The electrochemical reduction of nitrogen to ammonia is a promising way to produce ammonia at mild condition. The design and preparation of an efficient catalyst with high ammonia selectivity is critical for the real applications. In this work, a series of transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd) atoms supported by gt-C3N4 (TM/gt-C3N4) are investigated as electrocatalysts for the nitrogen reduction reaction (NRR) based on density functional calculations. It is found that Mo/gt-C3N4 with a limiting potential of -0.82 V is the best catalyst for standing-on adsorbed N2 cases. While for lying-on adsorbed N2 cases, V/gt-C3N4 with a limiting potential of -0.79 V is better than other materials. It is believed that this work provides several promising candidates for the non-noble metal electrocatalysts for NRR at mild condition.

gt-C 3 N 4 coordinated single atom as an efficient electrocatalyst for nitrogen reduction reaction

Industrial ammonia synthesis, now known as the Haber-Bosch process, began in 1913. For this process, the doubly promoted iron catalyst (Fe-Al2O3-K2O) was synthesized in 1909 and the preparation concepts are still applied today [1]. During the research of that time, most elements other than iron were also examined. Osmium was found to have the excellent activity, giving as high as 8% NH3 at 550 °C and 19 MPa for a long time. Continuous production of NH3 (80 g/h) was first demonstrated in July 1909 using Os [2]. However, osmium was too expensive and has not produced in quantities sufficient for commercial use. Uranium as its carbide was also very active, but it was irreversibly poisoned by traces of O2 of water vapor. These examples suggested to us that we might be able to develop catalyst containing active elements other than iron. In this chapter, various catalyst systems other than iron, which have not been applied commercially, will be reviewed. Several elements, for example ruthenium and rhenium, are quite interesting as active elements which might lead to second generation ammonia catalysts.

Ammonia Synthesis over Non-Iron Catalysts and Related Phenomena

A novel catalyst for ammonia synthesis at ambient temperature and pressure: Visible light responsive photocatalyst using localized surface plasmon resonance

Elucidation of a preparation method for copper ion-exchanged ZSM-5 samples exhibiting extremely efficient N2-adsorption at room temperature: effect of counter ions in the exchange solution

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.

https://www.mdpi.com/2305-7084/3/2/49/pdf

A. Ozaki

Papers

Catalytic Activation of Dinitrogen