Facile synthesis of a sintering-resistant zeolite confined Ni catalyst for efficient COx-free hydrogen generation from ammonia decomposition

Abstract

The thermal stability of a catalyst is equally important as its activity particularly for high-temperature catalysis reactions. This paper reports a facile method to synthesise highly stable ZSM-5 zeolite confined Ni catalysts (Ni@ZSM-5) for ammonia decomposition, a promising catalysis reaction for CO_x-free hydrogen production. The Ni@ZSM-5 catalysts were prepared by treating stabilised Ni complexes together with a dense gel of the zeolitic precursor in a one-step process. The Ni particles were then in situ encapsulated concurrently within the growing zeolite crystalline structure under hydrothermal synthesis conditions. The formation of the ZSM-5 crystalline structure was confirmed by XRD analysis. HRTEM and HAADF-STEM coupled with EDS revealed that Ni particles of ∼2 nm in diameter were homogeneously embedded in the ZSM-5 crystals. The performance of the catalysts was evaluated in ammonia decomposition at a high-temperature of 650 °C using a fixed-bed reactor. The Ni embedded catalyst (Ni@ZSM-5) exhibited not only high activity but also high stability without Ni sintering during a 100 h reaction time. For comparison, the ammonia conversion for the supported Ni catalyst (Ni/ZSM-5) prepared via the conventional impregnation method subjected to severe sintering showed a 20% decrease in ammonia conversion under the same reaction conditions.