Sustainable Production of High-Purity Hydrogen by Sorption Enhanced Steam Reforming of Glycerol over CeO2-Promoted Ca9Al6O18-CaO/NiO Bifunctional Material

The present work investigates the sustainable production of high-purity hydrogen through sorption enhanced steam reforming of glycerol (SESRG) over Ca9Al6O18-CaO/xNiO (x = 15, 20, and 25 wt %) and Ca9Al6O18-CaO/20NiO-yCeO(2) (y = 5, 10, and 15 wt %) bifunctional catalyst-sorbent materials. A wet mixing method involving limestone acidification coupled with two-step calcination was employed to prepare the bifunctional materials. Cyclic carbonation/calcination tests revealed that the bifunctional materials promoted with 10 and 15 wt % of CeO2 possessed an excellent CaO conversion (97% in both cases) and a remarkable cyclic stability (up to 15 cycles). This was mainly attributed to the thin shell-connected structure formed by the addition of CeO2 and the oxygen mobility characteristic of CeO2. The use of Ca9Al6O18-CaO/xNiO materials in five consecutive SESRG/regeneration cycles revealed that they suffered from fast deactivation mainly due to CaO sintering and coke deposition. Despite the high H-2 purity obtained (similar to 98%), the prebreakthrough time and hydrogen yield decreased significantly over five cycles. Interestingly, the addition of CeO2 to the most efficient catalyst (Ca9Al6O18-CaO/20NiO) resulted in a significant improvement in material stability during cyclic operation. The performance of CeO2-promoted materials was shown to depend strongly on the CeO2 content which controlled the number of adjacent Ni active sites, the amount of coke deposition, and the degree of CaO sintering. The bifunctional material promoted with 10 wt % of CeO2 showed the best performance over five consecutive SESRG/regeneration cycles, with a stable H-2 purity of similar to 98%, H-2 yield of similar to 91%, and prebreakthrough time of 48 min. The long-term cyclic stability test of Ca9Al6O18-CaO/20NiO-10CeO(2) over 20 cycles exhibited a very stable performance with a H-2 yield of 91% and H-2 purity of 98% within 20 cycles, confirming the high potential of this material for SESRG process.