Egg-shell Ru catalysts on K-added Al2O3 spherical pellet toward industrial ammonia decomposition

Abstract

NH3 decomposition for industrial hydrogen production requires pellet-type catalysts that deliver high activity at low temperatures while maintaining mechanical robustness and low pressure drop. This work presents a facile and scalable strategy for constructing egg-shell Ru catalysts on K-added Al2O3 spherical pellets via K impregnation and successive Ru loading (targeting 1 wt.% Ru), conceptually analogous to industrial spray-drying processes. Uniformly distributed K species throughout the entire pellet volume strengthen Ru-O-K interaction and promote Ru localization near the pellet surface up to 5.2 wt.% K, whereas higher K contents induce deeper Ru penetration into the pellet interior. As K content increases, Ru dispersion shows a volcano-type trend with a peak at 5.2 wt.% K while the electron density and basicity of Ru species steadily rise. The optimized Ru/5.2K/Al catalyst achieves complete NH3 conversion at 516 degrees C and 40,000 mL gcat rate of 44.6 mmolH2 gcat - 1 min- 1 and excellent stability for 100 h without deactivation. Beyond alleviating internal diffusion limitations, the remarkable catalytic performance originates from enhanced intrinsic kinetics, which is derived from synergistic promotion of NH3 activation, N-H cleavage and product desorption through modulation of rate-determining step and optimized surface intermediate coverage. This work provides a high-performance Ru-based pellet catalyst for industrial NH3 decomposition.