Tuning adsorption energies and reaction pathways by alloying: PdZn versus Pd for CO2 reduction to methanol
Résumé
The decrease of greenhouse gas emission due to fossil fuel combustion is one of the most important challenges to slow down the rate of climate change while replacing fossil sources. Methanol is a safe, easily transportable and fastly biodegradable liquid fuel which could be a carbon neutral alternative to fossil fuels. Catalytic CO2 hydrogenation to methanol (CO2 + H2 → H2O + H3COH), with hydrogen produced from water electrolysis, has proven to be a viable process at the pilot plant scale in several countries. However, efficient catalysts are required to convert the stable CO2 molecule to methanol.
We focus on the PdZn(111) model catalyst, with density functional theory calculations to investigate how the addition of an ancillary metal (Zn) to a metallic catalyst (Pd) influences the mechanism of methanol synthesis through CO2 hydrogenation. We show that the preferred pathway varies with the model catalyst. On pure Pd, the carboxyl route is more likely to be followed and formate routes are favored by the insertion of Zn. The relative donor character of PdZn weakens carbon-bound species and strengthens oxygen-bound species. Alloying Pd with another metal offers then the possibility of tuning the CO2 reduction to methanol by favoring a specific pathway or step on a wisely chosen catalyst. The extension of our study to other ancillary metals combined with Pd may stimulate the discovery of novel alloy catalysts for CO2 hydrogenation to alcohols.