Optimization of nickel-iron bimetallic oxides for coproduction of hydrogen and syngas in chemical looping reforming with water splitting process

Chemical looping reforming with water splitting (CLRWS) to coproduce the syngas and high purity hydrogen was investigated using Ni–Fe bimetallic oxygen carriers (OCs). The oxygen carrier with 20 wt% of NiO (termed as Ni20Fe80) was more suitable for CLRWS at 900 °C with a mass ratio of steam to bio-oil (S/B) of 1.2. Under the condition, the syngas exhibited a yield of 1.79 Nm3/kg with a H2/CO ratio of 2.01 in fuel reactor (FR), meanwhile, the hydrogen presented a yield of 0.70 Nm3/kg with a purity of 96.04% in steam reactor (SR). However, the stability of Ni20Fe80 gradually decreased during the cyclic test. Three metal oxide additives, including CeO2, Al2O3 and TiO2, with a mass fraction of 25 wt%, were used to modify the Ni20Fe80. The corresponding OCs were abbreviated as Ni15Fe60Ce25, Ni15Fe60Al25 and Ni15Fe60Ti25. The Ni15Fe60Ce25 exhibited the best performance during the cyclic test. After 5 cycles, the syngas yield, hydrogen yield and purity were 2.01 Nm3/kg, 0.75 Nm3/kg and 96.26%, respectively. The Ni15Fe60Al25 has good potential for syngas production, but not suitable for hydrogen production in SR. It was attributed to that the formation of iron-aluminum spinel regulated the lattice oxygen reactivity to favor the syngas production, as well inhibited the reduction of Fe species, which resulted in a low hydrogen yield in SR.