A bi-functional Co-CaO-Ca₁₂Al₁₄O₃₃ catalyst for sorption-enhanced steam reforming of glycerol to high-purity hydrogen

Sorption enhanced steam reforming of glycerol (SESRG) enables the production of high-purity hydrogen from the by-product of biodiesel manufacture. To this end, highly stable catalysts and CO₂ sorbents are desired to overcome the performance degradation at high temperatures. Herein, a bi-functional catalyst, Co-CaO-Ca₁₂Al₁₄O₃₃, is proposed to couple CO₂ sorption and catalytic reforming of glycerol on nanoscale. The catalyst was derived from a Co-Ca-Al hydrotalcite-like (HTl) material to achieve homogeneous mixing of Co, CaO and Ca₁₂Al₁₄O₃₃ as a spacer to prevent CaO sintering. At Ca/Al of 2.8, the highest catalytic activity and sorption capability were reached. Over the optimized catalyst, high-purity H₂ of 96.4% was produced at 525°C through SESRG during the pre-breakthrough stage. High stability of the bi-functional catalyst was demonstrated by a cyclic SESRG-calcination operation up to 50 times. The role of Ca₁₂Al₁₄O₃₃ as spacer of CaO was proved by XRD and TEM-EDS analysis. In addition, it was found that Ca₃Co₂O₆, which is formed during the calcination stage and is reduced during the SESRG to release Co catalysts, may act as a dynamic reservoir of Co catalysts to prevent Co from sintering, leading to an excellent SESRG activity and stability.