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

Resumen del trabajo presentado a la conferencia Tailored surfaces in operando conditions (Tailor): A Marcus Wallenberg symposium, celebrada en Ystad (suecia) del 11 al 14 de junio 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. We explore chemical-structural interplays among crystal planes using curved crystals and near-ambient X-ray photoemission (XPS) at CIRCE beamline, ALBA (Spain) synchrotron. As a test case for the approach, we use 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 facets in A-type [beyond (557)] and B-type [beyond (443)] vicinal planes, respectively.We acknowledge financial support from the Spanish Ministry of Economy (Grant MAT2013-46593-C6-4-P) and Basque Government (Grant IT621-13).Peer Reviewe