Deoxygenation of IrO_2(110) surface: Core-level spectroscopy and density functional theory calculation

摘要

Deoxygenation of the IrO_2(110) surface is investigated at 403-493 K, using the core-level spectroscopy and density functional theory (DFT) calculation. The Ir-4f_(7/2) signals of 1f-cus-Ir with and without on-top oxygen (O_(top)) emerge as surface features of the baked-out surface, whose positive and negative shifts in binding energy are in line with the DFT computation results. Progressively increasing the reduction temperature, the 1f-cus-Ir feature quickly disappears and the signal of 2f-cus-lr emerges at 403 K. Meanwhile the feature of 1f-cus-Ir + O_(top) diminishes but persists when the Ir metal signal is evident. The intriguing coexistence of 1f-cus-Ir + O_(top) and Ir metal at 433-443 K is elucidated in the theoretical pathway study. DFT calculation reveals that O_2 desorption via pairing two neighboring O_(top) atoms is the rate-determining step of surface deoxygenation. Under the UHV conditions, O_(top) is replenished via migration of the surface oxygen species, including the threefold coordinated oxygen (O_(3f)) of a reduced surface. Hence the O_(top) atom is an active and long-lived surface species, which does not vanish until O_(3f) is consumed and surface Ir begins to cluster. Under the realistic pressure conditions, O_(top) can also be refreshed via the dissociative adsorption of gas-phase oxygen, in either pathway, O_(top) is a critical intermediary of IrO_2(110) oxidation catalysis.