Improved Sorption-Enhanced Steam Methane Reforming via Calcium Oxide-Based Sorbents with Targeted Morphology

Calcium oxide (CaO)-based sorbents for sorption enhanced steam methane reforming (SE-SMR) that achieve stoichiometric capacity are synthesized via thermal and electrospinning methods. Small CaO crystallites (39 nm) and macroporous intrafiber networks imparted by electrospinning lead to stoichiometric capacities (0.79 gCO2 gsorbent-1) and uptake kinetics (first order rate constant, k = 8.9 x 10(-4) +/- 1.8 x 10(-5) cm(4) mol(-1) s(-1)) at 873 K that are superior to CaO derived from thermal syntheses (0.05-0.7 gCO2 gsorbent-1 and k < 5.0 x 10(-4) +/- 2.5 x 10(-6) cm(4) mol(-1) s(-1)). Al-doped electrospun CaO samples (Al:Ca ratios of 3:10, 1:10 and 2:10) also exhibit high sorption capacities (0.35-0.74 gCO2 gsorbent-1 at 873 K) and are stable over multiple reaction-regeneration cycles (<5% loss in initial capacity after 15+ cycles). X-ray diffraction and scanning electron microscopy analysis reveal that thermally stable Al-Ca mixed phases (Ca12Al14O33) mitigate crystallite agglomeration and maintain macroporous structures imparted by electrospinning. Nanofibers and Al-doped nanofibers (Al:Ca 2:10) exhibit more than a factor of three longer CO2 breakthrough time compared to CaO from marble (1650, 6400, and 7500 mL g(sorbent)(-1) for CaO-marble, 2Al-10Ca-O-nanofibers, and CaO-nanofibers respectively) under reforming conditions, with Al-doped CaO-nanofibers retaining 94% of their initial performance after ten reforming-regeneration cycles, indicating their potential as improved sorbents for SE-SMR processes.