Solid-state interactions, adsorption sites and functionality of Cu-ZnO/ZrO2 catalysts in the CO2 hydrogenation to CH3OH

Hydrogen Utilization in Green Fuel Synthesis via CO2 Conversion to Methanol over New Cu-Based Catalysts

“…By contrast, the system with no CeO2 (CuZn_CZ_100) shows the highest exposure of total surface (~154 m 2 •g −1 ) and the lowest decay for the reduction treatment (ΔSA = 14%), confirming the strong effect of zirconia as structural promoter ( Figure 1). Indeed, along the replacement of Ce ions in the lattice, the total surface area As reported in our previous work [30][31][32], catalyst activation consists in a controlled reduction to obtain active metallic copper. The action of temperature and H 2 for oxygen removal (MeO x + xH 2 → xH 2 O; Me = Cu and Ce) leads to the reconstruction of catalyst which can also drive to a higher crystallization with a consequent loss of total surface area (sintering).…”

“…Indeed, a remarkable rise of both total and metallic surface area was reported with a consequent increase of the copper-zinc oxide interfacial area, accompanied by an also improved resistance to sintering due to the activation procedure (reduction). As reported in our previous work [30][31][32], catalyst activation consists in a controlled reduction to obtain active metallic copper. The action of temperature and H2 for oxygen removal (MeOx + xH2 → xH2O; Me = Cu and Ce) leads to the reconstruction of catalyst which can also drive to a higher crystallization with a consequent loss of total surface area (sintering).…”

“…The action of temperature and H 2 for oxygen removal (MeO x + xH 2 → xH 2 O; Me = Cu and Ce) leads to the reconstruction of catalyst which can also drive to a higher crystallization with a consequent loss of total surface area (sintering). On this address, the effects of the activation procedure were fully investigated in our previous works [30][31][32].…”

“…In catalysis, "Activation Energy" counts for the energy that must be supplied to catalyst to observe any chemical reaction. On this account, a further evaluation of the effects of carrier composition on the catalytic functionality of Cu-ZnO systems can be done comparing the values of Apparent Activation Energy (E app (kJ·mol −1 )), obtained from the Arrhenius's plot of differential conversion data at 0.1 MPa (X H 2 < 10%, T = 453-513 K), reported in Figure 3 [30,31,38]. Indeed, the progressive increase of CeO 2 content leads to a decrease in E app value from 97 kJ·mol −1 of CuZn_CZ_0 sample to 26 kJ·mol −1 of CuZn_CZ_100 system, as proof of the promoter effect of ceria.…”

“…Several metal oxides are reported in literature for improving the catalytic performance of copper-based catalysts, in term of activity, selectivity, and stability [24][25][26][27][28][29], also enhancing CO 2 adsorption with respect to un-promoted systems. In particular, in our previous works [30][31][32][33][34], we disclose the positive effects of ZrO 2 on the catalytic performance of Cu-ZnO catalyst with respect to that of Al 2 O 3 -supported, as a result of the lower hydrophilic nature of ZrO 2 than Al 2 O 3 , which facilitates water desorption, and its property of stabilizing Cu + -O species, which favor CO 2 adsorption/activation and methanol selectivity. Then, in more recent studies, we have clearly assessed that ZrO 2 affects structure/morphology and texture of Cu-ZnO based catalysts, while cerium oxides can divalently act as an electronic promoter and improver of surface functionality of Cu phase [33,34].…”