Various reactive intermediates and Cn
products from carbon dioxide reduction reaction (CO2RR)
play critical roles in the chemical and fuel industry. Developing
easily accessible activity descriptors to predict possible intermediates
and products of CO2RR is of great importance. The free
energy changes (ΔG) for all possible reaction
intermediate and product probability (P) of CO2 reduction to methanol, methane, and formaldehyde on 26 single-atom
catalysts (SACs) in zeolites were predicted by density functional
theory (DFT) calculations and machine learning (ML) models. The adsorption
free energies of ΔG
*OH and ΔG
*O*CH2 were highly correlated with catalytic
activity. Producing methanol was favorable for metal-zeolites with
early transition metals and main group elements. Methane production
was more feasible for some systems such as Co-zeolite, due to the
low free energy and high selectivity against the hydrogen evolution
reaction. Both XGBoost and ExtraTrees algorithms could give satisfactory
predictions of ΔG and P in
CO2RR using descriptors of reaction pathways, metal, charge
transfer (CT) between the metal and reaction intermediate, hydrogen
bond interaction between the intermediate and zeolite framework, and
geometry. The global electronegativity difference (δχT) and average ionization energy difference (δIE) between
the metal-zeolite and intermediate were introduced as features (along
with the valence electron number of metals and the atomic number of
reaction species) for prediction of CT values without the need of
DFT calculations. The CT feature could be replaced by some additional
descriptors such as the band gap (E
g)
or coordination number of metals to intermediates in training ML models
for free energy prediction. ML models on an external test such as
MOFs, 2D materials, and molecular complex materials indicate that
the proposed descriptors are general for the reaction free energy
change and product prediction of SACs in CO2RR.