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[Display omitted] • Much more coke forms in upper-layer Ni/KIT-6 in steam reforming of acetic acid. • Used Ni/KIT-6 is more effective to inhibit coking than fresh counterpart Ni/KIT-6. • More O-containing species form over used catalyst via influence from original coke. • O-containing species pass down to lower layer and promote polymeric coke formation. • Used catalyst in upper layer reduces the stability and crystallinity of coke. Deactivated or coked catalyst from steam reforming may not always be treated as a solid waste, which might be potentially used as a sacrificial or protective layer of catalyst for reducing coke formation of catalyst in the lower bed in the same steam reforming process. In this study, steam reforming of acetic acid over Ni/KIT-6 at 600 °C was conducted with used Ni/KIT-6 in upper layer and freshly reduced Ni/KIT-6 in lower layer (dual-bed system). The results suggested that significantly more coke (3 to 4 times) formed on upper-layer catalyst (used or fresh catalyst) than on lower-layer fresh catalyst. The upper-layer used catalyst was more effectively than counterpart of fresh catalyst for mitigating coking in lower-layer catalysts. The in-situ IR technique suggested that carbonaceous species on the used catalyst impacted or reacted with the intermediates newly formed, generating more oxygen-containing species with functionalities like C O C and C O of anhydride or ketones/aldehyde form. These oxygen-containing species could polymerize/condense and pass down to the lower bed, forming more polymeric coke of lower thermal stability. Differently, more unsaturated hydrocarbon species formed on the upper-layer fresh catalyst, making the coke of highly aromatic nature with a higher thermal stability and crystallinity. Additionally, modification of reaction intermediates with the used catalyst in upper layer also formed carbon nanotubes of irregular structures with coarse surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyro-reforming of sawdust co-produces H 2 and heavy organics effectively above 550℃. • Small acids and ketones are reformed while furans, anhydrate sugars, phenols retain. • Coking from cracking/polymerization of volatiles reached the maximum at 500℃. • Dominant reforming at 650℃ aids coke elimination and forms nanotube coke. • Coke at lower temperature is amorphous and more aliphatic with low crystallinity. In hydrotreatment of bio-oil, it is difficult to convert the aliphatic compounds with the carbon number less than four into liquid fuel via hydrodeoxygenation. Thus, ideally, the very light organics of bio-oil could be reformed to generate hydrogen for further upgrading the heavier organics in bio-oil to biofuel or fine chemicals. In this study, the pyrolysis of poplar sawdust coupled with the simultaneously steam reforming of the bio-oil (pyro-reforming) were studied over Ni/SBA-15 catalyst at the medium temperature range from 450 to 650 °C for transforming mainly the light aliphatic compounds into H 2. The results showed that the effective steam reforming of the aliphatic compounds like carboxylic acid and small aldehydes/ketones took place to remarkable extent from 550 °C, while the furans, anhydrate sugars, light phenols and heavy phenolics of fused ring structures could be largely retained in the resulting bio-oil. Coking reached the maximum with increasing temperature to 500 °C from cracking/polymerization of the volatiles. Further increase of temperature to 650 °C accelerated steam reforming and gasification of precursors of coke, shifting the morphology of coke from amorphous form to unregular carbon nanotube structures (stringed beads-like) and making the coke more aromatic and more resistant to oxidation. Nevertheless, in overall, the coke produced from 450 to 650 °C was aliphatic with low C/H ratio, low thermal stability and low crystallinity, originating from the significant contribution from the aliphatic compounds in the bio-oil for coking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reactions of volatile and biochar fill pores via forming carbon deposit on biochar. • Aliphatic of cellulose are more reactive than phenolics of lignin with biochar. • Volatile-char interaction consumes aldehydes/ketones and π-conjugated organics. • Volatile-char interaction dominate pore formation instead of activation with H 2 O/CO 2. • Interaction aids deoxygenation, forming C-rich biochar of higher energy yield. CO 2 and H 2 O are commonly used oxidants for activation of carbonaceous feedstock, which are also major products in biomass pyrolysis. The heated CO 2 and H 2 O from pyrolysis might be used directly to activate biochar without cooling down. This was investigated in a reactor with dual fixed beds with biochar on the bottom and biomass feedstock (poplar sawdust, cellulose, or lignin) of the same origin on top. The CO 2 and H 2 O together with the volatiles generated at 700 °C from the top bed passed through the lower-bed biochar for activation. The results indicated that, except for CO 2 and H 2 O, the volatiles from pyrolysis of upper-bed biomass were highly reactive with the lower-bed biochar, especially for the cellulose-derived aliphatic volatiles. This formed carbonaceous deposit and enhanced the yield of biochar at expense of the volatiles (i.e. aldehydes/ketones and heavy organics of large π-conjugated structures), leading to lower yields of bio-oil. The carbonaceous deposit formed via cracking and/or polymerization filled the pores and substantially decreased the surface specific area by 99.9 % for sawdust-biochar, 87.4 % for cellulose-biochar, and 33.1 % for lignin-biochar. The volatile-char interaction, instead of the activation with CO 2 and H 2 O, dominated the pore development of biochar. Additionally, the interaction of volatiles with biochar enhanced deoxygenation, producing the carbon-rich biochar of higher heating value and energy yield. [ABSTRACT FROM AUTHOR]