Photocatalytic-assisted production of ammonia using Fe 3 O 4 /g-C 3 N 4 hybrid materials José M. Monteiro 1,2 , Joana C. Lopes 1,2 , Rita A.M. Barros 1,2 , Amala Joy 1,2 , Maria J. Sampaio 1,2 , Joaquim L. Faria 1,2 , Cláudia G. Silva 1,2 1 LSRE-LCM – Laboratory of Separation and Reaction Engineering - Laboratory of Catalysis and Materials, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal, 2 ALiCE - Associate Laboratory in Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal Background & Aim: Ammonia stands as one of the most significant chemicals in industry, which is primarily used in fertilizer manufacturing, a crucial process for maintaining the world food supply [1] . The search for renewable energy sources to replace fossil fuels has become a major societal focus, driven by concerns over environmental harm, particularly carbon emissions. However, progress toward sustainable and economically viable alternatives remains challenging. Ammonia offers potential as an energy carrier, serving as an effective hydrogen transporter with high volumetric density and the ability to be easily liquefied [1,2] . With an energy density of approximately 18.6 MJ/kg and containing 17.8 % hydrogen by weight, ammonia can store hydrogen more efficiently than compressed hydrogen itself [1] . Additionally, ammonia liquefies at moderate pressure (8.6 bar at 20°C) or at -33°C under atmospheric pressure, facilitating storage and transportation [1] . Currently, the Haber-Bosch process remains the leading industrial method for ammonia synthesis, accounting for over 96% of global production [3] . Yet, this traditional process depends on highly energy-intensive methane sources and results in significant CO 2 emissions [4] . The scope of this work is to investigate heterogeneous photocatalysis as an alternative to sustainably produce ammonia from renewable resources including atmospheric nitrogen, water, heterogeneous catalysts, and, ideally, sunlight to drive the reaction. Methods: Pristine and exfoliated graphite-like carbon nitride (g-C3N4) catalysts, each modified with varying iron oxide (Fe 3 O 4 ) loadings, were synthesized and characterized using a range of textural, microscopic, and spectroscopic methods. The photocatalytic performance of these catalysts was tested under 420 nm light irradiation. Results: Catalyst performance was evaluated in batch reactions with different scavengers. The efficiency was evaluated in terms of the amount of ammonia generated.Future work will involve assessing the reusability of top- performing materials and investigating their immobilization on fixed substrates for continuous operation. Conclusions: Hybrid materials composed of graphitic carbon nitride and iron oxide have been produced.Their activity toward photocatalytic ammonia production is under assessment. Acknowledgements: This work was supported by project 2022.04682.PTDC - SuN2Fuel - Photo-assisted production of green ammonia-based fuels - (DOI: 10.54499/2022.04682.PTDC). This research was also supported by Fundação para a Ciência e a Tecnologia, I.P. /MCTES through national funds: LSRE-LCM, UID/50020; and ALiCE, LA/P/0045/2020 (DOI: 10.54499/LA/P/0045/2020). MJS acknowledges FCT funding under the Scientific Employment Stimulus - Institutional Call (DOI:10.54499/CEECINST/00010/2021/CP1770/ CT0011). AJ and RAMB acknowledge the FCT scholarships with reference 2023.02602.BD and 2022.12055.BD, respectively. JMM thanks Fundação Calouste Gulbenkian for his scholarship (Gulbenkian Talents Programme). References 1. Sharma, K.; Kumar, A.; Yadav, V.; Banerjee, D.K. " Green Ammonia: The Future of Clean Energy. " Book Saga Publications , 2025. ISBN: 978-93-6726-959-6. 2. Levikhin, A. A.; Boryaev, A. A. "Low-Carbon Ammonia-Based Fuel for Maritime Transport." Results in Engineering , Vol.25. 2025. 3. Juangsa, F.B.; Irhamna, A.R. "Production of Ammonia as Potential Hydrogen Carrier: Review on Thermochemical and Electrochemical Processes." International Journal of Hydrogen Energy , Vol.46 (27). 2021 4. Humphreys, J.; Lan, R.; Tao, S. "Development and Recent Progress on Ammonia Synthesis Catalysts for Haber–Bosch Process." Advanced Energy and Sustainability Research , Vol 2(1).2021.
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