Lattice nitrogen-mediated optimization of intermediate evolution pathways enhances ammonia decomposition reaction kinetics

Abstract

Thermocatalytic ammonia decomposition for hydrogen production is regarded as an effective strategy to tackle the challenges of hydrogen storage and transport. Most current strategies focus on the adsorption-evolution mechanism to balance kinetic barriers in rate-determining steps, thereby reducing the reaction temperature. Herein, we report a strategy to promote the kinetics of ammonia decomposition by altering the reaction pathway through lattice nitrogen mediation. The results indicate that using nitrogen-containing graphene-like g-C₃N₄ as a support, the ammonia decomposition efficiency and hydrogen production rate are improved by 72.11% and 80.11 mmol g_cat⁻¹ min⁻¹, respectively, compared to nitrogen-free graphene as the support (5 wt% Ru/Gr-AR), under conditions of only 20 mg catalyst, 500 °C, and a gas hourly space velocity (GHSV) of 18 000 mL g_cat⁻¹ h⁻¹. Under these conditions, the hydrogen production rate (99.45 mmol g_cat⁻¹ min⁻¹) is significantly higher than that of previously reported Ru-based catalysts, and a 100-hour test further confirms its excellent stability. In addition, by proposing a nitrogen-cycle pathway model for ammonia decomposition potentially mediated by lattice nitrogen, we can not only provide a plausible explanation for the enhanced catalytic activity of nitrogenous catalysts but also provide important guidance for the design of new catalysts.