Interfacial synergistic catalysis of Cun single-cluster catalysts anchored on α-Al2O3(0001) for promoting hydrogenation of CO2 to methanol

The size-selected copper single-cluster catalysts(SCCs) play a crucial role in catalyzing of CO2 hydrogenation. However, nature of size effect and hydrogenation mechanism is still unclear. Here, Density functional theory(DFT) calculations were performed to investigate activation and reaction mechanism of CO2 hydrogenation to methanol over copper single-clusters catalyst anchored on α-Al2O3(0001). Our results show that Cun(n = 1–9)/Al2O3 catalysts significantly promote activation of CO2 in a bent configuration due to the synergistic interaction associated with Cun-Al2O3(0001) interfacial site. Bader charge analysis suggested electron transfer occurring from Cun-Al2O3(0001) interface to CO2, leading to negatively charged CO2. We find descriptors of deviation of CO2 bonds length and bonds angle, d-band center of Cun(n = 1–9) cluster that can well descript for determining activation degree of CO2. Especially, the Cu5/α-Al2O3(0001) has the best activity for CO2 hydrogenation among them. Furthermore, reaction mechanism of CO2 hydrogenation at Cu5/Al2O3 interface have been explored. Methanol synthesis takes formate route and direct CO bond cleavage route competitive with rate-dominant step of HCOO* and HO* hydrogenation, respectively. While CO-hydrogenation produced by RWGS route is not feasible because of high activation barrier of formed CO intermediate(1.95 eV). This study will provide insight into designing and application of ultrahigh-performance Cu-based single-cluster catalysts for CO2 hydrogenation.