Exploiting phase transitions in catalysis: reaction ofCO2andH2on dopedVO2-polymorphs.

VO2is well known for its reversible transition between two phases with tetragonal rutile and monoclinic structure. In a previous theoretical study (Stahl and Bredow 2022ChemPhysChem23e202200131) we showed that the adsorption energy of CO is different on surfaces of the two Mo-stabilized polymorphs. This can be exploited to promote catalytic reactions by removing CO from the catalyst surface. As proof-of-principle, we investigated the hydrogenation reaction ofCO2. For this purpose, the adsorption energies ofCO2and possible intermediates and productsH2O, HCOOH,H2COand CO were calculated. Significant differences were found for the reaction energies of the hydrogenation ofCO2to formic acid and formaldehyde on the two polymorphs. This shows that it is in principle possible to alter the reaction thermodynamics by applying reaction conditions which stabilize a particular polymorph. In order to investigate the influence of the polymorph on kinetic properties, the reactions barriers of a step-wise reaction ofCO2+2H2→H2CO+H2Owas calculated using the nudged elastic band method.VO2was found to reduce the reaction barriers compared to the gas phase. Additionally, the minimum energy path of the bulk phase transition of undopedVO2was calculated using the distinguished reaction coordinate method. A catalytic cycle exploiting the phase transition is proposed based on the theoretical results.