Manipulating the Geometric and Electronic Structures of Manganese Nitrides for Ammonia Synthesis. Issue 8 (11th March 2020)

• Record Type: Journal Article
• Authors: Shan, Nannan; Huang, Chaoran; Lee, Robert T.; Manavi, Narges; Xu, Lianbin; Chikan, Viktor; Pfromm, Peter Heinz; Liu, Bin
• Is Part Of: ChemCatChem. Volume 12:Issue 8(2020)
• Page Start: 2233
• Page End: 2244
• Publication Date: 2020-03-11
• Subjects: Ammonia synthesis -- Density Functional Theory -- manganese nitrides; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201902383
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: Manganese (Mn) nitrides are important nitrogen (N) carriers for small‐scale intermittent ammonia (NH3 ) synthesis. However, only 3∼8 % of lattice N are converted into NH3 . In this study, the geometric and electronic structures of well‐defined Mn4 N and Mn2 N lattices were altered using transition metal heteroatoms (Cr, Fe, Co, Ni, Mo) to understand the driving force behind lattice N diffusion and extraction. Density Functional Theory (DFT) revealed that the binding of early hydrogenation product (NH) follows a linear relationship with lattice N over a wide range of close‐packed surfaces. But, the binding of NH2 and NH3 are more sensitive to the geometric and electronic structures. Further, the chemical bonding can be quantitatively characterized with the covalency derived from Crystal Orbital Hamiltonian Population (COHP). In the Eley Rideal‐Mars van Krevelan pathway, the overall NH3 formation free energy ( Δ G N H 3 ) and lattice N diffusion barrier ( E a ) are the respective thermodynamic and kinetic determining factors. Aided by a rate‐determining step (RDS) model, Mn4 N modified with Fe, Co, Ni single‐atom dopants all show enhanced rates for NH3 formation. Abstract : The Haber‐Bosch challenge : The geometric and electronic structures of well‐defined Mn nitrides and their relation to NH3 formation rates were understood using Density Functional Theory (DFT) calculations. Carefully placed Fe, Co, Ni single‐atoms dopants are capable of promoting NH3 formation rates. A more complex pattern was also observed for Mn‐based ternary nitrides.