Isocyanate (NCO) evidence in the CO + NO reaction over palladium

• NCO formation is exothermic on Pd(111) and endothermic on Pd(100).
• Thermodynamic balance is related to NCO polarization.
• Energy barriers are larger on Pd(100), compared with Pd(111).
• Energy barriers are related to coupling of N and Pd orbitals.
• Results are in complete agreement with previous PM-IRAS data.

In the present work the NCO formation from N and CO species is theoretically studied using a computational method based on density functional theory (DFT) and a periodic slab model. For that purpose, the (100) and (111) faces of Pd have been considered, with two different pathways on both surfaces comprising the displacement of CO species. The overall processes are endothermic on Pd(100) and exothermic on Pd(111) and the corresponding energy barriers are larger on Pd(100), compared to Pd(111). Hence, in agreement with the experimental data the NCO formation is more favored on Pd(111). The results are rationalized taking into account charge distributions and electronic structure parameters.

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