Steam reforming of sugar and its derivatives: Functionality dictates thermal properties and morphologies of coke

Abstract Coking is a major challenge in steam reforming of oxygenated organics, especially the ones in bio-oil with multiple oxygen-containing functionalities. The property of the resulting coke is believed to relate with structures of the organics. In this study, steam reforming of xylose, xylitol and furfural, which are representatives of sugars, alcohols of multiple hydroxyl groups, and furans, were performed to correlate molecular structure and property of coke. The results showed that xylose polymerized rapidly during the steam reforming, forming initially π-conjugated polymeric organics and substantial amount of coke that was amorphous, aliphatic, thermally unstable with abundant olefin C = C and –OH. In comparison, steam reforming of xylitol generated little coke, as xylitol contains no C = O that was the primary reason for the serious coking in xylose reforming. Steam reforming of furfural also generated large amount of coke that was mainly aromatic with high thermal stability and high resistance towards oxidation, due to the reserve of the furan ring-like structure in the coke. Functionalities of the reactants dictated the thermal properties of the coke and also their morphologies. The amorphous coke formed in xylose reforming was bubble-like, while the coke in furfural reforming mainly included carbon nanofiber of rugged surface and carbon nanotubes of thick wall. The multiple hydroxyl groups in xylitol, however, resulted in the coke of carbon nanotube form with large inner diameters.