Towards solar fuels

Oriol Angurell Garreta - LEITAT Technological Center

In this chapter we will see a general overview of the NEFERTITI project, trying to understand the complexity and difficulty of the system and exploring the proposed solutions for such a big challenge. First, we will set-up the global scenario of photochemistry and the important role of CO2 nowadays with all the problems associated. After that, we will present the consortium of the project and see what is the role of each one.

Once the scenario has been set-up, the general objectives of the project will be presented. Finally, we will start overviewing and detailing the general methodology:

• Advantages of using continuous flow technology and the importance of combining it with photochemistry.

• The ability of the photocatalysts for the simultaneous CO2 reduction and H2O oxidation.

• The ability of the photocatalysts for CO reduction and C-C bond formation to obtain solar fuels.

• The power of light harvesting systems to increase the efficiency of the process.

  o Luminescent solar concentrators

  o Optical devices

• Integration and validation of the system.

  o Test both reactors for each transformation

  o Integrate both reactors and scale-it up x10

Kathryn McCarthy and Dr. Roberto González Gómez - University of Galway

"Photocatalysis: Enhanced photoactivity and improved stability: A case study on ruthenium-polypyridyl complexes"

Derivatives of the linear [Ru(dqp)2]2+ (dqp: 2,6-di(quinolin-8-yl)-pyridine) complexes hold significant promise due to their extended emission lifetime in the μs time scale while retaining comparable redox potential, extinction coefficients, and absorption profile in the visible region to [Ru(bpy)3]2+ (bpy:2,2′-bipyridine) and [Ru(tpy)2]2+ (tpy: 2,2′:6′,2″-terpyridine) complexes.

Nevertheless, its photostability in aqueous solution needs to be improved for its widespread use in photocatalysis. Carbon-based supports have arisen as potential solutions for improving photostability and photocatalytic activity, yet their effect greatly depends on the interaction of the metal complex with the support.

Herein, we present a strategy for obtaining Ru−polypyridyl complexes covalently linked to aminated reduced graphene oxide (rGO) to generate novel materials with long-term photostability and increased photoactivity.

Literature

1. Hennessey, S., González-Gómez, R., McCarthy, K., Burke, C. S., Le Houérou, C., Sarangi, N. K., ... & Farràs, P. Enhanced Photostability and Photoactivity of Ruthenium Polypyridyl-Based Photocatalysts by Covalently Anchoring Onto Reduced Graphene Oxide. ACS omega, 2024, 9(12), 13872-13882.

2. Sayama, K. Production of High-Value-Added Chemicals on Oxide Semiconductor Photoanodes under Visible Light for Solar Chemical-Conversion Processes. ACS Energy Lett. 2018, 3 (5), 1093− 1101.

3. Hennessey, S.; Farràs, P. Production of Solar Chemicals: Gaining Selectivity with Hybrid Molecule/Semiconductor Assemblies. Chem. Commun. 2018, 54 (50), 6662−6680.

4. Hübner, S.; de Vries, J. G.; Farina, V. Why Does Industry Not Use Immobilized Transition Metal Complexes as Catalysts? Adv. Synth. Catal. 2016, 358 (1), 3−25.

5. Hennessey, S.; Burke, C. S.; González-Gómez, R.; Sensharma, D.; Tong, W.; Amal; Kathalikkattil, C.; Cucinotta, F.; Schmitt, W.; Keyes, T. E.; Farràs, P. A Photostable 1D Ruthenium−Zinc Coordination Polymer as a Multimetallic Building Block for Light Harvesting Systems. ChemPhotoChem 2022, 6 (5), 1−7.

Kathryn McCarthy and Dr. Roberto González Gómez - University of Galway

Concerning levels of CO2 in the atmosphere have urged researchers to develop technologies that can not only reduce its atmospheric concentration, but also use CO2 as a feedstock for producing carbon-based fuels and value-added chemicals. Solar irradiation, a renewable and abundant source of energy, can be used to drive these chemical transformations in a process known as artificial photosynthesis. Recently, porous materials, such as covalent organic frameworks (COFs), have been explored as photo-responsive supports for catalysts due to their remarkable physical and chemical stability, structural diversity and large surface areas. Furthermore, through careful selection of building blocks, a wider photo-absorption window can be targeted, while also tuning the bandgap to extend the lifetime of electron-hole pair separation, thus establishing a thermodynamically favourable process.

The incorporation of metal catalysts, such as metal nanoparticles (MNPs), into these types of organic, photo-active supports creates a hybrid material which can facilitate redox reactions via an electron “donor-acceptor” type mechanism, i.e., electrons excited within the framework can be accepted by the MNP and subsequently used to carry out CO2 reduction.

Literature

1. Wang, H., Wang, H., Wang, Z., Tang, L., Zeng, G., Xu, P., ... & Tang, J. Covalent organic framework photocatalysts: structures and applications. Chemical Society Reviews, 2020, 49(12), 4135-4165.

2. Guo, K., Zhu, X., Peng, L., Fu, Y., Ma, R., Lu, X., ... & Fan, M. Boosting photocatalytic CO2 reduction over a covalent organic framework decorated with ruthenium nanoparticles. Chemical Engineering Journal, 2021, 405, 127011.

3. Galushchinskiy, A., González-Gómez, R., McCarthy, K., Farràs, P., & Savateev, A. Progress in development of photocatalytic processes for synthesis of fuels and organic compounds under outdoor solar light. Energy & Fuels, 2022, 36(9), 4625-4639.

4. Zhang, Y., Liu, H., Gao, F., Tan, X., Cai, Y., Hu, B., ... & Wang, X. Application of MOFs and COFs for photocatalysis in CO2 reduction, H2 generation, and environmental treatment. EnergyChem, 2022, 4(4), 100078.

5. Li, J., Yuan, H., Zhang, W., Jin, B., Feng, Q., Huang, J., & Jiao, Z. Advances in Z‐scheme semiconductor photocatalysts

Dr. Tiancheng Pu, Peking University

Conversion of syngas (including CO and H2) through heterogeneous catalytic routes to desired liquid fuels or valuable chemicals, including hydrocarbons and oxygenates, is of great significance for future energy sustainability. The source of syngas can be coal, biomass, natural gas (shale gas) as well as the photoreduction reaction of CO2. Traditional thermocatalytic FTS requires harsh reaction conditions including high temperature (230– 350 °C) and pressure (2–5 MPa), which results in massive energy consumption and carbon footprint. Meanwhile the chain length distribution of products represents a broad and non-selective, Anderson–Schulz–Flory (ASF) distribution.1 Recently, photocatalytic FTS have attracted significant research attention as an energy-efficient route towards value-added products.2,3 Develop new catalysts that can convert syngas through photocatalytic approaches to fuels with high solar efficiency and product selectivity is an ideal way to alleviate the dependence of petroleum.

Since C2+ alcohols generation with high selectivity is desired for NEFERTITI project, rhodium-based catalysts of interest. Nonetheless, in thermocatalysis, unpromoted rhodium catalyst favors CO methanation over oxygenate formation, the C2+ alcohol selectivity is typically below 20%.4,5 In the past decades, various strategies have been reported to improve the selectivity of oxygenates, especially C2+ alcohols over Rh based catalysts under thermocatalytic conditions.

Dr. Tiancheng Pu, Peking University

The role of PKU in NEFERTITI is synthesis and characterization of novel catalyst for converting syngas to C2+ alcohols through photocatalytic approach. Among all the modification strategies on Rh, confinement and adding promoters are the most effective ones. Mn, Fe, Li and La have been reported with the most significant improvements in C2+ alcohol selectivity.6,7.

We have first attempted the application of well-know RhMnLiFe catalyst embedded in carbon nanotubes (CNT) for photocatalytic ethanol production, which utilized the confinement effect of CNT as well as synergistic promoting effect of Mn, Li and Fe.8 Such a catalyst were among the best in ones used in thermocatalytic FTS processes and have demonstrate its capacity in photocatalytic syngas conversion to C2+ alcohols here in this project.

See additional resources:

The procedure for preparing such a catalyst is demonstrated in Figure 1 and reactor set up is demonstrated in Figure 2. The HNO3 treatment is essential to open the channel of CNT9 and allow RhMnLiFe particles to grow inside.

Dr. José Ignacio Lozano - Funditec (Fundación Tecnológica Advantx)

Anchoring provides important advantages in heterogeneous catalysis, but due to the catalyst and substrate have different chemical composition, properties and shape, it is necessary to define a combination of physical and chemical methods to make them compatible.

The objective of the chapter is to talk about the different anchoring techniques for a chemical catalyst and how they can be modulated depending on the nature of the catalyst and the substrates on which they should be supported.

Different aspect of the anchoring technique will be discussed, such as:

• Why anchor catalyst on substrates, advantages and limitations.

• The need of substrate preparation and the methods involved.

• Typical Anchoring elements and their functionalities.

• Catalysts deposition: different methods for the coating step

• Chemical/Physical characterization of achieved surfaces, techniques and some typical values for each one.

Anchoring techniques will be explained in three use cases, namely Organic catalyst, Organometallic catalysts and Inorganic catalysts. Finally, conclusions section will summarise the most important tips in the field.

Dr. Santiago Aparicio - University of Burgos

In silico methods are a valuable tool for researchers in diverse scientific fields, from chemistry and biology to materials science and beyond. This methodology involves the use of computer simulations and theoretical methods such as: Quantum Mechanics; Classical Mechanics and Statistical Mechanics to understand and predict the properties and behavior of chemical systems.1 The combination of experimental and in silico approaches can significantly boost research efficiency, accelerating the process of discovery and development in various scientific and technological field such as: drug discovery;2 materials science; catalyst design; environmental chemistry;3 reaction mechanism studies;4 spectroscopic property prediction;5 nanotechnology6 among others. The aim of this chapter is to show how a novel catalytic material type COFs (Covalent Organic Frameworks) proposed in the Nefertiti project can be developed and characterized by IR (Infrared Spectroscopy), and XRD (X-ray Diffraction) using molecular simulations.

Bibliography

(1) Alavi, S.: Molecular Simulations: Fundamentals and Practice, 2020. pp. 344.

(2) Awad, M. E.; Escamilla-Roa, E.; Borrego-Sánchez, A.; Viseras, C.; Hernández-Laguna, A.; Sainz-Díaz, C. I. Adsorption of 5-aminosalicylic acid on kaolinite surfaces at a molecular level. Clay Minerals 2019, 54, 49-56.

(3) Rozas, S.; Gutiérrez, A.; Atilhan, M.; Bol, A.; Aparicio, S. Understanding the CO2 capture potential of tetrapropylammonium-based multifunctional deep eutectic solvent via molecular simulation. Journal of Molecular Liquids 2024, 393, 123416.

(4) Iuga, C.; Vivier-Bunge, A.; Hernández-Laguna, A.; Sainz-Díaz, C. I. Quantum Chemistry and Computational Kinetics of the Reaction between OH Radicals and Formaldehyde Adsorbed on Small Silica Aerosol Models. The Journal of Physical Chemistry C 2008, 112, 4590-4600.

(5) Escamilla-Roa, E.; Hernández-Laguna, A.; Sainz-Díaz, C. I. Theoretical study of the hydrogen bonding and infrared spectroscopy in the cis-vacant polymorph of dioctahedral 2:1 phyllosilicates. J Mol Model 2014, 20, 2404.

(6) Aguilar, N.; Rozas, S.; Escamilla, E.; Rumbo, C.; Martel, S.; Barros, R.; Marcos, P. A.; Bol, A.; Aparicio, S. Theoretical Multiscale Study On the Properties, Aqueous Solution Behavior and Biological Impact of Zinc Oxide Nanoparticles. Surfaces and Interfaces 2024, 103965.

Dr. Charlotte Wiles - Chemtrix

Photocatalytic Flow Reactors!

As the size of a reactor increases, photocatalytic processes become challenging to scale, largely due to inefficient light introduction into the reaction media. In comparison, continuous flow reactors maintain a relatively small path length, even when their volume is increased & this allows photocatalytic processes to be scaled from the lab through to production scale.

Small-footprint, flexible, modular reaction units present an opportunity to disrupt conventional supply chains via strategies such as point-of-use production & just in time manufacturing. In addition, these small, turn-key units lend themselves to replication to scale output & since the location of such units does not need to be fixed, continuous manufacturing enables rapid deployment of manufacturing capabilities to new locations – particularly to those without conventional chemical manufacturing infrastructure.

Continuous flow reactors are part of the solution for the energy transition & increasing the sustainability associated with the production of key raw materials for the fine, specialty & pharmaceutical industries.

Key to any industrial shift is the formation of multi-disciplinary Teams, as is demonstrated throughout the NEFERTITI Project!

References:

• ‘Flow Photochemistry: Shine Some Light on Those Tubes’, C. Sambiagio & T. Noel, Trends in Chemistry, 2020, 2(2), 92-106.

• ‘Design & Characterization of Visible-light LED Sources for Microstructured Photoreactors’, A. Roibu, R. Morthala, M. Enis Leblebici, D. Koziek, T. Van Gerven & S. Kuhn, React. Chem. Eng., 2018, 3, 849-865.

• ‘Recent Advances Toward Sustainable Flow Photochemistry’, J. D. Williams & C. O. Kappe, Curr. Opin. Green & Sus. Chem., 2020, 100351. https://doi.org/10.1016/j.cogsc.2020.05.001

• ‘Scalability of Photochemical Reactions in Continuous Flow Mode’, K. Donnelly & M. Baumann, J. Flow Chem., 2021, 11, 223-241.

• www.chemtrix.com/flowchemistry

Dr. Eugenia Martínez Ferrero, Institute of Chemical Research of Catalonia (ICIQ)

Luminescent solar concentrators (LSC) are materials or optoelectronic devices that, upon sun irradiation, collect the light and re-emit it in the visible part of the electromagnetic spectrum. The materials have fluorescent properties and are therefore called fluorophores. These fluorophores are dispersed in host matrixes, usually based on polymers that do not interact neither chemically nor optically with the guest molecules. The host-guest mixture allows the deposition of the LSC onto the desired target device, where the reemitted visible light is needed. The efficiency of the LSC is determined by the photoluminescent quantum yield and the Stokes shift of the fluorophore. The synergy between the LSC and the target device is determined as well by the match between the emission spectrum of the fluorophore and the absorption spectrum of the target. In NEFERTITI, the target are the photocatalysts described in the previous chapters and the objective of the LSC is to collect a wide portion of the solar irradiation and emit in the wavelength regions where the photocatalyst are more efficient absorbers.

The objectives of the chapter are to provide a general overview of what luminescent solar concentrators are, including which are the figures of merit to determine their performance and examples of candidates to be used in NEFERTITI.

Recommended literature:

• “Luminescence solar concentrators: A technology update” Nano Energy 2023, Volume 109, 108269.

• “Luminescent solar concentrators with outstanding optical properties by employment of D–A–D quinoxaline fluorophores” J. Mater. Chem. C, 2021, 9, 15608.

• “Standardized reporting of power-producing luminescent solar concentrator performance“ Joule 2022, Volume 6, Issue 1, Pages 8-15.

• “The Hidden Potential of Luminescent Solar Concentrators” Adv. Energy Mater. 2021, 11, 2002883.

• “Towards Efficient Spectral Converters through Materials Design for Luminescent Solar Devices” Adv. Mater. 2017, 28, 1606491.

Paloma Ortiz Albo - Leitat Technological Center

Solar fuels, like hydrogen, ammonia, and ethanol, are synthetic chemical fuels produced from solar energy that potentially represent an ample supply of sustainable, storable and portable energy. The NEFERTITI project will develop an innovative highly efficient photocatalytic system that will simultaneously convert CO2 and H2O into solar fuels (ethanol). However, the ethanol produced requires a purification before it can be further processed. Pervaporation (PV) and vapor permeation (VP) allow the economic and efficient separation of azeotropic mixtures, specifically compared to more energetic intensive traditional separation processes such as evaporation and distillation. Pervaporation and vapor permeation are membrane-based separation technologies, using a thin, dense and permselective membrane. The separation of water-ethanol can be approached in two different ways: ethanol dehydration using hydrophilic membranes; or ethanol recovery using hydrophobic membranes.

Ethanol dehydration via pervaporation processes can be found integrated in industrial sites, where commonly polymeric PVA (poly(vinyl alcohol)) based membranes are used. On the other hand, organophilic membranes have been used to recover ethanol from diluted aqueous solutions. Different hydrophobic polymers such as PDMS (polydimethylsiloxane), POMS (Poly (octyl methyl siloxane)) or Pebax® (Polyether block amide) can be used for the development of selective layer for these organophilic membranes. However, the selective recovery of ethanol from water is still challenging due to the low membrane selectivity. Furthermore, membrane stability is also affected by the permeation of organic vapours, which inflict physical aging of the membrane.

Next generation membranes consider the incorporation of nanoparticles (NPs) to maximise the perm-selectivity. The combination of selective nanoparticles with a polymeric matrix constitutes a different type of membrane, called mixed-matrix membranes (MMMs). Different types of NPs can be classified in four categories depending on the filler dimensional properties: zero-, one-, two-, and three dimensions, such as traditional inorganic materials as silica and zeolites, or more recent and emerging as Metal-Organic Frameworks (MOFs), among others. Multiple combinations can be evaluated to improve the performance of pervaporation membranes. However, a crucial aspect in their viability and defect-free preparation are the homogenous dispersion of the filler in the polymeric matrix and the compatibility polymer/filler.

In NEFERTITI project, it is aimed to develop nanoparticle enhanced mixed matrix membranes for obtaining increased ethanol separation factors with acceptable permeation rates and good stability.

Celal G. Ogulgönen - SOCAR Türkiye Ar-Ge

This chapter is focused on setting up a TRL3-4 flow system, emphasizing the NEFERTITI demo unit, which is currently under development and expected to be operational in 2025. Firstly, we introduce the NEFERTITI project and highlight its innovative features and ambitious goals for the future of photochemical reactors and chemical production. We then present the general design approach of the NEFERTITI reaction system using a simplified flowchart. Through a step-by-step process, we describe the basic principles and thought processes involved in designing the demo unit. We also provide a basic process diagram to illustrate the partial results of the design approach. Finally, we discuss the main challenges encountered during the pre-design and design phases.

To summarize, this chapter explains the steps involved in setting up a TRL3-4 flow system, with a focus on the NEFERTITI demo unit. We introduce the NEFERTITI project, which aims to revolutionize photochemical reactors and chemical production. We then describe the general design approach of the NEFERTITI reaction system, followed by a step-by-step process of designing the demo unit. Finally, we discuss the main challenges faced during the pre-design and design stages.

Recommended literature (at least 5 references).

Peters, M. S., Timmerhaus, K. D., & West, R. E. (2006). Plant Design and Economics for Chemical Engineers. McGraw-Hill.

McConville, F. X. (2007). The Pilot Plant Real Book: A Unique Handbook for the Chemical Process Industry. FXM Engineering and Design.

Walas, S. M. (2012). Chemical Process Equipment: Selection and Design. BH, Butterworth-Heinemann, an imprint of Elsevier.

YouTube. (2020, December 1). Process Equipment Design. YouTube. https://www.youtube.com/playlist?list=PLneTajpJ8kXCasXFwpEW3jmDAyLEwUrzX

Green, D. W., & Southard, M. Z. (2019). Perry’s Chemical Engineers’ Handbook. McGraw Hill Education.

Natalia Fernández y Mario Santiago Herrera - ICCRAM University of Burgos

The European Commission has proposed a framework to define Safe and Sustainable by Design (SSbD) criteria for chemicals and materials to achieve the Green Deal ambitions.

The SSbD framework includes the dimensions, aspects, methods and indicators to evaluate chemicals and materials, and also how to define the criteria in order to identify those chemicals and materials that are SSbD.

Moreover, it considers a (re)-design phase in which the design of the chemicals and materials is based on safety, environmental and socio-economic sustainability principles. The safety and sustainability assessment consists of five steps. The first three steps assess safety aspects: Step 1 is related to the hazard properties, Step 2 is about human health and safety aspects in the chemical / material production and processing phase, and Step 3 considers the human health and environmental effects in the final application phase. Step 4 evaluates the impacts along the entire chemical / material life cycle and Step 5 assess socio-economic aspects.

The information contained in the SSbD framework is employed in the development of guidelines and recommendations for Safe and Sustainable by Design.

References:

• Caldeira, C., Farcal, L., Moretti, C., Mancini, L., Rauscher, H., Rasmussen, K., Riego Sintes, J.,Sala, S. (2022). Safe and Sustainable by Design chemicals and materials - Review of safety and sustainability dimensions, aspects, methods, indicators, and tools. EUR 30991, Luxembourg (Luxembourg): Publications Office of the European Union, 2022, ISBN 978-92-76-47560-6

• Bjørn, A., Chandrakumar, C., Boulay, A.M., Doka, G., Fang, K., Gondran, N., Hauschild, M.Z., Kerkhof, A., King, H., Margni, M., McLaren, S., Mueller, C., Owsianiak, M., Peters, G., Roos, S., Sala, S., Sandin, G., Sim, S., Vargas- Gonzalez, M., Ryberg, M. (2020). Review of life-cycle based methods for absolute environmental sustainability assessment and their applications. Environmental Research Letters 15, 083001. https://doi.org/10.1088/1748- 9326/AB89D7

• Corona, B., Shen, L., Reike, D., Rosales Carreón, J., Worrell, E. (2019). Towards sustainable development through the circular economy—A review and critical assessment on current circularity metrics. Resources, Conservation and Recycling 151, 104498. https://doi.org/10.1016/j.resconrec.2019.104498

• Croes, P. R., Vermeulen, W. J. V. (2019). Quantification of corruption in preventative cost-based S-LCA: a contribution to the Oiconomy project. International Journal of Life Cycle Assessment. https://doi.org/10.1007/s11367-018-1507-z