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Net carbon management of agro-residues has been an important pathway for reducing the environmental burdens of agricultural production. Converting agro-residues into biochar through pyrolysis is a prominent management strategy for achieving carbon neutrality in a circular economy, meeting both environmental and social concerns. Based on the latest studies, this study critically analyzes the life cycle assessment (LCA) of biochar production from different agro-residues and compares typical technologies for biochar production. Although a direct comparison of results is not always feasible due to different functional units and system boundaries, the net carbon sequestration potential of biochar technology is remarkably promising. By pyrolyzing agro-residues, biochar can be effectively produced and customized as: (i) alternative energy source, (ii) soil amendment, and (iii) activated carbon substitution. The combination of life cycle assessment and circular economy modelling is encouraged to achieve greener and sustainable biochar production., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Nitrogen (N) species in biomass-based carbon can be adjusted through pyrolysis at different temperatures, optimizing the valence band structure of supported metal nanoparticles through electronic metal-support interactions (EMSIs). Herein, ginkgo leaves-based carbon supported cobalt phosphide (CoP@NSPC-T, T = 850, 900 and 950 °C) was obtained via carbothermal reduction method at different pyrolysis temperature. Pyridinic N and pyrrolic N in carbon lattice were dramatically decreased with pyrolysis temperature raised, whereas the graphitic N showed the opposite trend. The change in N species (pyridinic N, pyrrolic N and graphitic N) reconfigured the valence band structure of CoP@NSPC-T, inducing the enhancement of work function and the upshift of d-band center. A relationship between the ratio of (pyridinic N + pyrrolic N)/graphitic N, work function, d-band center, and HER activity (η 10) of catalysts was established. CoP@NSPC-900 with a moderate work function value and d-band center tend to achieve a balance for Volmer process and Heyrovsky process, exhibiting the lowest η 10 value activity among the resulted catalysts as the ratio of (pyridinic N + pyrrolic N)/graphitic N is 1.33. [Display omitted] • Nitrogen species in biomass derived carbon support is tuning by adjusting the pyrolysis temperature. • The impact of differ nitrogen species on the d-band center of CoP has been in-depth studied. • A relationship between nitrogen species, d-band center, work function and catalytic activity is finally established. [ABSTRACT FROM AUTHOR]

In order to realize a promissing disposal of solid wastes, especially for biomass and plastics, and the recovery of high value-added products, lignin (LG) and polyethylene (PE) were co-pyrolyzed with the addition of transition metals. Thermal behavior and kinetics of the mixtures affected by the type of transition metals (0.5 mmol/g Ni, Co, Fe and Mn), the concentration of Ni (0–1 mmol/g Ni), the ratio of LG to PE (4:1-1:4) and heating rate (10–40 °C/min) were investigated according to thermogravimetric analysis (TGA). It is found that the treatment of LG/PE with 0.5 mmol/g Ni, Co, Fe or Mn results in the decrease of the initial decomposition temperature of LG and PE in the mixture by 10–53 °C and 9–18 °C, respectively. According to the difference of weight loss (Δ W), the introduction of Fe and Mn has slight influences on the interaction between LG and PE while a negative effect of PE on the devolatilization of LG in LG/PE can be largely diminished with the involvement of Ni and Co. Kinetic analysis reveals that the pyrolysis of LG and PE can be well fitted by a single first order model reaction while two consecutive first order model reactions are needed to exactly describe the co-pyrolysis of LG/PE with or without transition metals. The E value of LG and PE in the mixture is reduced by 6.11–21.62 kJ/mol and 7.67–50.11 kJ/mol, respectively, when 0.5 mmol/g Ni, Co, Fe or Mn was involved. Moreover, the concentration of Ni, the ratio of LG to PE and the heating rate play important roles on the thermal behavior and kinetics of the co-pyrolysis of LG/PE. • Transition metals were introduced into the co-pyrolysis of LG and PE. • Thermal behaviour and kinetics of transition metal-treated LG/PE were investigated. • Transition metals greatly promoted the decomposition of LG and PE in mixtures. • Ni and Co can greatly intensify the synergistic interaction between LG and PE. [ABSTRACT FROM AUTHOR]

A stainless-steel mesh loaded with nickel catalyst was produced and used for the pyrolysis–catalysis of waste high-density polyethylene with the aim of producing high-value carbon products, including carbon nanotubes (CNTs). The catalysis temperature and plastic-to-catalyst ratio were investigated to determine the influence on the formation of different types of carbon deposited on the nickel–stainless-steel mesh catalyst. Increasing temperature from 700 to 900°C resulted in an increase in the carbon deposited on the nickel-loaded stainless-steel mesh catalyst from 32.5 to 38.0 wt%. The increase in sample-to-catalyst ratio reduced the amount of carbon deposited on the mesh catalyst in terms of g carbon g−1plastic. The carbons were found to be largely composed of filamentous carbons, with negligible disordered (amorphous) carbons. Transmission electron microscopy analysis of the filamentous carbons revealed them to be composed of a large proportion (estimated at ∼40%) multi-walled carbon nanotubes (MWCNTs). The optimum process conditions for CNT production, in terms of yield and graphitic nature, determined by Raman spectroscopy, was catalysis temperature of 800°C and plastic-to-catalyst ratio of 1:2, where a mass of 334 mg of filamentous/MWCNTs g−1plastic was produced. [ABSTRACT FROM PUBLISHER]

To explore the mechanism of the influence of Ni-Fe bimetallic catalyst for the producing high-value carbon nanotubes (CNTs) with clean hydrogen from waste plastic pyrolysis, the pyrolysis-catalysis of plastics were performed using a two stage fixed bed reaction system with Ni and Fe loading at variant molar ratios. The catalysts and produced carbon were analysed with various characterization method, including temperature-programed reduction/oxidation, X-ray diffraction, scanning electron microscopy or/and Raman spectroscopy. Both the H 2 concentration and H 2 yield reached maximum values of 73.93 vol.% and 84.72 mg g −1 plastic, respectively, as the ratio of Ni:Fe at 1:3. The amount and quality of CNTs were greatly influenced by the catalyst composition, and Ni and Fe display different roles to the overall reactivity of Ni-Fe catalyst for the pyrolysis-catalysis of waste plastics. Catalyst with more Fe loading produced more hydrogen and deposited carbon, due to higher cracking ability and the relatively lower interaction between active sites and support. The presence of Ni in Ni-Fe bimetallic catalyst enhanced the thermal stability and graphitization degree of produced carbons. The thermal quality of filamentous carbons might be associated with carbon defects. [ABSTRACT FROM AUTHOR]

Hydrogen production from the thermochemical conversion of biomass was carried out with nano-sized NiZnAlOx catalysts using a two-stage fixed bed reactor system. The gases derived from the pyrolysis of wood sawdust in the first stage were catalytically steam reformed in the second stage. The NiZnAlOx catalysts were synthesized by a co-precipitation method with different Ni molar fractions (5, 10, 15, 25 and 35%) and a constant Zn:Al molar ratio of 1:4. The catalysts were characterized by a wide range of techniques, including N 2 adsorption, SEM, XRD, TEM and temperature-programmed oxidation (TPO) and reduction (TPR). Fine metal particles of size around 10–11 nm were obtained and the catalysts had high stability characteristics, which improved the dispersion of active centers during the reaction and promoted the performance of the catalysts. The yield of gas was increased from 49.3 to 74.8 wt.%, and the volumetric concentration of hydrogen was increased from 34.7 to 48.1 vol.%, when the amount of Ni loading was increased from 5 to 35%. Meanwhile, the CH 4 fraction decreased from 10.2 to 0.2 vol.% and the C 2 –C 4 fraction was reduced from 2.4 vol.% to 0.0 vol.%. During the reaction, the crystal size of all catalysts was successfully maintained at around 10–11 nm with lowered catalyst coke formation, (particularly for the 35NiZn4Al catalyst where negligible coke was found) and additionally no obvious catalyst sintering was detected. The efficient production of hydrogen from the thermochemical conversion of renewable biomass indicates that it is a promising sustainable route to generate hydrogen from biomass using the NiZnAl metal oxide catalyst prepared in this work via a two-stage reaction system. [ABSTRACT FROM AUTHOR]

The influence of process conditions on the production of syngas and H 2 from biomass in the form of rice husks was investigated using a two-stage pyrolysis/catalytic reforming reactor. The parameters investigated were, reforming temperature, steam flow rate and biomass particle size and the catalyst used was a 10 wt.% Ni–dolomite catalyst. Biomass was pyrolysed in the first stage, and the product volatiles were reformed in the second stage in the presence of steam and the Ni–dolomite catalyst. Increase in catalyst temperature from 850 °C to 1050 °C marginally improved total syngas yield. However, H 2 yield was increased from 20.03 mmol g −1 at 850 °C to 30.62 mmol g −1 at 1050 °C and H 2 concentration in the product gas increased from 53.95 vol.% to 65.18 vol.%. Raising the steam flow rate increased the H 2 yield and H 2 gas concentration. A significant increase in H 2 :CO ratio along with a decrease in CO:CO 2 ratio suggested a change in the equilibrium of the water gas shift reaction towards H 2 formation with increased steam flow rate. The influence of particle size on H 2 yield was small showing an increase in H 2 production when the particle size was reduced from 2.8–3.3 to 0.2–0.5 mm. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) contains significant amounts of polyvinyl chloride (PVC). The reactivity of PVC may form polycyclic aromatic hydrocarbons (PAHs) during the pyrolysis of MSW, which can become a key challenge during the development of pyrolysis technologies. However, there is very limited work in relation to the influence of pyrolysis process conditions in terms of temperature and heating rate on PAHs formation during pyrolysis of PVC. In this work, the formation of 2–4-ring PAHs from the pyrolysis of PVC at temperatures of 500, 600, 700, 800, or 900 °C and at fast and slow heating rates was investigated under a N 2 atmosphere in a fixed bed reactor. With the increase of temperature from 500 to 900 °C, HCl yield decreased from 54.7 to 30.2 wt.%, while the yields of gases and PAHs in the tar increased. Slow pyrolysis generated higher HCl yield, and lower gas and tar yield than fast pyrolysis; the PAH yield obtained from the slow pyrolysis was much lower compared to fast pyrolysis. The results suggest that for fast pyrolysis, the dehydrochlorination of the PVC might be incomplete, resulting in the formation of chlorinated aromatic compounds. [ABSTRACT FROM AUTHOR]

The production of hydrogen-enriched syngas from the thermo-chemical conversion of biomass was studied using Ni/CaAlO x catalysts prepared by co-precipitation method. The effect of Ca addition with different molar ratios of Ca:Al (1:3, 1:2, 1:1, 2:1, 3:1) on the properties and catalytic behavior in relation to syngas production and the coke formation on the surface of the catalysts were investigated. Catalysts were characterized by BET, XRD, TPR, SEM, and TEM. The SEM and TEM results showed that rod-shaped nano-particles were highly dispersed on the surface of the catalyst. The particle size of NiO was slightly affected with the increase of Ca content in the catalyst. It appeared that the selectivity of CO was increased and the selectivity of CO 2 was reduced with the increase of Ca addition to the catalyst. For example, CO 2 concentration was reduced from 20 to 12 vol.%, when the molar ratio of Ca/Al was increased from 1:3 to 3:1 for the Ni/CaAlO x catalyst; it is suggested that the water gas shift reaction was inhibited and CO 2 reforming reactions were promoted in the presence of the catalyst with higher Ca content. The CO/H 2 molar ratio could be manipulated by changing the Ca content in the catalyst, while the H 2 concentration remained almost constant (around 45 vol.%). Thus, using the Ni/CaAlO x catalyst developed in this work could provide a promising route to control the syngas composition, which is an important factor for syngas applications. [ABSTRACT FROM AUTHOR]

Thermal–chemical processing of biomass is expected to provide renewable and clean energy and fuels in the future. Due to the nature of endothermic reactions, microwave and conventional heating have been applied to this technology. However, more studies need to be carried out to clarify the difference between these two heating technologies. In this work, we investigated two bio-char samples produced from conventional pyrolysis of wood biomass (yield of bio-char: 38.48 and 59.70 wt.%, respectively) and one bio-char produced from microwave pyrolysis with a yield of 45.16 wt.% from the same biomass sample at different process conditions. Various methodologies have been used to characterise the bio-chars. CO 2 gasification of bio-char has also been studied using a thermogravimetric analyser (TGA) and a fixed-bed reaction system. The results show that volatile and carbon contents of the bio-char derived from microwave pyrolysis were between the two conventional bio-chars. However, the microwave bio-char is more reactive for CO 2 gasification, as more CO was released during TGA experiments, and the CO release peak was narrower compared with the CO 2 gasification of the conventional bio-chars. It is suggested that the conventional bio-char is less reactive due to the presence of more secondary chars which are produced from secondary reactions of volatiles during the conventional biomass pyrolysis. While the microwave pyrolysis generates more uniform bio-chars with less secondary char, and therefore, has advantages of producing bio-char for downstream char gasification. [ABSTRACT FROM AUTHOR]

Thermo-chemical processing of biomass is a promising alternative to produce renewable hydrogen as a clean fuel or renewable syngas for a sustainable chemical industry. However, the fast deactivation of catalysts due to coke formation and sintering limits the application of catalytic thermo-chemical processing in the emerging bio-refining industry. In this research, Fe–Zn/Al 2 O 3 nanocatalysts have been prepared for the production of hydrogen through pyrolysis catalytic reforming of wood sawdust. Through characterization, it was found that Fe and Zn were well distributed on the surface with a narrow particle size. During the reactions, the yield of hydrogen increased with the increase of Zn content, as Zn is an efficient metal promoter for enhancing the performance of the Fe active site in the reaction. The 20% Fe/Al 2 O 3 catalyst with Zn/Al ratio of 1:1 showed the best performance in the process in relation to the hydrogen production and resistance to coke formation on the surface of the reacted catalyst. All the catalysts showed ultra-high stability during the process and nearly no sintering were observed on the used catalysts. Therefore, the nanocatalysts prepared in this work from natural-abundant and low-cost metals have promising catalytic properties (high metal dispersion and stability) to produce H 2 -rich syngas with optimal H 2 /CO ratio from the thermo-chemical processing of biomass. [ABSTRACT FROM AUTHOR]

Carbon nanotubes have been produced from a low density polyethylene (LDPE) feedstock via a two stage pyrolysis process. The temperature of the second stage, where carbon deposition on an iron alumina catalyst occurs (growth temperature), was varied using catalyst temperatures of 700, 800 and 900 °C. An increase in catalyst temperature led to a higher yield of both carbon nanotubes and hydrogen, as the rate of carbon deposition increased. Changing the amount of feedstock relative to the catalyst also had an effect on the production of both carbon nanotubes and hydrogen. As more feedstock is used a larger source of carbon gives rise to a larger amount of carbon nanotubes per gram of catalyst. However, in terms of the percentage of feedstock converted into carbon nanotubes and hydrogen gas, a reduction was observed. Conversion of plastic into carbon nanotubes was 29.1 wt.% when 0.5 g LDPE was used, but reduced to 13.1 wt.% with 1.25 g LDPE. This is because the catalyst activity reduces as it becomes overloaded, and much of the hydrocarbon gases are left unreacted. This gives an economic playoff between large conversion of plastics into carbon nanotubes and hydrogen gas, and large yields of carbon nanotubes per gram of catalyst used. [ABSTRACT FROM AUTHOR]

The formation of 2–4 ring polycyclic aromatic hydrocarbons (PAH) from the pyrolysis of nine different municipal solid waste fractions (xylan, cellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)) were investigated in a fixed bed furnace at 800 °C. The mass distribution of pyrolysis was also reported. The results showed that PS generated the most total PAH, followed by PVC, PET, and lignin. More PAH were detected from the pyrolysis of plastics than the pyrolysis of biomass. In the biomass group, lignin generated more PAH than others. Naphthalene was the most abundant PAH, and the amount of 1-methynaphthalene and 2-methynaphthalene was also notable. Phenanthrene and fluorene were the most abundant 3-ring PAH, while benzo[ a ]anthracene and chrysene were notable in the tar of PS, PVC, and PET. 2-ring PAH dominated all tar samples, and varied from 40 wt.% to 70 wt.%. For PS, PET and lignin, PAH may be generated directly from the aromatic structure of the feedstock. [ABSTRACT FROM AUTHOR]

This paper investigates the co-production of hydrogen and carbon nanotubes from the pyrolysis–catalytic gasification of waste plastics (polypropylene). We report on the influence of a range of metal additions to a nickel based catalyst based on ternary mixed oxide types Ni–Metal–Al, where the metal was Zn, Mg, Ca, Ce or Mn. The results showed that of the different metal–nickel catalysts investigated, the Ni–Mn–Al catalyst was the most promising catalyst in relation to the co-production of hydrogen and CNT. For example, the Ni–Mn–Al catalyst produced 71.4 mmol hydrogen g − 1 plastic, while the hydrogen production using Ni–Ca–Al, Ni–Ce–Al and Ni–Zn–Al catalysts were 68.5 mmol g − 1 , 63.1 mmol g − 1 and 45.9 mmol hydrogen g − 1 plastic respectively. In addition, carbon deposition on the catalyst was highest in the order of: Ni–Mn–Al > Ni–Ca–Al > Ni–Zn–Al > Ni–Ce–Al > Ni–Mg–Al. The carbon deposition for the Ni–Mn–Al catalyst was found to consist of mostly carbon nanotubes. Further investigation of the Ni–Mn–Al catalyst demonstrated that the interaction between Ni and catalyst support plays a significant role in the gasification process; weak metal support interaction (for the Ni–Mn–Al catalyst calcined at 300 °C) resulted in a lower hydrogen production and much higher yield of carbon products. In addition, the influence of steam injection rate on hydrogen and carbon nanotube production was investigated for the Ni–Mn–Al catalyst. Increasing the steam injection rate significantly increased hydrogen production and decreased carbon deposition. However, at lower steam injection rates, the quality of the product carbon nanotubes was improved. [ABSTRACT FROM AUTHOR]

The interactions of biomass constituents (hemicellulose, cellulose and lignin) were investigated during fast pyrolysis at 800 °C in a fixed bed reactor. The formation of polycyclic aromatic hydrocarbons (PAH) as well as mass distribution and gas products is presented. The possible interactions of biomass constituents were compared with the results of the expected results based on the pyrolysis of single components. For the interaction of xylan and cellulose, the mass distribution was similar to that expected from calculation of single component addition, however, PAH were increased. The interaction of xylan and lignin produced a decrease in PAH concentration compared to that expected from single component data. There was evidence of strong interaction between cellulose and lignin, where gas and solid residue yield was decreased and tar/oil yield was increased. In addition, naphthalene, acenaphthylene, and chrysene/benzo[ a ]anthracene were decreased compared with the concentrations expected from the single component pyrolysis. However, the amounts of 1-methynaphthalene, 2-methynaphthalene, acenaphthene, fluorene, phenanthrene, anthracene, and pyrene were increased. [ABSTRACT FROM AUTHOR]

Hydrogen production from renewable resources has received extensive attention recently for a sustainable and renewable future. In this study, hydrogen was produced from catalytic steam reforming of the aqueous fraction of crude bio-oil, which was obtained from pyrolysis of biomass. Five Ni–Al catalysts modified with Ca, Ce, Mg, Mn and Zn were investigated using a fixed-bed reactor. Optimized process conditions were obtained with a steam reforming temperature of 800 °C and a steam to carbon ratio of 3.54. The life time of the catalysts in terms of stability of hydrogen production and prohibition of coke formation on the surface of the catalyst were carried out with continuous feeding of raw materials for 4 h. The results showed that the Ni–Mg–Al catalyst exhibited the highest stability of hydrogen production (56.46%) among the studied catalysts. In addition, the life-time test of catalytic experiments showed that all the catalysts suffered deactivation at the beginning of the experiment (reduction of hydrogen production), except for the Ni–Mg–Al catalyst; it is suggested that the observation of abundant amorphous carbon formed on the surface of reacted catalysts (temperature programmed oxidation results) may be responsible for the initial reduction of hydrogen production. In addition, the Ni–Ca–Al catalyst showed the lowest hydrogen production (46.58%) at both the early and stabilized stage of catalytic steam reforming of bio-oil. [ABSTRACT FROM AUTHOR]

Highlights: [•] Conventional and microwave pyrolysis of biomass has been compared. [•] Conventional pyrolysis produces higher gas yield. [•] Microwave pyrolysis produces more char. [•] Two stages of gas release are seen, first CO & CO2 and second CH4 & H2. [Copyright &y& Elsevier]

Hydrogen production from the pyrolysis/reforming of refuse derived fuel (RDF) was investigated with a series of Ni/SiO2 catalysts. The catalysts were prepared by homogeneous precipitation derived from a sol–gel method (HPG) and compared to Ni/SiO2 catalysts prepared by adding a phase separation step to the HPG process (B-HPG). All the catalysts had a NiO loading of 10 wt.%, and three different calcination temperatures (500 °C, 700 °C and 900 °C) were used for each method. The prepared Ni/SiO2 catalysts were analysed to determine their surface area, and porosity characteristics; additionally scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), and X-Ray diffraction (XRD) analyses were carried out. The results showed that the catalyst prepared by HPG and calcined at 700 °C (HPG700), presented a relatively high surface area (∼347 m2 g−1), large pore diameter (12.50 nm), and also resulted in the highest catalytic activity towards H2 production, attaining ∼60 vol.% hydrogen. The lowest hydrogen concentration of about 42 vol.% was obtained using the catalysts prepared by the combined HPG-phase separation method, and calcined at 900 °C (B-HPG900). It was also observed that at calcination temperatures higher than 700 °C the catalytic activity for hydrogen production was diminished for both preparation methods. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two-stage pyrolysis-gasification of plastics can produce H2 and carbon nanotubes. [•] Carbon nanotube quality or H2 yield can be optimised by control of steam content. [•] Therefore, wastes can be processed for environmental and economic benefit. [Copyright &y& Elsevier]

Abstract: A series of Ni/SiO2 catalysts have been prepared and investigated for their suitability for hydrogen production and tar reduction in a two-stage pyrolysis-reforming system, using refuse derived fuel (RDF) as the raw material. Experiments were conducted at a pyrolysis temperature of 600°C, and a reforming temperature of 800°C. The product gases were analysed by gas chromatography (GC) and the condensed fraction was collected and quantified using gas chromatography-mass spectrometry (GC–MS). The effects of the catalyst preparation method, nickel content and the addition of metal promoters (Ce, Mg, Al), were investigated. Catalysts were characterised using BET surface area analysis, temperature programmed oxidation (TPO), and scanning electron microscopy (SEM). The TPO and SEM analysis of the reacted catalysts showed that amorphous type carbons tended to be deposited over the Ni/SiO2 catalysts prepared by impregnation, while filamentous type carbons were favoured with the sol-gel prepared catalysts. The influence of catalyst promoters (Ce, Mg, Al) added to the Ni/SiO2 catalyst prepared by the sol-gel method was found not to be significant, as the H2 production was not increased and the tar formation was not reduced with the metal-added catalyst. The highest H2 concentration of 57.9vol.% and lower tar amount produced of 0.24mgtar/gRDF; were obtained using the 20wt.% Ni/SiO2 catalyst prepared by sol-gel. On the other hand a low catalytic activity for H2 production and higher tar produced were found for the impregnated series of catalysts, which might be due to the smaller surface area, pore size and due to the formation of amorphous carbons on the catalyst surface. Alkenes and alcohol functional groups were mainly found in the analysed tar samples, with major concentrations of styrene, phenol, indene, cresols, naphthalene, fluorene, and phenanthrene. [Copyright &y& Elsevier]

Abstract: Cellulose, hemicellulose and lignin are the main components of biomass. This work presents research into the pyrolysis/gasification of all three main components of biomass, in order to evaluate and compare their hydrogen production and also understand their gasification processes. A fixed bed, two-stage reaction system has been used employing various nickel-based catalysts. Gas concentration (CO, H2, CO, CO2 and CH4) was analysed for the produced non-condensed gases. Oil byproducts were analysed by gas chromatography/mass spectrometry (GC/MS). Various techniques such as X-Ray Diffraction (XRD), scanning electron microscopy (SEM) coupled to an energy dispersive X-ray spectroscopy (EDXS), temperature-programmed oxidation (TPO) were applied to characterize the fresh or reacted catalysts. The experimental results show that the lignin sample generates the highest residue fraction (52.0wt.%) among the three biomass components. When Niph name="sbnd" />Al (1:1) catalyst was used in the gasification process, gas yield was increased from 62.4 to 68.2wt.% for cellulose, and from 25.2 to 50.0wt.% for the pyrolysis/gasification of lignin. Hydrogen production was increased from 7.0 to 18.7 (mmolg−1 sample) when the Niph name="sbnd" />Al (1:1) catalyst was introduced in the pyrolysis/gasification of cellulose. Among the investigated catalysts, Niph name="sbnd" />Al (1:1) was found to be the most effective for hydrogen production from cellulose pyrolysis/gasification. [Copyright &y& Elsevier]

Abstract: Hydrogen and syngas production have been investigated from the pyrolysis/gasification of biomass components (cellulose, xylan and lignin) in the presence of Ni-based catalysts by using a two-stage fixed-bed reaction system. Biomass samples were pyrolysed at the first stage and the derived products were gasified at the second stage. The Ni–Mg–Al and Ni–Ca–Al catalysts, prepared by co-precipitation, were applied in the gasification process. The lignin sample pyrolysed with more difficulty (56.0wt.% of residue fraction) compared with cellulose and xylan at 500°C, and therefore resulted in the lowest gas yield (42.7wt.%) for the pyrolysis/gasification of lignin. However, the highest H2 concentration from the three types of feedstock (55.1vol.%) was collected for the lignin sample in the presence of steam and catalyst. Carbon deposition was very low as indicated from the TPO and SEM analyses of the reacted Ni–Mg–Al catalyst. The investigation of reaction conditions showed that water injection rate (0.02 and 0.05gmin−1) had little influence on the gas production from the pyrolysis/gasification of lignin in the presence of the Ni–Ca–Al catalyst; however, the increase of gasification temperature from 700 to 900°C resulted in a higher gas and hydrogen production due to the promotion of secondary reactions during the gasification process. Furthermore, coking was highest for the reacted Ni–Ca–Al catalyst at the gasification temperature of 800°C (7.27wt.%), when the temperature was increased from 700 to 900°C. This work shows that the components of biomass have a significant influence on the catalytic gasification process related to hydrogen and syngas production. [Copyright &y& Elsevier]

Abstract: A two-stage continuous screw-kiln reactor was investigated for the production of synthesis gas (syngas) from the pyrolysis of biomass in the form of waste wood and subsequent catalytic steam reforming of the pyrolysis oils and gases. Four nickel based catalysts; NiO/Al2O3, NiO/CeO2/Al2O3, NiO/SiO2 (prepared by an incipient wetness method) and another NiO/SiO2 (prepared by a sol–gel method), were synthesized and used in the catalytic steam reforming process. Pyrolysis of the biomass at a rapid heating rate of approximately 40°C/s, was carried out at a pyrolysis temperature of 500°C and the second stage reforming of the evolved pyrolysis gases was carried out with a catalytic bed kept at a temperature of 760°C. Gases were analysed using gas chromatography while the fresh and reacted catalyst was analysed by scanning electron microscopy, thermogravimetric analysis, transmission electron microscopy with energy dispersive X-ray and X-ray photoelectron spectroscopy. The reactor design was shown to be effective for the pyrolysis and catalytic steam reforming of biomass with a maximum syngas yield of 54.0wt.% produced when the sol–gel prepared NiO/SiO2 catalyst was used, which had the highest surface area of 765m2 g−1. The maximum H2 production of 44.4vol.% was obtained when the NiO/Al2O3 catalyst was used. [Copyright &y& Elsevier]

Abstract: Pyrolysis of waste materials, biomass wood waste, waste tyre, refuse derived fuel (RDF) and waste plastic was performed using two thermogravimetric analysers (TGA). One TGA was coupled to a mass spectrometer (MS) and the other to an infrared spectrometer (FTIR). The kinetic parameters of the pyrolysed waste materials obtained for TGA-MS and TGA-FTIR were compared using a model based on first-order reactions with a distribution of the activation energies. A further comparison of the volatile species evolved by thermal degradation (TGA) and the subsequent characterisation by the MS and FTIR spectra was performed. The first-order reaction pathways and subsequent activation energies calculated from the differential TGA data presented good repeatability between the TGA-MS and TGA-FTIR. The TGA-MS and TGA-FTIR produced a broad spectrum of qualitative data characterising the volatile gaseous fraction of the waste materials pyrolysed. TGA-MS and TGA-FTIR are shown to be valuable techniques in corroborating the respective thermograms and spectrograms of the volatile species evolved during the pyrolysis of waste materials. However both techniques are prone to interference and careful interpretation of the spectra produced is required. [Copyright &y& Elsevier]

Abstract: The steam pyrolysis-gasification of biomass, wood sawdust, was carried out with a Ni/MCM-41 catalyst for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor. The synthesised MCM-41 mesoporous catalyst supports were impregnated with different Ni loadings (5, 10, 20 and 40wt.%), which were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). NiO particles were homogeneously dispersed inside the pores of 5, 10, and 20wt.% Ni/MCM-41 catalysts; however, more bulkly NiO particles (up to 200nm particle size) were detected outside the pores with an increase of the Ni loading up to 40wt.%. Gas production was increased from 40.7 to 62.8wt.%, hydrogen production was increased from 30.1 to 50.6vol.% of total gas composition when the Ni loading was increased from 5 to 40wt.% during the pyrolysis-gasification of wood sawdust. This work showed low coke deposition (from 0.5 to 4.0wt.%) with valuable bio-oil by-products using the Ni/MCM-41 catalyst. The highly efficient conversion of renewable biomass resource to hydrogen and bio-oil with very low coke deposition indicates that biomass gasification on Ni/MCM-41 catalysts via two-stage reaction is a promising method for the development of the biorefinery concept. [Copyright &y& Elsevier]

Abstract: Hydrogen production from the pyrolysis–gasification of waste tyres has been investigated with a Ni/CeO2/Al2O3 catalyst using a two-stage fixed bed reaction system. The conditions of catalyst preparation such as Ni and CeO2 content and calcination temperature were investigated in relation to product yield and composition. The fresh and reacted catalysts were analysed using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that there were small changes in the gas and hydrogen yield by adding 5 wt.% of CeO2 into the Ni/CeO2/Al2O3 catalyst. The gas yield related to the mass of waste tyre and the amount of reacted water were increased with the increase of CeO2 content from 5 to 15 wt.%. However, with the further increase of CeO2 content to 30 wt.%, the gas yield related to the mass of tyre and the amount of reacted water was reduced. Increasing the Ni content of the catalyst showed a positive influence on the gas yield and hydrogen production. The investigation of the calcination temperature of the Ni/CeO2/Al2O3 catalyst showed that the oil yield related to the mass of tyre and reacted water decreased from 28.4 to 23.4 wt.% for the catalyst calcined at 500 °C, and decreased from 24.2 to 17.7 wt.% for the catalyst calcined at 750 °C. When the Ni content of the catalyst was increased from 5 to 20 wt.%. there were only small changes in total gas and hydrogen production from the pyrolysis–gasification of waste tyre. Lower coke deposition on the reacted catalyst was obtained for the Ni/CeO2/Al2O3 catalyst prepared at the calcination temperature of 750 °C compared with the 500 °C calcination temperature. [Copyright &y& Elsevier]

Abstract: Polypropylene, polystyrene, high density polyethylene and their mixtures and real-world plastic waste were investigated for the production of hydrogen in a two-stage pyrolysis–gasification reactor. The experiments were carried out at gasification temperatures of 800 or 850°C with or without a Ni–Mg–Al catalyst. The influence of plastic type on the product distribution and hydrogen production in relation to process conditions were investigated. The reacted Ni–Mg–Al catalysts were analyzed by temperature-programmed oxidation and scanning electron microscopy. The results showed that lower gas yield (11.2 wt.% related to the mass of plastic) was obtained for the non-catalytic non-steam pyrolysis–gasification of polystyrene at the gasification temperature of 800°C, compared with the polypropylene (59.6 wt.%) and high density polyethylene (53.5 wt.%) and waste plastic (45.5 wt.%). In addition, the largest oil product was observed for the non-catalytic pyrolysis–gasification of polystyrene. The presence of the Ni–Mg–Al catalyst greatly improved the steam pyrolysis–gasification of plastics for hydrogen production. The steam catalytic pyrolysis–gasification of polystyrene presented the lowest hydrogen production of 0.155 and 0.196 (g H2/g polystyrene) at the gasification temperatures of 800 and 850°C, respectively. More coke was deposited on the catalyst for the pyrolysis–gasification of polypropylene and waste plastic compared with steam catalytic pyrolysis–gasification of polystyrene and high density polyethylene. Filamentous carbons were observed for the used Ni–Mg–Al catalysts from the pyrolysis–gasification of polypropylene, high density polyethylene, waste plastic and mixed plastics. However, the formation of filamentous carbons on the coked catalyst from the pyrolysis–gasification of polystyrene was low. [Copyright &y& Elsevier]

Abstract: A novel Ni–Mg–Al–CaO catalyst/sorbent has been prepared by integration of the catalytic and CO2 absorbing properties of the material to maximise the production of hydrogen. The prepared catalyst was tested for hydrogen production from the pyrolysis–gasification of polypropylene by using a two-stage fixed-bed reaction system. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDXS) were used to characterize the prepared Ni–Mg–Al–CaO catalyst/sorbent. Ni–Mg–Al–CaO and calcined dolomite showed a stable carbonation conversion after several cycles of carbonation/calcination, while CaO showed a certain degree of decay. The calcined dolomite showed low efficiency for hydrogen production from pyrolysis–gasification of polypropylene. Increasing the gasification temperature resulted in a decrease of H2/CO ratio for the Ni–Mg–Al catalyst mixed with sand; however, a stable H2/CO ratio (around 3.0) was obtained for the Ni–Mg–Al–CaO catalyst. An increased Ni–Mg–Al–CaO catalyst/polypropylene ratio promoted the production of hydrogen from the pyrolysis–gasification of polypropylene. Approximately 70wt.% of the potential H2 production was obtained, when the Ni–Mg–Al–CaO catalyst/polypropylene ratio and gasification temperature were 5 and 800°C, respectively. [Copyright &y& Elsevier]

Abstract: Co-precipitated Ni-Mg-Al catalyst was prepared and investigated in relation to the production of hydrogen from the catalytic steam pyrolysis-gasification of polypropylene using a two-stage reaction system. Coke formation on the Ni-Mg-Al catalyst was investigated by using temperature-programmed oxidation (TPO), X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM) and focused ion beam (FIB)/scanning electron microscopy (SEM). The coke formation mechanism on the Ni-Mg-Al catalyst is proposed. It is suggested that the Ni-Mg-Al catalyst is initially reduced during the gasification process, the reactions of decomposition/reforming of hydrocarbons gases occur on the surface and inside the catalyst; this resulted in partial fragmentation of the catalyst into small particles. Layered carbons, perhaps containing monoatomic carbon, metal carbides, etc., are suggested to be a transition layer for the formation of filamentous carbons. The addition of Mg into the Ni-Al catalyst was found to increase the catalytic activity and the physical stability of catalyst. In addition, increasing the calcination temperature from 750 to 850°C reduced the surface area of the fresh Ni-Mg-Al catalyst, increased the NiO crystal size, and resulted in a decrease of catalytic activity in the pyrolysis-gasification of polypropylene; however, a more stable catalyst was obtained with higher calcination temperature. [Copyright &y& Elsevier]

Abstract: Post-consumer plastic waste derived from municipal solid waste was investigated using a two-stage, catalytic steam pyrolysis–gasification process for the production of hydrogen. The three important process parameters of catalyst:plastic ratio, gasification temperature and water injection rate were investigated. Temperature-programmed oxidation (TPO) and scanning electron microscopy (SEM) methods were used to analyse the reacted catalysts. The results showed that there was little influence of catalyst:plastic ratio between the range 0.5 and 2.0(g/g) on the mass balance and gas composition for the pyrolysis–gasification of waste plastics; this might be due to the effective catalytic activity of the Ni–Mg–Al catalyst. However, increasing the gasification temperature and the water injection rate resulted in an increase of total gas yield and hydrogen production. The coke formation on the catalyst was reduced with increasing use of catalyst; however, a maximum coke formation (9.6wt.%) was obtained at the gasification temperature of 700°C when the influence of gasification temperature was investigated. The maximum coke formation was obtained at the water injection rate of 4.74gh−1, and a more reactive form of coke seemed to be formed on the catalyst with an increase of the water injection rate, according to the TPO experiments. [Copyright &y& Elsevier]

Abstract: The production of hydrogen from the two-stage pyrolysis–gasification of polypropylene using a Ni/CeO2/ZSM-5 catalyst has been investigated. Experiments were conducted on CeO2 loading, calcination temperature and Ni loading of the Ni/CeO2/ZSM-5 catalyst in relation to hydrogen production. The results indicated that with increasing CeO2 loading from 5 to 30wt.% for the 10wt.% Ni/CeO2/ZSM-5 catalyst calcined at 750°C, hydrogen concentration in the gas product and the theoretical potential hydrogen production were decreased from 63.0 to 49.8vol.% and 50.4 to 21.6wt.%, respectively. In addition, the amount of coke deposited on the catalyst was reduced from 9.5 to 6.2wt.%. The calcination temperature had little influence on hydrogen production for the catalyst containing 5wt.% of CeO2. However, for the 10wt.% Ni/CeO2/ZSM-5 catalyst with a CeO2 content of 10 or 30wt.%, the catalytic activities reduced when the calcination temperature was increased from 500 to 750°C. The SEM results showed that large amounts of filamentous carbons were formed on the surface of the catalysts. The investigation of different Ni content indicates that the Ni/CeO2/ZSM-5 ((2-10)-5-500) catalyst containing 2wt.% Ni showed poor catalytic activity in relation to the pyrolysis–gasification of polypropylene according to the theoretical potential H2 production (7.2wt.%). Increasing the Ni loading to 5 or 10wt.% in the Ni/CeO2/ZSM-5 ((2-10)-5-500) catalyst, high potential hydrogen production was obtained. [Copyright &y& Elsevier]

Abstract: Co-precipitated nickel-based catalysts with different metallic molar ratios and calcination temperature were investigated for the production of hydrogen from the pyrolysis–gasification of polypropylene. The experiments were carried out at a pyrolysis temperature of 500°C and gasification temperature of 800°C in the presence of steam using a two-stage reaction system. The results suggest that with increasing Ni content in the Ni-Al or Ni-Mg-Al catalyst, the catalytic activity of the catalyst increased, in relation to hydrogen production. For example, the potential hydrogen production increased from 48.8 to 57.7wt.%, and the amount of water reacted increased from 1.2 to 1.3 (g water/g polypropylene), when the Ni-Al molar ratio was increased from 1:4 to 1:1. After reaction in the pyrolysis–gasification process, the non-reduced Ni-Al catalyst was reduced into metallic Ni, as observed from XRD and TGA analysis. The introduction of Mg into the Ni-Al catalyst significantly increased the amount of reacted water and improved the performance of the catalyst in relation to coke formation, although the hydrogen production was not significantly improved. For the Ni-Al or Ni-Mg-Al catalyst, a 850°C calcination temperature resulted in a lower catalytic activity compared to the lower calcination temperature of 750°C. The substitution of Cu for Mg in the Ni-Mg-Al catalyst significantly reduced the catalytic ability for hydrogen production. [Copyright &y& Elsevier]

Abstract: Several nickel-based catalysts (Ni/Al2O3, Ni/MgO, Ni/CeO2, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO2/Al2O3) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500°C and gasification temperature was kept constant at 800°C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al2O3 was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H2 production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H2 production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3wt.% of theoretical) from the pyrolysis–gasification of polypropylene. [Copyright &y& Elsevier]

Abstract: A zeolite catalyst of ultrastable Y-type (USY) was investigated in the research of two staged pyrolysis–catalysis of scrap tyres. Scrap tyres were pyrolysed in a fixed bed reactor and the evolved pyrolysis gases were passed through a secondary catalytic reactor. The main objective of this paper was to investigate the effect of zeolite USY on the yield of products and the composition of derived oil. The influences of several parameters such as pyrolysis temperature, catalytic temperature, catalyst/tyre ratio, heating rate, etc. on the yield of the derived oil, char and gas were investigated. It showed that the increase of catalytic temperature and catalyst/tyre ratio resulted in high yield of gas at the expense of the oil yield. For example, when the catalyst/tyre ratio increased from 0.25 to 1.0, the yield of gas increased from 30.5 to 49.9wt.%, and the oil yield decreased nearly two-fold from 31.6 to 12.7wt.%. The concentration of light naphtha (boiling point<160°C) was also investigated in this study. And the high catalyst/tyre ratio favored to increase the concentration of light naphtha (<160°C) in oil. In order to study the composition of derived oil, a distilled fraction (<280°C), which was 92.5wt.% of the oil obtained from catalytic pyrolysis of scrap tyre at a pyrolysis temperature, catalytic temperature and catalyst/tyre ratio of 500, 400°C and 0.5, respectively, was analyzed with gas chromatography/mass spectrometry (GC/MS). The distillate was found to contain 1.23wt.% benzene, 9.35wt.% toluene, 3.68wt.% ethylbenzene, 12.64wt.% xylenes, 1.81wt.% limonene and 13.89wt.% PAHs, etc., where the single ring aromatics represented a significant potential use as chemicals. [Copyright &y& Elsevier]

The influence of the addition of transition metals involving nickel (Ni), cobalt (Co), iron (Fe) and manganese (Mn) on the thermal behavior and kinetic of co-pyrolysis of cellulose (CL) together with polyethylene (PE) was investigated according to thermogravimetric analysis (TGA). It is found that the involvement of transition metals acting as catalysts could promote the decomposition of individual component (CL and PE) in the mixture. The initial decomposition temperature of CL and PE in the mixture is reduced by 91–136 °C and 8–15 °C, respectively, after the addition of transition metals in comparison with that of the mixture of CL and PE. Meanwhile, transition metals could intensify the synergistic interactions between CL and PE, especially during the pyrolysis stage assigned to CL decomposition. The maximum difference of weight loss in this stage is −9.30% to −14.10% for transition metals treated-mixtures while that of the mixture without transition metal treatment is −2.99%. Kinetic results show that the co-pyrolysis of transition metal-involved CL/PE mixtures can be well described as two consecutive first order reactions. The activation energy (E) of CL and PE in the mixture is reduced by 53.21–80.53 kJ/mol and 8.23–12.36 kJ/mol, respectively, as transition metals were involved. In addition, the content of transition metal makes a large influence on the thermal behavior and kinetics of co-pyrolysis of CL/PE mixture. [ABSTRACT FROM AUTHOR]

[Display omitted] • RWWP-1,2,5,6 achieved a greater pyrolysis performance than RWWP-3,4. • The activation energy for RWWP ranged from 131.04 kJ mol−1 to 171.04 kJ mol−1. • RWWP samples could be identified by Py-TG/MS: PS, PE, PET, PP. • High-value CNTs can be obtained from RWWP-1,2,5,6 by catalytic pyrolysis process. • The carbon yield and CNTs purity top at 32.21 wt% (RWWP-1) and 93.04 % (RWWP-2). The investigation of the pyrolysis behaviour of real-world waste plastics (RWWP) and using them as the feedstock to produce carbon nanotubes (CNTs) could serve as an effective solution to address the global waste plastics catastrophe. This research aimed to characterize the pyrolysis behaviour of RWWP via thermogravimetric analysis (TG) and fast pyrolysis-TG/mass spectrometry (Py-TG/MS) analyses. Activation energies (131.04 kJ mol−1 –171.04 kJ mol−1) for RWWP pyrolysis were calculated by three methods: Flynn-Wall-Ozawa (FWO) method, Kissinger-Akahira-Sunose (KAS) method, and Starink method. Py-TG/MS results indicated that the RWWP could be identified as polystyrene (RWWP-1), polyethylene (RWWP-2), polyethylene terephthalate (RWWP-3, 4), and polypropylene (RWWP-5, 6). In addition, RWWP-1, 2, 5, 6 outperform RWWP-3 and 4 as sources of carbon for producing CNTs. The results showed a high carbon yield of 32.21 wt% and a high degree of CNT purity at 93.04%. [ABSTRACT FROM AUTHOR]

Producing hydrogen from catalytic gasification of biomass represents an interesting process to facilitate the development of hydrogen economy. However, the design of catalyst is a key challenge for this technology. In this work, cost-effective Ca added Ni-based catalysts were developed and studied for producing hydrogen with a fixed-bed reactor. The relationship between Ca addition and the performance of catalyst in terms of the yield of hydrogen and catalyst deactivation (metal sintering and coke formation) was studied. The results showed that hydrogen production was largely enhanced when Ca was added, as the yield of hydrogen was enhanced from 10.4 to 18.2 mmol g −1 sample in the presence of Ca-based catalyst. However, the yield and concentration of hydrogen were kept at similar levels with the increase of Ca. By normalizing the yield of hydrogen in relation to the amount of Ni presented inside the catalyst, the hydrogen yield per mole of nickel was increased from 50 g Ni −1 (0.1Ca catalyst) to 80 g Ni −1 (0.8Ca catalyst) when the Ca addition was increased from 10 mol% to 80 mol%. TPO-FTIR analysis of the experimented catalysts showed that 0.5 Ca catalyst had the highest amount of coke formation, in particular, most of the deposited carbons were amorphous which could deactivate the catalyst seriously. It is therefore concluded that the addition of cost-effective Ca could enhance the yield of hydrogen from biomass gasification. However, the concentration of Ca in the catalyst needs to be controlled to mitigate the generation of coke on the used catalyst. [ABSTRACT FROM AUTHOR]

There is great interest in producing hydrogen from renewable sources such as biomass rather than from fossil fuels. This paper presents new experimental results at different pyrolysis temperature and development of a dynamic model for a biomass pyrolysis/steam reforming process in a two stage fixed bed reactor. The model considers the hydrodynamics of the fixed bed reactor, the interfacial mass and energy transfer between the fluid–solid systems and the porous catalyst, and the energy transfer on a kinetic model. The 2D dynamic model resulted in a system of partial differential equations which was solved numerically in gPROMS®. The model was validated with the experimental results. The model predictions show good agreement with the experimental results. The model can be used as a useful tool for design, operation, optimisation and control of the biomass steam gasification process. [ABSTRACT FROM AUTHOR]

Abstract: The addition of plastics to the steam pyrolysis/gasification of wood sawdust with and without a Ni/Al2O3 catalyst was investigated in order to increase the production of hydrogen in the gaseous stream. To study the influence of the biomass/plastic ratio in the initial feedstock, 5, 10 and 20 wt.% of polypropylene was introduced with the wood in the pyrolysis reactor. To investigate the effect of plastic type, a blend of 80 wt.% of biomass and 20 wt.% of either polypropylene, high density polyethylene, polystyrene or a mixture of real world plastics was fed into the reactor. The results showed that a higher gas yield (56.9 wt.%) and a higher hydrogen concentration and production (36.1 vol.% and 10.98 mmol H2 g−1 sample, respectively) were obtained in the gaseous fraction when 20 wt.% of polypropylene was mixed with the biomass. This significant improvement in gas and hydrogen yield was attributed to synergetic effects between intermediate species generated via co-pyrolysis. The Ni/Al2O3 catalyst dramatically improved the gas yield as well as the hydrogen concentration and production due to the enhancement of water gas shift and steam reforming reactions. Very low amounts of coke (less than 1 wt.% in all cases) were formed on the catalyst during reaction, with the deposited carbonaceous material being of the filamentous type. The Ni/Al2O3 catalyst was shown to be effective for hydrogen production in the co-pyrolysis/gasification process of wood sawdust and plastics. [Copyright &y& Elsevier]

• Hard plastic was catalytic processed to produce carbon nanotubes. • TGA-FTIR was used to analysis the decomposition of hard plastic. • Fe-based catalyst is more preferred than Ni-based catalyst. • The yield and purity of CNTs using Fe-catalyst are 34.39 % and 97.45 %, respectively. The management of waste hard plastics is a big challenge in the world. Conventional pyrolysis and gasification of hard plastics have been extensively reported. However, producing high values carbon nanotubes as the main product or byproduct from hard plastics has been rarely reported. In this work, we studied and reported this work by using pyrolysis of phenolic formaldehyde resin producing high value carbon nanotubes to promote the economic competitiveness of the technology. The produced carbon nanotubes were characterized by scanning electronic microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and temperature programme oxidation. The yield of CNTs using the Ni catalysts is about 24.07 % and its purity is 93.13 %. Compared with the Ni catalysts, the Fe catalysts have higher yield and purity of CNTs, reaching 34.39 % and 97.45 %, respectively. Through transmission electron microscopy and Raman characterization, it is found that the graphitization quality of CNTs produced from Fe catalysts is higher than that of the CNTs produced from Ni catalysts. [ABSTRACT FROM AUTHOR]

• Ni- and Fe- based catalysts were studied for CNTs production. • Nickel catalyst produced the largest amount filamentous carbons. • A strong metal-support reaction suppressed the growth of CNTs. • The yield and the uniformity of CNTs are increased at a high reaction pressure. The production of carbon nanotubes (CNTs) by catalytic pyrolysis of plastics is an environmentally friendly and promising method of waste treatment and energy/materials production. Three types of metal catalysts (Fe/cordierite, Ni/cordierite and Ni-Mg/cordierite) were utilized during the catalytic pyrolysis process of polypropylene in this work. Meanwhile, the influence of reaction pressure (0.5–1.25 MPa) on the synthesis of CNTs was investigated. Carbon formation, especially CNTs, through catalytic pyrolysis of plastics has been tested in a fixed bed reactor, and the materials have been analyzed by temperature program oxidation (TPO), scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM) and Raman spectroscopy. The highest yield around 93 wt.% filamentous carbon was obtained using the Ni-based catalyst. The strong metal-support interaction within the Ni-Mg-based catalyst suppressed CNTs growth and resulted in shorter and irregular cylindrical carbon tubes. The yield of more uniform and thick CNTs increased with the additional of appropriate reaction pressure, especially at 1.0 MPa (198 mg/g PP). However, an excessive reaction pressure weakened CNTs growth and produced shorter length and larger diameters (around 30–50 nm) CNTs. The fraction of CNTs decreased when the reaction pressure was higher than 0.5 MPa. [ABSTRACT FROM AUTHOR]

Abstract As a multi-beneficial amendment, biochar is reasonable and reliable to be employed as an amendment to implement soil remediation. An overview on the manufacture, applications for contaminated soil restoration and revegetation, as well as recommended aspects for future work has been accomplished. One of the objectives of this work presented herein was to determine the effect of feedstock and preparation conditions such as pyrolysis temperature, retention time, gas flow rate, additives on the biochar characteristics and application potentials. Besides, relevant modification or activation technologies have been discussed for the improvement of the biochar functions. The application of biochar could adjust the soil structure (surface area, pore size and distribution etc.), improve the soil physicochemical properties (pH, cation exchange capacity, water retention capacity etc.) and enhance the uptake of soil nutrients for plant growth; In addition, it also can be used to adsorb various contaminants (heavy metals, organic matters), modify the habit and function of microorganism and mitigate climate problem by changing the bioavailability of elements (C, N, K etc.) in soil. These results also provided the possibility to expend the application of biochar to modify the degraded soils in the saline-alkali soil and industrial regions, further increase the usable area of cultivated land. The future research directions could be suggested as long-term field trials, the evaluation of environmental risk and the optimization of biochar production. Moreover, the relevant mechanisms should be adequately considered for maximizing the all-around efficiency of biochar amendments. Graphical abstract Unlabelled Image Highlights • An overview on the soil remediation by biochar has been accomplished. • Feedstock and production conditions affected the properties and functions of biochar. • Biochar modifiers had multiple benefits for the diverse soil management purposes. • Challenges and prospects of restoring degraded soil by biochar have been illustrated. • Optimization of the soil remediation based on biochar should be considered further. [ABSTRACT FROM AUTHOR]