On the Reactivity of the Cu/ZrO₂ System for the Hydrogenation of CO₂ to Methanol: A Density Functional Theory Study

Abstract

Zirconia-modified copper catalysts are being actively discussed to be beneficial in CO2/H2 conversion to methanol. The nature of the promotional effect of ZrO2 is still an intense matter of debate. Here, we report a density functional theory study investigating the CO2 hydrogenation reaction using a tetragonal ZrO2(101)-supported copper nanowire model of the copper–zirconia interface. We calculated adsorption energies of reactants and intermediates relevant for CO2 hydrogenation at different copper and zirconia adsorption sites. We suggest that in general adsorption at the Cu/ZrO2 interface and at zirconia facets is far too strong and that these sites will therefore be largely inactive for the hydrogenation of CO2 to methanol. We observe that adsorption at zirconia-supported copper sites further from the support is increased compared to that on unsupported Cu(111) and Cu(211) surfaces. We thus speculate that CO2 hydrogenation on these types of systems has the highest activity in close proximity to but not directly at the Cu/ZrO2 interface.

Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

“…The exact cause of the promotional effect of ZrO 2 is still vividly debated [14,15,17,[21][22][23]. Among the possibilities being discussed are an enhanced CO 2 adsorption by ZrO 2 [11], and an increased adsorption at the Cu-ZrO 2 interface [14,24] or at copper particles in close contact with the ZrO 2 support [25].…”

Copper–Zirconia Catalysts: Powerful Multifunctional Catalytic Tools to Approach Sustainable Processes

“…On this so positively charged Cu, which just for the sake of clarity must be in the form of very small nanoparticles or even clusters, the barrier of H 2 O dissociation is small, and the WGS reaction is enhanced [84]. Recently, Polierer et al [85] have found that the interphase, although critical, is not the adsorption site of the reactants and intermediates during the CO 2 hydrogenation. They have reported a volcano-shaped relation between the activity and the adsorption energy of various sites of a modelled Cu/ZrO 2 system ( Figure 5).…”

“…For instance, Azenha et al [94] have described a quite active CuPd catalyst on m-ZrO2 active at 180 °C ( Figure 6). Alternatively, CeO2 is introduced However, there is still debate on which is the precise role of each site and on which reaction pathway is the most favorable [52,60,[85][86][87]. Formate (HCOO) has been recognized in many studies as an intermediate during MS [88] and MSR alike (see below).…”

“…Theoretical activity volcano plot for the hydrogenation of CO 2 to methanol[85]. (https: //pubs.acs.org/doi/10.1021/acs.jpcc.9b06500).…”

CO2 hydrogenation to methanol: the structure–activity relationships of different catalyst systems

“…Both direct and indirect promotion of Cu by ZrO 2 has been suggested based on theoretical and experimental investigations. Polierer et al (2019) studied the Cu/ZrO 2 interface by density functional theory (DFT) calculations. Their results indicate that the intermediates bind too strongly on the ZrO 2 surface as well as on the Cu/ZrO 2 interface for further hydrogenation to methanol.…”