High-purity COx-free H2 generation from NH3 via the ultra permeable and highly selective Pd membranes

A compact H2 generation system that coupled NH3 decomposition with Pd membrane separation has been developed to provide high-purity COx-free H2 for the fuel cell uses. The ultra permeable and highly selective Pd membranes supported on porous ceramic tubes were successfully synthesized. Firstly, the NH3 decomposition reaction over the Ni-based catalyst was carried out in a Pd membrane reactor, through which the in situ removal of H2 product significantly enhanced the NH3 conversion. It is further observed that the permeation performance was greatly limited by the low effective utilization of membrane in the NH3-rich zone. When having integrated reaction with separation separately, we obtained a 54 m3 m−2 h−1 99.96% H2 stream with a H2 recovery yield of 77%. Therefore, it is suggested that the combination of an NH3 cracker with a followed Pd membrane separator is more preferable for on-site H2 generation. Throughout a 500-h lifetime test, both the reaction and separation units showed a good stability. The residual NH3 slightly inhibited the permeability of the Pd membrane. Nevertheless, the permeability of the used membrane could be recovered and finally increased by the air and followed H2 treatments.