Role of monodentate formate in product selectivity for CO₂ hydrogenation on Pd-based alloy catalysts

The hydrogenation of CO₂ to methanol is a key reaction for sustainable fuel synthesis. A crucial aspect of the catalytic mechanism is the role of monodentate formate (HCOO^m*) in the initial steps of CO₂ hydrogenation on Pd-based alloy catalysts, which we have investigated using density functional theory (DFT) together with subgroup discovery (SGD) analysis. The reactivity and stability of CO₂ and formate species are examined on monometallic Pd, Cu, Zn surfaces and alloyed CuPd and PdZn surfaces. PdZn surfaces show low activation energy barriers for CO₂ hydrogenation and, combined with weak CO₂^δ- adsorption energy, this suggests that an Eley-Rideal mechanism may dominate over Langmuir-Hinshelwood pathways. The adsorption energy of the monodentate formate intermediate is found to correlate significantly with the activation energy of CO₂ hydrogenation across all investigated facets, where stronger adsorption yields lower activation energy, enabling its use as a predictive descriptor. To determine possible new catalytic materials, a dataset of 49 Pd-based single-atom alloy (SAA) surfaces is screened using SGD, identifying key electronic parameters, the dopant and site electron affinity, as drivers of strong HCOO^m* adsorption. The obtained subgroup discovery rules highlight Mo, Nb, and W as promising earth-abundant dopants for Pd-based catalysts, further confirmed by DFT calculations. These findings offer a mechanistic rationale for catalyst design and demonstrate the utility of AI-guided screening in identifying efficient, sustainable alloy compositions to be used as catalysts for CO₂ conversion.