Ni3Fe embedded in oxygen carriers to improve CH4 conversion and H2 production during chemical looping reforming

Abstract

Chemical looping reforming is an efficient technology for the stepwise production of syngas and hydrogen, which significantly contributes to reducing carbon emissions. However, the imbalance between the catalytic performance and lattice oxygen transport rate of oxygen carriers (OCs) can induce severe carbon deposition and diminished conversion. Therefore, this study proposes a spinel OC embedded with Ni₃Fe to balance them to improve conversion and reduce carbon deposition during chemical looping reforming. After H₂-20 min reduction, the Ni₃Fe embedded in the spinel structure generated abundant catalytic sites and suitable lattice oxygen transport rates. Moreover, increasing the reduction degree can enhance the active catalytic sites while moderating the lattice oxygen transport rate. However, over-reduction can lead to over-catalytic effect and insufficient lattice oxygen, potentially resulting in a significant carbon deposition. It is worth noting that temperature plays a more critical role in determining the lattice oxygen transport rate than the catalytic activity. Higher temperatures enhanced the lattice oxygen transport and CH₄ conversion, resulting in H₂/CO ratio that stabilized at 2. After 10 cycles, the CH₄ conversion, H₂ selectivity and CO selectivity respectively reached 94.46 %, 91.62 % and 81.63 % during CH₄ conversion step, while H₂ production reached 28.58 mol/h/kg during the water splitting step and carbon deposition remained below 1.79 %. The reaction kinetic showed that the reaction model of the Ni₃Fe embedded OC with CH₄ was Phase boundary-controlled model Infinite slabs, which facilitated the catalytic cracking of methane and reduced the activation energy of the reaction.