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

• Published in: Surface science 2021-07, Vol.709 (C), p.121846, Article 121846
• Main Authors: Li, Sha, Rangarajan, Srinivas, Scaranto, Jessica, Mavrikakis, Manos
• Format: Article
• Language: English
• Subjects: Adsorbates; Carbon dioxide; Decomposition; Decomposition reactions; Density functional theory; Destabilization; Formic acid; Sensitivity
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2021.121846

•Formic acid decomposition is a structure-sensitive reaction on Pd•CO coverage affects Pd-catalyzed HCOOH decomposition both energetically and mechanistically•HCOOH decomposes through COOH or HCOO on clean Pd(111) and Pd(100)•At high CO coverage, HCO or COH plays a vital role in HCOOH decomposition on Pd 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. [Display omitted]