Advancing nitrate reduction to ammonia: insights into mechanism, activity control, and catalyst design over Pt nanoparticle-based ZrO2

Abstract

The reduction of nitrogen oxides (NO_x) to NH₃, or N₂ represents a crucial step in mitigating atmospheric NO₃ and NO₂ emissions, a significant contributor to air pollution. Among these reduction products, ammonia (NH₃) holds particular significance due to its utility in nitrogen-based fertilizers and its versatile applications in various industrial processes. Platinum-based catalysts have exhibited promise in enhancing the rate and selectivity of these reduction reactions. In this study, we employ density functional theory (DFT) calculations to explore the catalytic potential of Pt nanoparticle (PtNP)-supported ZrO₂ for the conversion of NO₃ to NH₃. The most favorable pathway for the NO₃ reduction to NH₃ follows a sequence, that is, NO₃ → NO₂ → NO → ONH → ONH₂/HNOH → NH₂/NH → NH₂ → NH₃, culminating in the production of valuable ammonia. The introduction of low-state Fe and Co dopants into the ZrO₂ support reduces energy barriers for the most challenging rate-determining hydrogenation step in NO_x reduction to NH₃, demonstrating significant improvements in catalytic activity. The incorporation of dopants into the ZrO₂ support results in a depletion of electron density within the Pt cocatalyst resulting in enhanced hydrogen transfer efficiency during the hydrogenation process. This study aims to provide insights into the catalytic activity of platinum-based ZrO₂ catalysts and will help design new high-performance catalysts for the reduction of atmospheric pollutants and for energy applications.