Chemical looping co-conversion of CH4 and CO2 using Fe2O3/Al2O3 pellets as both oxygen carrier and catalyst in a fluidized bed reactor

Abstract

Chemical looping reforming of CH4 (CH4-CLR) is a safe and efficient CH4 upgrading technology for syngas production. The Fe2O3-based oxygen carriers (OCs) possess a higher potential for CH4-CLR among so many transition metal oxides as high syngas selectivity can be obtained from partial CH4 oxidation by OCs with the step-by-step reduction of Fe3+/Fe2+ to Fe0. However, the impurity CO2 in CH4-source feed gas, when using Fe2O3-based OCs, often causes the inhibition of reaction between CH4 and OCs resulting in no partial CH4 oxidation to syngas. The present work has employed the Fe2O3/Al2O3 pellets as OCs with introducing the fully reduced same pellets as a catalyst in a bubbling fluidized-bed reactor to eliminate the inhibition effect of CO2 during CH4-CLR. It has been demonstrated that the Fe species with low valent, e.g., Fe0, in the catalyst can effectively catalyze the dry CH4 reforming. Thus, the CO2 has been consumed before contacting with Fe2O3-based OCs and the inhibition effect of CO2 has been eliminated. Meanwhile, both CO2 and CH4 can be converted to syngas in the reducer leading to an opportunity for CO2 utilization. With the help of the catalyst of reduced OCs, not only the CO2 in the feed gas but also that formed from full CH4 oxidation by Fe2O3/Al2O3 at the early CH4 reforming stage is converted into syngas of CO and H2. Semi-continuous cyclic CH4-CLR test has demonstrated the good stability of both Fe2O3/Al2O3 OC and counterpart catalyst, which suggests the potential of such OC/catalyst pair in practical applications.