Saturation of carbonyl functionality in xylose and glucose via hydrogenation minimizes coke formation in steam reforming

Sugar is known to be reactive at elevating temperature and its carbonyl functionality is a reactive center. Saturation of CO in sugars to –OH via hydrogenation might reduce reactivity of sugars towards especially coking in steam reforming (SR). Such a hypothesis was verified herein by hydrogenation of xylose and glucose to xylitol and sorbitol first and subsequent SR of the resulting polyols. The results indicated that the polyols could actively involve in SR to generate H2, while xylose/glucose or their derivatives formed via dehydration and retro-aldol condensation mainly polymerized, forming significantly more coke (ratio of coke in catalyst: 59.9% from xylose versus 16.3% from xylitol and 44.5% from glucose versus 19.5% from sorbitol). Absence of CO blocked conversion of xylitol and sorbitol via retro-aldol condensation, diminishing formation of coke precursors like aldehydes/ketones. Coke formed from SR of the sugars was polymeric type of highly aliphatic nature with low C/H ratio (1.0–1.3), highly thermally unstable, reactive towards oxidization and highly amorphous. The coke from homogeneous polymerization of xylose/glucose was similar in nature, with oxygen content reaching ca. 30%. In comparison, the coke from SR of xylitol and sorbitol was mainly catalytic coke of higher aromatization degree/crystallinity and existed mainly in carbon nanotube form.