Highly efficient dual-phase hydrogen-transporting membranes for NH3 decomposition coupling with CO2 reduction

Abstract

Hydrogen-transporting membrane reactors play active roles in ammonia (NH3) decomposition and carbon dioxide (CO2) reduction by combining reaction and separation in one unit, simplifying the processes and reactor design and therefore saving the cost. These important reactions normally occur at high temperatures and in reducing and acidic atmosphere, thus posing great challenges on the membrane stability. Previous effort was devoted to thin Pd membranes, which however, suffer the shortcomings of hydrogen embrittlement, CO poisoning and high costs. Herein, we develop a H2-COx-tolerant and non-noble metal-ceramic dual-phase hydrogen permeable membrane reactors with a nominal composition of 60 vol% Ni-40 vol% La5.5WO11.25-δ (Ni-LWO). NH3 decomposition and hydrogen permeation was observed via the developed mixed protonic and electronic conducting membrane. A considerable production of CO in the sweep (CO2) side could also be achieved from CO2 reduction when the membrane was coupled by NH3 decomposition where the permeated hydrogen can consume the produced oxygen from favorable CO2 decomposition. Furthermore, we systematically investigated the performance of NiO–CeO2 catalyst coated Ni-LWO membrane reactor for CO2 reduction. Noteworthy that the CO generation rate obtained from Ni-LWO membrane reactor was increased in the presence of NiO–CeO2 catalysts. Hydrogen separation process coupled with surface reactions is jointly controlled by hydrogen surface exchange and bulk diffusion kinetics. These findings reveal a vital step towards the development of efficient hydrogen-transporting membrane reactor for the integration of chemical reactions and separation processes.