The use of catalytic reactions to produce a large variety of valuable chemicals is a crucial process in the catalysis industry. In particular, the synthesis of methanol (CH3OH) from the catalytic CO2 hydrogenation reaction (CO2 HR), (CO_2+3H_2→CH_3 OH+ H_2 O), has grown tremendously within the last few years, as it is an attractive approach to mitigate CO2 by converting it into high value-added chemicals. Within this framework we have conducted a comparative study of the CO2 hydrogenation on two analogues nanocatalysts, the first in the form of mixed nanopowders of Cu-ZrO2-Al2O3 (CZA), and the second consisting of ultrathin films with various thicknesses of ZrO2 grown on the CuOx/Cu(111) surface. To this end, we have conducted in situ Raman spectroscopy measurements using autoclave cells under realistic reaction conditions of the pressure (1-50 bar) and step-wise annealing from room temperature up to 400°C. Figure: Operando Raman spectra as a function of the temperature for two nanocatalysts. (A): ultrathin film of ZrO2 grown on CuOx/Cu(111) surface; (B) nanopowders of Cu-ZrO2 -Al2O3 (ZZA) We have used isotopic labeling (D2) to detect unambiguously the characteristic species of the CO2 HR reaction. Although details of elementary steps of the CO2 HR to methanol is still not well established on these NCs, we found that the reaction occurred according to the formate pathway and reverse water gas shift mechanism for ZrO2 thick and thin films, respectively. We attribute the better performances of the ZrO2 ultrathin films to the following effects: (i) the ZrO2—CuOx/Cu interface where synergistic phenomena occur (CO2 dissociation on ZrO2 and D2 dissociation on CuOx-Cu), (ii) the unique role of the dual-reaction sites of ZrO2, present in the ultrathin film, that are the strong Lewis acidity of Zr4+ cations and the strong Lewis basicity of both O2- anions and oxygen vacancies (Ov) associated with Zr3+ states. We have evidenced the presence of these sites thanks to XPS investigations conducted on the ZrO2 ultrathin films where the core-level spectra in the Zr binding energy region show the presence of two contributions, Zr4+ and Zr3+.