Adsorbents development for hydrogen cleanup from ammonia decomposition in a catalytic membrane reactor

Abstract

Copper-exchanged faujasite (Cu-FAU) zeolites have been investigated in this work as promising adsorbent materials to further purify hydrogen produced via ammonia decomposition in a membrane reactor. Samples have been prepared via ion-exchange procedure using commercially available NaY, HY and 13X zeolites and their performance was evaluated and compared to the one of their parent zeolites. The introduction of copper species in the zeolites framework was demonstrated to enhance the NH3 useful and saturation capacities of the zeolites. However, the Cu-FAU zeolites synthesized in presence of copper(II)nitrate trihydrate and calcined in air showed significant deactivation after a first adsorption/desorption cycle. Samples characterization revealed that this phenomenon can be attributed to dealumination which is on the other hand prevented when ion-exchange procedure occurs in presence of ammonium hydroxide and inert environment is adopted during calcination. The most promising adsorbent material was found to be the one-time ion-exchanged form of zeolite 13X, showing a useful capacity stable at 3.07 ± 0.39 mmol NH3/gsorbent over ten cycles during which saturation was performed with a He/NH3 mixture containing 3000 ppm of NH3 and regeneration was performed in He. As similar performance has been achieved under operating conditions emulating the outlet stream of a membrane reactor for ammonia decomposition, the one-time ion-exchanged form of zeolite 13X can be regarded as a promising adsorbent material to effectively purify NH3-derived H2 produced via ammonia decomposition in a membrane reactor.