Bifunctional Ni–CaO catalysts modified with CeO2 and inert Ca12Al14O33 for sorption-enhanced steam reforming of ethanol

Abstract

In this work, sorption-enhanced steam reforming of ethanol (SE-SRE) process was studied using Ni–CaO-based bifunctional catalysts modified with Ca12Al14O33 (mayenite) and CeO2. The CaO and CaO/Ca12Al14O33 sorbents were synthesized by a sol-gel method and, subsequently, CeO2 and Ni were added by the incipient wetness impregnation method. These materials were characterized by BET surface area, thermogravimetric analysis (TGA), in situ X-ray diffraction (XRD), and in situ X-ray absorption near edge structuare (XANES). In addition, the catalysts were tested on 10 cycles of SE-SRE reaction and regeneration. In general, the characterization results revealed an inverse relationship between average crystallite size of CaO and CO2 sorption capacity. By the in situ XRD/XANES, the addition of the mayenite reduced by half the average crystallite size of CaO and increased the interaction between support and active phase. As a consequence, the catalyst containing mayenite (NiCaAl) showed the best CO2 capture uptake and stability, which could be justified mitigation of the CaO sintering effect by the inert material presence. Great stability was also observed in the catalytic tests, since the duration of the pre-breakthrough stage for NiCaAl and for the catalyst containing maynite and ceria (NiCaAlCe) remained constant over the reaction cycles. In terms of hydrogen production, NiCaAl catalyst showed the highest H2 molar fraction during the pre- (90%) and post-breakthrough. The CeO2 addition slightly favored the methane formation, although did not bring significant benefits in the CO2 capture and catalytic performance. Therefore, NiCaAl showed the best CO2 capture capacity and stability, which led to the best SE-SRE performance.