Distinct coking depth in steam reforming of oxygen-containing organics and hydrocarbons.

In steam reforming of organics in a fixed-bed reactor, catalyst particles in varied location of catalyst bed will experience different history of contacting with reactants/products. This may affect accumulation of coke in varied section of catalyst bed, which are investigated in steam reforming of some typical oxygen-containing organics (acetic acid, acetone and ethanol) and hydrocarbons (n-hexane and toluene) in a fixed-bed reactor with double layers of catalyst bed for investigating coking depth at 650 °C over Ni/KIT-6 catalyst in this study. The results indicated that the intermediates derived from the oxygen-containing organics in steam reforming could hardly penetrate the upper-layer catalyst to form coke in the lower-layer catalyst. In converse, they reacted quickly over the upper-layer catalyst via gasification or coking, forming coke almost exclusively in the upper-layer catalyst. The hydrocarbon intermediates from the dissociation of hexane or toluene could easily penetrate and reach the lower-layer catalyst to form even more coke therein than the upper-layer catalyst. The characterization showed that the insufficient gasification of *CxHy species led to their aggregation/integration to form more aromatic coke, especially from n-hexane. The aromatic-ring containing intermediates from toluene tended to integrate with *OH species to form ketones that further involved in coking, forming coke of less aromatic nature than that from n-hexane. Steam reforming of oxygen-containing organics also produced oxygen-containing intermediates and coke of higher aliphatic nature, lower carbon to hydrogen (C/H) ratio, lower crystallinity and thermal stability.