Cu/BNx catalysts for electrocatalytic reduction of nitrogen and nitrate waste

Author

Siming Huo, New Jersey Institute of TechnologyFollow

Document Type

Dissertation

Date of Award

5-31-2023

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical and Materials Engineering

First Advisor

Xianqin Wang

Second Advisor

Xiaoyang Xu

Third Advisor

Joshua Young

Fourth Advisor

Mengqiang Zhao

Fifth Advisor

Zafar Iqbal

Abstract

Ammonia (NH₃) is one of the most important chemicals to the whole human society. The invention of the Haber-Bosch process enabled the industrial production of NH₃. However, owing to the high capital costs of the centralized plant and the equipment and the negative environmental impact, it is no longer suitable for today's needs of human development. As a result, there is an urgent need to investigate sustainable approaches for ammonia production. Among those reported studies, nitrogen reduction (NRR) and nitrate reduction reaction (NO₃RR) are considered applicable in the future. However, after decades of studying them for years, the catalysts are still suffering from limited activity.

The main objective of this study is to develop a series of promising transition metal based single atom catalysts for NRR and NO₃RR. For the stabilization of metal atoms as the single atomic sites, porous boron nitride (BN_x) is used as the substrate. Catalysts with tuned metal loading and substrate porosity are synthesized by controlling the content of precursors in the synthesis process. First, different metals are screened for the optimized NH₃ productivity and obtain the highest NH₃ productivity of 118.3µg /h/mg_cat in NRR is obtained on the CuBN_x catalysts. Then the CuBN_x catalysts are studied in NO₃RR to further improve the NH₃ yield. The Lewis acidity and interaction between boron atoms and Cu atoms are the origin of the promising activity. Meanwhile, the catalysts are investigated using X-ray Absorption Spectroscopy (XAS), the XAS results confirm the formation of Cu single atomic sites by bonding with BN_x. With XAS and H₂H temperature programmed reduction, we prove the preference of higher oxidation states of Cu for NO₃RR. Thus, O₂ plasma is used to further improve the NH₃ production rate by increasing the oxidation state of Cu atoms of the single atomic sites. The highest NH₃ productivity in this work obtained is 4029 µg /h/mg_cat which is currently the highest productivity ever reported. A systemic study with different plasma treatment further confirms the interaction between Cu, BN and O species plays a key role for NRR and NO₃RR . However, a thorough understanding of the Cu-BN_x-O system, and NRR and NO₃RR reaction mechanisms are required for the future work in order to further improve NH₃ productivity.

Recommended Citation

Huo, Siming, "Cu/BNx catalysts for electrocatalytic reduction of nitrogen and nitrate waste" (2023). Dissertations. 1663.
https://digitalcommons.njit.edu/dissertations/1663