Abstract
The growing atmospheric CO2 concentration calls for urgent action for CO2 capture in hard-to-abate industries and its use in combination with renewable energy or greenH2 for energy storage and production of liquid fuels. In this field catalytic reduction of CO2 to methanol, electro or photoelectroreduction of CO2 into liquid products (alcohols, acids which can be further converted to alcohols using H2) are key process even if they have not yet achieved results suitable for their industrial development. Here the development of a catalyst able to synergistically combining and tailoring the CO2 interaction and conversion is crucial. The unique properties of layered double hydroxides (LDH) structures in CO2 adsorption (related to basicity and high dynamic exchange rate of CO2 inside the interlayer) and their preparation flexibility (able to tailor CO2 converting active phases) can represent a breakthrough for CO2 conversion systems. Therefore, the project aims to study the interaction between CO2 and LDH and to develop catalyst and process for CO2 reduction to MeOH at high temperature and pressure and electro and photoelectro CO2 reduction routes for green fuels production in gas and liquid phases at low temperature. The project also opens the field for conversion of CO2 in diluted stream such as the one derived by direct air capture. LDHs are materials composed by inter-dispersed M2+ and M3+ cationic hydroxide nanosheets alternated with anionic layers with (Figure 1). They are very versatile materials and most M2+ and M3+ transition metals (with some M+ and M4+ also reported) and anions can be inserted (usually CO32- but also other anions which can increase the layer height and modify the thermal evolution). They can be fine-tuned in the structure giving versatile properties as such or high surface area of the derived mixed oxides obtained by calcination and reduction of LDH to oxide and metal nanoparticles. Specifically, Cu eventually combined or partially substituted with Fe, Ni or Ga depending of the tested reaction can be used as active phase. In recent years, the LDH interlayer have been also used to accommodate active phases, increasing the contact with carbonates. Finally LDH structure can be reformed on mixed oxide surface in the presence of CO2 and H2O matching the advantages of combining the formation of high surface area and basic sites of the oxide with dynamic interaction with CO2 of LDH. Notably, LDH reformation is favored in the reaction conditions used for the processes selected in the project (i.e. presence of CO2 and H2O at r.t. or at 200-300°C and high pressure). The aim of the project is i) to deepen the study of the CO2-material interaction and reactivity, ii) to use the knowledge and the unique properties of LDH to develop advanced catalysts for the three processes. iii) to define the process conditions to maximize the fuel production iv) to prove the possibility of converting CO2 during direct air capture.
Results achieved
The CO2CoReAtLaSt project successfully achieved its scientific and technological objectives, contributing significantly to the development of new strategies for CO₂ capture and utilization using innovative materials based on Layered Double Hydroxides (LDHs). Research activities deepened the understanding of the fundamental mechanisms governing the interaction between carbon dioxide and LDH materials and translated this knowledge into the development of advanced catalytic systems to produce renewable fuels and chemicals. One of the project's most significant results involves the design and synthesis of an extensive library of LDH materials, characterized by precisely tuned compositions and containing various combinations of active metals. Controlled co-precipitation procedures yielded Mg-Al, Mg-Fe, Mg-Al-Fe, Cu-Mg-Al, Cu-Mg-Fe, and Cu-Zn-Al based materials, as well as systems promoted with gallium and zirconium. The versatility of the developed synthetic methodology allowed for the simultaneous incorporation of multiple metal elements while preserving the characteristic lamellar structure of LDHs and ensuring high control over structural and surface properties. Comprehensive physicochemical characterization activities provided insight into the role of material composition regarding CO₂ adsorption and activation capacity. Analyses, including X-ray diffraction, BET surface area measurement, thermogravimetric analysis, CO₂ temperature-programmed desorption, and temperature-programmed reduction techniques, revealed how varying the ratios of the different metals profoundly influences the distribution of basic sites and the strength of the interaction with carbon dioxide. A scientific result of particular interest concerns the systematic study of the so-called "memory effect" of LDHs. It has been demonstrated that, following calcination and the resulting transformation into mixed oxides, these materials are capable of reconstructing their original layered structure when exposed to atmospheres containing CO₂ and moisture. Structural analyses revealed a progressive reconstruction of the LDH phase as exposure time to the CO₂/H₂O mixture increased, confirming the high structural adaptability of these materials and their ability to interact dynamically with carbon dioxide. This behavior is of great interest for future applications in CO₂ capture and conversion processes. The project also enabled the identification of direct correlations between chemical composition, the distribution of basic sites, and catalytic performance. In Mg-Al and Mg-Al-Fe systems, it was demonstrated that the presence of aluminum significantly increases CO₂ adsorption capacity within the temperature range most favorable for methanol synthesis, while the introduction of iron modifies the nature of surface sites by introducing redox properties that can influence CO₂ molecule activation. The results obtained in the development of catalysts for the hydrogenation of CO₂ to methanol were particularly significant. LDH-derived materials belonging to the Cu-Zn-Al family, including those promoted with gallium and zirconium, exhibited superior properties compared to conventional catalysts. Studies on reducibility and copper dispersion highlighted how the LDH-derived structure promotes a better distribution of active species and more effective interaction between the metal phase and the support. Catalytic tests conducted in a high-pressure reactor confirmed the effectiveness of the developed approach. Catalysts CZA3 and CZAG3 demonstrated high performance in CO₂ conversion, achieving methanol yields exceeding 5%, a value identified as a key performance indicator for the project. Even more significant was the improvement in methanol selectivity compared to reference catalysts. Indeed, the LDH-derived materials significantly limited the reverse water-gas shift reaction—responsible for the unwanted formation of carbon monoxide, thereby enabling greater overall efficiency in the CO₂ conversion process. Alongside the heterogeneous catalysis activities, the project successfully developed new electrodes for electrochemical and photoelectrochemical applications. By integrating the expertise of the University of Bologna and CNR-ISMMC, two distinct preparation strategies were developed: screen-printing deposition of synthesized powder materials and direct electrodeposition of LDHs onto conductive substrates. The developed electrodeposition method yielded homogeneous, reproducible coatings with material loadings exceeding the initial targets. Structural and morphological characterization confirmed the formation of continuous, well-adhered films featuring the simultaneous presence of the LDH structure and copper nanoparticles active for CO₂ reduction. Electrocatalytic performance tests revealed a clear advantage of LDH-based electrodes over analogous systems composed solely of copper nanoparticles. The new materials demonstrated superior Faradaic efficiencies and higher yields of high-value-added products, such as alcohols and carboxylic acids. This result confirms the fundamental role of the layered structure in increasing the local CO₂ concentration near active sites and facilitating the electron transfer processes required for its reduction. A further milestone was achieved in the field of photoelectrochemical CO₂ conversion. By modulating the composition and electronic properties of the LDHs, it was possible to produce photocathodes capable of utilizing light energy to drive the formation of CO₂ reduction products. In particular, CuMg-LDH-based materials showed highly promising performance, enabling the selective production of higher-carbon compounds and demonstrating the potential of using a single material as a multifunctional photocathode. The project's scientific impact is evidenced by the publication of findings in prestigious international journals and their presentation at numerous international conferences. Dissemination activities helped boost the visibility of Italian research in the CO₂ valorization sector and fostered the establishment of new scientific collaborations. Overall, the CO2CoReAtLaSt project demonstrated that integrating the CO₂ adsorption properties characteristic of LDHs with specifically designed catalytic phases is an effective strategy for enhancing the activity, selectivity, and stability of carbon dioxide conversion processes. The results provide a solid scientific and technological foundation for future industrial developments in the sustainable production of fuels and chemicals from CO₂, making a tangible contribution to the climate neutrality and circular economy goals promoted at both national and European levels.Project details
Unibo Team Leader: Francesco Basile
Unibo involved Department/s:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinator:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Total Eu Contribution: Euro (EUR) 199.147,00
Total Unibo Contribution: Euro (EUR) 132.000,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
