(685e) Understanding the Influence of Photo-Thermal Inputs on Ammonia Synthesis Via Drifts

Photocatalysis is able to produce small amounts of ammonia at ambient conditions in batch reactors, providing a promising alternative to the energy-intensive Haber-Bosch process.¹ Still, improvements in ammonia yields are necessary for photocatalysis to become a more feasible alternative to fossil-fuel driven ammonia production.¹ Coupling solar radiation with thermal inputs is a possible strategy to overcome high activation energy barriers, facilitate more appreciable rates of NH₃ synthesis at moderate temperatures and pressures, and split water for the hydrogen feedstock. To inform the design of catalysts with sufficient activity, a more complete understanding of the reaction pathway is critical. Specifically, deeper insight into the nitrogen reduction pathway can help advance solar-thermal nitrogen fixation yields and eventually deploy distributed, low-emission ammonia synthesis systems in resource-constrained communities.

Previous works have used light and heat inputs to increase the production rate of NH₃ and CH₄ on Ru/TiO₂ during batch reactor experiments.^1,2 Although production rates are quantifiable, it remains difficult to gain a clear picture of reaction mechanisms in these experiments. To address this challenge, in situ diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS) is a helpful tool that can elucidate surface species by their vibrational modes.

We leverage DRIFTS to monitor the transformation of reaction intermediates over Ru/TiO₂ while tuning light and temperature inputs. After establishing a DRIFTS protocol using CO₂ hydrogenation to CH₄ as a model system, we study the effect of light inputs on adsorbed surface species during N₂ reduction to NH₃. In this way, DRIFTS can help understand how sunlight and heat synergistically affect NH₃ formation over Ru/TiO₂. Equipped with this knowledge, we can potentially engineer superior photocatalysts to harness sunlight and deliver decentralized, green-ammonia to resource-constrained communities.

References

[1] Lim, J., et.al. ACS Catal. (2017)

[2] Novoa-Cid, M., et.al. J. Nanomater. (2020)