Coke Precursors Research Articles

Numerical analysis of pyrolysis and coking of aviation kerosene in a rectangular U-bend tube under one-side heating

Pyrolysis and coking of Chinese aviation kerosene RP-3 in a rectangular U-bend tube of nonuniformly heating was numerically simulated. Discussion was held regarding how the bending structure affected temperature distribution, thermal cracking, and pyrolytic deposition. Results indicated that the secondary flow induced by centrifugal forces effectively promoted thermal convection between near-wall and core regions. This effect further decreased the fuel temperature of near-wall region. Furthermore, nonuniform distribution of temperature in the U-bend tube was reduced. More RP-3 reacted along the heated wall in the straight tube, which significantly accelerated the average reaction rate in the cross section and increased the yield of coke precursors formed by secondary reactions. Notably, the curved structure promoted heat transfer and anticoke deposition performance. Under the same inner surface area, the total amount of pyrolytic deposition of U-bend tube was reduced by 17.77 mg during coking duration of 5 min.

Cooperative catalysis of Co-promoted Zn/HZSM-5 catalysts for ethane dehydroaromatization

Zn/HZSM-5 is a promising catalyst for ethane dehydroaromatization despite rapid deactivation within 13 h. Herein, the effect of introducing a cobalt promoter into the Zn/HZSM-5 catalyst was investigated to improve catalytic performance. Co-promoted Zn/HZSM-5 was superior to unpromoted Zn/HZSM-5 in terms of both catalytic activity and stability. Additionally, the total yield of benzene, toluene, and xylene over 1CoZn/HZSM-5 was 10.2%, even after 25 h of reaction, compared to the total yield over Zn/HZSM-5 catalyst at less than 1% at the time. XRD, UV–vis, TEM, and H2-TPR demonstrated that Co introduction improved ZnO dispersion in the prepared catalysts. Furthermore, the characterization of the spent catalyst via XRD, TEM, Raman, TGA, and N2 adsorption/desorption proposed that the conversion of graphite coke precursor to carbon nanotube and amorphous carbon prevented the micropores in the zeolite from being blocked. Thus, a considerable number of Brønsted acid sites in micropore could be preserved, thereby enhancing their catalytic stability. However, excessive Co clusters favored CC and CH bond dissociation, primarily producing methane and coke rather than aromatics. Therefore, adding an appropriate amount (1 wt%) of Co to Zn/HZSM-5 improves catalytic performance and the resistance to deactivation.

Front Cover: Fine‐Tuning Texture of Highly Acidic HZSM‐5 Zeolite for Efficient Ethanol Dehydration (ChemCatChem 9/2023)

The Front Cover illustrates how different morphologies of highly acidic ZSM-5 zeolite control the product distribution of ethanol dehydration. In their Research Article, E. J. M. Hensen, C. Wattanakit and co-workers demonstrate that very thin nanolayers of this zeolite with a large external surface area and abundant mesopores enhance the ethylene yield up to 95% with a high longevity. In contrast, nanoplate and bulk structures of ZSM-5 result in low ethanol conversion, high selectivity to diethyl ether, and rapid deactivation. Reducing the crystal size of highly acidic zeolites to ultra-thin nanosheets can shorten the residence time of ethanol and its intermediates in the shape-selective environments, significantly suppressing the formation of coke precursors and achieving high and stable yield of the important chemical building block ethylene. More information can be found in the Research Article by E. J. M. Hensen, C. Wattanakit and co-workers.

Comparative effects of mesopores and framework defects on the deactivation of HZSM-5 catalyst during alkylphenol dealkylation

The dealkylation of alkylphenols over HZSM-5 is regarded as a promising way for the production of phenol from both fossilized and raw lignocellulose-derived oils. However, the pure microporous HZSM-5 deactivates fast due to coking. Although the introduction of mesopores into microporous HZSM-5 can enhance the catalyst stability, the relationship between the catalytic performance and changed properties caused by alkaline treatment remains ambiguous. In this study, the coke analysis reveals that the mesopore introduction primarily promotes the formation of external coke by providing additional diffusion paths for coke precursors. However, the phenolates bound to the Lewis acid sites generated on external surface facilitates the deposition of external coke, the total coke amount is thus not significantly impacted. Furthermore, the reduction of internal silanols (Si-related framework defects) and Lewis acid sites (Al-related framework defects) by ammonium hexafluorosilicate treatment declines the total amount of coke and alleviates catalyst deactivation.

Single-step conversion of ethanol into n-butene-rich olefins over metal catalysts supported on ZrO2-SiO2 mixed oxides

With airlines committed to drastically reduce their carbon footprint by 2050, producing jet fuel from renewable ethanol is of particular interest. Recently, we reported on an Ag/ZrO2/SBA-16 catalyst that is very effective for directly converting ethanol into to n-butene-rich olefins jet fuel precursors (i.e., 88% at full conversion). Here, we report on a Cu/ZrO2/SBA-16 catalyst that presents remarkable olefins selectivity (i.e., 89% at 96% conversion) and enhanced stability as compared to Ag/ZrO2/SBA-16 catalyst. Under severe operating conditions a conversion loss < 10% was observed with the Cu/ZrO2/SBA-16 catalyst as compared to a 50% loss of conversion with the Ag/ZrO2/SBA-16 catalyst. Combined experimental and computational tools revealed that replacing Ag with Cu shifts the reaction pathway of crotonaldehyde hydrogenation from 1,3-butadiene (i.e., coke precursor) production to butyraldehyde formation. Experiments conducted with 4%Cu/4%ZrO2 supported on SBA-16, dealuminated zeolite Beta, and aluminum silicate revealed the performance and stability advantage of the SBA-16-supported catalyst.

Coking propensity and reactive radical evolution during thermal reaction of heavy residue and SARA fractions at 250–400 °C

In this study, the coking propensity and reactive radical evolution of heavy residue and SARA fractions at 250–400 °C were studied to gain an insight into the coke induction process. The interactions among fractions for thermal coking were discussed. Results showed that residue started to form coke (i.e. toluene-insoluble at room temperature) at 350 °C for longer times while resins and asphaltenes have already extensively produced coke at 250 °C with no coke induction period. This indicates that the coke induction depends on the solubility gap of reactant and coke. The coking process can be fitted with the second-order and autocatalytic kinetics for residue while second-order kinetics for heavy fractions with initial coke precursor amount varying with temperature. Asphaltenes are the sole fraction that generated reactive radicals at 250 °C and responsible for the radicals of thermal residue. The explosion of reactive radicals began when the temperature exceeded 350 °C and became steady as the thermal reaction proceeded. The coke at low temperatures mainly originated from the molecules aggregation with faint radical emergence while that at high temperatures is strongly correlated with the radical evolution. The maltene subfractions could suppress the coking of asphaltenes possibly because of the physical solvation and chemical hydrogen donating behavior to cap reactive radicals. It can serve as the intrinsic immunity for coke inhibition of heavy residue during thermal partial upgrading.

Fine‐Tuning Texture of Highly Acidic HZSM‐5 Zeolite for Efficient Ethanol Dehydration

AbstractAchieving high and stable ethylene yield from (bio)ethanol dehydration over highly active acidic zeolite remains challenging due to undesired side‐reactions. To overcome this issue, the fine‐tuned textural property of the HZSM‐5 catalyst with a hierarchical structure is crucial to overcome diffusion restrictions and limit undesired side‐reactions. Herein, the texture of high acid catalysts obtained via hydrothermal synthesis was simply tuned in the presence of tetrabutylammonium hydroxide as a meso‐ and micropore directing agent and the controlled molar ratio of NaF‐to‐Al2O3. The hierarchically designed HZSM‐5 with the small nanosheet size of 6.5 nm exhibits a high external surface area and mesopores, largely enhancing the catalytic performance of ethanol dehydration up to 95 % ethylene yield as well as preventing the formation of heavy hydrocarbons. To gain insights into the mechanistic points of view, the in situ DRIFTS study revealed that ethylene could form through ethoxy‐mediated mechanism or decomposition of diethyl ether (DEE). The catalyst deactivation caused by polyaromatics obtained from side‐reactions is the reason for low ethanol conversion and high DEE selectivity. Reducing the crystal size of highly acidic zeolite to ultra‐thin nanosheet can shorten the residence time of ethanol, intermediates, and products in porous structures, substantially suppressing the transformation of coke precursors into heavy hydrocarbons to achieve high and stable ethylene yield.

Bi-reforming of model biogas to syngas over Ru nano-catalysts supported on Mg-Al oxide derived from layered double hydroxides

A series of Ru/Mgx(Al)O (x=3, 4, 5) nano-catalysts, derived from Ru/MgAl layered double hydroxide, were facilely synthesized. The properties of Ru/Mgx(Al)O catalysts, before and after stability tests, were comprehensively characterized via N2 physisorption, XRD, ICP-OES, XRF, SEM, H2-TPR, CO2-TPD, XPS, TEM, TGA, Raman spectroscopy. In the bi-reforming of model biogas, at 800 °C, CH4/CO2/N2/H2O = 3/2/1/2.6, WHSV = 30960 mL g−1 h−1, 0.7Ru/Mg4(Al)O and 0.9Ru/Mg5(Al)O catalysts display high catalytic activity and stability without obvious deactivation within 100 h time-on-stream. The basic Mgx(Al)O mixed oxides facilitate the CO2 activation and generation of active O* species, contributed to prompt removal of coke precursor and effective coke-resistance behavior. The highly-dispersed Ru ultrafine NPs also contributed to the inhibited coke deposition due to size effect. In addition, the strong interaction between Ru NPs and Mgx(Al)O mixed oxides, result in the satisfying anti-sintering performance. The combined support effect, size effect as well as metal-support interaction over Ru/Mgx(Al)O (x=4, 5) catalyst result in excellent catalytic performance.

Catalytic co-pyrolysis of lignin and spent bleaching clay via binder-modified HZSM-5: Evolution of coke composition

In this present study, the composite catalysts were synthesized by agglomeration method using HZSM-5 and calcined spent bleaching clay (CSBC) for lignin with spent bleaching clay (SBC) co-pyrolysis vapors upgrading. The coke characteristics were investigated by NH3-TPD, FTIR, N2 adsorption-desorption, XRD, TGA, Raman, and UV–vis. The results showed that the addition of CSBC could convert the graphite-like coke of HZSM-5 into oxygenated coke, which was beneficial to the regeneration of the catalysts. The skeletal structure of the catalysts was not severely broken by the coke, but there were different degrees of deterioration of the pore structure and acidity (mainly strong acids). The composition of soluble coke (coke precursors) was analyzed by FTIR, GC-MS and HPLC. The soluble coke adsorbed on the catalyst was dominated by long-chain alkanes and oxygenated aromatic compounds. These compounds would continuously polymerize on the acidic sites of HZSM-5 to produce graphite-like coke. The modulation of HZSM-5 by CSBC could inhibit this process. This result explained the binder modification to improve the MAHs selectivity and catalyst stability from the side. This study provides a feasible direction for the modification of zeolite catalysts in the future.

Chemoselective derivatisation and ultrahigh resolution mass spectrometry for the determination of hydroxyl functional groups within complex bio-oils.

Bio-oils are a renewable alternative resource for the production of fine chemicals and fuels. Bio-oils are characterised by a high content of oxygenated compounds with a diverse array of different chemical functionalities. Here, we performed a chemical reaction to transform the hydroxyl group of the various components in a bio-oil prior to characterisation with ultrahigh resolution mass spectrometry (UHRMS). The derivatisations were first evaluated using twenty lignin-representative standards with different structural features. Our results indicate a highly chemoselective transformation of the hydroxyl group despite the presence of other functional groups. Mono- and di-acetate products were observed in acetone-acetic anhydride (acetone-Ac2O) mixtures for non-sterically hindered phenols, catechols and benzene diols. Dimethyl sulfoxide-Ac2O (DMSO-Ac2O) reactions favoured the oxidation of primary and secondary alcohols and the formation of methylthiomethyl (MTM) products of phenols. The derivatisations were then performed in a complex bio-oil sample to gain insights into the hydroxyl group profile of the bio-oil. Our results indicate that the bio-oil before derivatisation is composed of 4500 elemental compositions containing 1-12 oxygen atoms. After the derivatisation in DMSO-Ac2O mixtures, the total number of compositions increased approximately five-fold. The reaction was indicative of the variety of hydroxyl group profiles within the sample in particular the presence of phenols that were ortho and para substituted, non-hindered phenols (about 34%), aromatic alcohols (including benzylic and other non-phenolic alcohols) (25%), and aliphatic alcohols (6.3%) could be inferred. Phenolic compositions are known as coke precursors in catalytic pyrolysis and upgrading processes. Thus, the combination of chemoselective derivatisations in conjunction with UHRMS can be a valuable resource to outline the hydroxyl group profile in elemental chemical compositions in complex mixtures.

Improved catalytic performance in gas-phase dimethyl ether carbonylation over facile NH4F etched ferrierite.

Gas-phase dimethyl ether (DME) carbonylation to methyl acetate (MA) initiates a promising route for producing ethanol from syngas. Ferrierite (FER, ZSM-35) has received considerable attention as it displays excellent stability in the carbonylation reaction and its modification strategy is to improve its catalytic activity on the premise of maintaining its stability as much as possible. However, conventional post-treatment methods such as dealumination and desilication usually selectively remove framework Al or Si atoms, ultimately altering the intrinsic composition, crystallinity, and acidity of zeolites inevitably. In this study, we successfully prepared a series of hierarchical ZSM-35 materials through post-treatment with NH4F etching, which dissolved framework Al and Si at similar rates and preferentially attacked the defective sites. Interestingly, the produced pore systems effectively penetrated the [100] plane, offering elevated access to both the 8-membered ring (8-MR) and 10-membered ring (10-MR) channels. The physicochemical and acid properties of the pristine and NH4F etched ZSM-35 samples were comprehensively characterized using various techniques, including XRD, XRF, FESEM, HRTEM, Nitrogen adsorption-desorption, NH3-TPD, Py-IR, 27Al MAS NMR, and 29Si MAS NMR. Under moderate treatment conditions, the intrinsic microporous structure, acid properties, and crystallinity of zeolite were retained, leading to superior catalytic activity and stability with respect to the pristine sample. Nonetheless, severe NH4F etching disrupted the crystalline framework and created additional defective sites, bringing about faster deposition of coke precursors on the interior Brønsted acid sites (BAS) and decreased catalytic performance. This technique provides a novel and efficient method to slightly enhance the micropore and mesopore volume of industrially pertinent zeolites through a straightforward post-treatment, thus elevating the catalytic performance of these zeolites.

Influence of n‐butanol and isomers on the combustion mechanisms of isooctane and coke formation based on ReaxFF simulation

AbstractFuel additives play a significant role in enhancing the thermal stability of fuel combustion. The effect of additives on the combustion of hydrocarbon fuels and the combustion performances of isooctane with three different isomer additives, (n‐butanol (1‐BuOH), diethyl ether (DEE), and 2‐butanol(2‐BuOH)), and additive‐free isooctane were explored by ReaxFF simulation in this work. The simulation system was heated to 3000 K at a heating rate of 10 K/ps and kept stable at 3000 K. A variety of combustion products (e.g., small gas molecules and C1‐C8 hydrocarbon compounds) in each system were analyzed, and the reaction paths were speculated based on the computed trajectory. The simulation results showed that the CC bond scission reaction dominated the combustion process of the three additives. All three additives promote the formation of toxic carbonyl compounds such as formaldehyde, while the pure DEE additive has the best inhibition effect on the formation of the coke precursor, C2H2, C3H4, and C3H6. The pure 1‐BuOH additive can shorten the initial reaction time of the reactants. The effects of DEE/1‐BuOH additive on the combustion of isooctane were investigated to obtain a desirable additive mixture with good performance. The expansion of the DEE proportion (80%/20% DEF/1‐BuOH) shows a slightly better coke (C3H4 and C3H6) reduction effect, while the inhibition effect is not as obvious as that of a pure DEE additive.

Methane direct conversion to olefins, aromatics, and hydrogen over silica entrapped bimetallic MeFe-SiO2 (Me = Co, Ni, Pd, Pt) catalysts

Here, MeFe-SiO2 (Me = Co, Ni, Pd, Pt) catalysts with bimetallic sites entrapped in a highly crystalline SiO2 structure were synthesized and used for the conversion of methane to olefins, aromatics, and hydrogen (MTOAH) at 1020°C. The MeFe-SiO2 catalysts showed polymorphic forms of cristobalite, quartz, and tridymite after reaction. Among the bimetallic catalysts, 0.5Pt1.0Fe-SiO2 exhibited the highest methane conversion (10.0%) with high hydrocarbon selectivity (79.9%) at 1020°C. In C2 (ethane, ethylene, acetylene) conversion with hydrogen co-feeding at 1020°C, acetylene was identified as a major coke precursor. MTOAH with different gas hourly space velocities (GHSV) showed that the 0.5Pt1.0Fe-SiO2 catalyst exhibited higher methane conversion and aromatics selectivity than the 1.0Fe-SiO2 catalyst. Density functional theory calculations showed that the Pt-Fe3C surface is energetically favorable for methane activation and inhibits graphitic coke deposition by C2 dehydrogenation. Consequently, a modification of the entrapped Fe sites by Pt addition improved the methane conversion and hydrocarbon selectivity of the catalyst.

Pyrolysis-reforming of cellulose to simultaneously produce hydrogen and heavy organics

The small molecular organics in bio-oil could not be effectively transformed into hydrocarbons with long aliphatic chains or aromatic rings via hydrotreatment, but they could be reformed with steam to generate hydrogen for the hydrotreatment. In this study, the pyrolysis of cellulose coupled with steam reforming of volatiles of small molecular size were performed at 400–600 °C over Ni/Al2O3 catalyst, which is termed as a pyro-reforming process for simultaneous production of hydrogen and heavy organics for further production of biofuels. The results indicated that the effective reforming of small volatiles became dominant at 600 °C. The coke formed at the low temperatures was mainly polymeric coke of aliphatic nature with low thermal stability, low carbon crystallinity, high reactivity towards oxidation and high hydrophilicity. Increase of temperature to 600 °C reduced the formation of coke (from maximum of 15.0%–12.8%) and suppressed the formation of polymeric coke by promoting gasification of precursors of coke. This enhanced formation of catalytic coke with amorphous morphology as well as defective ring structures. However, homogeneous polymerization of volatiles also took place, forming amorphous coke between catalyst particles. Formation of polymeric coke should be tackled for the successful implementation of pyro-reforming process.

Intensifying gasoline production in the hydrocracking of pre-hydrotreated light cycle oil by means of Pt and Pd supported on a spent FCC catalyst

Motivated by the necessity of intensifying the valorization of secondary refinery streams and of extending the life cycle of the catalysts, this study aims to obtain high quality gasoline in the hydrocracking of a pre-hydrotreated light cycle oil (HT-LCO) using noble metals catalysts supported on a spent fluid catalytic cracking (FCC) catalyst. Hydrocracking runs have been carried out in a fixed bed reactor with two different catalysts (Pt/FCC and Pd/FCC) under the following conditions: 320–400 °C; 80 bar; hydrogen to HT-LCO ratio, 1000 NmL mL−1; weight hourly space velocity (WHSV), 4.48 h−1; and time on stream (TOS), 8 h. The results have exposed that 400 °C is the optimal temperature for hydrocracking the HT-LCO, since the yield of gasoline is clearly maximized (yielding up to 80 wt%) at the same time that the formation of gases is minimized. Comparing both catalysts, the Pt/FCC catalyst has offered better performance as its high hydrogenation capacity has allowed for obtaining an isoparaffinic gasoline fraction with a RON of 93.0. These good results lay on two facts that avoid the blocking of the micropores of the zeolite HY by the deposition of coke: (i) the hydrocracking of the coke precursors; and (ii) the matrix of the FCC catalyst where a fraction of the coke is deposited. In this way, after an initial deactivation period, the catalysts have reached a pseudo-stable state with a notorious remaining catalytic activity (higher for the Pt/FCC catalyst).

Steam reforming of ethanol, acetaldehyde, acetone and acetic acid: Understanding the reaction intermediates and nature of coke

The small aliphatic organics like ethanol, acetaldehyde, acetone and acetic acid are frequently used as feedstocks for hydrogen production via steam reforming. These organics have distinct functionalities, which might result in formation of different reaction intermediates and coke. This was investigated in this study with Ni/KIT-6 as a catalyst under normalized conditions. The results indicated that dehydration to ketene but not cracking was major route for dissociative adsorption of acetic acid on Ni/KIT-6 from 100 °C. Thermally stable CH and CC in alkenes, formed via dehydration of ethanol and aromatization of acetone/intermediates via bimolecular Aldol-condensation, were important precursors of coke in ethanol and acetone reforming. Although acetone strongly adsorbed on Ni/KIT-6, it did not polymerize to heavy oxygen-containing organics that were difficult to be gasified with steam. In comparison, the similar strong adsorption of acetaldehyde led to rapid polymerization even at 100 °C, forming the polymeric coke of highly aliphatic nature. The coking tendency in reforming followed the order: acetone > acetic acid > ethanol > acetaldehyde. Nevertheless, the amorphous form of coke in acetaldehyde reforming led to the rapid deactivation of Ni/KIT-6. The coke in ethanol, acetone and acetic acid reforming were mainly the catalytic type with the highly aromatic nature, high carbon crystal crystallinity, high thermal stability, high resistivity towards oxidation and the carbon nanotube morphology. Nevertheless, the varied reaction intermediates involved in reforming of these varied feedstock also formed the coke of some unique features.

VGO from shale oil. FCC processability and co-processing with conventional VGO

A vacuum gas oil from an Argentinian shale oil (VGONC), another from a conventional extraction crude oil (VGOC) and their 50:50 (mass basis) mixture were converted over two equilibrium, octane-barrel and resid types, catalysts in a fluidized bed CREC Riser Simulator reactor (reaction time: 5–30 s, temperature: 550 °C, cat-to-oil: 5). The conversions and yields of gases ranked VGONC > mixture ≈ VGOC over both catalysts. The higher conversions of VGONC are attributed to its paraffinic character, the conversions of the mixture being closer to those of VGOC and not the average of the individual conversions of each VGO due to the larger contribution of aromatics, resins, and asphaltenes from VGOC to the mixture. These compounds, with marked basic character, adsorb more strongly than paraffins, which are predominant in VGONC, thus inhibiting their conversion when present in the mixture. VGONC yielded selectively less gasoline, with lower fuel quality, in consistency with its composition. The yield and fuel quality of gasoline obtained from the mixture was intermediate between those of the individual VGO. Coke yields followed the order VGOC ≈ mixture > VGONC due to the lower content of coke precursors and CCR of VGONC.

Catalytic fast pyrolysis of herbal medicine wastes over zeolite catalyst for aromatic hydrocarbons production

Catalytic pyrolysis is an effective method to upgrade biomass pyrolytic bio-oil. In this study, catalytic fast pyrolysis (CFP) of licorice residue (LR) over ZSM-5 was conducted using pyrolysis–gas chromatography/mass spectrometry. The effects of temperature, Si/Al atomic ratio (SAR) and catalyst to feedstock (C/F) ratio on the formation of aromatic hydrocarbons (AHs) were investigated. The results indicated that ZSM-5 effectively converts oxygenates into AHs. Specifically, benzene, toluene, ethylbenzene, p-xylene and naphthalene (BTEXN) were the dominant components. The pyrolysis temperature and acidity of zeolite exert a greater influence on the formation of BTEXN. The maximum content of BTEXN was 73.45 % at 500 °C and 72.21 % at lower SARs (27 and 36). Coke can be formed and deposited on the zeolite during CFP of LR, which cause the deactivation of catalyst. A higher pyrolysis temperature and C/F ratios inhibits the coke formation, while a higher SAR is beneficial to coke formation. The large oxygenated molecules and aliphatic hydrocarbons (AHCs) was the precursors of coke during catalytic pyrolysis. The coke was tended to disperse on the surface of catalyst at low temperature. However, it was largely deposited in the channels of zeolite catalyst at high temperatures. This study reveals that ZSM-5 is an effective catalyst for the utilization of herbal medicine wastes. The pyrolytic bio-oil has high potential for use in fuels or renewable chemical production.

Integrated Design from Microstructural Engineering to Binder Optimization Enabling a Practical Carbon Anode with Ultrahigh ICE and Efficient Potassium Storage.

Potassium-ion batteries (PIBs) are emerging as a powerful alternative to lithium-ion battery systems in large-scale energy storage owing to plentiful resources. Nevertheless, pursuing high-yield anode materials with high initial Coulombic efficiency (ICE) and superior rate capability is still one of the most critical challenges in practical application. Herein, an integrated electrode (PC-x) derived from a petroleum coke precursor (carbon residue rate as high as 89%) is regulated from microstructural engineering to binder optimization devoting to high ICE and efficient potassium storage. Excitingly, with a strong assist from a sodium carboxymethyl cellulose (CMC) binder, the PC-900 anode displays an ultrahigh ICE of 80.5%, one of the highest values reported for PIB carbon anodes. Simultaneously, the PC-900 anode submits a high capacity (304.3 mAh g-1), superb rate (138.2 mAh g-1 at 10C), and excellent stability. Furthermore, the full cell exhibits an outstanding rate and cycling performance (210.7 mAh g-1 at 0.5C), confirming its large-scale application prospects. The ultrahigh ICE and excellent performance are mainly attributable to the beneficial microstructures (low surface area, functional group content, and larger interlayer spacing) created by microstructural engineering. Meanwhile, binder optimization also plays a crucial role in reducing the irreversible capacity and interface impedance, further improving the ICE and rate capability. Importantly, mechanism analysis confirms two-stage K+ storage behavior: reversible adsorption at edges and defects (>0.25 V) and intercalation into crystalline layers (<0.25 V). This work provides an efficient and easily scalable electrode design strategy for future practical applications of PIBs.

Flash pyrolysis of oil shale assisted by Zr-doped TiOSO4 nanocomposites: Excellent selectivity for hydrocarbons and toluene

Oil shale (OS) is among the most promising alternatives to replace/complement the conventional fossil fuels of limited reserves. The manufacture of qualified petroleum-like fuels and/or value-added chemicals by a catalytic OS pyrolysis with low energy consumptions has drawn broadattention from numerous scientific and engineering communities. While the past decades have witnessed great advancements in this regard, it is still strongly desired to inaugurate new catalysts for efficient OS utilizations, since most of the currently existing catalysts either suffer from tedious pretreatments on OS, complicated fabrication, high costs, easy deactivation by pore blockage, time-consuming impregnation, or unsatisfied selectivity etc. Herein, we report that Zr-doped TiOSO4 nanocomposites could be facilely synthesized via a simple wet-chemical-calcination method. It is found that the as-fabricated nanohybrids could induce ∼10% decrements in the activation energy of OS pyrolysis, and the quality of the pyrolyzates could be greatly enhanced, where the content of heteroatomic compounds decreases from ca. 38.3% to 17.1% (55.4% reduction), that of the medium/long-chain aliphatic hydrocarbons decreases from ca. 27.7% to 17.8% (35.7% decrease), while that of hydrocarbons and short-chain aliphatic hydrocarbons increases from ca. 61.7% to 82.9% (34.4% increase) and from ca. 19.6% to 46.3% (136.2% enhancement), respectively. More significantly, our catalyst could also induce an evident increase in the content of monoaromatic hydrocarbons, especially toluene (466.7% enriched, substantially), which is an important value-added platform chemical of broad interests, and a distinct decrease in the content of polyaromatic coke precursors (36.4% reduction), which are among the most frequently encountered undesired species during OS pyrolysis. It is proposed that the synergistic yet competitive effects of Brønsted and Lewis acid sites play important roles in the excellent catalytic performances of our nanocatalyst. Considering the strategic significance of OS and the easy availability of zirconium/titanium-based nanohybrids, our nanocatalyst with excellent heteroatom removal, anti-coke and cracking capabilities, and high selectivity for hydrocarbons, short-chain aliphatic and monoaromatic hydrocarbons (especially toluene), likely initiates new opportunities for OS pyrolysis, which is a subject of broad interest and general concern.