Spatial variation of the active phases during the catalytic oxidation of CO measured on a curved Pd(111) surface

Resumen del póster presentado al 5th Annual Ambient Pressure X-ray Photoelectron Spectroscopy Workshop, celebrado en Berlin (Alemania) del 11 al 14 de diciembre de 2018.For decades, the study of chemical reactions on single metal surfaces has been aimed at identifying those active sites and crystal planes that feature nanoparticles. However, nanocrystal facets coexist in a reduced space, and are expected to simultaneously undergo chemical and structural transformations during catalytic reactions. In ALBA we explore chemical-structural interplays among crystal planes using curved crystals and near-ambient X-ray photoemission (XPS) at CIRCE. As a test case for the approach, we recently used a curved Pd(111) surface, on which we freeze the CO oxidation reaction at the ignition temperature. By scanning the photon beam across the curved surface, we observe a smooth spatial variation of chemisorbed phases, demonstrating a different reaction stage at each crystallographic plane. As shown in the Figure, the XPS signal from chemisorbed CO reveals the linearly decreasing fraction of CO-poisoned areas, from the (111) direction up to a 10º critical angle, and at various temperatures around light-off. This behavior is explained as a collective structural response of the surface at the reaction onset, consisting in the weighted segregation of less-active (111) phase and highly-active (223) and (332) facets in A-type and B-type vicinal planes, respectively.We acknowledge financial support from the Spanish Ministry of Economy (Grant MAT2013-46593-C6-4-P) and Basque Govemment (Grant IT621-13).Peer Reviewe