CO2 hydrogenation on Pt, Pt/SiO2 and Pt/TiO2: Importance of synergy between Pt and oxide support

In the current study we combined density functional theory (DFT), kinetic Monte Carlo (KMC) simulations and experimental measurements to gain insight into the mechanisms of CO2 conversion by hydrogen on the Pt nanoparticle (NP). The results show that in spite of the presence of active, low-coordinated sites, Pt NP alone is not able to catalyze the reaction due to the weak CO2 binding on the catalyst. Once CO2 is stabilized, the hydrogenation of CO2 to CO via the reverse-water–gas shift (RWGS) reaction is promoted; in contrast, the enhancement for further *CO hydrogenation to CH4 is less significant and no CH3OH is observed. The selectivity to CO is mainly determined by CO binding energy and the energetics of *CO hydrogenation to *HCO, while that for CH4 and CH3OH is determined by the competition between hydrogenation and C–O bond scission reactions of the *H2COH species. Using SiO2 and TiO2 as the support, Pt NP is able to promote the overall CO2 conversion, while the impact on the selectivity is rather small. The theoretically predicted trend in activity and selectivity is in good agreement with the experimental results. The enhanced activity of Pt/oxide over Pt is originated from the sites at the Pt–oxide interface, where the synergy between Pt and oxide plays an important role.