Atomically Dispersed Ru Catalyst for Low-Temperature Nitrogen Activation to Ammonia via an Associative Mechanism

Abstract

The industrial synthesis of NH 3 using Fe-or Ru-based catalysts usually requires harsh reaction conditions. It is desirable to develop catalysts that perform well at low temperature and pressure (250−400 °C, <2 MPa). The main challenge of low-temperature NH 3 synthesis is the dissociation of the extremely stable NN triple bond. Herein, we report the design of homogeneous single-atom Ru centers on an H-ZMS-5 (HZ) support with the Ru atoms individually anchored in the micropores of HZ, effectively boosting NH 3 synthesis under mild conditions via an associative pathway. Synchrotronbased near-edge X-ray absorption fine structure (NEXAFS) and in situ DRIFTS analyses show that N− groups are the primary intermediates, and DFT calculations further show that, unlike Ru nanoclusters, the cooperation of a single Ru atom and hydrogen species in HZ leads to N 2 hydrogenation rather than direct N 2 dissociation, and the indirect N−N bond dissociation occurs much more easily via the formation of the NHNH 3 * intermediate; the energy barrier for breaking the N−N bond keeps falling from 2.90 eV for *N 2 to 0.04 eV for *NHNH 3 , showing that N 2 hydrogenation is an effective way for sharp weakening of N−N bonds. Moreover, the rate-determining step is shifted from the dissociation of the NN triple bond to the formation of *N 2 H 2 . As a consequence, the single-atom 0.2 wt % Ru/H-ZSM-5 catalyst shows the highest NH 3 synthesis rate per gram of Ru (1.26 mol NH3 g Ru −1 h −1 at 300 °C and 1 MPa) among the Ru-based catalysts ever reported.

Single-Atom Ruthenium Biomimetic Enzyme for Simultaneous Electrochemical Detection of Dopamine and Uric Acid

“…Recently, single-atom catalysts (SACs), exhibiting full atom utilization have demonstrated promising applications in electrocatalysis due to their advantages of abundant active sites and unique catalytic functions . Among the noble metals, Ruthenium (Ru)-based single-atom catalysts are applied in ammonia synthesis, oxidative cyanation, CO 2 hydrogenation systems, and oxygen − and hydrogen evolution reactions . However, preparing catalysts to the single-atom level is difficult because they are thermodynamically unstable and tend to aggregate into clusters or nanoparticles during the preparation process .…”

Facile Synthesis and High‐Value Utilization of Ammonia

“…DFT calculations further demonstrated that the cooperation of a single Ru atom and hydrogen species in HZ leads to N 2 hydrogenation instead of direct N 2 dissociation (Figure 5). [ 20 ] Therefore, the 0.2 wt% Ru/H‐ZSM‐5 SAC realized a superior NH 3 synthesis performance among the Ru‐based catalysts ever reported. In addition to Ru‐based SACs, we developed an atomically dispersed Co‐N‐C catalyst with a high NH 3 synthesis rate via the combination of associative and chemical looping routes.…”

“…Proposed route of NH 3 synthesis over Ru‐HZ SAC based on experimental and theoretical simulation results. [ 20 ] …”

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

“…14 In addition, very recently, a limited number of researches have provided us with experimental evidence that the N 2 hydrogenation to N 2 H x species is preferred over atomically dispersed Ru and Co, as well as Li-promoted Ru catalysts. 6,15,16 Among them, atomically dispersed catalysts present well, having the potential for NH 3 synthesis at mild conditions, as the direct N 2 dissociation is difficult while the N 2 hydrogenation is feasible on single-atom sites. 15 Meanwhile, atomically dispersed catalysts with definite structures offer the possibility to investigate the geometric and electronic effects on NH 3 synthesis at the atomic level.…”

“…6,15,16 Among them, atomically dispersed catalysts present well, having the potential for NH 3 synthesis at mild conditions, as the direct N 2 dissociation is difficult while the N 2 hydrogenation is feasible on single-atom sites. 15 Meanwhile, atomically dispersed catalysts with definite structures offer the possibility to investigate the geometric and electronic effects on NH 3 synthesis at the atomic level. Differing from nanoparticle catalysts, in which the particle size and crystal face usually play an important part in the reactivity, catalytic activity of atomically dispersed catalysts is mainly determined by the coordination environment of single-atom sites.…”