On the structure sensitivity of and CO coverage effects on formic acid decomposition on Pd surfaces

Using density functional theory calculations, the Pd-catalyzed vapor-phase formic acid decomposition was studied, with a focus on the structure sensitivity and CO coverage effects. A comprehensive reaction network was developed on both the (111) and (100) facets of Pd, at CO coverages of 0 and 5/9 monolayer (ML). Pd(100) was determined to be more reactive than Pd(111) at both CO coverages. The introduction of 5/9 ML CO decreased the activity of both facets significantly, due to destabilization of the surface intermediates and transition states on the CO-decorated surfaces. Three reaction pathways were explored on the clean surfaces: the formate (HCOO) pathway, the carboxyl (COOH) pathway leading to the formation of CO2, and the COOH pathway leading to the formation of CO (COOH -> CO). Based on the DFT-derived energetics alone, it appears that all three pathways contribute to the reaction on clean Pd, whereas the presence of 5/9 ML of CO inhibits the HCOO pathway on both facets and favors the COOH -> CO pathway on the (111) facet, but the COOH -> CO2 one on the (100) facet. Moreover, at high CO coverages, alternative spectator CO-assisted adsorbate decomposition pathways were discovered, which could potentially play a role in formic acid decomposition on Pd catalysts under realistic reaction conditions.

Automated summary

Using density functional theory calculations, this study investigated the structure sensitivity and CO coverage effects of Pd-catalyzed vapor-phase formic acid decomposition. The results showed that Pd(100) exhibited higher reactivity compared to Pd(111), with the presence of 5/9 ML CO significantly decreasing activity on both facets. Three reaction pathways were explored on clean surfaces, with alternative spectator CO-assisted adsorbate decomposition pathways discovered at high CO coverages.