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Biomass is promising renewable energy because of the possibility of value-added fuels production from biomass thermochemical conversion. Among the thermochemical conversion technology, gasification could produce the H 2 -rich syngas then into value-added chemicals via F-T (Fischer-Tropsch) synthesis. However, a variety of difficulties, such as tar formation, reactors impediment, complex tar cracked mechanism, etc. make it difficult to develop for further application. This paper sheds light on the developments of biomass thermochemical conversion, tar classifications, tar formation, and elimination methods. Secondly, we provide a comprehensive the state-of-the-art technologies for tar elimination, and we introduce some advanced high activity catalysts. Furthermore, many represent tar models were employed for explanation of the tar-cracked pathway, and real tar-cracked mechanism was proposed. Following this, some operational conditions and effective gasified models were concluded to give an instruction for biomass catalytic gasification. • Overview of tar formation and elimination during biomass conversion. • In-depth discussion of tar-cracked mechanisms via tar model compounds. • A comprehensive review of tar cracked catalysts is presented. • Prospects and disadvantages of gasification reactions are discussed. [ABSTRACT FROM AUTHOR]

Catalytic fast pyrolysis of sawdust was investigated over HZSM-5 zeolites (SiO 2 /Al 2 O 3 = 25, 50 and 80) in a drop tube quartz reactor for production of green aromatics and olefins. The effects of temperature, weight hourly space velocity (WHSV), SiO 2 /Al 2 O 3 ratio and atmosphere on yield and selectivity of aromatics were investigated. The results show that almost all small organic oxygen species in initial volatiles were converted into gaseous hydrocarbons and aromatics after in situ catalysis of HZSM-5. HZSM-5 whose SiO 2 /Al 2 O 3 is 25 exhibited the best performance with the aromatics yield of 21.8% on carbon basis at 500 °C. However, HZSM-5 can act as cracking and aromatization catalyst, but not as an agent to promote hydrogenation. The ESI-MS revealed the most abundant macromolecular compounds in initial volatiles were O 1 O 27 species with 0–20 double bond equivalent (DBE) values and 5–40 carbon numbers, while the macromolecules were O 1 O 9 species with 2–12 DBE and 10–25 carbon numbers after upgrading. Furthermore, the formation of coke on catalysts was influenced by the properties of HZSM-5 and experimental conditions. Image 1 • In situ catalytic reforming of volatiles from sawdust fast pyrolysis. • Renewable olefins and aromatics were produced directly using HZSM-5. • The yield and selectivity of aromatics can be adjusted. • The macromolecular substances in bio-oils was significantly changed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interaction has insignificant effects on biochar without the presence of potassium salts. • More C-O-K bonds are formed after the interaction for biochar of wood doped with K 2 CO 3 /K 2 SO 4. • The interaction generates more active sites and decreases the biochar order. • Insignificant additional release of potassium after the interaction. Co-gasification of biomass and coal has many advantages. However, the volatile-char interaction during co-pyrolysis, which is the first step of co-gasification, significantly changes the properties and the structure of biochar, thus affecting gasification. The present work investigated the effect of the interaction between the volatile from a coal and the biochar of K-salt-doped (K 2 CO 3 , K 2 SO 4 and KCl) pine wood in a lab-scale, fixed-bed reactor at 600, 700 and 800 °C to understand how the occurrence mode of inorganic K in biomass alters the volatile-char interaction during co-pyrolysis. The volatile-char interaction has insignificant effects on the biochar of pine wood without the doping of K salts while it has significant effects on the biochar of K-salt-doped pine wood, especially for K 2 CO 3 and K 2 SO 4. The volatile-char interaction significantly increases the formation of C-O-K bonds, the content of oxygen containing compounds and the aromaticity of the biochar for K 2 CO 3 -doped and K 2 SO 4 -doped pine wood. In contrast, the evident presence of C-O-K bonds can only be found for KCl-doped pine wood at 800 °C after the volatile-char interaction. The increase in the pyrolysis temperature and the presence of the volatile-char interaction make the carbon structure of the biochar of K 2 SO 4 -doped and KCl-doped pine wood less ordered and generate more active sites. However, although the char order is lower and the number of active sites is higher for the biochar of K 2 CO 3 -doped pine wood than for that of K 2 SO 4 -doped and KCl-doped pine wood, the volatile-char interaction has insignificant effects on improving the activity of its biochar. Lastly, the volatile-char interaction causes insignificant additional release of K from the biochar. This may indicate that significant amounts of stable C-O-K bonds have been formed in the biochar to retain K. [ABSTRACT FROM AUTHOR]

Graphical abstract Preparation and formed mechanism of layered uniformly lignite char supported Ni catalyst, and its catalytic activity for reforming of toluene and biomass tar. Highlights • Lignite is a great material for environmental friendly catalyst preparation. • Desirable and layered Ni/HSL catalyst was produced by modified lignite. • Ni/HSL shows the high stability and activity for toluene and tar reforming. • High Ni loading and dispersed Ni/HSL was prepared by HCl treatment of lignite. Abstract Lignite rich in oxygen-containing species (OCSs) was employed as perfect ion-exchange material for high activity catalyst preparation. HCl treatment Shengli lignite (HSL) selectively removed the organic salt and improved capability of ion exchange. In this paper, highly desirable and layered carbon supported Ni catalyst was prepared by modified lignite. Thanks to the excellent role of Ni (1 1 1) plane and porous layered graphene-like delocalized electronic structure, specific structure of lignite provides an exchange platform in facilitating the Ni electron transfer during the catalytic reaction process. Ni loaded on HSL (Ni/HSL) showed the great catalytic activity and stability for reforming of toluene and biomass tar. Ni/HSL prepared at 650 °C shows the great activity and stability for toluene steam reforming (TSR) and biomass tar reforming (BTR). A series of instruments (XRD, SEM, TEM, H 2 -TPR, XPS, CO pulse adsorption, etc.) were employed for characterization. Based on these significant characterizations of catalyst, calculation of turnover frequency (TOF), and results of conversion of toluene and corncob tar. The results revealed the layered delocalized electronic structure of Ni/HSL, which has lower activation energy than other reported catalysts. Uniform dispersed catalyst was synthesized successfully for reforming of toluene and biomass tar. [ABSTRACT FROM AUTHOR]

A novel porous carbon catalyst was prepared by carbonization of D151 resin exchanged with nickel ion (Ni/RC). TEM images and XRD patterns manifest that nickel crystallite size (NCS) relies greatly on solution pH value and carbonization temperature. The as-prepared Ni/RC in pH 11 at 650 °C achieved the maximal specific surface area of 213 m 2 /g and metallic nickel particles are highly dispersed with a NCS of 5.7 nm. Ni/RC exhibited higher activity for corncob tar reforming than commercial Ni/Al 2 O 3 and produced a gas yield of 46.8 mmol/g at 650 °C. The nickel particles growth above 650 °C causes the decline in catalytic activity of Ni/RC. In the presence of steam, a high tar-free gas of 84.5 mmol/g was obtained at 650 °C. This study sheds light on the possibility of Ni/RC as a promising candidate for H 2 -rich gas production from biomass under mild conditions. [ABSTRACT FROM AUTHOR]

• Simple method for the preparation of highly-dispersed Co-based catalysts. • Co 0.15 -C 2 H 3 O 2 − has high Co loading (16 wt%) and small metallic particles (3.77 nm). • 98.7 % toluene conversion was achieved at 400 °C over Co 0.2 -C 2 H 3 O 2 −. • Co 0.15 -C 2 H 3 O 2 − exhibits excellent stability during 100 h reforming test. • Co 0.15 -C 2 H 3 O 2 − help to produce 283.8 mL.g corncob −1.g cat −1.h−1 H 2 at 480 °C. The removal of generated tar during the biomass gasification is a serious issue. Catalytic tar cracking is one of the most efficient methods to reduce tar deposition while many common tar cracking catalysts suffer problems of serious carbon deposition and active metal sintering, especially at low temperatures. Therefore, developing catalysts with both high activity and stability is critical. In this work, we aim to prepare catalysts with a high active metal contents, a small metal particle size and a high dispersion to contribute to the highly efficient tar removal at relatively low temperatures. By adjusting the type and the concentration of the Co precursor solution when lignite is used as the carbon precursor, we prepared a series of catalysts which were then applied for both activity and stability test of the steam reforming of model tar and biomass tar. The results show that Co 0.15 -C 2 H 3 O 2 − prepared with a 0.15 M solution of Co(C 2 H 3 O 2) 2 ·4H 2 O achieves a Co content of about 16.0 wt% with an average particle size of about 3.77 nm and a relatively high metallic Co dispersion. For steam reforming of toluene, the catalyst achieves an almost 100 % toluene conversion at 400 °C and exhibits a high stability in the 100 h test. Moreover, Co 0.15 -C 2 H 3 O 2 −, which produces approximately 283.8 mL.g corncob −1.g cat −1.h−1 H 2 catalytically, is also active and stable in biomass tar cracking. The catalyst prepared in the present study by using the economic and simple ion-exchange method also has a well-dispersed nano-metal-loaded structure and can efficiently remove the tar at a low temperature with a high stability, which will contribute to the industrial application in the future. [ABSTRACT FROM AUTHOR]

Thermochemical conversion of crops straw is receiving renewed attention, due to the energy and material recovery that can be achieved. However, it still lacks the kinetic background which is of great importance for a successful design of thermochemical process. In this work, pyrolysis test for soybean straw was performed in a non-isothermal thermogravimetric analysis (TGA) in order to determine the thermal degradation behavior. Pyrolysis experiments were carried out under inert conditions and operated at different heating rates (5, 10, 20, and 30 K/min). Three different kinetic models, iso-conversional Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW) models, and Coats–Redfern method were applied on TGA data of soybean straw to calculate the kinetic parameters including activation energy, pre-exponential factor, and reaction order. The activation energy values were 154.15 and 156.22 kJ/mol based on KAS and OFW models, respectively. Simulation of the soybean straw thermal decomposition using the obtained kinetic parameters and comparison with experimental data are in good agreement. [ABSTRACT FROM AUTHOR]

[Display omitted] • Detailed review of tar reforming and downstream development. • Analysis of tar reforming pathways over different catalysts. • The review sheds light on active catalysts for tar elimination. • Possible integration of gasification and downstream technology. In the last few decades, the development of biomass energy has become a key research focus to press the emissions of greenhouse gas. Syngas production from biomass tar reforming in the presence of the heterogeneous catalyst has been proved to be a clean and promising technology, which could be further connected to the downstream for fuel valorization. Up to now, some literatures has screened the reaction pressure, temperature, atmosphere, and heterogeneous catalyst in tar elimination during the biomass thermochemical conversion process. However, there are some problems, like the economical catalyst chosen for the industrial development of gasification, and integration difficulties between gasification and downstream technologies are still not well discussed. Hence, in this review, we first assess the recent advancements in catalyst fabrication and the activity performance in reforming biomass tar and tar model compounds. After that, the clean-up of produced gas for the next-step application is reviewed. Importantly, we discuss the composition of the produced gas, the possibilities and challenges of the integration with the production of methane, methanol, ethanol, and C 2+ alcohols. Finally, the conclusion and prospective are concluded to give an outlook for the development of catalyst, biomass tar reforming, and integration with downstream technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metallic Co highly dispersed on char using lignite as carbon precursor. • The Co nanoparticles loaded by ion exchange method are smaller than Ni. • The interaction between Co and lignite is stronger than Ni. • Co/modified lignite char efficiently catalyzes tar cracking at low temperature. • The oxygen affinity of Co is key to carbon-deposition resistant. The development of cheap and highly dispersed nano-catalyst is one of the key technologies for low temperature steam reforming (SR) of biomass tar. This work used acid-washed and oxidized Shengli lignite char (OXAWSL) as carbon precursor to load Co (Co/OXAWSL) and Ni (Ni/OXAWSL) via ion exchange method to SR of toluene and biomass tar. The Co/OXAWSL was more active and stable than Ni/OXAWSL during the 30 h test with a final toluene conversion of 85% at a relatively low temperature of 450 °C and steam to carbon ratio (S/C) of 3.4, which resulted from its small particle size (5.6 nm) and high dispersion (12.3%) of Co. The relatively high H 2 production (42.59 mmol/g-biomass) over Co 0.1 /OXAWSL (450 °C, S/C = 3.4) in SR of tar was also obtained. A low E a (22.0 kJ/mol) value of Co/OXAWSL and good affinity to oxygen for Co explained its excellent performance. The low-temperature tar cracking process can provide theoretical and technical support for the large-scale industrial utilization of biomass pyrolysis and gasification. [ABSTRACT FROM AUTHOR]

Ni-encapsulated (Ni@HZ5) and Ni-incorporated (x Ni/HZ5) zeolites were prepared via one-pot hydrothermal synthesis and impregnation method, respectively, and further employed for hydroconversion of pyrolytic volatiles of spent coffee grounds into benzene, toluene, ethylbenzene, xylene, naphthalene (BTEXN) in a drop tube reactor under H 2 atmosphere. The properties of metallic Ni species on Ni@HZ5, x Ni/HZ5 and Ni/Al 2 O 3 were comparably characterized. Ni@HZ5 displayed superior selectivity for BTEXN production among those catalysts, especially for B and T. Metallic Ni species encapsulated MFI-type framework plays crucial roles in enhancing aromatics selectivity, promoting oligomerization, cyclization and aromatization of small molecular hydrocarbons in channels. On the contrary, Ni species presented on the external zeolite surface is in favor of hydrocracking and hydrogenolysis of macromolecular pyrolytic fragments. It also exhibited high coke content containing "soft" and "hard" coke, which was mainly caused by metallic particles sintering. An important difference was proposed in the effect of Ni species on reaction pathway for catalytic upgrading of volatiles to BTEXN. The configured Ni@HZ5 inhibits sintering and has potential of enhancing BTEXN by catalytic hydropyrolysis of biomass. [Display omitted] • Ni-encapsulated zeolite was synthesized by organic ligands assisting. • Ni-encapsulated zeolite enhanced light aromatics formation remarkably. • The catalytic performance of metal active sites is dependent of metallic location. • Ni species embedded in HZSM-5 can inhibit metallic sintering. [ABSTRACT FROM AUTHOR]

Due to the interconnected network and high porosity, melamine foam has been selected as the template to obtain hierarchical porous carbon. In this paper, porous carbon with hierarchical porous structure, high pore volume and high specific surface area is prepared by using melamine foam as template and waste liquid (from the production of vitamin C) as carbon precursor coupled with KOH-activation. Owing to these favorable structural characteristics, the supercapacitors electrodes based on the as-prepared products have outstanding electrochemical performances in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF 4) electrolyte. The optimized electrode (WMFPC 700-5) reaches a high specific capacitance (217 F g−1 at 0.1 A g−1) and superior cycling stability (specific capacitance retention of 89% after 10000 cycles at 5 A g−1). Notably, supercapacitors displays an ultra-high energy density of 107 Wh kg−1 at a power density of 94 W kg−1 in EMIMBF 4 electrolyte system. In addition, the all-solid-state symmetric supercapacitors based on WMFPC 700-5 demonstrates a remarkable specific capacitance of 180 F g−1 at 0.5 A g−1 in the EMIMBF 4 /PVDF-HFP gel polymer electrolyte. [ABSTRACT FROM AUTHOR]

• HF treated HZSM-5 has more mesopores and less acid sites. • Ni/HF modified HZSM-5 for effectively tar steam reforming. • 9%Ni/HF modified HZSM-5 exhibited a high dispersion with small particle size. • 9%Ni/HF modified HZSM-5 showed superior H 2 production capacity. • More mesopores and less acid sites are key to anti-coke property. This paper investigated the performance of HF modified HZSM-5 supported nickel catalysts (Ni/FZ5) in steam reforming of toluene (TSR) and biomass pyrolysis tar (BSR). The mesopores volume of support increased from 0.021 to 0.061 cm3/g with decreasing acid amount from 2.27 to 0.41 mmol/g after HF treatment. Catalysts with different Ni loadings were prepared and characterized. The Ni/FZ5 with Ni loading of 9 wt% possesses relatively large specific surface area (337 m2/g) and average pore size (2.91 nm), as well as small Ni particle size (23 nm) and high dispersion. In the process of TSR, 9Ni/FZ5 was kept above 70% for 7 h. Owing to the calculated lower apparent activation energy (30.76 KJ/mol), 9Ni/FZ5 exhibited the best performance in BSR at 650 °C, achieving the largest H 2 yield of 52.8 mmol/g and the highest selectivity of H 2 at 72.8%. Additionally, only 1.6 mg/g catalyst of coke deposition was detected. Moreover, its high activity was still identified with excellent hydrothermal stability even after 7 times of regeneration. All findings suggest that 9Ni/FZ5 is a promising catalyst for biomass tar cracking. [ABSTRACT FROM AUTHOR]

[Display omitted] • The formation of K aluminosilicates mainly contributes to the retention of K in ash. • For K 2 CO 3 and K 2 SO 4 in biomass, coal retains much higher content of K than for KCl in biomass. • For KCl in biomass, organic compounds in coal facilitates K to form aluminosilicates. A steam atmosphere increases the retention of K. • The agglomerates formed after co-gasification are more easily to be broken than that formed from the gasification of biomass alone. Co-gasification of biomass and coal has many advantages, which also mitigates some of the ash-related problems induced by potassium (K) in biomass. However, this effect varies with the occurrence mode of inorganic K in biomass, which varies with the species of biomass. Therefore, the present work investigated the effect of a bituminous coal on the transformation of K and the ash chemistry of bed agglomeration (without considering the effect of fluidization) during co-gasification (steam and CO 2 atmospheres) for different types of inorganic K (K 2 CO 3 , K 2 SO 4 and KCl) in biomass. The results show that for both K 2 CO 3 and K 2 SO 4 in biomass, K is mainly retained as KAlSiO 4 and K 2 SO 4 in the gasification ash with KAlSiO 4 being the dominant phase. In addition, for K 2 CO 3 in biomass, more KAlSiO 4 and less K 2 SO 4 are formed under the steam atmosphere than under the CO 2 atmosphere. However, the K retention of the ash or the agglomerate for both K 2 CO 3 and K 2 SO 4 in biomass is similar and is much higher than that for KCl in biomass, which tends to release and to induce other ash-related problems. In addition, both the organic compounds of coal and the gasification atmosphere significantly alter the reaction between coal with KCl in biomass: The majority of KCl reacts with coal to form KAlSiO 4 , the formation of which is quite limited for the coal ash; More K is retained in the ash and more KAlSiO 4 is formed under the steam atmosphere than under the CO 2 atmosphere. Lastly, although co-gasification with coal (silica sand as the bed material) cannot stop the formation of agglomerates for K 2 CO 3 , K 2 SO 4 and KCl in biomass, these agglomerates are more easily to be broken than those produced from the gasification of biomass alone, thus mitigating bed agglomeration in fluidized-bed reactors. [ABSTRACT FROM AUTHOR]

In this study, interlinked porous carbon nanoflakes (IPCNs), using soybean straw as precursor and urea as nitrogen source, were fabricated by a facile co-hydrothermal pretreatment, subsequent KOH activation procedure. The influence of the mass ratio of urea to soybean straw and activation temperature on the overall structure, pore size distribution and surface element composition of IPCNs was investigated. Unique pore distribution provides more active sites and interconnected ion transmission paths, which is beneficial for improving the electrochemical performance of IPCNs. The specific surface area of N 1 SSC-700 is as high as 2631 m2 g−1 with a total pore volume of 1.23 cm3 g−1, and the N and O doping amounts are 3.46% and 11.89%, respectively. The suitable heteroatoms doping content on IPCNs surface not only contribute to shortening the wetting time of electrolyte solution to electrode material, but also increasing pseudocapacitance. Therefore, N 1 SSC-700 possesses high specific capacitances of 325 F g−1 for a three-electrode system and of 161 F g−1 for a two-electrode system at 0.5 A g−1 in 6 M KOH. Moreover, the energy density of N 1 SSC-700 is high up to 22.36 W h kg−1 at a power density of 0.51 kW kg−1. These results indicated that unique IPCNs derived from soybean straw are a promising material for supercapacitors. Unlabelled Image • The N/O co-doped IPCNs was prepared from soybean stalk and urea. • Hydrothermal pretreatment can achieve quantitative doping of N on IPCNs. • Urea has multiple functions in the preparation of IPCNs. • The specific capacitance of the IPCNs exceeds that of similar carbon materials. [ABSTRACT FROM AUTHOR]

Traditional fossil fuel overuse could lead to global warming and environmental pollution. As a renewable energy, biomass energy is a sustainable and low pollution carbon energy, which has a wide range of sources. Syngas production from biomass thermochemical conversion is a promising technology to realize effective utilization of the renewable energy. Syngas produced from gasification could be further converted into value-added chemicals via the method of Fischer-Tropsch synthesis. Syngas and CO 2 methanation could transform renewable energy into feasible transport and high-density energy. However, tar formation and catalyst deactivation are the main problem during the biomass gasification and methanation. This review sheds light on the development of biomass gasification and syngas methanation. Firstly, we presented the common reactors and some other factors during gasification. Secondly, we provide a comprehensive introduction of the advanced active catalyst for gasification and syngas methanation. Finally, some representative large-scale and commercial plants and companies for biomass gasification were compared and discussed in details. Then the prospective developments in combination of gasification and methanation were concluded to give an outlook for biomass gasification and its downstream development. • Detailed review of gasification and methanation development. • Discussion of high active catalyst for gasification and methanation. • It sheds light on effective reactors for biomass gasification. • Large-scale commercial development of gasification and methanation are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pine and its liquefaction residue were liquefied in a methanol/water mixed solvent. [•] The mixed solvent showed significantly synergic effect on pine liquefaction. [•] The compositions of bio-oils obtained in different solvent are quite different. [•] The synergic effect is mainly ascribed to the interaction between the two solvents. [ABSTRACT FROM AUTHOR]