Catalytic activities of K-modified zeolite ZSM-5 supported rhodium catalysts in low-temperature steam reforming of bioethanol

摘要

Recently, zeolite materials have attracted attention as efficient catalysts for low-temperature steam reforming of bioethanol (SRE). However, cost-effective zeolite ZSM-5 materials, one of the most popular industrial reforming catalysts, were rarely reported for SRE. In this study, low-load rhodium (Rh) catalysts are prepared using commercial high-silica zeolite ZSM-5 as the supports. The commercial zeolite ZSM-5 has strong acidic sites that lead to fairly extensive dehydration of bioethanol. To generate basic sites and mesoporous structure, zeolite supports are modified by K ion exchange and alkali treatment. The effect of the physicochemical properties of the modified supports on low-temperature SRE reaction is investigated by SEM, TEM, XRD, XRF, TPD, NMR and N-2 adsorption. The results indicate that strong acidic sites in zeolite ZSM-5 can be effectively neutralized by K ion exchange, while basic sites in zeolite ZSM-5 are noticeably altered only by alkali treatment. The hydrogen selectivity can be significantly promoted by the alkalinity of the zeolite KZSM-5, however, only the moderate alkali-treated Rh/S2 catalyst retains its high activity during reaction. Our results appear to demonstrate the positive effect of the special zeolitic structure of the Rh/52 catalyst with uniform mesopores, which can improve the Rh dispersion and avoid its sintering. Moreover, there seem to be a unique synergy between the Rh active component and the alkali-treated zeolite support, which might result in the lowest CO selectivity at 300-400 degrees C. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.