# Mechanistic insights into N2 activation by RhCo3via d–d orbital coupling

## TL;DR

This paper explains how a RhCo3 catalyst activates nitrogen for ammonia synthesis through electron interactions and orbital coupling, with performance depending on temperature.

## Contribution

The study reveals a bimetallic synergy and spin effects in RhCo3 via d–d orbital coupling, offering new insights into efficient ammonia synthesis catalysts.

## Key findings

- The RhCo3 cluster shows optimal catalytic performance in the septet state due to bimetallic synergy and spin effects.
- N2 adsorption governs catalytic activity at low and moderate temperatures, with a δE value of 2.03 eV at 298 K.
- At higher temperatures, NH3 desorption becomes the rate-determining step, increasing the energy span to 2.95 eV.

## Abstract

The synthesis of ammonia (NH3) from nitrogen (N2) under mild conditions is a great challenge, in which the electron-donating ability of the catalyst is the key for N2 activation. In this work, the above process was studied using quantum chemical calculations using the density functional method. The results show that Rh and Co exhibit unsaturated d-electron configurations, with d–d orbital coupling occurring within the RhCo3 metal cluster, resulting in bimetallic synergy and spin effects. The Rh atom serves as an electron modulation center and active site for reactant activation, while the Co metal synergistically enhances electron back-donation effects. The RhCo3 cluster exhibits different adsorption and kinetic behaviors across the triplet, quintet, and septet potential energy surfaces, among which the septet state shows the most favorable catalytic performance. Energy span (δE) model analysis further indicates that, at low and moderate temperatures, the N2 adsorption is the key factor governing the catalytic activity of RhCo3. At 298 K, the reaction displays a δE value of 2.03 eV, and the catalytic activity increases with the temperature. However, at higher temperatures, the NH3 desorption becomes the rate-determining process, shifting the turnover-determining transition state beyond the turnover-determining intermediate, and the energy span increases to 2.95 eV. These findings elucidate the temperature-dependent catalytic mechanism of RhCo3 and provide theoretical insights for the rational design of efficient bimetallic catalysts for ammonia synthesis.

The RhCo3 catalyst exhibits bimetallic synergy and spin effects via Rh–Co d–d orbital coupling, facilitating efficient N2 activation for ammonia synthesis in the septet state.