Structure Of Polycyclic Aromatic Hydrocarbons Research Articles

Polycyclic aromatic hydrocarbons and petroleum products in soil samples of urban areas in Eastern Siberia

Introduction. In industrial cities, the problem of environmental pollution by supertoxicants, which include the class of polycyclic aromatic hydrocarbons (PAHs), is especially acute. Since among PAHs there are substances that have a carcinogenic effect, their quantitative identification in environmental objects is an urgent task.
 Materials and methods. The content of PAHs and petroleum products (PP) in the soil of an industrial city, taken in various functional zones, was studied. Determination of sixteen PAHs was carried out by gas chromatography-mass spectrometry (GC-MS) with optimized sample preparation. It is proposed to determine PAHs by GC-MS using dispersive liquid-liquid microextraction (DLLME). Petroleum products (PP) were determined by the fluorimetric method.
 Results. Total PAHs content (ΣPAH) varied from 7.50 to 319.11 µg/kg. ΣPAH-carcinogens in the residential and sanitary protection zones was on average 25.1–31.2 times higher than in the background site. PP content levels in urban soils ranged from 3.0 to 62.4 mg/kg.
 Limitations. The study is limited to the study of the upper layers of soil up to 5 cm. The possibility of PAH migration into groundwater has not been studied.
 Conclusion. The structure of PAHs was dominated by 4-6-nuclear structures: dibenz(a,h)anthracene, benzo(g,h,i)perylene, fluoranthene, benzo(b)fluoranthene, etc., making up > 87% of the total amount of PAHs. The proportion of these polyarenes in the total ΣPAH in the residential area increases by 1.3 times compared to the background, which indicates the possibility of their technogenic origin. The PAH and PP indicators are characterized by a scatter of data and, as a result, 
 a large influence of the local factor on the formation of soil cover pollution.

Effect of phospholipids on the oxidative reactivity and microstructure of soot particles from Jatropha biodiesel combustion

Excessive phosphorus content can aggravate the formation and emission of particulate matter (PM) during biodiesel combustion, which can lead to the performance degradation of automobile exhaust catalytic converters and make it difficult to control pollutant emissions. However, the influential mechanism of phosphorus in biodiesel on PM formation is not clear yet. Therefore, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy are used to study the formation, oxidation characteristics, and nanostructures of soot particles produced from Jatropha biodiesel (JB100) combustion under different phospholipid (PE:phosphatidylethanolamine, main phospholipid type in JB100) contents. The results show that with increasing PE content in JB100, the amount of soot particles first increases and then decreases. When the PE content is 400 ppm, the amount of soot particles is the largest, almost 13.40% higher than that produced from neat JB100. Further, the activation energy (AE) of soot oxidation first increases and then decreases with increasing PE content. The apparent AE is the largest (131.40 kJ/mol) at 400 ppm. Furthermore, when the PE content is 400 ppm, the strength of oxygen-containing functional groups in the soot particles is the weakest, and the ratio of nanocrystal height to polycyclic aromatic hydrocarbons (PAHs) interlayer spacing (Lc/d002) (4.396), the average lattice spacing of PAHs (0.367 nm), and the ratio of D1 and G peaks integral intensity (ID1/IG) (2.566) are minimum. This verifies that the PE content in JB100 can affect the strength of active oxygen-containing functional groups and the size and structure of PAHs in the soot particles and that the oxidative reactivity of soot particles is lowest at 400 ppm.

(Invited) Synthetic Exploration of Functional Nanographenes for Photonic Applications

Nanographenes, or large polycyclic aromatic hydrocarbons (PAHs), have been attracting renewed attentions for their unique optical, electronic, and magnetic properties [1]. Nanographenes can also be considered as atomically precise graphene quantum dots (GQDs), which are promising as an environmentally friendly alternative of semiconductor quantum dots, especially for photonic applications ranging from light-emitting devices to bioimaging. To this end, we have been exploring the synthesis and functionalization of dibenzo[hi,st]ovalene (DBOV) as a nanographene with zigzag and armchair edges, which demonstrated high stability, strong red emission, and optical gain properties [1,2]. For example, the functionalization of DBOV with two fluoranthene imide (FAI) groups induced red-shift of the absorption and emission bands, increase of the Stokes shift, and enhancement of the stimulated emission (SE) signals with significantly reduced excited state absorption, allowing the efficient lasing at 720 nm [3]. More recently, we have synthesized dibenzo[a,m]dinaphtho[3,2,1-ef:1',2',3'-hi]coronene (DBDNC) with armchair, zigzag, and fjord edges, which also showed high stability and red emission [4]. Notably, DBDNC has a nonplanar structure around the fjord edges, as revealed by the single-crystal X-ray analysis, and displayed a SE signal at 710 nm with a longer lifetime than that of DBOV, presumably due to the suppression of intermolecular interactions. These results provide a further insight into the relationship between the PAH structures and their photophysical properties, paving the way toward their photonic applications.[1] Paternò, G. M.; Goudappagouda, Chen, Q.; Lanzani, G.; Scotognella, F; Narita A., Adv. Optical Mater. 2021, 9, 2100508.[2] Paternò, G. M.; Chen, Q.; Wang, X.-Y.; Liu, J.; Motti, S. G.; Petrozza, A.; Feng, X.; Lanzani, G.; Müllen, K.; Narita, A.; Scotognella, F., Angew. Chem. Int. Ed. 2017, 56, 6753–6757.[3] Paternò, G. M.; Chen, Q.; Muñoz-Mármol, R.; Guizzardi, M.; Bonal, V.; Kabe, R.; Barker, A. J.; Boj, P. G.; Chatterjee, S.; Ie, Y.; Villalvilla, J. M.; Quintana, J. A.; Scotognella, F.; Müllen, K.; Díaz-García, M. A.; Narita, A.; Lanzani, G., Mater. Horiz. 2022,9, 393–402.[4] Xu, X.; Serra, G.; Villa, A.; Muñoz-Mármol, R.; Vasylevskyi, S.; Gadea, M.; Lucotti, A.; Lin, Z.; Boj, P. G.; Kabe, R.; Tommasini, M.; Díaz-García, M. Á.; Scotognella, F.; Paternò, G. M.; Narita, A., Chem. Sci. 2022, 13, 13040–13045

Machine learning identified molecular fragments responsible for infrared emission features of polycyclic aromatic hydrocarbons

ABSTRACT Machine learning feature importance calculations are used to determine the molecular substructures that are responsible for mid- and far-infrared (IR) emission features of neutral polycyclic aromatic hydrocarbons (PAHs). Using the extended-connectivity fingerprint as a descriptor of chemical structure, a random forest model is trained on the spectra of 14 124 PAHs to evaluate the importance of 10 632 molecular fragments for each band within the range of 2.761 to $1172.745\, \mu$m. The accuracy of the results is confirmed by comparing them with previously studied unidentified infrared emission (UIE) bands. The results are summarized in two tables available as Supplementary Data, which can be used as a reference for assessing possible UIE carriers. We demonstrate that the tables can be used to explore the relation between the PAH structure and the spectra by discussing about the IR features of nitrogen-containing PAHs and superhydrogenated PAHs.

Aggregation-Induced Emission of Contorted Polycondensed Aromatic Hydrocarbons Made by Edge Extension Using a Palladium-Catalyzed Cyclopentannulation Reaction.

Contorted polycyclic aromatic hydrocarbons (PAHs), CPA1-2 and CPB1-2, bearing peripheral five-membered rings were synthesized employing a palladium-catalyzed cyclopentannulation reaction using specially designed diaryl acetylene synthons TPE and TPEN with commercially available dibromo- anthracene DBA and bianthracene DBBA derivatives. The resulting target compounds CPA1-2 and CPB1-2 were isolated in excellent yield and found to be highly soluble in common organic solvents, which allowed for their structural characterization and investigation of the photophysical properties, disclosing their aggregation-induced emission (AIE) properties in THF at selective concentration ranges of water fractions in the solvent mixture. Examination of the contorted PAH structures by means of density functional theory (DFT) revealed higher electronic conjugation in the more rigid and planar anthracene-containing CPA1-2 derivatives when compared to the twisted bianthracene-bearing moieties CBPA1-2 with HOMO-LUMO bandgaps (ΔE) of ∼2.32 eV for the former PAHs and ∼2.78 eV for the latter ones.

Electron-Deficient Contorted Polycyclic Aromatic Hydrocarbon via One-Pot Annulative π-Extension of Perylene Diimide.

The synthesis of a class of contorted electron-deficient polycyclic aromatic hydrocarbons (PAHs) has been achieved by a one-pot bay annulation of perylene diimide involving a mild Suzuki coupling and subsequent air-mediated, ambient-light-induced photocyclization. X-ray crystallography unambiguously confirmed the contorted PAH structure bearing four imide groups. The photophysical and electronic properties of these contorted PAHs were also analyzed, showing a high fluorescence quantum yield of 86% and moderate electron mobility of 0.017 cm2 V-1 s-1.

Exploiting the "Lego brick" approach to predict accurate molecular structures of PAHs and PANHs.

Polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen heterocycles (PANHs) are important and ubiquitous species in space. However, their accurate structural and spectroscopic characterization is often missing. To fill this gap, we exploit the so-called "Lego brick" approach [Melli et al., J. Phys. Chem. A, 2021, 125, 9904] to evaluate accurate rotational constants of some astrochemically relevant PAHs and PANHs. This model is based on the assumption that a molecular system can be seen as formed by smaller fragments for which a very accurate equilibrium structure is available. Within this model, the "template molecule" (TM) approach is employed to account for the modifications occurring when going from the isolated fragment to the molecular system under investigation, with the "linear regression" model being exploited to correct the linkage between different fragments. In the present work, semi-experimental equilibrium structures are used within the TM model. The performance of the "Lego brick" approach has been first tested for a set of small PA(N)Hs for which experimental data are available, thus leading to the conclusion that it is able to provide rotational constants with a relative accuracy well within 0.1%. Subsequently, it has been extended to the accurate prediction of the rotational constants for systems lacking any spectroscopic characterization.

Evaluation of an Ozone Chamber as a Routine Method to Decontaminate Firefighters' PPE.

Ozone chambers have emerged as an alternative method to decontaminate firefighters’ Personal Protective Equipment (PPE) from toxic fire residues. This work evaluated the efficiency of using an ozone chamber to clean firefighters’ PPE. This was achieved by studying the degradation of pyrene and 9-methylanthracene polycyclic aromatic hydrocarbons (PAHs). The following experiments were performed: (i) insufflating ozone into PAH solutions (homogeneous setup), and (ii) exposing pieces of PPE impregnated with the PAHs to an ozone atmosphere for up to one hour (heterogeneous setup). The ozonolysis products were assessed by Fourier Transform Infrared Spectroscopy (FTIR), Thin-Layer Chromatography (TLC), and Mass Spectrometry (MS) analysis. In the homogeneous experiments, compounds of a higher molecular weight were produced due to the incorporation of oxygen into the PAH structures. Some of these new compounds included 4-oxapyren-5-one (m/z 220) and phenanthrene-4,5-dicarboxaldehyde (m/z 234) from pyrene; or 9-anthracenecarboxaldehyde (m/z 207) and hydroxy-9,10-anthracenedione (m/z 225) from 9-methylanthracene. In the heterogeneous experiments, a lower oxidation was revealed, since no byproducts were detected using FTIR and TLC, but only using MS. However, in both experiments, significant amounts of the original PAHs were still present even after one hour of ozone treatment. Thus, although some partial chemical degradation was observed, the remaining PAH and the new oxygenated-PAH compounds (equally or more toxic than the initial molecules) alerted us of the risks to firefighters’ health when using an ozone chamber as a unique decontamination method. These results do not prove the ozone-advertised efficiency of the ozone chambers for decontaminating (degrading the toxic combustion residues into innocuous compounds) firefighters’ PPE.

Adsorption of polycyclic aromatic hydrocarbons by surfactant-modified clinoptilolites for landfill leachate treatment

The authors report the potential adsorption capacities of three surfactant-modified clinoptilolites (MC)—cetylpyridinium chloride (CPC)-MC, didodecyldimethylammonium bromide (DDAB)-MC, and hexadecyltrimethylammonium bromide (HDTMA)-MC—for the removal of polycyclic aromatic hydrocarbons (PAHs) from aquatic environments and landfill leachate. A liquid–liquid extraction method was used to extract PAHs from water and GC/MS was used to analyse the PAHs. PAH accumulations on CPC-MC, DDAB-MC, and HDTMA-MC were linear over 21 successive batch adsorption tests for anthracene (708, 737, and 750 µg/g), fluoranthene (1355, 1583, and 1303 µg/g), fluorene (973, 1060, and 1147 µg/g), phenanthrene (844, 1057, and 989 µg/g), and pyrene (1343, 1569, and 1269 µg/g). The leachability after 21 successive accumulations was <2% for anthracene, <4% for fluoranthene, <3% for fluorene, <4% for pyrene, and <5% for phenanthrene for each adsorbent. PAH removals from landfill leachate for anthracene, fluoranthene, fluorene, phenanthrene, and pyrene were 97.8%, 98.6%, 95.7%, 97.0%, and 98.5% for CPC-MC and 99.0%, 99.6%, 98.0%, 99.0%, and 99.6% for DDAB-MC, respectively, meeting the fresh water quality standards established by British Columbia and the World Health Organization (WHO) for anthracene, fluoranthene, and fluorene. The molecular weight and molecular structure of PAHs and the hydrophobicity of adsorbents can fundamentally influence the PAH adsorption mechanism based on π–π stacking.

Effects of polycyclic aromatic hydrocarbon structure on PAH mineralization and toxicity to soil microorganisms after oxidative bioremediation by laccase

While bioremediation using soil microorganisms is considered an energy-efficient and eco-friendly approach to treat polycyclic aromatic hydrocarbon (PAH)-contaminated soils, a variety of polar PAH metabolites, particularly oxygenated ones, could increase the toxicity of the soil after biodegradation. In this study, a typical bio-oxidative transformation of PAH into quinones was investigated in soil amended with laccase using three PAHs with different structures (anthracene, benzo[a]anthracene, and benzo[a]pyrene) to assess the toxicity after oxidative bioremediation. The results show that during a 2-month incubation period the oxidation process promoted the formation of non-extractable residues (NERs) of PAHs, and different effects on mineralization were observed among the three PAHs. Oxidation enhanced the mineralization of the high-molecular-weight (HMW) PAHs (benzo[a]anthracene and benzo[a]pyrene) but inhibited the mineralization of the low-molecular-weight (LMW) PAH (anthracene). The inhibition of anthracene suggests increased toxicity after oxidative bioremediation, which coincided with a decrease in soil nitrification activity, bacterial diversity and PAH-ring hydroxylating dioxygenase gene copies. The analysis of PAH metabolites in soil extract indicated that oxidation by laccase was competitive with the natural transformation processes of PAHs and revealed that intermediates other than quinone metabolites increased the toxicity of soil during subsequent degradation. The different metabolic profiles of the three PAHs indicated that the toxicity of soil after PAH oxidation by laccase was strongly affected by the PAH structure. Despite the potential increase in toxicity, the results suggest that oxidative bioremediation is still an eco-friendly method for the treatment of HMW PAHs since the intermediates from HMW PAHs are more easily detoxified via NER formation than LMW PAHs.

Effect of π‒conjugation on aggregation–induced emission of α–cyanostilbene incorporated polycyclic aromatic hydrocarbons

The development of facile approaches to inhibit aggregation‒caused quenching of polycyclic aromatic hydrocarbons (PAHs) due to strong π‒π interactions is a necessity to be employed in organic electronic applications. In this work, this challenging task was addressed by using α–cyanostilbene moiety in the PAH structures to achieve an opposite phenomenon, aggregation‒induced emission (AIE). The design, synthesis, and AIE properties of α–cyanostilbene consisting of PAHs (e.g., pyrene, anthracene, and naphthalene) were broadly explored. The results indicate that the steric hindrance due to cyano units and rotator vinylenes facilitate the PAH molecules to attain a twisted conformation which induced distinctive AIE attributes without requiring bulky groups on the PAHs. As a result of the extended π‒conjugation and intramolecular charge transfer in the D–π–A–π–D design, these molecules rendered variable emission colors ranging from green–to–yellowish/green–to–orange and also a white emission in THF‒water solvent system.

Solubilization of polycyclic aromatic hydrocarbons (PAHs) in PEO-PPO-PEO type linear and star block copolymers

Pluronics® and Tetronics® are used in industry for solubilizing various kinds of hydrophobic compounds since decades. In present study, moderately hydrophobic linear and star block copolymer viz. Pluronic® P104 and Tetronic® T1304 are employed for the solubilization of four polycyclic aromatic hydrocarbons (PAHs) viz. naphthalene (Np), anthracene (An), phenanthrene (Ph) and pyrene (Py). The aggregation behaviour of these block copolymers in an aqueous media has been investigated by cloud point (CP), viscometry, dynamic light scattering (DLS), and small angle neutron scattering (SANS) techniques. The aqueous solubilities of these PAHs are quite poor, hence their extractions from contaminated areas are difficult. Cloud point of block copolymers linearly decreases as a function of PAHs concentration and strongly depends on the structure of PAHs. The aqueous solutions of both block copolymers are Newtonian fluid. The solubilization of PAHs in these copolymeric micelles leads to increase in the viscosity of solution suggesting the growth of micelles. The effect of concentration and temperature on the size and shapes of micelles were evaluated from DLS and SANS studies. The study provides an alternative method for the remediation of PAHs using inexpensive commercially available block copolymers.

Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers.

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.

Identification of structural properties influencing the metabolism of polycyclic aromatic hydrocarbons by cytochrome P450 1A1

Cytochrome P450 1A1 (CYP1A1) has served as a known metabolic enzyme that mediates the carcinogenesis of polycyclic aromatic hydrocarbons (PAHs). However, the structural mechanism involved in the metabolic capacity remains unclear. In this study, thirty-three calculated properties representing the physicochemical and electronic properties of PAH and PAH-CYP1A1 interactions were utilized to identify the key structural properties that affect metabolic processes, including binding ability, metabolic clearance, and mutagenicity, using a quantitative structure-activity relationship (QSAR) strategy combined with docking methods, QM/MM calculations and ab initio calculations. van der Waals interactions (glide vdw) appeared to be important for PAH binding to CYP1A1 and were mainly affected by the molecular weight and hydrophobic structures of PAHs. Interaction features between PAHs and heme, including the distance between iron and carbons of PAHs (Fe_Cmin) and heme vdw, coordinately influence the metabolic clearance of PAHs. Furthermore, the electronic properties (ESP neg variance) appeared to be critical for the mutagenicity of PAHs by CYP1A1 through influencing epoxide metabolite formation. The QSAR models with these key properties provide a new perspective on the structural mechanism of PAH metabolism and provide a useful in silico tool for screening, classifying and predicting PAHs for their metabolism-related toxicities and risk assessment in the environment.

On the growth of Polycyclic Aromatic Hydrocarbons (PAHs) in a coflow diffusion flame of ethylene

In the last two decades several mechanisms have been proposed for the growth of PAHs during combustion. Studies have suggested that the growth of PAHs of different structures should be analyzed carefully to improve our understanding of PAH formation during combustion. In this study, a wide of range of PAHs of different structures have been measured along the centreline of a coflow diffusion flame of ethylene using GC/MS, allowing for a previously not possible detailed analysis of potential formation routes. The discussed potential global empirical pathways can help in the development of accurate and detailed chemical mechanisms in the future. The experimental results show that the difference in reactivity of the sites of a PAH where growth takes place limits the formation of benzenoid PAHs at high temperatures. This difference in reactivity also leads to the formation of PAHs with a five-membered ring at high temperatures. The recombination of PAH radicals may not be favoured in this flame which explains the small amounts of alkyl-bridged PAHs at high temperatures. PAHs with an alkyl sidechain are favoured only along the free edge. Alkyl substituted PAHs are formed in low amounts and decrease with an increase in temperature. Methylene-bridged PAHs can lead to faster growth of large PAHs and become significant at intermediate temperatures. The target flame has also been simulated using state-of-the-art models. The simultaneous measurements of both PAHs and soot allowed for a comprehensive assessment of the chemical mechanisms and soot aerosol dynamics. The assessment suggests that both the chemical mechanisms and the soot aerosol dynamics need further improvements. The results confirm the importance of accounting for PAH structure when developing kinetic mechanisms and their coupled soot formation models. A complete database comprising of PAHs, soot and temperature is generated for future model validations.

Desorption and re-adsorption of PAHS on aircraft soot surface

Polycyclic Aromatic Hydrocarbons (PAHs) in aircraft soot are capable to distribute in the gas phase and particulate phase in chemical transformations in the atmosphere. The desorption of PAHs from the soot surface is a preliminary step in the study of the reactivity of particulate PAHs. The desorption kinetics of PAHs are measured from soot samples to determine desorption rate constants for different PAHs as a function of temperature and the binding energies between PAHs and soot. The kinetics of degradation of particulate PAHs were studied in the flow reactor. The soot samples previously deposited on a Pyrex tube are introduced into the reactor along its axis and the concentrations of PAHs adsorbed on soot are determined by the High-Performance Liquid Chromatography (HPLC) as a function of the desorption time. The results show a correlation between the size of PAHs and the thermodynamics of desorption: with the PAHs have the same number of carbon atoms, their energies of desorption are very similar and increase with this number. The activation energies EA and the number of carbon atoms in PAHs have a linear correlation. It is consistent with the additivity of the laws Van der Waals. The similarity between the activation energies of desorption of PAHs and the corresponding sublimation enthalpies is consistent with the similarity between the graphitic structure of soot and the structure of PAHs.

APEX Strategy Represented by Diels-Alder Cycloadditions-New Opportunities for the Syntheses of Functionalised PAHs.

Diels-Alder cycloaddition of various dienophiles to the bay region of polycyclic aromatic hydrocarbons (PAHs) is a particularly effective and useful tool for the modification of the structure of PAHs and thereby their final properties. The Diels-Alder cycloaddition belongs to the single-step annulative π-extension (APEX) reactions and represents the maximum in synthetic efficiency for the constructions of π-extended PAHs including functionalised ones, nanographenes, and π-extended fused heteroarenes. Herein we report new applications of the APEX strategy for the synthesis of derivatives of 1,2-diarylbenzo[ghi]perylene, 1,2-diarylbenzo[ghi]perylenebisimide and 1,2-disubstituted-benzo[j]coronene. Namely, the so far unknown cycloaddition of 1,2-diarylacetylenes into the perylene and perylenebisimide bay regions was used. 1,2-Disubstituted-benzo[j]coronenes were obtained via cycloaddition of benzyne into 1,2-diarylbenzo[ghi]perylenes by using a new highly effective system for benzyne generation and/or high pressure conditions. Moreover, we report an unprecedented Diels-Alder cycloaddition-cycloaromatisation domino-type reaction between 1,4-(9,9-dialkylfluoren-3-yl)-1,3-butadiynes and perylene. The obtained diaryl-substituted core-extended PAHs were characterised by DFT calculation as well as electrochemical and spectroscopic measurements.

Rate rules for hydrogen abstraction reaction kinetics of polycyclic aromatic hydrocarbons and vinyl radical

Hydrogen abstraction reaction from polycyclic aromatic hydrocarbons (PAHs) is an important reaction class for PAHs consumption and soot formation. In this work, the reaction kinetics for a series of PAHs containing up to seven aromatic rings by vinyl radical are systematically investigated using the M06-2X/cc-pVTZ method. Based on the electronic structure calculations, the rate constants of title reactions are calculated by using transition state theory coupled with Eckart tunneling correction at the temperature range of 500–2500 K. The effects of PAH sizes, structures, and reaction sites on the rate constants are examined. The results show that the PAH sizes and reaction sites have little effect on the rate constants, while the structures of PAHs influence the rate constant significantly. Hence, the hydrogen abstraction reactions are simplified into C5 and C6 reaction classes depending on the abstraction site on the five- or six-membered ring. The simple two classes are conducive to construct the combustion model of PAHs. The reactivity with C6 class possesses the higher activity than the C5 class. Moreover, the difference in rate constants between the two classes is large at low temperatures while the two reaction classes are competitive above 1000 K. The rate rules are summarized by taking the average values of rate constants of a representative set of reactions in each class, which are applicable for the chemical model construction of PAHs.

Molecular elucidating of an unusual growth mechanism for polycyclic aromatic hydrocarbons in confined space

Extension and clustering of polycyclic aromatic hydrocarbons (PAHs) are key mechanistic steps for coking and deactivation in catalysis reactions. However, no unambiguous mechanistic picture exists on molecule-resolved PAHs speciation and evolution, due to the immense experimental challenges in deciphering the complex PAHs structures. Herein, we report an effective strategy through integrating a high resolution MALDI FT-ICR mass spectrometry with isotope labeling technique. With this strategy, a complete route for aromatic hydrocarbon evolution is unveiled for SAPO-34-catalyzed, industrially relevant methanol-to-olefins (MTO) as a model reaction. Notable is the elucidation of an unusual, previously unrecognized mechanistic step: cage-passing growth forming cross-linked multi-core PAHs with graphene-like structure. This mechanistic concept proves general on other cage-based molecule sieves. This preliminary work would provide a versatile means to decipher the key mechanistic step of molecular mass growth for PAHs involved in catalysis and combustion chemistry.

Preparation of layered-porous carbon from coal tar pitch narrow fractions by single-solvent extraction for superior cycling stability electric double layer capacitor application

Coal tar pitch (CTP) with high carbon content and wide source of raw materials was an excellent precursor for the preparation of porous carbons (PCs). CTP was composed of polycyclic aromatic hydrocarbons (PAHs) with complex molecular size and chemical structure, the separation of CTP into several fractions with relatively narrow molecular weight by solvent extraction was of significance for CTP utilization. In this paper, CTP was treated by single-solvent extraction (carbon disulfide, acetone and ethyl acetate), and the six fractions were used as raw materials to prepare PCs as electrode material for electric double layer capacitor. The fractions were well characterized and the effect of mass distribution of different narrow fractions on structure property and electrochemical performance of the PCs was studied. The PCs prepared by carbon disulfide extract, acetone raffinate and ethyl acetate extract, containing more PAHs, exhibited the excellent specific capacitance performance in comparison with its residual components. The remarkable performance might contribute in the enhanced transport of electrolyte ions via the molecular graphene structure of PAHs. Additionally, the PC prepared by carbon disulfide raffinate showed outstanding cycling performance (99.7% at 2 A g−1 after 15,000 cycles) which was related to its unique layered porous structure.