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During pyrolysis, the intrinsic organic species in coals play an important role on the formation of tar but the relationship between them has not been elucidated in detail. In this study, the composition and structural characteristics of pyrolysis tars and soluble portions (SPs) via thermal dissolution from Baoqing lignite were analyzed with Fourier transform infrared spectroscopy (FTIR), gas chromatograph/mass spectrometer (GC/MS) and quadrupole/Orbitrap mass spectrometer (Orbitrap MS), and the formation mechanisms of main components in pyrolysis tars were proposed. FTIR analyses showed that both the SPs and tars are rich in -OH, C O, aromatic C C, C-O, aliphatic and aromatic C-H functional groups, suggesting they are partially similar in composition and structure. GC/MS and Orbitrap MS analyses indicated that a part of soluble organic species was directly volatilized into the tars, while others were suffered from complex reactions during pyrolysis, such as the cleavage of bridged bonds, the decomposition of oxygen-containing functional groups and the condensation of aromatics. Compared with the SPs, the higher contents of CH and O 1 classes but lower contents of O 2 -O 6 classes in the tars demonstrated that the soluble organic species are partially or completely deoxygenated during pyrolysis. [Display omitted] ● The yield of pyrolysis tars is obvious lower than that of soluble organic species. ● The components of tars are very closely related to soluble organic species. ● A part of soluble organic species is directly volatilized into pyrolysis tars. ● The soluble organic species were subjected to deoxygenation during pyrolysis. [ABSTRACT FROM AUTHOR]

Ni and Zr modified nanosheet ZSM-5 zeolites as tandem catalysts were designed using co-impregnation method (Zr-Ni/S-Z5) or combining in-situ hydrothermal synthesis of Ni@S-Z5 and sequential impregnation of Zr (Zr/Ni@ S-Z5). Their applications in upgrading of lignite pyrolysis volatiles coupling with methanol to light aromatics were investigated. The results demonstrated that nanosheet zeolites with larger surface areas and shorter b-axis length benefited the production of light aromatics due to exposing more active sites and improved diffusion limitation compared with conventional ZSM-5 zeolites. Adding Ni and Zr into tandem catalysts further enhanced BTEXN yields, which was attributed to the induction of oxyphilic ZrO 2 for activating C Ar -O bonds combining the promotion of Ni for hydrogenation. Comparing to Zr-Ni/S-Z5 catalyst, lower BTEXN yield was observed due to the decrease in exposing active sites over Zr/Ni@ S-Z5 catalyst. Moreover, enhancing diffusion behaviors in shorter b-axis length and the presence of more fractions of external coke indicated less effective in blocking pore channels, thus nanosheet zeolite series showed lower deactivation rates. [Display omitted] • Nanosheet zeolites with larger surface areas and shorter b-axis benefited the production of light aromatics. • Adding Ni and Zr into tandem catalysts further enhanced BTEXN yields. • Nanosheet zeolites with more fractions of external coke presented lower deactivation rate. [ABSTRACT FROM AUTHOR]

• Ga-Sn/AT 0.2 H5 exhibits hierarchical meso-microporesity to rich BTEXN at 600 °C. • Ga and Sn exhibited a strong synergy during the formation of aromatics. • Ga-Sn/AT 0.2 H5 keep high stability after 6 cycle reactions. • Multifunctional catalysts promote the formation of H 2 by dehydrogenation. A multifunctional catalyst of Ga-Sn anchored on hierarchical HZSM‑5 (Sn-Ga/AT 0.2 H5) was investigated in catalytic reforming of lignite pyrolysis volatile. A strong synergy was observed between Ga and Sn for the production of aromatics. The addition of Ga into AT 0.2 H5 remarkably promoted the selectivity of aromatics including benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN) compared to pure HZSM-5 (H5). The BTEXN yields increased to 24.1 mg/g over monometallic 5%Ga/AT 0.2 H5, in which the benzene yield was attained to 14.8 mg/g. With the introduction of Sn, the yield of aromatics was further improved to 25.1 mg/g. An explanation of this scenario was that introduced active metals could enhance the transformation of cyclic intermediates into aromatics and H5 support with an appropriate concentration of the acid sites provided acidic protons for aromatization. Additionally, the bimetallic Sn-Ga/AT 0.2 H5 exhibited higher stability with the yield of BTEXN maintained over 22 mg/g after three recycle experiments, which offered an efficient strategy to prolong the catalyst lifetime. [ABSTRACT FROM AUTHOR]