Metallurgical Residue-Derived Cu–ZnO-Based Catalyst for CO₂ Hydrogenation to Methanol: An Insight on the Effect of the Preparation Method

Abstract

Valorization of residual materials in the development of catalytic materials has an appealing potential from the perspective of a sustainable development. For the first time, Fe/Mg-containing metallurgical waste (UGSO) was utilized as a support for the development of innovative catalysts for CO2 hydrogenation into methanol. A series of different CuZn/UGSO catalysts were developed by conventional and modified deposition–coprecipitation methods. The addition of Cu/Zn into the structure of Fe3O4/MgxFe y O4 was found to improve Cu2+ and Zn2+ dispersion, while the presence of MgO favors methanol selectivity. Compared to 10Cu7.5Zn/UGSO (10 wt % Cu, 7.5 wt % Zn), the higher methanol yield obtained over 10Cu7.5Zn/UGSO–EtOH (10 wt % Cu, 7.5 wt % Zn, ethanol addition after coprecipitation) is a result of both higher CO2 conversion [attributed to (i) finer particle sizes of CuO and ZnO, (ii) a higher Cu0/Cu+ percentage, and (iii) higher oxygen vacancies and number of strong basic sites on the catalyst surface] and higher methanol selectivity [assigned to (i) the stronger interaction of Cu and ZnO and (ii) a higher number of medium basic sites] in comparison with its counterpart. This residue-based catalyst offers a 150% higher methanol yield than a commercial Cu-based methanol synthesis catalyst at 260 °C and 20 bar. These promising results can open a window to the utilization of this residue as a catalytic support in other CO2 hydrogenation processes.

New Insights on Catalytic Valorization of Carbon Dioxide by Conventional and Intensified Processes

“…In a recent work by Vu et al, the high activity of Cu/ZnO-based catalysts was partly attributed to the high dispersion of the Cu active phase within the mixed Fe and Mg oxide structure of the UGSO support (a metallurgical residue), which was further enhanced alongside the BET surface area after ZnO addition. 127 The choice of catalytic support can also have an impact on methanol production. It was supported by Choi et al that using a basic catalytic support such as AlOOH could lead to an increased methanol production compared to an acidic catalytic support (like Al 2 O 3 ) due to the presence of coordinated unsaturated O 2− ions that could facilitate CO 2 adsorption and activation.…”

“…Methanol production from CO 2 hydrogenation (Reaction ) is the result of an exothermic reaction that is thermodynamically favored at lower temperatures compared to the RWGS reaction, although these reactions compete with one another in the reaction environment. ,− normalC normalO 2 + 3 normalH 2 ⇔ normalC normalH 3 normalO normalH + normalH 2 normalO goodbreak0em1em⁣ normalΔ H = prefix− 49.2 .25em normalk normalJ / normalm normalo normall normalC normalO + 2 normalH 2 ⇔ normalC normalH 3 normalO normalH goodbreak0em1em⁣ normalΔ H = prefix− 90.4 .25em normalk normalJ / normalm normalo normall Methanol synthesis can also occur through the hydrogenation of CO (Reaction ), which could originate from the RWGS reaction as an intermediate step . However, the conversion of CO 2 into methanol through this pathway is actually very limited .…”

“…To improve their performance, Cu-based catalysts can be modified by the addition of several suitable promoters (e.g., ZnO, , In 2 O 3 ). In a recent work by Vu et al, the high activity of Cu/ZnO-based catalysts was partly attributed to the high dispersion of the Cu active phase within the mixed Fe and Mg oxide structure of the UGSO support (a metallurgical residue), which was further enhanced alongside the BET surface area after ZnO addition . The choice of catalytic support can also have an impact on methanol production.…”

“…Methanol production from CO 2 hydrogenation (Reaction ) is the result of an exothermic reaction that is thermodynamically favored at lower temperatures compared to the RWGS reaction, although these reactions compete with one another in the reaction environment. ,− Methanol synthesis can also occur through the hydrogenation of CO (Reaction ), which could originate from the RWGS reaction as an intermediate step . However, the conversion of CO 2 into methanol through this pathway is actually very limited .…”

“…As seen in Table , copper has been often employed as an active metal for methanol production from CO 2 hydrogenation. ,,,,,,, As introduced earlier, Cu-based catalysts are far more prone to sintering than Fe-based ones, which limits their utilization at high temperatures in the RWGS process, yet they are well suited for methanol synthesis favored by lower operating temperatures (usually below 400 °C). To improve their performance, Cu-based catalysts can be modified by the addition of several suitable promoters (e.g., ZnO, , In 2 O 3 ).…”