Ammonia on site: Separating charge generation from dark N2 reduction on tailored TiO2 aerogels

• Applicants: Professor Dr. Roland Marschall; Professorin Dr. Barbara Milow; Professor Dr. Dirk Ziegenbalg
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501591928

In this project, we will build on our previous work to systematically investigate the concept of a sustainable and inexpensive process for generating ammonia on-site. Having proven that high amounts of sunlight-charged electrons in synthetically tailored TiO₂ aerogels can be used to reduce N₂ to ammonia in the dark and having investigated reaction parameters and reactor concepts to optimize this process, we will now explore synthetic variations of TiO₂ aerogels to enhance the efficiency of photocharging and dark NRR processes. These will be compared to other nanostructures, such as TiO₂ nanofibers. Hybrid and hierarchical aerogels will be employed in particular, while doping and upscaling strategies will be investigated. Furthermore, we will develop our reactor concept further, as it has proven to be ideal for separating light harvesting and TiO₂ photocharging from dark NRR. The insights gained from our developed capillary reactor will be utilized here to improve light usage efficiency and minimize equipment costs. We will investigate using an oscillatory baffled flatbed reactor to increase the photonic efficiency of photocharging. Meanwhile, the process conditions will be systematically investigated and optimized by modelling support. Based on preliminary results, we will also compare gas-phase photocharging/NRR with liquid-phase processes. All materials will be carefully characterized in terms of photocharging and dark NRR conditions, wavelength and temperature dependence, and the use of waste organics as hole scavengers. Furthermore, TiO₂ nanofibers will be prepared by electrospinning and compared with aerogels. Photoelectrochemical investigations will further elaborate on the influence of nanostructure on photocharging and catalytic performance. In the final stages of the project, we will attempt to reduce N₂ and CO₂ simultaneously in the dark to form urea.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2370: Interlinking catalysts, mechanisms and reactor concepts for the conversion of dinitrogen by electrocatalytic, photocatalytic and photoelectrocatalytic methods (“Nitroconversion”)