Influence of steam on nature of coke formed in thermal conversion of ethanol using Ni/SBA-15 catalyst

In steam reforming, polymerization/cracking of reactant could take place in parallel with reforming reactions, which are important routes for coking and might form coke of distinct nature with that from reforming. This study investigated the decomposition or steam reforming of ethanol over a Ni/SBA-15 catalyst at 400, 550, and 700 °C, respectively. The results indicated that decomposition of ethanol formed more abundant carbonaceous species bearing C=C at 500–600 °C than that from steam reforming. These carbon-rich intermediates were precursors of coke, rendering production of more coke (mass ratio of coke to catalyst in decomposition versus reforming: 48.6 % versus 28.2 % at 400 °C; 86.4 % versus 57.8 % at 550 °C; 28.7 % versus 8.7 % at 700 °C), due to lack of steam to oxidize them into aliphatic oxygen-containing species. A high concentration of carbonaceous intermediates in decomposition of ethanol formed more aromatic and thermally more stable coke than that from steam reforming. Coking was the most significant at 550 °C in decomposition or reforming, because of accumulation of carbonaceous intermediates from cracking and low efficiency for their gasification. This formed coke of irregular carbon nanotubes or carbon nanobeads with abundant aliphatic structures.