Highly dispersed Ru nanoparticles induced by the atmosphere for hydrogen production from ammonia decomposition

Background

Ammonia (NH₃) serves as a promising medium for hydrogen storage and transportation, addressing the challenges associated with these processes. However, the ammonia decomposition reaction urgently requires catalysts with high activity and stability.

Methods

Here, we present a synergistic strategy for the preparation of a highly dispersed Ru/Al₂O₃ catalyst using an atmosphere-induced method. Under an oxidizing atmosphere (Ru/Al₂O₃-O), the particle size of RuO₂ exceeds 10 nm. Conversely, by oxygen vacancies anchoring in a reducing atmosphere, highly dispersed and structurally stable Ru catalysts with particle sizes < 2 nm can be prepared. HRTEM, XPS, TPR and XRD have been employed to elucidate the morphology and electronic structure of the Ru metal.

Significant Findings

This research investigated the impact of atmosphere-induced effects on the particle size and ammonia decomposition activity of Ru/γ-Al₂O₃ catalysts. A reducing atmosphere induced the formation of oxygen vacancies in the alumina support, leading to highly dispersed Ru/γ-Al₂O₃ catalysts. The interaction between Ru species and oxygen vacancies led to Ru particles of catalyst smaller than 2 nm and a stable structure. The removal of Cl ions from the Ru-based catalyst positively influenced the enhancement of ammonia decomposition activity. XPS and TPD results indicated that the introduction of the alkali metal potassium increased the electron density of Ru species, facilitating the ammonia decomposition reaction process. The K-Ru/γ-Al₂O₃-RW catalyst achieved a conversion rate of 97 % at 450 °C at a flow rate of 18,000 mL/g_cat/h. Stability tests showed that the K-Ru/γ-Al₂O₃-RW catalyst did not deactivate after undergoing a 700-hour lifetime test. This work provides an effective method for synthesizing Ru-based catalysts to enhance ammonia decomposition for hydrogen production.