Progress of Metal Oxide (Sulfide)-Based Photocatalytic Materials for Reducing Nitrogen to Ammonia

Jianjun Yang

doi:10.1155/2018/3286782

Abstract

The Haber–Bosch process has been an important approach to produce ammonia for meeting the food need of increasing population and the worldwide need of nitrogenous fertilizers since 1913. However, the traditional ammonia production process is a high energy-consumption process, which usually produces 1 metric ton ammonia with releasing around 1.9 metric tons CO2. Photocatalytic ammonia synthesis under solar light as energy source, an attractive and promising alternative approach, is a very challenging target of reducing fossil energy consumption and environmental pollution. Therefore, photocatalytic ammonia production process would emerge huge opportunities by directly providing nitrogenous fertilizers in a distributed manner as needed in the agricultural fields. In this article, different metal oxide (sulfide)-based photocatalytic materials for reducing nitrogen to ammonia under ambient conditions are reviewed. This review provides insights into the most recent advancements in understanding the photocatalyst materials which are of fundamental significance to photocatalytic nitrogen reduction, including the state-of-the-art, challenges, and prospects in this research field.

Highlights

As the important chemicals to our planet, nitrogen(N2) compounds, such as ammonia (NH3), nitrates, and urea, have played an essential role in meeting the growing demand for food and the worldwide need of nitrogenous fertilizer since 1913 [1]
N2 photoreduction to nitrogenous compounds (e.g., NH3) in soils and sands as catalysts is an important part of global N2 cycle. rough continuous exploration of nitrogen fixation, the Haber–Bosch process, a thermo-chemical catalytic conversion technology, becomes a primary choice of synthesizing N2 fixation compounds which were produced from the reaction: N2 + 3H2 ⟶ 2NH3 (1)
Energy coming from sustainable source as solar, an alternative, sustainable NH3 synthesis process based on the biological N2 fixation would be more energy efficient than Journal of Chemistry the Haber–Bosch process [7]

Summary

Introduction

As the important chemicals to our planet, nitrogen(N2) compounds, such as ammonia (NH3), nitrates, and urea, have played an essential role in meeting the growing demand for food and the worldwide need of nitrogenous fertilizer since 1913 [1]. The metal oxide-based material as photocatalyst is dynamically converted between its oxidized and reduced states in the process. Erefore, something must be taken into account that both reduction potential of the adsorbate and position of the energy band are important for the photocatalytic redox reaction occurrence when making a decision on the choice of semiconductor photocatalyst materials. Observing no reduction of N2 to NH3 in the presence of pure TiO2 material, Augugliaro et al [47] put forward a hypothesis that Fe3+ of photoassisted organ iron compound could temporarily trap photons and promote the separation of charge carriers, which has played an important role in the NH3 production processes. Ranjit and Viswanathan [48] observed that the FeTi2O5 phase in Fe-doped titanium materials could

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Findings

Conclusions