Oscillatory surface chemistry in Co(Rh) catalysts during CH₄/CO₂ reforming: an operando NAP-XPS study

Dry reforming of methane (DRM, CH₄+CO₂ ⇋ 2H₂+2CO) simultaneously valorizes the two main greenhouse gases into syngas. Cobalt-based systems offer a cost-effective alternative to noble metals, and their activity further improves when alloyed with small amounts of noble metals; however, the fundamental dynamics governing their performance are poorly understood. At UPC, we have developed highly active and stable Co-noble metal catalysts on CeO₂ (redox-active) and layered double hydroxide (LDH, non-redox) supports. Operando XRD/XAS at ALBA’s NOTOS beamline has uncovered oscillations with well-defined minute-scale periods, opposite CH₄/CO₂ activation trends, and strong support dependence. However, these bulk-sensitive techniques cannot resolve the surface/subsurface rearrangements that drive the oscillations. We now propose operando NAP-XPS at the CIRCE beamline to track in real time the oxidation state and coordination of Co, the influence of noble metal dopants, the role of the support, and the dynamics of surface carbon and oxygen species, correlating these with oscillatory behavior under DRM at 550 °C (plus pure CH₄/CO₂ controls). Two kinetic energies will provide depth profiling of Ce 3d/4d, Co 2p, Rh 3d, O 1s, and C 1s, enabling unprecedented resolution of active site evolution during the catalytic cycle. The oscillation period is long enough to acquire high-quality spectra or track specific binding energies, ensuring statistically robust data. We request 12 shifts to measure four catalysts (Co/CeO₂, Co(Rh)/CeO₂, Co/LDH, Co(Rh)/LDH) under DRM, CH₄, and CO₂ separately, integrating AP-XPS (surface-sensitive) with our existing operando XRD/XAS (bulk-sensitive) dataset to deliver a complete mechanistic picture. The outcomes will provide the first direct surface-level insight into oscillatory DRM catalysis, guiding the rational design of high-performance and durable DRM catalysts for carbon-neutral syngas production.