Gabriela Kopacka

This paper demonstrates the successful synthesis of novel hybrid heterogeneous catalysts for the sustainable conversion of CO₂ into cyclic organic carbonates (COCs). The nanocat-alysts have been fabricated by encapsulating pre-formed ultra-small gold nanostructures into a nascent zinc-coordination polymer (ZnCP) framework formed from two organic building blocks, 2,4-naphthalenedicarboxylic acid (1,4-NDC) and 5-amino-1H-tetrazole (5-Atz), which serves as a nitrogen-rich ligand. Applying the fabricated catalysts in the synthesis of COCs yields high yields (up to 97%) and high selectivity (up to 100%), with exceptionally high turnover frequencies (TOFs) (up to 408 h⁻¹). The catalytic process can be carried out under mild conditions (80 °C, 1.5 MPa CO₂) and without the use of solvents. Nitrogen-rich ligand molecules in the structure of ZnCPs enhance catalytic performance thanks to additional nucleophilic centres, which are effective in the epoxides’ ring-opening process. The hybrid catalysts with encapsulated gold nanostructures, which modify the liquid–gas interface between epoxide and CO₂, give significantly higher yields and TOFs for less active epoxides. The designed hybrid nanocatalysts exhibit superior stability under the studied reaction conditions and can be reused without loss of activity. The developed coordination polymers are constructed from green components, and green chemistry principles are applied to prepare these catalytic materials.

This paper demonstrates the successful synthesis of novel hybrid heterogeneous catalysts for the sustainable conversion of CO2 into cyclic organic carbonates (COCs). The nanocat-alysts have been fabricated by encapsulating pre-formed ultra-small gold nanostructures into a nascent zinc-coordination polymer (ZnCP) framework formed from two organic building blocks: 2,4-naphthalenedicarboxylic acid (1,4-NDC) and 5-amino-1H-tetrazole (5-Atz), which serves as a nitrogen-rich ligand. Applying the fabri-cated catalysts in the synthesis of COCs yields high yields (up to 97%) and high selectivity (up to 100%), with exceptionally high turnover frequencies (TOFs) (up to 408 h-1). The cat-alytic process can be carried out under mild conditions (80°C, 1.5 MPa CO2) and without the use of solvents. Nitrogen-rich ligand molecules in the structure of ZnCPs enhance catalytic performance thanks to additional nucleophilic centres, which are effective in the epoxides' ring-opening process. The hybrid catalysts with encapsulated gold nanostructures, which modify the liquid-gas interface between epoxide and CO2, give significantly higher yields and TOFs for less active epoxides. The designed hybrid nanocatalysts exhib-it superior stability under the studied reaction conditions and can be reused without loss of activity. The developed coordination polymers are built of green components, and green chemistry principles are employed to prepare these catalytic materials.

The fixation of carbon dioxide with epoxides is one of the most attractive methods for the green utilisation of this greenhouse gas and leads to many valuable chemicals. This process is characterised by 100% atom efficiency; however, an efficient catalyst is required to achieve satisfactory yields. Metal–organic frameworks (MOFs) are recognised as being extremely promising for this purpose. Nevertheless, many of the proposed catalysts are based on ions of rare elements or elements not entirely safe for the environment; this is notable with commercially unavailable ligands. In an effort to develop novel catalysts for CO₂ fixation on an industrial scale, we propose novel MOFs, which consist of aluminium ions coordinated with commercially available 1,4-naphthalene dicarboxylic acid (Al@NDC) and their nanocomposites with gold nanoparticles entrapped inside their structure (AlAu@NDC). Due to the application of 4-amino triazole and 5-amino tetrazole as crystallization mediators, the morphology of the synthesised materials can be modified. The introduction of gold nanoparticles (AuNPs) into the structure of the synthesised Al-based MOFs causes the change in morphology from nano cuboids to nanoflakes, simultaneously decreasing their porosity. However, the homogeneity of the nanostructures in the system is preserved. All synthesised MOF materials are highly crystalline, and the simulation of PXRD patterns suggests the same tetragonal crystallographic system for all fabricated nanomaterials. The fabricated materials are proven to be highly efficient catalysts for carbon dioxide cycloaddition with a series of model epoxides: epichlorohydrin; glycidol; styrene oxide; and propylene oxide. Applying the synthesised catalysts enables the reactions to be performed under mild conditions (90 °C; 1 MPa CO₂) within a short time and with high conversion and yield (90% conversion of glycidol towards glycerol carbonate with 89% product yield within 2 h). The developed nanocatalysts can be easily separated from the reaction mixture and reused several times (both conversion and yield do not change after five cycles). The excellent performance of the fabricated catalytic materials might be explained by their high microporosity (from 421 m² g⁻¹ to 735 m² g⁻¹); many catalytic centres in the structure exhibit Lewis acids’ behaviour, increased capacity for CO₂ adsorption, and high stability. The presence of AuNPs in the synthesised nanocatalysts (0.8% w/w) enables the reaction to be performed with a higher yield within a shorter time; this is especially important for less-active epoxides such as propylene oxide (two times higher yield was obtained using a nanocomposite, in comparison with Al-MOF without nanoparticles).