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Abstract Baiyinhua lignite (BL) was sequentially treated in cyclohexane, CH 3 OH, CH 3 CH 2 OH, and (CH 3) 2 CHOH at 300 °C to afford soluble portions (SPs) 1–4 (SP 1 –SP 4), which were analyzed with a Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer (GC/MS), and quadrupole exactive orbitrap mass spectrometer (QEOTMS) with atmosphere pressure chemical ionization source in negative-ion mode. In addition, it was characterized with a solid-state 13C nuclear magnetic resonance and X-ray photoelectron spectrometer (XRPES). The results show that aliphatic and aromatic carbons, accounting for 37.1% and 59.2%, respectively, are dominated in BL. Each aromatic cluster contains 2 rings on average with 3 substituent groups on each ring. According to the analysis with XRPES, –OH group is the most abundant existing form of oxygen in BL. The analysis with GC/MS shows that the most abundant group components are arenols in SP 1 and SP 2 , and alkanoates in SP 3. Thousands of oxygen-containing aromatics (OCAs) were resolved with the QEOTMS and the molecular masses are mainly in the range of 250–400 μ. The main OCAs detected are O 1 – O 6 class species, dominated by O 2 – O 5 class species, which could be mainly assigned to acidic species, such as alkylarenediols, alkylarenetriols, and alkylarenoic acids. Highlights • Aliphatic and aromatic carbons are the dominant carbon types in Baiyinhua lignite. • Most of the organic oxygen exists in OH in Baiyinhua lignite. • O 2 – O 5 class species are the major acidic species in the soluble portions. [ABSTRACT FROM AUTHOR]

• Arenols and esters are the most abundant OCAs in the ER-derived soluble portions. • O 1 and O 2 class species are predominant detected in positive-ion mode. • O 2 - O 4 class species are the major acidic species detected in negative-ion mode. Thermal dissolution and alkanolyses of the extraction residue (ER) from Baiyinhua lignite were successively processed in cyclohexane, CH 3 OH, CH 3 CH 2 OH, and (CH 3) 2 CHOH at 300 °C to afford soluble portions (SPs) 1–4. The oxygen-containing aromatics (OCAs) in the SPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and quadrupole exactive orbitrap mass spectrometer (QEOTMS) with atmosphere pressure chemical ionization source in positive-ion mode (PIM) and negative-ion mode (NIM), while carbon types and oxygen functional groups in ER were characterized with a solid-state 13C nuclear magnetic resonance and X-ray photoelectron spectrometer, respectively. The results show that the aromatics contain 2 aromatic rings (ARs) and 2 substituents on average. -OH group is the dominant existing form of oxygen on the ER surface. Arenols and esters are the most abundant OCAs identified with GC/MS in the SPs. For O 1 - O 6 class species detected with QEOTMS, O 1 - O 2 class species detected in PIM and O 2 - O 4 class species detected in NIM are predominant. The oxygen species detected in PIM mainly appear in >C-O-C<, -CO-C<, and furan rings, but they were mainly detected in the forms of -OH and -COOH in NIM. [ABSTRACT FROM AUTHOR]

Organic matter in Baiyinhua lignite (BL) was characterized by direct characterizations with solid-state 13C nuclear magnetic resonance spectrometer and X-ray photoelectron spectrometer, thermal approaches with thermogravimetric analyzer, Curie-point pyrolyzer-gas chromatograph/mass spectrometer, and sequential thermal dissolution (TD) followed by the analysis with a gas chromatograph/mass spectrometer. The results show that normal alkanes, alkylnaphthalenes, and oxygen-containing organic compounds with Ar–O– and –(C O)–O– moieties are predominant in BL. Aliphatic carbon atoms are dominated by methylene with the average carbon number of 2. The number of aromatic rings (ARs) and substituents attached on the ARs are 2 and 4, respectively. The most abundant organic oxygen species contain Ar–O– moieties. The cleavage of >C al -C al <, >C ar -C al <, and >C ar –O– bonds is the main reaction during the pyrolysis at 500 °C, which plays the most important role in devolatilizing organic species from BL. The products from the TD differ greatly due to the distinct pathways. When using methanol as the solvent, >C–O–C < bonds in BL can be broken easily, while the cleavage of –(C O)–O– is negligible, which is the main reaction of TD in ethanol. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pretreatment increases benzenecarboxylic acid and alkanedioic acid yields sharply. • Methyl attached to aromatic rings is the active site of pretreatment. • Mellitic acid appears only in E 2 and E 3. To realize carbon neutrality in energy transition process, a two-step oxidation of Huolinhe lignite (HL) with less CO 2 emissions is proposed, including pretreatment with H 2 O 2 (PT) or pretreatment with Fenton's reagent (PTF) and further oxidation in aqueous sodium hypochlorite (ASHC). The results indicate that the insoluble macromolecular moieties in HL are mainly oxidized into alkanedioic acids (ADAs) and non-substituted benzenecarboxylic acids (NSBCAs) and the yield of soluble portion is elevated by PTF from 60.56 % to 74.99 %. The increase in the ADA carbon number indicates that PT and PTF could enhance the oxidation ability of ASHC to break bridged linkages with longer chains. As for NSBCAs, the carboxylic group number (CGN) ranges from 2 to 5 in E 1 and 2 to 6 in E 2 and E 3 , respectively. The absence of mellitic acid in E 1 states the limited oxidation capacity of ASHC to degrade highly condensed aromatic rings, which could be improved by PT and PTF. Moreover, the highest yield of NSBCAs is achieved at CGN = 2 in E 2 and CGN = 4 in E 3 , implying that PTF is more effective to destruct highly condensed aromatic species in HL. According to the characterizations of coal samples, PT could increase the volatile matter and oxygen contents of HL and create new micropores to corrode HL via OH attack, which would be enhanced by the introduction of Fe2+ during PTF to break weak covalent bonds, resulting in the preliminary degradation of macromolecular networks in HL. Then, cleavage of strong bonds undergoes easily via the attack of O 2 − generated from ASHC, leading to the deep decomposition of macromolecular moieties in HL. [ABSTRACT FROM AUTHOR]

• A R TT obtained at a higher temperature has a higher CD ARs. • Oxidizing a R TT resulting from lower-temperature TT produces more BPCAs. • HOO· produced in aqueous AHPO/AA could be crucial for the oxidation. Shengli lignite (SL) was thermally treated at 150 °C–650 °C. SL and each residue (R TT) from the thermal treatment (TT) were oxidized using aqueous hydrogen peroxide (AHPO)/acetic acid (AA) to afford a soluble portion (SP). SL and each R TT were characterized with a X-ray diffractometer and Fourier transform infrared spectrometer, and 11 typical benzenepolycarboxylic acids (BPCAsI) in the SPs were analyzed with a high-performance liquid chromatograph. The results show that the condensation degree (CD ARs) of aromatic rings (ARs) in each R TT is higher than that of SL and increases with raising the TT temperature, while the oxidation of a R TT resulting from lower-temperature TT produces BPCAsI, especially mellitic acid, in higher yields. HOO· produced in AHPO/AA could play an crucial role in oxidizing AR-containing macromolecular species in SL and each R TT to BPCAsI. [ABSTRACT FROM AUTHOR]

• Alkylbenzenes, ketones, and alkenes and alkanes have similar biogenic precursors. • Alkenes with different carbon number correspond to diverse biogenic precursors. • BL is a typical non-marine lignite formed in mild climate. • Both chemical and biochemical reactions contribute to the formation of biomarkers. Sequential thermal dissolution (STD) of Baiyinhua lignite (BL) in cyclohexane, methanol, and ethanol was performed at 300 °C to characterize the biomarkers (BMs) in BL. To confirm the origin of the BMs, BL pyrolysis was investigated using a Curie-point pyrolyzer. According to the analysis with a gas chromatograph/mass spectrometer, the BMs detected can be classified into n -alkanes, isoprenoid alkanes, n -alkenes, long-chain alkylbenzenes (ABs), polyarenes, n -alkanones, alkyl-substituted cyclopentanones, and alkyl-substituted cyclopent-2-enones. Except n -alkenes, other BMs are enriched into soluble portions from the STD. The absence of n -alkenes in BL indicates that BL was formed in a mild climate during geological times. The occurrence and distribution of BMs reflect the various pathways of BMs during coalification. The distribution of n -alkanes confirms that BL is a typical non-marine coal. Long-chain n -alkenes could inherently exist in BL, while mid-chain ones were mainly produced from the cleavage of side chains on aromatic rings. In most cases, the distribution of ABs is similar to that of n -alkanes in cyclohexane-soluble portion, suggesting a product-precursor relationship between ABs and n -alkanes. The much higher relative proportion of retene than cadalene illustrates that as for high terrestrial plants, pinaceae significantly contributed to the formation of BL. Organic molecules in living organisms undergo a series of physical, chemical and biochemical changes to produce different BMs. Related mechanisms for the formation of BMs during coalification were discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract The synergic attack of H+ and H rather than the simple H+ attack or H attack results in effective aromatic ring hydrogenation and > C O- bond cleavage over a mordenite-supported nickel catalyst. Abstract A highly active mordenite (M)-supported nickel catalyst Ni/ M was prepared via a modified deposition-percipitation and used for catalyzing hydroconversion of ethanol-soluble portion (ESP) from the ethanolysis of Dahuangshan lignite. The Ni nanoparticles were uniformly dispersed on the support without apparent agglomeration. Moreover, the number and yields of the species detected in ESP are obviously different from those detected in catalytically hydrogenated ESP (CHESP). The contents of aromatic ring (AR)-containing compounds and/or heteroatom-containing compounds (HACCs, some of which also contain an AR or ARs) in CHESP are significantly lower than those in ESP, while the alkanes (30.4%) and cyclanes (54.7%) contents in CHESP are much higher than those in ESP according to the analysis with a gas chromatograph/mass spectrometer. Furthermore, according to the analysis with a quadrupole exactive orbitrap mass spectrometer using atmospheric-pressure chemical ionization in positive-ion mode, the number and yields of HACCs in CHESP are significantly lower than those in ESP. The catalytic hydroconversion of lignite-related model compounds further confirms that the synergy between Ni nanoparticles and the M skeleton plays a crucial role in activating H 2 to H ··· H and further activating H ··· H to H · and H+, which is the key to achieving the AR hydrogenation and the heteroatom removal at 160 °C. [ABSTRACT FROM AUTHOR]

Modified microfiber attapulgite (MFA)-supported nickel was prepared by thermally decomposing nickel tetracarbonyl on MFA modified with an acidic ionic liquid (AIL, 1-sulfobutyl-3-methylimidazolium trifluoromethanesulfonate). It was characterized with multiple instruments and used for catalyzing hydroconversion of lignite-related model compounds (LRMCs) oxydibenzene, benzyloxybenzene, and oxybis(methylene)dibenzene. The results indicate that Ni 15% /MFA@AIL effectively catalyzes hydroconversion of the LRMCs to afford cyclanes by inducing the formation of H + , H − , and biatomic active hydrogen. [ABSTRACT FROM AUTHOR]