Fe-Zr/CaO Catalyst-Sorbent for Sorption-Enhanced Steam Gasification of Lignin: Co-promotion Effects, Apparent Kinetics, and Cyclic Performance

Abstract

Sorption-enhanced steam gasification (SE-SG) is a promising route for producing H2-rich syngas with in-situ CO2 capture, but the cyclic deactivation of CaO through sintering and pore collapse limits long-term operation. This study evaluates Fe-Zr co-promoted CaO catalyst-sorbents for lignin steam gasification at 700 degrees C. A Zr-Fe/CaO material containing 85 wt% CaO and 15 wt% mixed ZrO2-Fe2O3 was prepared by incipient-wetness impregnation and compared with CaO and Fe/CaO. Zr-Fe/CaO delivered the highest total syngas yield (65.9 mol kg-1) and H2 yield (6.26 mol kg-1), exceeding Fe/CaO and CaO by approximately 8 and 19%, respectively. Because a Zr/CaO-only control was not included, the calculated lower-bound empirical co-promotion index (CPImin = 1.96) is interpreted as an internal comparative indicator rather than definitive proof of Fe-Zr physicochemical synergy. Shrinking-cylinder-model analysis gave apparent rate constants of 0.005217, 0.005116, and 0.004836 min-1 for Zr-Fe/CaO, Fe/CaO, and CaO, respectively, indicating improved apparent carbon-conversion behavior for the dual-promoted formulation. TGA-DTG and Avrami-Erofeev analysis suggested faster CaCO3 decomposition and improved thermal response, while BET and SEM-EDX showed higher surface area (10.85 m2 g-1), better mesoporosity retention, and morphology consistent with Ca-Zr stabilization. Fe-containing phases may have contributed to redox-mediated reforming and WGS-related pathways. After ten gasification-regeneration cycles, Zr-Fe/CaO retained approximately 77% of its initial apparent activity, suggesting its potential for integrated CO2 capture and H2-rich syngas production under the tested conditions.