Computational insights into selective CO2 hydrogenation to CH3OH catalysed by ZnO based nanocages

Cu and ZnO based nanostructures were extensively studied for CO2 hydrogenation reaction. In this study, we have performed density functional theory (DFT) calculations for understanding the CO2 hydrogenation reaction mechanism on ZnO and Cu doped ZnO based nanocages (NCs). Two different ZnO based NCs and three different Cu doped ZnO based NCs have been considered for the investigation. The stabilities of the NCs have been investigated using the formation energy, cohesive energy, phonon dispersion and ab initio molecular dynamics (AIMD) calculations. Our calculated adsorption energy values show that the CO2 hydrogenation reaction intermediates adsorb strongly on the NCs compared to that on the bulk Cu(111), Cu(111) monolayer and Cu nanocluster. Besides, the detailed mechanistic investigation and the calculated ZPE corrected reaction energy values show that the ZnO and Cu doped ZnO based NCs show excellent selectivity for CH3OH. These catalysts also work under very low working potentials (0.55 V for ZnO NC and 0.39 V for Cu doped ZnO NC) compared to the bulk Cu(111), Cu(111) monolayer and Cu nanocluster. Hence, Cu@ZnO based nanocages can be highly efficient and selective catalysts compared to ZnO based nanocages and Cu based catalysts for CO2 hydrogenation to CH3OH. Moreover, the influence of *COOH and *COH coverage for ZnO NC, *COH and *CHOH coverage for Cu@ZnO NC on adsorption energy values show that the catalysts can be used at high surface coverage.