(360af) Investigating the Electrocatalytic Reduction of 2,4,6-Tri-Nitro-Toluene (TNT) across Late Transition Metal Surfaces Using Density Functional Theory Methods

Remediation of 2,4,6-tri-nitro-toluene (TNT) to 2,4,6-tri-amino-toluene (TAT) is important in the application of environmental remediation, demilitarization efforts, and national security.¹ Electrocatalytic reduction of TNT is promising for these applications due to its potential to be an energy efficient process that operates at ambient reaction conditions. Recent experimental work investigating the reduction of TNT on Pd/Pt and glassy carbon electrodes (GCE) observed three distinct reduction peaks occurring at similar potentials across all electrodes, questioning the role of the electrocatalyst.² Lack of fundamental understanding of the elementary electrocatalytic mechanism inhibits the development of active TNT reduction electrocatalysts. We utilized DFT methods to determine the outer-sphere (non-catalyzed) and inner-sphere (catalyzed) elementary step mechanisms of TNT electrochemical reduction across late transition metal surfaces.

We observed that TNT reduction in the solution phase is inhibited by the initial reduction of the NO₂ group, where each subsequent reduction of the NO₂ group becomes more difficult. The non-catalyzed mechanism is potentially competitive for the reduction of the first NO₂ group when compared to the electrocatalytic reduction of TNT on the Fe (110) and Au (111) surfaces. Late transition metals for the electrocatalytic reduction of TNT are optimized by two activity tradeoff reactions: initial reduction of the adsorbed nitro species (NO₂-R*) and reduction of adsorbed hydroxyl species derived from TNT reduction (OH*). Using O affinity as the surface descriptor, we predict that late transition metal surfaces with intermediate binding of O*, such as Cu (111), and Pd (111), will exhibit higher activity towards TNT reduction. We extend our investigation to bimetallic and Fe₂O₃ (0001) surfaces as potential TNT reduction electrocatalysts.

References:

1. Ayoub, K., van Hullebusch, E. D., Cassir, M. & Bermond, A. Application of advanced oxidation processes for TNT removal: A review. Journal of Hazardous Materials 178, 10–28 (2010).
2. Soomro, R. A., Akyuz, O. P., Akin, H., Ozturk, R. & Ibupoto, Z. H. Highly sensitive shape dependent electro-catalysis of TNT molecules using Pd and Pd–Pt alloy based nanostructures. RSC Adv. 6, 44955–44962 (2016).