Regulating cobalt chemical state by CeO2 facets preferred exposure for improved ethanol steam reforming

Regulating the chemical state of Co sites to develop high-performance Co-based catalysts for ethanol steam reforming reaction is desirable but challenging. Herein, we report an effective strategy of tuning chemical states of Co sites by preferred exposure of CeO2 facets. The as-prepared Co/CeO2-(M) and Co/CeO2-(U) catalysts have exposure preference of (111) facet and (100) facet of CeO2 supports, respectively. The results demonstrate that the Co/CeO2-(M) has Co sites in lower oxidation state and exhibits higher C-C bond cleavage capability and more excellent catalytic performance for ethanol steam reforming reaction than Co/CeO2-(U), the hydrogen selectivity reaches as high as 97% at ethanol conversion of 100%. In situ synchrotron radiation photoionization mass spectrometry and density functional theory calculations reveal that Co site in low oxidation state has a significant preference for carbon chain shortening by C-C cleavage over carbon chain lengthening by condensation reaction, thus improving the hydrogen production efficiency of ethanol steam reforming reaction. This work provides an effective strategy to enhance the catalytic performances of Co-based catalysts for ethanol steam reforming reaction and expands the understanding about ethanol steam reforming reaction mechanism.