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Metal/biochar is an important category of catalyst that can be prepared via direct impregnation of metal salt to a biomass feedstock. However, during pyrolysis of metal salt@biomass for catalyst preparation, metal-volatiles interaction might affect exposure or dispersion of metal species. To verify this, loading of nickel acetate to poplar sawdust directly and to the sawdust-derived biochar was conducted to prepare Ni/biochar and biochar/Ni at 500 or 750 °C, aiming to understand the effect of metal-volatiles interaction on exposure of nickel species in resulting Ni/biochar. The results indicated Ni species catalyzed cracking, dehydrogenation, and reforming reactions in sawdust pyrolysis, producing more bio-oil/gases at the expense of biochar and also making biochar of higher aromatic degree with improved thermal stability. The in-situ IR characterizations also evidenced high activity of Ni towards dehydration and cracking of carbonyls for enhancing aromatization of biochar. In biochar/Ni catalysts prepared via loading nickel to biochar, little metal-volatiles interaction existed and nickel species weakly interacted with the biochar, resulting in remarkable migration and agglomeration of nickel, forming nickel size of 2–3 times larger than that in Ni/biochar. However, biochar/Ni possessed higher capability for adsorption/activation of H 2 , thus exhibiting superior catalytic activity than Ni/biochar for hydrogenation of phenolics. [Display omitted] • Ni accelerates removal of O-containing species in pyrolysis, enhancing aromatization of Ni/biochar. • In-situ IR characterization shows superior activity of Ni for dehydration, dehydrogenation, and cracking. • Migration of Ni in biochar/Ni prepared from impregnating biochar forms larger Ni size. • Ni in Ni/biochar is partially covered by deposits from cracking/polymerization of volatiles. • Biochar/Ni shows higher capability for H 2 adsorption and hydrogenation than Ni/biochar. [ABSTRACT FROM AUTHOR]

Almost all small organics, in theory, could be potential feedstock for production of hydrogen via steam reforming (SR). Nevertheless, not all organics contain a linear carbon chain like ethanol or acetone. How do ring structure of an organic substrate impacted coking behaviors in SR were explored herein with n-butanol and tetrahydrofuran (THF) as the research objects over Ni/SiO 2 catalyst, due to the same carbon number but distinct carbon chains in these two molecules. The results indicated that furan ring in THF lowered reactivity towards SR, as its adsorption on metallic sites was more difficult than n-butanol. The in-situ IR analysis for measuring reaction intermediates suggested that n-butanol and THF involved generation of intermediates with C O formed via dehydrogenation, C x H y formed via cracking and C C species that can be further gasified or aggregate to coke. However, more oxygenated intermediates generated in SR of n-butanol than in THF, rendering n-butanol more reactive towards SR. This, however, also formed substantially more coke of aliphatic nature in amorphous form, which led to the coke of thermally unstable and had higher tendency being oxidized. In converse, coke formed from SR of THF was more aromatic, showing less impact on catalytic activity, higher thermal stability, and larger crystal size with more carbon nanotube form of coke. This was closely connected with the ring structures that could dehydrogenated to form the unsaturated ring with capability to involve in Diels-Alder reactions, forming coke of aromatic nature. [Display omitted] • The short-term stability reforming activity of THF remained unchanged, while the activity of n-butanol decreased. • The coke formed by steam reforming of THF has the superior antioxidant properties and the higher thermal stability. • More oxygenated intermediates formed (e.g. C O) in steam reforming of n-butanol than that in THF. • In the steam reforming process of THF, the coke formed to the catalyst surface is more aromatic. • Coke on THF steam reforming is much less and is mainly catalytic type with high crystallinity. [ABSTRACT FROM AUTHOR]

• In-situ IR characterization shows more C x H y * species from cracking of butanol while more unsaturated ketones from diethyl ether (DEE). • Reforming of ethanol generates more O-containing species, making coke more aliphatic and thermally unstable. • Reforming of butanol and DEE forms much more coke than from ethanol, due to aggregation of abundant carbonaceous intermediates. • Carbon-rich intermediates from butanol or DEE forms coke of aromatic nature with high crystallinity. • Coke from DEE is more defective with rough surface, while that from butanol is more graphitic with smooth surface. Molecular structures of organics play key roles in determining the tendency of coking and property of coke through governing reaction intermediates formed. Diethyl ether (DEE) can be produced from etherification of ethanol and has same carbon number with n-butanol (butanol), while they may show distinct coking behaviors in steam reforming (SR). Herein, SR of DEE, ethanol and butanol over Ni/SBA-15 catalyst were performed, aiming to probe impacts of ether functionality and length of carbon chain of the alcohols on coke formation. The results indicated that cracking of DEE formed C x H y * species and unsaturated ketone intermediates, serving as precursors of coke. Dissociative adsorption of butanol formed abundant C x H y * species even from 100 °C, due to its longer carbon chain and lower oxygen content. In comparison, abundant oxygen-containing intermediates were generated from degradation of ethanol and reactions with steam. Abundant C x H y * species from DEE and butanol prompted formation of more coke than that from ethanol (60.6 % of coke in the catalyst for DEE, 66.8 % for butanol and 32.9 % for ethanol). Moreover, the coke from SR of ethanol was thermally less stable than that from DEE or butanol, due to the involvement of more oxygen-containing intermediates, which resulted in more aliphatic coke of amorphous form in ethanol reforming. Additionally, the coke from DEE reforming was more defective with carbon nanotube form of thick walls and little internal cavity. The coke produced from butanol reforming was more graphitic and mainly in carbon nanotube form of smooth surface. Varied abundance of C x H y * and ketone species in reforming of DEE and butanol created such a difference. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Adding Fe weakens adsorption of O-containing organics while Cu is opposite. • Zn or Co addition enhances adsorption of –OH/CO 2 for gasifying amorphous coke. • Zn, Cu or Co addition enhanced catalytic stability and tolerance to coking. • Coke on Ni/Al 2 O 3 or Ni-Fe/Al 2 O 3 is polymeric, caused rapid catalyst deactivation. • Zn, Cu or Co addition produces catalytic coke of higher C/H ratio and crystallinity. Modification of Ni/Al 2 O 3 with transition additives is known to affect physiochemical properties of the catalyst, while this will also inevitably impact evolution of reaction intermediates and property of coke formed in steam reforming. In this study, Ni/Al 2 O 3 catalyst was modified with Fe, Zn, Cu or Co and the influences on formation of intermediate product and nature of coke was paid particular attention in steam reforming of acetic acid. The results indicated that iron or cobalt oxide reacted with NiO, forming NiFe 2 O 4 and NiCo 2 O 4 , while copper or zinc oxide reacted with alumina, forming Al 2 CuO 4 and ZnAl 2 O 4 , respectively. This weakened interaction between nickel oxide and alumina but also led to increase of nickel size, except Zn additive. Presence of Zn or Co in the catalyst enhanced adsorption of –OH or CO 2 , facilitating gasification of precursors of amorphous coke. The Cu additive intensifies adsorption/activation of oxygen-containing intermediates, while Fe was the opposite. The additive of Zn, Cu or Co, with exception of Fe, enhanced catalytic stability by suppressing formation of polymeric coke, although overall amount of coke was much higher. The coke formed in Zn, Cu or Co modified catalyst was mainly catalytic coke with a higher C/H ratio, higher crystallinity, higher thermal stability, higher portion of graphite structures, and nanotube-like structure of irregular inner cavity but with less impacts on catalytic stability. [ABSTRACT FROM AUTHOR]

• HNO 3 treatment weakens interaction between nickel and biochar in Ni/biochar. • HNO 3 treatment leads to bigger Ni size, lower Ni dispersion and more acidic sites. • HNO 3 treatment enhances contact angle from 37.4 to 92.2°, improving hydrophobicity. • Ni/biochar with medium hydrophobicity achieving H 2 yield of 82.9%. • Too high hydrophobicity does not favor gasifying intermediates bearing carbonyls. Biochar is a major product from the pyrolysis of biomass, which can be potentially used as the low costly support of nickel catalyst for steam reforming reactions. In this study, the rice husk-derived biochar supported nickel catalysts were prepared and the impacts of the treatment of the biochar support with HNO 3 on catalytic performance of the Ni/biochar catalysts in steam reforming of acetic acid were investigated. The results showed that the treatment of the biochar with the varied concentration of HNO 3 led to the change of the hydrophilicity, the pore structure, distribution of functionalities on surface of biochar, weakening of the interaction between nickel and biochar, increased size of metallic nickel, decreased lower nickel dispersion and enhanced abundance and strength of acidic sites. Among these aspects, the hydrophobicity showed the most significant effects on the catalytic activity for steam reforming of acetic acid. The Ni/biochar catalyst with medium hydrophobicity showed superior catalytic activity, as it showed capability for strong adsorption of the reaction intermediates with the C–O–C aliphatic structures and for gasification of the reaction intermediates with carbonyl functionalities. The Ni/biochar catalyst with too high hydrophobicity could not effectively gasifying the intermediates bearing C O and showed the low activity and high coking tendency. [ABSTRACT FROM AUTHOR]

The Ni/Atta catalysts with the different pores activated by KOH showed the distinct resistivity towards coke formation in steam reforming of acetic acid or guaiacol and affected the type of the reaction intermediates formed. [Display omitted] • Activation of attapulgite (Atta) with KOH enhances surface area via creating micropores. • The activation enhances Ni dispersion and abundance of basic sites Ni/attapulgite. • The activation effectively enhances activity in steam reforming of guaiacol. • Acetic acid and guaiacol encounters distinct steric hindrance over Ni/attapulgite. • Catalyst shows varied sensitivity to coke in reforming of acetic acid and guaiacol. Attapulgite clay (Atta), a natural mineral, can be used as support of various catalysts. Nevertheless, the limited surface affects its applications. In this study, the activation of Atta with KOH to enhance surface area was developed and supported nickel catalysts were evaluated in steam reforming of acetic acid or guaiacol. The results showed that the activation by KOH created abundant micropores in Atta via the solid phase reaction between KOH and SiO 2 and Al 2 O 3. The activation also enhanced reduction degree of nickel oxide, interaction between nickel and Atta, dispersion of nickel species and alkalinity of the catalyst, rendering the superior catalytic activity in steam reforming of either acetic acid or guaiacol. The in-situ Diffused Reflectance Infrared Fourier Transform Spectroscopy characterization of the steam reforming reaction indicated that the activation facilitated absorption of *OH and *CO 2 species on catalyst for gasifying the coke precursors such as the ones containing C = O, enhancing resistivity of the catalyst towards coking. In addition, owing to the different molecular structures, steam reforming of acetic acid and guaiacol over the catalyst encountered the different steric hindrance, different tendencies towards coking and different properties of coke. Specially, the catalyst showed varied sensitivity towards coking in steam reforming reaction. [ABSTRACT FROM AUTHOR]

• Na or Mg addition to Ni/SiO 2 reduces nickel dispersion while La enhanced that. • Na or Mg addition significantly increased abundance of basic sites while La did not. • The strong alkalinity induced by Na or Mg decreased catalytic activity remarkably. • Strong alkalinity favored O-containing species (i.e. CO*, C–O–C and C O) formation. • The distinct reaction intermediates led to formation of coke in varied morphology. Alkalinity is an important parameter affecting adsorption and evolution of reaction substrates in steam reforming reactions. In this study, steam reforming of guaiacol, a model compounds in the volatiles in gasification of biomass, over Ni/SiO 2 modified with Na, Mg or La was investigated. The results showed that the strong alkalinity induced by Na or Mg addition to Ni/SiO 2 led to remarkably decreased catalytic activity. The high alkalinity also promoted formation and accumulation of the oxygen-containing species such as CO*, C–O–C aliphatic structure and carbonyl functionalities, which were precursors of the polymeric products with big π-conjugated structures and coke. La addition increased the alkalinity to a mild extent and promoted the nickel dispersion, enhancing the catalytic activity and the resistivity towards coking. The formation of the thermally stable amorphous coke in the Na or Mg modified catalyst wrapped nickel sites and led to rapid catalyst deactivation. Both amorphous form and in carbon nanotube form of coke defective structures were formed over La-Ni/SiO 2 and Ni/SiO 2 catalysts, resulting from the distinct reaction intermediates formed during the steam reforming of guaiacol. [ABSTRACT FROM AUTHOR]