Description
Ammonia, primarily used in agriculture as the main feedstock for fertiliser production, is gaining attention as a potential energy carrier across various sectors. As demand continues to grow, there is a strong need for alternative production routes that enable decentralised, more sustainable, small-scale synthesis under milder conditions. Non-thermal plasma reaction systems have been widely researched for this purpose due to their ability to generate reactive species even at ambient conditions and their short response times, which make them suitable for operation with intermittent energy sources.[1] The main drawback of plasma-catalytic ammonia production systems has been low energy efficiency, mainly caused by ammonia dissociation in the plasma region. To overcome this limitation, many micro- and mesoporous materials have been used as catalyst supports. Plasma formation is limited to pores with diameters greater or equal to the Debye length.[2] Since the threshold diameter for DBD plasmas is usually larger than the pore size of these materials, ammonia produced inside the porous framework can be shielded from dissociation in the plasma.[3] However, the diffusion of ammonia into the porous framework may not be as pronounced in a typical DBD reactor system, where the temperature in the discharge region can exceed 100°C. To take advantage of the shielding effect at such temperatures, zeolite acidic sites could be employed to adsorb ammonia. Zeolite 4A[4], and alumina-modified SBA-15[2] have been tested so far, while adsorbed ammonia has been recovered by temperature-programmed desorption.
It has been demonstrated in this study that the catalytic performance in sorption-enhanced DBD plasma-catalytic ammonia synthesis is strongly governed by the properties of the porous support. By comparing the performance of pristine MCM materials as well as their NiO supported catalysts, the correlation of catalytic activity with porous structure, active phase location, and surface acidity of the support has been demonstrated. Finally, power-swing experiments have been employed as an alternative to temperature-programmed desorption of ammonia in sorption-enhanced plasma-catalytic ammonia synthesis.
References
1 L. R. Winter and J. G. Chen, Joule, 2021, 5, 300–315.
2 S. E. Arumuganainar, S. Sartzetakis, C. W. Hullfish, B. E. Koel and M. L. Sarazen, Energy & Fuels, 2024, 38, 23150–23166.
3 Y. Wang, W. Yang, S. Xu, S. Zhao, G. Chen, A. Weidenkaff, C. Hardacre, X. Fan, J. Huang and X. Tu, J. Am. Chem. Soc., 2022, 144, 12020–12031.
4 K. H. R. Rouwenhorst, S. Mani and L. Lefferts, ACS Sustain. Chem. Eng., 2022, 10, 1994–2000.