Poisonous Species in Complete Ethanol Oxidation Reaction on Palladium Catalysts

Abstract

Direct ethanol fuel cell technology suffers from a lack of effective anode catalysts for complete ethanol oxidation reaction (EOR). Pd and Pd-based catalysts showed some promise, but only a trace amount of CO 2 was detected as the product. The difficulty of C−C bond cleavage and the formation of acetic acid are commonly believed to be great obstacles toward complete EOR. The limited formation of CO 2 also suggests that acetic acid may not be the only dead-end product that prevents complete EOR. A careful study on the reaction pathway leading to complete EOR is needed to better understand and design effective EOR catalysts. As such, we studied 17 key elementary reactions on Pd surfaces using density functional theory (DFT) and designed experiments to confirm some of the DFT findings. The results show that, in addition to the acetic acid formation, other poisonous species, C, CH, CCO, or dimerization of acetaldehyde, are also largely responsible for the limited formation of CO 2 on Pd catalysts due to their strong adsorptions to the catalysts which block the active sites. The ethanol oxidation shows totally different reaction pathways in neutral and alkaline media. The DFT calculation result provided important insights into the catalysis of complete ethanol oxidation. The experiment result showed that EOR on PdCu alloy nanoparticle catalyst has higher catalytic activity than that on Pd nanoparticle catalyst, suggesting fast kinetics of initial dehydrogenation on the alloy catalyst.

Pd‐Ru Alloy Nanocages with a Face‐Centered Cubic Structure and Their Enhanced Activity toward the Oxidation of Ethylene Glycol and Glycerol

“…Additionally, in contrast to the commercial Pd nanoparticles which were enclosed by a mix of {100} and {111} facets, the as‐synthesized Pd‐Ru nanocages were predominantly covered by {100} facets. The {100} facets have been demonstrated to be more active than {111} facets toward alcohol oxidation, which could bind more strongly to alcohol molecules and thus facilitating the CC bond scission . With regard to the durability, the presence of Ru atoms in the nanocages could greatly mitigate CO poisoning of the catalysts by reducing the adsorption energy of CO on the metal surface, which is advantageous to the removal of CO .…”

Alloying–realloying enabled high durability for Pt–Pd-3d-transition metal nanoparticle fuel cell catalysts

“…DFT calculations to obtain the reaction barriers of some representative elementary steps were carried using three-layer periodic slab models with the bottom two layers fixed. The simulation details can also be found in our previous DFT work on calculating transition states 56 , 57 . The binding energies of the adsorbates which were fully relaxed were calculated by where E R , E metal surface , and E R/metal surface are the total energy of the adsorbates, such as H 2 O and O 2 molecules, the isolated model metal surface, and the adsorbates that were adsorbed on the metal surfaces, respectively.…”

“…The slab models of Pt (111), Pd (111), and Pt 20 Pd 20 Cu 60 (111) surfaces were used. The Gibbs free reaction barriers and reaction energies of some key elementary steps, e.g., the O–O bond cleavage of OOH, the protonation reactions of O 2 , O, and OH species on different surfaces were calculated by: where E IS , E TS , and E FS denote the total energies of the reactant, the transition state, and the product, respectively, while S IS , S TS , and S FS denote the entropies of the reactant, the transition state, and the product, respectively 56 . We note here that the zero point energy correction was considered for all calculations.…”

Phosphorous incorporation in Pd2Sn alloys for electrocatalytic ethanol oxidation

“…According to previous literature, in alkaline media, EtOH is dehydrogenated into adsorbed acetyl, which is further oxidized to acetate by hydroxide species. The oxidation of the acetyl to acetic acid by adsorbed hydroxyl is regarded as the rate-limiting step, while the stripping of the acetic acid in the form of acetate ions in alkaline solution is very rapid [59,60]. We calculated the OHadsorption energies at different sites of the catalysts surface (Table 1) and related these values to the catalyst activity considering that a higher chemical adsorption of OHallows increases activity by facilitating the formation of CH3COOH [61].…”