Multi-scale modelling of various copper-based catalysts showed how and why different catalysts perform in methanol synthesis via carbon dioxide hydrogenation.

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In heterogeneous catalysis, bifunctional catalysts often outperform one-component catalysts. The activity is also strongly influenced by the morphology, size, and distribution of catalytic particles. For CO 2 hydrogenation, the size of the active copper area on top of the SrTiO 3 perovskite catalyst support can affect the activity, selectivity, and stability. Here, a detailed theoretical study of the effect of bifunctionality on an important chemical CO 2 transformation reaction, the reverse water gas shift (RWGS) reaction, is presented. Using density functional theory computation results for the RWGS pathway on three surfaces, namely, Cu(111), SrTiO 3 , and the Cu/SrTiO 3 interface between both solid phases, we construct the energy landscape of the reaction. The adsorbate–adsorbate lateral interactions are taken into account for catalytic surfaces, which show a sufficient intermediate coverage. The mechanism, combining all three surfaces, is used in mesoscale kinetic Monte Carlo simulations to study the turnover and yield for CO production as a function of particle size. It is shown that the reaction proceeds faster at the interface. However, including copper and the support sites in addition to the interface accelerates the conversion even further, showing that the bifunctionality of the catalyst manifests in a more complex interplay between the phases than just the interface effect, such as the hydrogen spillover. We identify three distinct effects, the electronic, cooperative, and geometric effects, and show that the surrounded smaller Cu features on the set of supporting SrTiO 3 show a higher CO formation rate, resulting in a decreasing RWGS model trend with the increasing Cu island size. The findings are in parallel with experiments, showing that they explain the previously observed phenomena and confirming the size sensitivity for the catalytic RWGS reaction.

As the increasing concentration of the atmospheric CO2 is being progressively recognized as a global environmental problem due to its greenhouse effect, the catalytic hydrogenation of carbon dioxide to methanol has been repeatedly put forward as a way of carbon fixation. Time and again have been copper-based heterogeneous catalysts shown to be best suited for this technological purpose, but their performance must be improved with secondary metal oxides, dopants, and supports. Herein, first-principles surface simulations of a Cu phase with four prospective perovskite substrate materials were performed. Cu/CaTiO3, Cu/SrTiO3, Cu/BaTiO3, and Cu/PbTiO3 were systematically studied. After extensive density functional theory (DFT) calculations, aimed at elucidating their stable structure, mapping out a complex reaction network, and pinpointing the rate-determining mechanism steps, the results were fed into a kinetic Monte Carlo (kMC) setup at industrially relevant operating conditions (the temperature of 420–660 K, pressure 0.001–100 bar, and different reactant ratios). It was found out that all studied systems outperformed the pure Cu. Among them, Cu/PbTiO3 was shown to offer very high selectivity and an overall good activity. With lead-containing metallic compounds being problematic due to their toxicity, Cu/SrTiO3 is a very good alternative, closely followed by Cu/BaTiO3. In all instances, CH3OH was observed to form via the formate route (from CO2 to HCOO, HCOOH, H2COOH, H2CO, H3CO, and CH3OH), while CO is produced from CO2 through t-COOH and c-COOH. The direct dissociation pathway of CO2 or CO hydrogenation was not notable, as indicated by the linked multiscale description.