Importance of oxygen-containing functionalities and pore structures of biochar in catalyzing pyrolysis of homologous poplar

Biochar and bio-oil are produced simultaneously in one pyrolysis process,and they inevitably contact and may interact,influencing the composition of bio-oil and modifying the structure of biochar.In this sense,biochar is an inherent catalyst for pyrolysis.In this study,in order to investigate the influence of functionalities and pore structures of biochar on its capability for catalyzing the conversion of homologous volatiles in bio-oil,three char catalysts(600C,800C,and 800AC)produced via pyrolysis of poplar wood at 600 or 800℃or activated at 800℃,were used for catalyzing pyrolysis of homologous poplar wood at 600℃,respectively.The results indicated that the 600C catalyst was more active than 800C and 800AC for catalyzing cracking of volatiles to form more gas(yield increase by 40.2%)and aromatization of volatiles to form more light or heavy phenolics,due to its abundant oxygen-containing functionalities acting as active sites.The developed pores of the 800AC showed no such catalytic effect but could trap some volatiles and allow their further conversion via sufficient aromatization.Nevertheless,the interaction with the volatiles consumed oxygen on 600C(decrease by 50%),enhancing the aromatic degree and increasing thermal stability.The dominance of deposition of carbonaceous material of a very aromatic nature over 800C and 800AC resulted in net weight gain and blocked micropores but formed additional macropores.The in situ diffuse reflectance infrared Fourier transform spectroscopy characterization of the catalytic pyrolysis indicated superior activity of 600C for removal of -OH,while conversion of the intermediates bearing C=O was enhanced over all the char catalysts.

Thermal pretreatment of willow branches impacts yield and pore development of activated carbon in subsequent activation with ZnCl_(2) via modifying cellulose structure

Development of pore structures of activated carbon(AC)from activation of biomass with ZnCl_(2) relies on content and structure of cellulose/hemicellulose in the feedstock.Thermal pretreatment of biomass could induce dehydration and/or aromatization to change the structure of cellulose/hemicellulose.This might interfere with evolution of structures of AC,which was investigated herein via thermal pretreatment of willow branch(WB)from 200 to 360℃and the subsequent activation with ZnCl_(2) at 550℃.The results showed that thermal pretreatment at 360℃(WB-360)could lead to substantial pyrolysis to form biochar,with a yield of 31.9%,accompanying with nearly complete destruction of cellulose crystals and remarkably enhanced aromatic degree.However,cellulose residual in WB-360 could still be activated to form AC-360 with specific surface area of 1837.9 m~2·g^(-1),which was lower than that in AC from activation of untreated WB(AC-blank,2077.8 m~2·g^(-1)).Nonetheless,the AC-200 from activation of WB-200 had more developed pores(2113.9 m~2·g^(-1))and superior capability for adsorption of phenol,due to increased permeability of ZnCl_(2) to the largely intact cellulose structure in WB-200.The thermal pretreatment did increase diameters of micropores of AC but reduced the overall yield of AC(26.8%for AC-blank versus 18.0%for AC-360),resulting from accelerated cracking but reduced intensity of condensation.In-situ infrared characterization of the activation showed that ZnCl_(2) mainly catalyzed dehydration,dehydrogenation,condensation,and aromatization but not cracking,suppressing the formation of derivatives of cellulose and lignin in bio-oil.The thermal pretreatment formed phenolic-OH and C=O with higher chemical innerness,which changed the reaction network in activation,shifting morphology of fibrous structures in AC-blank to“melting surface”in AC-200 or AC-280.

Key Considerations on the Industrial Application of Lignocellulosic Biomass Pyrolysis Toward Carbon Neutrality

1.The importance of biomass in carbon neutrality With the increasing urgency to mitigate climate change,over 100 countries have committed to net-zero carbon emissions by the mid-21st century[1].For example,China has announced that it will reach a carbon peak and carbon neutrality,with the rapid development of renewable energy undoubtedly playing a key role in achieving these goals.Compared with other renewable energy sources,such as wind energy,solar energy.

Steam reforming of acetic acid over Ni/biochar of low metal-loading:Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming,which could influence the formation of reaction intermediates and modify catalytic behaviors.Herein,the Ni/biochar as well as two comparative catalysts,Ni/Al_(2)O_(3) and Ni/SiO_(2),with low nickel loading(2%(mass))was conducted to probe involvement of the varied carriers in the steam reforming.The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO_(2) and Ni/Al_(2)O_(3),as the biochar carrier facilitated quick conversion of the -OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C=O and C-O-C,resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance.In converse,strong adsorption of aliphatic intermediates over Ni/Al_(2)O_(3) and Ni/SiO_(2) induced serious coking with polymeric coke as the main type(21.5%and 32.1%,respectively),which was significantly higher than that over Ni/biochar(3.9%).The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity.The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam,which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al_(2)O_(3) and Ni/SiO_(2) catalysts.

Two-dimensional nanomaterials confined single atoms: New opportunities for environmental remediation

Two-dimensional(2D)supports confined single-atom catalysts(2D SACs)with unique geometric and electronic structures have been attractive candidates in different catalytic applications,such as energy conversion and storage,value-added chemical synthesis and environmental remediation.However,their environmental appli-cations lack of a comprehensive summary and in-depth discussion.In this review,recent progresses in synthesis routes and advanced characterization techniques for 2D SACs are introduced,and a comprehensive discussion on their applications in environmental remediation is presented.Generally,2D SACs can be effective in catalytic elimination of aqueous and gaseous pollutants via radical or non-radical routes and transformation of toxic pollutants into less poisonous species or highly value-added products,opening a new horizon for the contami-nant treatment.In addition,in-depth reaction mechanisms and potential pathways are systematically discussed,and the relationship between the structure-performance is highlighted.Finally,several critical challenges within this field are presented,and possible directions for further explorations of 2D SACs in environmental remediation are suggested.Although the research of 2D SACs in the environmental application is still in its infancy,this review will provide a timely summary on the emerging field,and would stimulate tremendous interest for designing more attractive 2D SACs and promoting their wide applications.

Hydrothermal carbonization pretreatment makes a remarkable difference in activation of rice and lettuce in food waste

Cooked rice and the vegetables like lettuce are common kitchen waste,which are carbonaceous materials and have the potential as feedstock for the production of activated carbon.Cooking is similar to hydrothermal treatment(HTC),which might impact the subsequent activation of kitchen waste.In this study,the HTC of lettuce,rice,or their mixture and the activation of the resulting hydrochars were conducted.The results indicated that cross-polymerization between the N-containing organics from lettuce and the sugar derivatives from rice took place in their co-HTC,which significantly increased the hydrochar yield.Activation of the hydrochar from the coHTC generated the AC with a yield of 2 times that from direct activation of mixed lettuce/rice.However,the coHTC facilitated aromatization,reducing reactivity with K2C2O4in activation and producing the AC with main micropores and low specific surface area.Activation of the hydrochar from HTC of rice followed the above trend,while that from lettuce was the opposite.The organics in lettuce were thermally unstable and could not undergo sufficient aromatization.The activation of hydrochar from HTC of lettuce thus generated the AC with the lowest yield,but the highest specific surface area(1684.9 m2/g),abundant mesopores,and superior capability for adsorption of tetracycline.However,the environmental impacts and energy consumption for the production of AC from the hydrochar of lettuce were higher than that from hydrochar of co-HTC.

Sequential pyrolysis for understanding specific influence of cellulose- and lignin-derived volatiles on properties of counterpart char

Interactions of cellulose-and lignin-derived intermediates have been well documented during pyrolysis of lignocellulosic biomass.The reaction network for the interactions is rather complex,as cellulose-derived volatiles could interact/react with not only lignin-derived volatiles but also lignin-derived char and vice versa.To probe specifically the impacts of cellulose-derived volatiles on the lignin-derived char or the opposite,herein the sequential pyrolysis was performed by arranging cellulose in the upper bed with lignin in the lower bed or lignin above with cellulose below at 350 and 650℃,respectively.The results indicated that the sequential pyrolysis of cellulose→lignin or lignin→cellulose at 350℃induced increased char yield from formation of carbonaceous deposits via volatiles-char interactions.Compared with the lignin-derived volatiles,the cellulose-derived volatiles,especially aldehyde fractions,were more reactive towards the lignin-derived char at 350℃,forming oxygen-rich lignin-derived char with a higher yield,an abundance of aliphatic structures and consequently lower thermal stability.In sequential pyrolysis of lignin→cellulose,more aromatics-rich species were deposited on cellulose-derived char,but the lignin-derived volatiles were less reactive for enhancing the char yield.At 650℃,instead of polymerisation of the volatiles on the char,either the cellulose-or lignin-derived char catalyzed the cracking of the counterpart volatiles to remove the aliphatic functionalities,which made the char more aromatic and thermally more stable.

Mg-Al-hydrotalcite with alkaline sites protects Ni/KIT-6 from formation of amorphous coke in glycerol steam reforming via tailoring reaction intermediates

During steam reforming,the performance of a catalyst and amount/property of coke are closely related to reaction intermediates reaching surface of a catalyst.Herein,modification of reaction intermediates by placing Mg-Al-hydrotalcite above Ni/KIT-6 catalyst in steam reforming of glycerol was conducted at 300 to 600°C.The results revealed that the catalytic activity of Ni/KIT-6 in the lower bed was enhanced with either Mg1-Al5-hydrotalcite(containing more acidic sites)or Mg5-Al1-hydrotalcite(containing more alkaline sites)as upper-layer catalyst.The in situ infrared characterization of steam reforming demonstrated that Mg-Al-hydrotalcite catalyzed the deoxygenation of glycerol,facilitating the reforming of the partially deoxygenated intermediates over Ni/KIT-6.Mg-Al-hydrotalcite as protective catalyst,however,did not protect the Ni/KIT-6 from formation of more coke.Nonetheless,this did not lead to further deactivation of Ni/KIT-6 while Mg5-Al1-hydrotalcite even substantially enhanced the catalytic stability,even though the coke was much more significant than that in the use of single Ni/KIT-6(52.7%vs.28.6%).The reason beneath this was change of the property of coke from more aliphatic to more aromatic.Mg5-Al1-hydrotalcite catalyzed dehydration of glycerol,producing dominantly reaction intermediates bearing C=C,which formed the catalytic coke of with carbon nanotube as the main form with smooth outer walls as well as higher aromaticity,C/H ratio,crystallinity,crystal carbon size,thermal stability,and resistivity toward oxidation on Ni/KIT-6 in the lower bed.In comparison,the abundance of acidic sites on Mg1-Al5-hydrotalcite catalyzed the formation of more oxygen-containing species,leading to the formation of carbon nanotubes of rough surface on Ni/KIT-6.

Cross-interaction of volatiles from co-pyrolysis of lignin with pig manure and their effects on properties of the resulting biochar

Biomass and pig manure have distinct compositions and the co-pyrolysis of them has gained much attention.However,the influence of volatiles interaction on the properties of the char was still unclear.In this study,lignin was selected as the model component of biomass with pig manure for co-pyrolysis at 600°C.The results indicate that volatiles from co-pyrolysis promoted re-condensation reaction,resulting in the higher char yield(48.0%in co-pyrolysis versus 31.0%in pyrolysis of single manure)and the formation of more aromatics in bio-oil.The co-pyrolysis also facilitated the dehydrogenation and dehydration reactions,which accounted for the elimination of oxygen and nitrogen contents and thus a higher carbon content(64.7%in the co-pyrolysis versus the averaged value of 46.4%from the pyrolysis of single feedstock),higher crystallinity and thermal stability of the char.The in-situ diffuse reflection infrared Fourier transform spectroscopy(DRIFTS)characterization results demonstrated that the functionalities abundances of char with temperature was influenced by volatiles interaction via accelerating the carbonization reaction.In addition,the high heating value(HHV)of char was obviously improved by cross-interaction of volatiles during co-pyrolysis(24.4 MJ/Kg in co-pyrolysis versus averaged value of 15.1 MJ/Kg from single pyrolysis),implying that the co-pyrolysis enhanced the energy density of the resulting char.

Crystallization and viscosity-temperature characteristics during co-gasification of industrial sludge and coal

Co-gasification of industrial sludge(IS)and coal was an effective approach to achieve harmless and sustainable utilization of IS.The long-term and stable operation of a co-gasification largely depends on fluidity of coal-ash slag.Herein,the effects of IS addition on the crystallization and viscosity of Shuangmazao(SMZ)coal were investigated by means of high temperature stage coupled with an optical microscope(HTSOM),a scanning electron microscopy coupled with an energy dispersive Xray spectrometry(SEM-EDS),X-ray diffraction(XRD),a Fourier transform infrared spectrometer(FTIR),and FactSage software.The results showed that when the proportion of IS was less than 60%,with the addition of IS,the slag existed in an amorphous form.This was due to the high content of SiO_(2) and Al_(2)O_(3) in SMZ ash and blended ash,which had a high glass-forming ability(GFA).The slag formed at a high temperature had a higher polymerization degree and viscosity,which led to a decrease in the migration ability between ions,and ultimately made the slag difficult to crystallize during the cooling.When the proportion of IS was higher than 60%,the addition of IS increased the CaO and FeO content in the system.As network modifiers,CaO and FeO could provide O^(2−)at a high temperature,which reacted with silicate network structure and continuously destroyed the complexity of network structure,thus reducing the polymerization degree and viscosity of slag.At this time,the migration ability between ions was enhanced,and needle-shaped/rod-shaped crystals were precipitated during the cooling process.Finally,the viscosity calculated by simulation and Einstein-Roscoe empirical formula demonstrated that the addition of IS could significantly improve the fluidity of coal ash and meet the requirements of the liquid slag-tapping gasifier.The purpose of this work was to provide theoretical support for slag flow mechanisms during the gasifier slagging-tapping process and the resource treatment of industrial solid waste.

Carbon-based single-atom catalysts in advanced oxidation reactions for water remediation:From materials to reaction pathways

Single-atom catalysts(SACs)have been widely recognized as state-of-the-art catalysts in environment remediation because of their exceptional performance,100%metal atomic utilization,almost no secondary pollution,and robust structures.Most recently,the activation of persulfate with carbon-based SACs in advanced oxidation processes(AOPs)raises tremendous interest in the degradation of emerging contaminants in wastewater,owning to its efficient and versatile reactive oxidant species(ROS)generation.However,the comprehensive and critical review unraveling the underlying relationship between structures of carbon-based SACs and the corresponding generated ROS is still rare.Herein,we systematically summarize the fundamental understandings and intrinsic mechanisms between single metal atom active sites and produced ROS during AOPs.The types of emerging contaminants are firstly elaborated,presenting the prior pollutants that need to be degraded.Then,the preparation and characterization methods of carbon-based SACs are overviewed.The underlying material structure–ROS type relationship in persulfate-based AOPs is discussed in depth to expound the catalytic mechanisms.Finally,we briefly conclude the current development of carbon-based SACs in AOPs and propose the prospects for rational design and synthesis of carbon-based SACs with on-demand catalytic performances in AOPs in future research.