results indicate that the presence of subsurface species must be considered in the description of reactive processes on Pt–Rh catalysts.