Hydrogen production via chemical looping steam methane reforming process: Effect of cerium and calcium promoters on the performance of Fe2O3/Al2O3 oxygen carrier

High purity hydrogen can be produced through chemical looping with making use of the reaction between steam and lattice oxygen of an oxygen carrier. Since choosing a suitable oxygen carrier significantly affects the efficiency of this process, different oxygen carriers have been proposed. In this work, alumina supported Fe2O3 promoted with cerium or calcium oxides is assessed as an oxygen carrier. The effect of promoter type (M = Ca and Ce) and its loading weight percentage (x = 0, 5, 10) on the cyclic redox performance of 15Fe-xM/Al2O3 oxygen carrier is investigated. In addition, the reaction temperature (823-1023 K) and the oxygen carrier cyclic lifetime (up to 15 cycles) are studied at steam to methane ratio of 1.5. Surface and structural properties of some samples were characterized by various techniques such as X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and Brunauer-Emmett-Teller. The results show that the activity, long-term stability and coke formation resistance of the oxygen carrier are significantly affected by the promoter type. The catalytic activity of oxygen carrier improves successfully in the presence of 5% cerium or calcium promoter. At 923 K, the methane conversion is about 100% for 15Fe-5Ca/Al2O3 and 15Fe-5Ce/Al2O3 oxygen carriers, which is the highest conversion among all the tested samples. However, 15Fe-5Ca/Al2O3 oxygen carrier is consistently stable in chemical looping reforming with high hydrogen producing capacity.