Abstract
Biomass-derived alcohols (bio-ethanol) and polyols (glycerol, glucose and other monosaccharides) represent a class of abundant, natural and fossil-free feedstocks that can be exploited as sustainable platform chemicals to obtain commodities such as 1-butanol and higher alcohols (to be used as second generation bio-fuel, lubricant and bio-based platform for pharmaceuticals) and to generate hydrogen (high density energy vector and reducing agent in chemical syntheses), respectively. The key issue is to achieve high productivities and selectivities to the desired products under mild conditions of temperatures and pressures using green reaction protocols, such as those achievable in the presence of suitable, tailored catalysts. The focus of the Project will thus be to design and apply, for the desired reactions, a small library of bifunctional and proton-responsive homogeneous dehydrogenation/hydrogenation catalysts, able to decrease the energy demand of the processes by metal-to-ligand cooperation and/or proton shuttling. The most active polyol dehydrogenation systems will be used as in situ H-sources for the reduction of CO2 and CO -shuttle derivatives (carbamates, ureas) to formates (used in silage and deicing) or methanol (fuel, solvent), to replace dangerous and expensive pressurized hydrogen gas. The complementary expertises of the two Research Units (RUs) in synthesis and characterization of earth-abundant and platinum group transition metal complexes, optimization of catalytic processes, analysis of reaction products and mechanistic studies by experimental and computational approaches will be integrated and shared to ensure a smooth flow of information and exchange of catalysts and data. The Project will constitute a well-defined advanced training ground in innovative fundamental and applied research for early-stage researchers, giving a unified vision of catalyst design and applicability, in the timely fields of green chemistry for biomass-derived feedstock valorization and sustainable CO reduction processes.
Results achieved
The outcomes of the Project improve the known state-of-the-art in Guerbet reaction chemistry for which UNIBO remains among the best developer up to date. Large interest by research community in the published (and under publication) work is expected. The most interesting finding of this Activity regards the possibility to change the basic co-catalyst, reducing the waste of the reaction. Microwave heating output also highlights the possibility to develop lower energy cost process, maintaining the same efficiency. Mechanistic insight on the Ru/NaOEt and Ru/NaOEt/BQ catalytic systems were obtained both with DFT calculation and experimental approach, paving the way to a fine tuning of the design for future catalytic systems. Promising catalytic results from heterogenization experiments, together with process scale-up, will boost the field of catalyst recycling, one of the main drawbacks that currently hamper process industrial applicability. Although iron complexes were not suitable for the Guerbet reaction, they were employed in other green reactions such as dehydrogenation of ammonia borane, electrocatalytic water oxidation and in the future for magnetic applications. Hydrogen production by glycerol acceptorless dehydrogenation with Earth-abundant metals such as manganese proved to be more challenging than with precious metal (Ru) counterparts. By fine-tuning the ligand structure, it was possible to obtain more robust systems, able to resist at high temperatures. More in-depth information from this ongoing study will allow to improve the catalytic efficiency and attempt scale-up and catalyst recycling. Carbon dioxide hydrogenation to formate was obtained with very good activity using Ru(0) and Ru(II) catalysts. The fundamental aspects of this research will guide in the design of more robust ligand systems for Fe and Mn, through collaborative work that is already in progress. For the highly challenging CO2 hydrogenation to methanol, the information obtained from this study suggests that more complex catalytic systems may be required to achieve significant activities, for example the use of tandem catalysis, that is planned for the forthcoming studies at CNR. With regard to the Guerbet reaction, if on one hand Earth abundant (Fe, Mn) complexes did not give the desired results, more in-depth studies on neutral ruthenium cyclopentadienone NHC ruthenium catalyst and his heterogeneous congener gave outstanding results due to the optimization of parameters and conditions, including: - the possibility to use Cs2CO3 as the basic co-catalyst to improve the selectivity of the reaction overcoming the Cannizzaro side reaction; - the possibility to use microwave heating to reduce the reaction time from 240 min to 10 min, maintaining comparable conversion and high selectivity in homologated alcohols with improvement in alcohols higher than C4; - the possibility to obtain key mechanistic insight on the Ru/NaOEt and Ru/NaOEt/BQ catalytic systems, revealing the role of both catalyst and co-catalyst, providing information for the fine tuning of the catalytic systems; - the possibility to obtain heterogenization of catalyst as a co-polymer catalyst endowed with the same catalytic activity as the homogenous parent compounds, but with the possibility to easily recover and reuse the catalyst; - the implementation of scale-up experiments, allowing validation of the process in up to 60 times higher volume in autoclave. With regard to the iron complexes, they were active in alternative processes, not originally planned, such as dehydrogenation of ammonia borane and water oxidation. The scientific results have been published in 5 publications and communicated in 16 conferences as oral or poster presentations. Moreover, 3 manuscripts are currently in preparation. Hydrogen production by glycerol acceptorless dehydrogenation was successfully achieved with unprecedented application of Ru-PN3P systems, with good activity and complete reaction selectivity, one of the major drawbacks of this process for practical applications. Promising preliminary results were recently obtained with a tailore Mn catalyst. These results will likely add more knowledge and important results to the growing body of research in the field of application of Earth-abundant metal complexes in catalytic reactions and pave the way for further fine tuning of ligand architecture. Carbon dioxide hydrogenation to formate was obtained in the presence of Ru(II) and Ru(0) catalysts thanks to collaborative work with top Italian research groups in the field of organometallic chemistry and catalysis. Very good catalytic performances were demonstrated, and important fundamental aspects were clarified by combined laboratory and in silico approaches that will be intensified beyond the ALCOVAL Project, to design more efficient catalysts by a deeper understanding of structurereactivity correlation. Innovative solutions for CO2 capture were also demonstrated. Finally, ESR formation and ToK objectives were successfully achieved, together with efficient dissemination of the Project results at various audiences, thanks also to the available means of communication (webinars, social media).Dettagli del progetto
Responsabile scientifico: Rita Mazzoni
Strutture Unibo coinvolte:
Dipartimento di Chimica Industriale "Toso Montanari"
Coordinatore:
CNR - Consiglio Nazionale delle Ricerche(Italy)
Contributo totale Unibo: Euro (EUR) 79.809,00
Durata del progetto in mesi: 24
Data di inizio
16/10/2023
Data di fine:
28/02/2026
