High purity H2 production from sorption enhanced bio-ethanol reforming via sol-gel-derived Ni–CaO–Al2O3 bi-functional materials

Abstract

Catalytic steam reforming of renewable bio-oxygenates coupled with in-situ CO2 capture is a promising option for sustainable H2 production. The current work focuses on high purity H2 production over Ni–CaO–Al2O3 bi-functional materials via sorption enhanced steam reforming of ethanol (SEESR). To ensure the uniform distribution of catalytic sites (Ni), adsorptive sites (CaO) and stabilizer (Al2O3) in the bi-functional materials, a citrate sol-gel synthetic route was employed. These materials were characterized by XRD, N2 physical adsorption, SEM, TG and TPR techniques. It was revealed that the existence of CaO in bi-functional materials could not only in-situ remove CO2, but also play the role of inhibiting the formation of harmful spinel phase. The stabilizing role of Al component against capacity decay was confirmed, whereas the presence of Ni ions had a negative effect on the cycle CO2 uptake. The sample of Ni/Al/Ca-85.5 possessed large specific surface area, abundant porosity with fluffy morphology, and thereby, exhibited the best CO2 sorption capacity during 20 carbonation/calcination cycles. The highest H2 concentration of 96% was obtained through the SEESR during the pre-breakthrough period when the Ni/Al/Ca-85.5 was employed. Over the optimized bi-functional material, the effect of operating conditions on the SEESR was investigated and the results indicated that temperature of 600 °C, reaction liquid space velocity of 0.05 ml/min and steam/ethanol ratio of 4 were the suitable conditions. After 10 cycles, the bi-functional material of Ni/Al/Ca-85.5 also showed the best performance, with a H2 purity of about 90% and pre-breakthrough time of 18 min, conforming the high potential of this material for SEESR process.