Ammonia Synthesis Using Single-Atom Catalysts Based on Two-Dimensional Organometallic Metal Phthalocyanine Monolayers under Ambient Conditions

Abstract

We have identified three novel metal phthalocyanine (MPc, M = Mo, Re, and Tc) single-atom catalyst candidates with excellent predicted performance for the production of ammonia from electrocatalytic nitrogen reduction reaction (NRR) through a combination of high-throughput screening and first-principles calculations on a series of 3d, 4d, and 5d transition metals anchored onto extended Pc monolayer catalysts. Analysis of the energy band structures and projected density of states of N 2 -MPc revealed significant orbital hybridization and charge transfer between the adsorbed N 2 and catalyst MPc, which accounts for the high catalytic activity. Among 30 MPc catalysts, MoPc and TcPc monolayers were found to be the most promising new NRR catalysts, as they exhibit excellent stability, low onset potential, and high selectivity. A comprehensive reaction pathway search found that the maximum free energy changes for the MoPc and TcPc monolayers are 0.33 and 0.54 eV, respectively. As a distinctive nature of this work, the hybrid reaction pathway was considered extensively and searched systematically. The onset potential of the hybrid pathway is found to be smaller than or comparable to that of the commonly known pure pathway. Thus, the hybrid path is highly competitive with low onset potential and high activity. The hybrid pathway is expected to have an important impact on future research on the mechanism of NRR, and it will open up a new way to explore the mechanism of the NRR reaction. We hope that our work will provide impetus to the creation of new catalysts for reduction of N 2 to NH 3 . This work provides new insights into the rational design of NRR catalysts and explores novel reaction pathways under ambient or mild conditions.

Density Functional Theory for Electrocatalysis

“…For instance, Yang et al performed the DFT highthroughput screening of catalysts for NRR among a series of transition metal atoms supported on phthalocyanine or borophene monolayer, which provided insights to rational design and explore the efficient and stable NRR catalysts. [403,406] In particular, the NRR reaction (N 2 + 6H + + 6e − → 2NH 3 ) involves several intermediates (*N 2 H, *N 2 H 2 , *N 2 H 3 , *NH 2 , and *N) with two potential reaction pathways (Figure 11b). One is the dissociative pathway, in which the first step is N 2 dissociates into two separate N atoms before the hydrogenation.…”

“…[242] It has been proposed that the first protonation of *N 2 to from *N 2 H is the potential limiting step on catalysts with weakly nitrogen-binding capability (Figure 11c), while the most difficult step is suggested to be the reduction of *NH 2 to NH 3 or the protonation of *NH to form *NH 2 on catalysts with strong nitrogen binding (Figure 11d). [367,403,407] Moreover, the HER reaction is a competing reaction, decreasing the faradaic efficiency for NRR. Some studies demonstrated that NRR at more negative potentials (−1 to −1.5 V) will dominate over HER because of stronger nitrogen binding on the active site than that of H. [408]…”

“…d) Calculated free energy profile in NRR on the MoPc catalyst. Reprinted with permission from Ref [403]. Copyright 2020, American Chemical Society.…”

Theoretical studies of MXene-supported single-atom catalysts: Os1/Ti2CS2 for low-temperature CO oxidation

“…Since the concept of single-atom catalysis was firstly proposed by Zhang, Li, Liu et al in 2011 [1], considerable attention has been paid to this area because of its unique homogeneous structural characteristics of a single-atom (SA) active center and the excellent catalytic performance in heterogeneous catalysis [2][3][4][5][6][7][8][9][10]. Several reviews [11][12][13][14][15] have summarized the development of single-atom catalysts (SACs), the structure-function relationship between SACs and their catalytic performance, and the diverse applications of SACs in heterogeneous catalysis [16][17][18][19][20][21][22][23].…”

Application of a blast furnace slag carrier catalyst in flue gas denitration and sulfur resistance

“…In order to reduce pollution, one of the technologies adopted by most coal-red power plants is selective catalytic reduction denitration, and the core of the SCR technology is the catalyst. [2][3][4][5] Although some progress has been made in the study of SCR catalysts, the denitration catalyst is expensive and its sulfur resistance is insufficient. [6][7][8][9] Consequently, the preparation of high performance denitration and sulfur-resistant catalysts characterized by high efficiency, simplicity, and energy conservation has become a hot topic in this eld.…”