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Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are an important group of components produced from the thermal conversion of cellulose. Through using gas chromatography mass spectrometry (GC–MS), Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) and ultraviolet fluorescence spectroscopy (UV-F), the information for the evolution of OPAHs is obtained in this study. The tar produced at low temperature mainly contains light components such as homologues of pyran and furan, while the components in the tars at 700 °C and 900 °C show high double bond equivalent (DBE) values, indicating the existence of large aromatic structures. High temperature promote condensation reactions during cellulose thermal conversion, thus leading to a higher percentage of OPAHs in the tar at higher temperature process. According to Density Functional Theory (DFT) calculation, the energy barrier of Diels-Alder reaction (302.65 kJ/mol) is lower than the dehydration (583.26 kJ/mol), which means that Diels-Alder reaction could be the main route for OPAH formation rather than dehydration reaction. High reaction temperature is calculated to be favorable for the formation of naphthol during the cellulose thermal conversion because of the high energy barrier of dehydration between phenol and furan. It is consistent with the ESI FT-ICR MS result that there is a higher content of naphthol in the tar at 700 °C than that at 500 °C.

The knowledge about the formation of the heavy tars of bio-oil during pyrolysis is of great importance for the further utilization of bio-oil. This work focuses on the formation of the heavy tars during pyrolysis of bio-oil at various temperatures and heating rates in a fixed-bed reactor. In order to investigate the detailed composition of the heavy tar, the bio-oil and tars were characterized with a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Our results indicate that low temperature promotes the formation of heavy tars via the polymerization of bio-oil components, especially at slow heating rates, therein the condensed aromatics are formed via the polymerization of small aromatics with one or two rings. High temperature promotes the breakage of the oxygen-containing functional groups, meanwhile the highly condensed aromatics with more than 4 rings are formed at 800 °C via the strong secondary reactions (e.g. recombination), especially at fast heating rates.

Four types of biomass-derived organics (toluene/1-methylnaphthalene/phenol/ethanol) were catalytically decomposed and steam reformed over Ni/α-Al2O3 for co-production of hydrogen and carbon nanotubes (CNTs). In the decomposition reaction, the oxygen functional group in phenol and ethanol promoted the co-production of hydrogen and CNTs, while a small amount of toluene and 1-methylnaphthalene were cracked to hydrogen and amorphous carbon. In the reforming reaction, the yields of hydrogen and CNTs sharply increased. More than 2000 mmol/(g-cata∗h) of H2 and 260 mg/(g-cata∗h) of CNTs were produced after the reforming of toluene and ethanol. However, 1-methylnaphthalene was difficult to be reformed and small amount of CNTs were formed. The organics with low molecular weight and low degree of unsaturation conduced to the formation of hydrogen and CNTs. The growth of CNTs on Ni/α-Al2O3 mainly follows the tip-growth mechanism. The diameter distribution of CNTs is not only influenced by Ni particle size, but also related to the different organics and steam addition.

Heterogeneity of coal in micro-scale is significant and can affect coal thermal behavior. In this study, micro-Raman spectroscopy was developed for characterizing coal/char in the scale of micro- and bulk with a case study of Zhundong coal pyrolysis. More than 150 particles in micro-scale were analyzed for each sample by micro-Raman mapping technology controlled by a computer program. Individual Raman spectrum of each particles in micro-scale and average Raman spectrum for each sample were analyzed, respectively. The results indicate that the evolution characteristics of aromatic rings, C–H in methyl or methylene, and C = O groups can be revealed by combined deconvolution of first- and second-order Raman spectrum. The fluorescence interference in Raman spectrum defined as drift coefficient α can quantitate volatiles content and H/C atom ratio of individual coal/char particle in micro-scale. The results reveal that the chemical structures of the Zhundong coal in micro-scale are significantly heterogeneous. The structural evolution of char particle in micro-scale differs from each other, especially in the early stage of the Zhundong coal pyrolysis. The chemical structure of char particles in micro-scale tends to converge as the pyrolysis progresses. A more severe pyrolysis condition can generally lead to a char with higher heterogeneity. For the bulk structural evolution, the Zhundong coal pyrolysis can be mainly divided into two stages. Firstly, the C–H in methyl or methylene releases rapidly, and the relative amount of small aromatic rings and C = O groups decrease mildly. And then, the aromatization degree of char increases rapidly along with the significant release of C = O groups.

Fe-modified Ni/Al2O3 catalysts with Fe/Ni molar ratios of 0, 0.5, 1 and 2 were prepared to promote the co-production of H2 and carbon nanotubes (CNTs) during steam reforming of toluene as a tar model compound. After the addition of Fe, toluene conversion increased from 55.1% of Ni/Al2O3 to 73.6% of F1N1A (Fe/Ni ratio of 1), and H2 yield over F1N1A reached the maximum of more than 2000 mmol/(g-cata). Multi-walled carbon nanotubes with average diameter of 10–30 nm were generated and follow tip-growth mechanism. Compared with Ni/Al2O3, the addition of Fe remarkably increased the amount and quality of CNTs which had longer length and less tortuosity. These dual promoting effects on H2 and CNTs after the addition of Fe were attributed to the strong interaction between Ni and Fe in Fe-Ni alloy. Fe-Ni alloy had the high activity for the decomposition performance of toluene and H2O to generate more H2 and intermediates for improving the reforming reaction. Meanwhile, the high catalytic decomposition activity supplied more carbon species and the formation of Fe-Ni alloy enhanced the generation of metal carbide for promoting CNTs growth. Besides, the deposition of amorphous carbon was suppressed and the interaction between Ni particle and catalyst support was weakened after the addition of Fe, which kept the activity of catalyst and promoted the tip-growth of CNTs.

The effects of reaction temperature (range from 500 °C to 800 °C) on multiple competitive processes were studied for the co-production of hydrogen and carbon nanotubes (CNTs) during catalytic reforming of toluene over Ni/α-Al2O3. With the temperature raising from 500 to 800 °C, H2 yield increased by 7 times while H2 proportion slightly decreased 5 vol% due to the competitive effect between steam reforming and reverse water–gas shift (WGS) reaction. Coke amounts (including amorphous carbon and CNTs) firstly increased and then decreased, which was determined by the competitive rate of formation and consumption reaction. Detailed characterization indicated the yield and quality of CNTs improved with the temperature increasing from 500 to 650 °C and reached the maximum at 650 °C, resulting from the enhancing transformation from amorphous to CNTs and consumption of amorphous carbon by steam. However, the growth of CNTs was suppressed by further increasing temperature, and almost no CNTs were generated at 800 °C. The higher temperature aggravated the sintering of Ni and enlarged their particle size, which was not conduced to CNTs growth.