Novel Photocatalytic NH3 Synthesis by NO3− Reduction over CuAg/TiO2

Ryota Kato,Hideyuki Katsumata,Satoshi Kaneco,Ikki Tateishi,Mai Furukawa

doi:10.3390/chemengineering3020049

Abstract

The highly effective reaction system was investigated for the photocatalytic ammonia synthesis from the reduction of nitrate ions by using the semiconductor photocatalyst, Cu and Ag doped on TiO2 (CuAg/TiO2) at room temperature under UV light irradiation (max. 352 nm). In this study, CuAg/TiO2 gave the high efficiency and the selectivity for the ammonia synthesis by the photoreduction of nitrate in the presence of methanol as a hole scavenger. For the evaluation of the photocatalytic activity over CuAg/TiO2, various TiO2 samples, such as standard TiO2, Cu/TiO2, and Ag/TiO2, were evaluated in the same procedure. The chemical properties were investigated by XRD, TEM, XPS, PL, and DRS. We examined the optimum conditions for the experimental factors and the important issues, including the effect of the molar ratio of Cu and Ag onto TiO2, the optimization of the CuAg amount loaded on TiO2, the influence of the loading amount of the catalyst on the reduction of nitrate ions, the exploration of the optimum hole scavenger, and the reusability of the optimum photocatalyst. The very efficient conversion of nitrate ions (95%) and the highest selectivity (86%) were achieved in the reaction with the optimum conditions. Here, we reported the process that nitrate ions can efficiently be reduced, and ammonia can be selectively synthesized over CuAg/TiO2.

Highlights

Ammonia (NH3) has recently been recognized as one of the most important chemical products in the present world [1]
It clearly shows that the demand on the NH3 production expands, as the population increases in the future
As the method for the substitution of Haber Bosch process, various ammonia production processes were investigated such as following methods; the plasma catalysis [5], the electrochemical system [6], the production from biomass [7]

Summary

Introduction

Ammonia (NH3) has recently been recognized as one of the most important chemical products in the present world [1]. In the current NH3 synthesis, NH3 is directly synthesized by N2 and H2 over an iron-based catalyst (Haber-Bosch process) This method needs the conditions at high temperature (400–500 ◦C) and high pressure (150–250 bar), which is not a sustainable process in the NH3 production for a long time. Cu is one of the well-known metals and it is widely applied to the photocatalysts because it has several advantages of the high electro conductivity and the low cost Noble metals, such as Au, Ag, and Pt show the localized surface plasmonic resonance (LSPR), which has the ability to absorb the visible light [16]. We examined in detail the photocatalytic activity, the optimization of the experimental conditions, and the reusability of the optimum catalyst This reaction system would give the excellent approach for the selective NH3 synthesis by photocatalytic NO3− reduction over the optimized photocatalyst

Materials

Preparation of TiO2 Samples

Characterization

Results and Discussion

Conclusions