Carbon Products Research Articles

Controlling the surface oxidation state of halogenated Cu-based catalyst for electrochemical reduction of carbon dioxide to ethylene

The electrochemical CO2 reduction reaction (CO2RR) has attracted significant attention as strategy for achieving carbon neutrality. Among the candidate materials for the CO2RR, Cu-based electrocatalysts can potentially produce various high-value carbon products. However, the diversity of their products obtained via CO2RR induces low selectivity and hinders the acquisition of a specific product with a high yield. Herein, we suggest the strategies for enhancing ethylene production via CO2RR by reconstructing the oxidation states of the Cu-based catalysts. The introduced chemical oxidation and following halogenation contributes to modulate the electron structures and oxidation states of the electrodeposited polygonal Cu catalyst surface. In particular, the chemical oxidation step induces the coexistence of Cu0 and Cu+ on the catalyst surface which stabilize the CO2 adsorption onto the catalyst surface, and the halogenation maintains the Cu0/Cu+ ratio of the catalyst surface during the CO2RR. As a result, controlling the oxidation states of Cu-based catalyst improves the ethylene production selectivity up to 47.0 % of Faradaic efficiency. Furthermore, we employ a membrane electrode assembly-based electrolyzer for CO2RR which is used for commercialization, and achieve high ethylene production with a partial current density of 124.7 mA cm–2.

Mapping the constituent preference of tree species for capturing particulate matter on leaf surfaces using single-particle mass spectrometry and supervised machine learning

Respiratory health is negatively influenced by the dimensions and constituents of particulate matter (PM). Although mass concentration is widely acknowledged to be key to assessing dust retention by urban trees, the role of plant leaves in filtering PM from the urban atmosphere, particularly regarding the particle dimensions and chemical constituents of retained PM on the leaf, remains elusive. Here we combined single-particle aerosol mass spectrometry and a particle resuspension chamber to investigate how urban tree species capture PM constituents. Results indicate that leaves are efficient in capturing relatively larger particles (1.0–2.0 μm). Compositionally, airborne particles were mostly composed of elemental carbon (EC, 20%), organic carbon (OC, 17%), and secondary reaction products (13%). However, leaf surfaces revealed a preference for retaining crustal species, comprising 55% of captured particulates. Notably, specific tree species demonstrated varied affinities for different PM constituents: Osmanthus fragrans Lour. predominantly captured levoglucosan (LEV), indicative of its efficiency against biomass burning particles, whereas Cinnamomum camphora (L.) J.Presl and Sabina chinensis var. kaizuca W.C.Cheng & W.T.Wang were more effective in capturing heavy metals (HMs). XGBoost modelling identified indicator ions, e.g., CN−, NO3−, NO2−, PO3−, with SHAP values surpassing 0.035, suggesting a preferential adsorption of these ions among different tree species. These findings demonstrate that the particulate capture efficiency of urban tree species varies with species-specific leaf properties, particularly in their ability to selectively adsorb particles containing hazardous constituents such as LEV and HMs. This study provides a scientific basis for the strategic selection of tree species in urban forestry initiatives aimed at improving air quality and public health.

Impact of Local Environment on Selectivity of Ag and Cu Gas Diffusion Electrodes with Strong Hydrophobic Substrate during the Electrochemical Reduction of CO2

Electrochemical CO2 reduction (CO2RR) is a promising pathway to convert detrimental CO2 emissions into sustainable fuels and chemicals, and close the carbon loop1. To ensure the industrial applicability of this technology, electrocatalysts need to be highly active, selective towards a desired product, and offer long-term stability. High activity can be achieved with gas diffusion electrodes (GDEs), in which the CO2 reactant is supplied directly from the gas phase, however reaching high selectivity toward a single product over time remains a challenge. Recently, the control of the local environment around the catalyst has been identified to be a key factor to ensure high selectivity and stability2.In this work, we show that the local environment around the catalyst drives the selectivity of the catalyst depending on the pore size and hydrophobicity of the GDE. GDEs with large pores and weak hydrophobicity lead to poor selectivity toward carbon products, while GDEs with small pore and strong hydrophobicity yield a greatly improved Faradaic efficiency (FE) towards CO in the case of Ag (FE > 70%)2 and towards C2H4 in the case of Cu (FE > 50%) 3 at 200 mA/cm2 for several hours. The further increase of current density is detrimental to the performance of the GDEs, which points to a limitation of the transport of CO2 to the electrocatalyst. Additionally, CO reduction experiments show a qualitatively similar behavior but at much lower current densities. These findings are consistent with the presence of an electrolyte layer wetting the electrocatalyst that forces the electrocatalytic reaction to take place at double phase boundaries. Finally, we provide evidence for the correlation between the loss of selectivity towards carbon products over time and the precipitation of carbonates by operando synchrotron X-rays diffraction experiments4.In summary, our results highlight the importance of controlling the local environment near the catalyst to enhance the selectivity towards carbon products during CO2RR. References 1A. Senocrate, C. Battaglia, J. Energy Storage 2021, 36, 102373 2A. Senocrate, F. Bernasconi, D. Rentsch, K. Kraft, M. Trottmann, A. Wichser, D. Bleiner, C. Battaglia, ACS Appl. Energy Mater. 2022, 5, 14504 3F. Bernasconi, A. Senocrate, P. Kraus, C. Battaglia, Energy & Environ. Science Catalysis, 2023, 1, 1009 4F. Bernasconi, A. Senocrate, N. Plainpan, M. Mirolo, Q. Wang, C. Battaglia, submitted

(Invited) In Situ Study of Catalyst Structural Evolution during CO2 Electroreduction by Development of Electrochemical Liquid Cell TEM

The electrocatalytic CO2 reduction reaction (CO2RR) has attracted significant interest of study in the exploration of sustainable energy and environment. Cu-based materials have demonstrated the capability of converting CO2 to multi-carbon products with high catalytic activity and low cost. Since the performance of heterogenous catalysts is highly susceptible to the catalyst structural changes, unveiling the structure and catalytic active sites during reactions is crucial to the understanding of catalytic mechanisms. Although lots of efforts have been made, it remains a challenge to directly image the atomic structure of a working catalyst in liquid electrolytes due to technical difficulties. Here, I will show our development of in-situ electrochemical liquid cell transmission electron microscopy (TEM) for the study of Cu catalysts during electrocatalytic CO2RR. The novel electrochemical liquid cell allows unprecedented atomic imaging of the catalyst evolution during electrochemical reactions. Our observations reveal that the Cu catalyst-electrolyte interaction under an applied potential (-1.1 v) leads to structural changes of Cu catalyst surfaces. Intermediate structure dynamics have been captured. The propagations and transformations of intermediates result in atomically rough Cu crystal surfaces. The intermediates are further found mediating the mass loss of Cu. Control experiments demonstrate the intermediates can be utilized for enhanced carbon-carbon coupling and the formation of two carbon products. Insights gained from this study are not only valuable to designing novel catalysts, but also useful for understanding of electrified solid-liquid interfaces in general.

Electrochemical Plasma-Activated CO2 Reduction at a Plasma-Water Interface

The development of technologies and processes to decarbonize chemical and fuel production is key to reducing global anthropogenic greenhouse gas emissions. Electrochemical carbon dioxide reduction enables a sustainable pathway to circularize carbon-based chemical products by upgrading recovered carbon dioxide using renewable energy sources. Electrochemical CO2 reduction has successfully been employed to produce chemicals such as methanol and ethylene, but it has been hindered by dependence on elevated temperature to achieve high yields and limited ability to generate higher order carbon products. Non-thermal carbon dioxide plasma can be generated at ambient temperature and pressure and contains energetically excited oxygen and carbon species. When introduced to an electrocatalyst, these reactive species could more readily participate in reaction pathways with higher activation barriers towards forming higher order carbon species compared to electrochemical reactions involving ground-state reactants. Further, plasma discharges over water in an electrochemical cell generate plasma-activated water, introducing solvated electrons and secondary reactive oxygen species.In this work, we investigate how the use of plasma-activated carbon dioxide and a plasma-water interface impacts electrochemical product generation. We design a novel non-thermal plasma electrode to discharge carbon dioxide plasma into water in an electrochemical cell with a Cu nanoparticle electrocatalyst. Results suggest the potential for a plasma-water electrochemical system to generate value-added products that are less commonly generated in electrochemical processes at ambient pressure and temperature.

Assessing the impact of carbon quota allocation in enhancing supply chain members emission reduction and advertising efforts

Carbon quota allocation, a precise implementation approach within the cap-and-trade policy, exerts an enduring impact on the production and economic activities of supply chain members. Recognizing the dynamic fluctuations in product goodwill, this study formulates differential game models involving both the manufacturer and retailer within the supply chain. Subsequently, differences in carbon emission reduction efforts, advertising expenditures, product goodwill, and profitability among supply chain members within each contractual framework are comprehensively compared and analyzed. Numerical illustrations are then utilized to validate the theoretical findings and strengthen the subsequent key insights. First, the implementation of carbon quotas allocation, especially those grounded in the benchmarking-based contract, enhances carbon reduction and advertising efforts by supply chain members. Second, both grandfathering-based and benchmarking-based regulations improve the product goodwill, with the latter yielding more substantial improvements. Third, the escalation in unit emission permit price positively impacts the dedication and profitability of supply chain members, although variations in profit enhancements between the manufacturer and retailer hinge on the specific carbon quota allocation methods employed. Lastly, the grandfathering-based total carbon quotas exclusively benefit the manufacturer's profitability, whereas the per-unit carbon quotas under benchmarking-based contract fosters enhanced individual efforts and profitability for all supply chain members.

Investigation of Carbon Products Produced by Catalytic Pyrolysis of Natural Gas

Investigation of Carbon Products Produced by Catalytic Pyrolysis of Natural Gas

Developing the green operating room: exploring barriers and opportunities to reducing operating room waste.

The Australian health care system contributes 7% of the national greenhouse gas emission footprint and generates massive waste streams annually. Operating rooms are a particular hotspot, generating at least 20% of the total hospital waste. A systematic search of several global academic databases was conducted in mid-2022 (articles from 1992 to 2022) for peer-reviewed research relevant to waste management in the operating rooms. We then used thematic analysis to enumerate and characterise the strategies and barriers to sustainable waste management in the operating room. The waste reduction strategies focused on avoidance of high carbon products; correct waste segregation and reduced overage; reusing, reprocessing, and repurposing devices; and improved recycling. The first barrier identified was a constrained interpretation of the concept of "first do not harm", ingrained in surgeons' practices, in prioritising single-use surgical products. The second barrier was ineffective or insufficient waste education. The third barrier was the immediate cost of implementing waste management compared with the long term realisation of environmental and economic benefits. The last barrier to implementing institutional practice change was the lack of policies and regulations at the local hospital, federal and international levels. We also evaluated the knowledge gaps in current surgical waste research, including lack of benchmarking data and standardised regulations concerning reusable or reprocessed devices, as well as the methods used to promote pro-sustainability behavioural change.

Cation‐Infused Bilayer Ionomer Coating Enables High Partial Current Density Toward Multi Carbon Products in CO2 Electrolysis

AbstractElectrochemical CO2 reduction (eCO2R) stands as a pivotal technology for carbon recycling by converting CO2 into value‐added products. While significant strides have been made in generating multi‐carbon (C2+) products like ethylene (C2H4) and ethanol (C2H5OH) at industrial‐scale current densities with high Faradaic efficiency (FE), cathode flooding and (bi)carbonate salt accumulation remain a fundamental concern in an alkaline electrolyte. In this work, ion‐conducting polymers are used to tailor the micro‐environment mitigating cathode flooding and salt precipitation and thus, enhancing the local CO2 availability. The impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA‐9 are examined on overall eCO2R performance. The use of an ultra‐thin bilayer configuration significantly reduces cathode flooding and salt accumulation by ≈58% compared to commercial anion exchange membrane (AEM). Alongside, cation infusion improves the C─C bond formation inducing a favorable micro‐environment for selective C2+ formation. This cation‐infused bilayer ionomer (CIBLI) achieves a high partial current density of ≈284 mA cm−2 toward C2+ products maintaining a stable eCO2R performance for 24 hours (h). This scalable approach of directly deposited ultra‐thin CIBLI offers a minimal conversion energy of 117 GJ/ ton C2+ products with an energy efficiency (EE) of 29% at 350 mA cm−2 current density in one‐step CO2 conversion.

CO2 transformed into highly active catalysts for the oxygen reduction reaction via low-temperature molten salt electrolysis

The implementation of a technology capable of capturing and converting CO2 into valuable products is one of the key requirements for limiting the effects of our carbon-intensive industries. At the same time, future CO2 emissions need to be reduced to combat climate change, meaning that new devices capable of storing and converting energy without CO2 emissions have to be adopted widely. In this work, we demonstrate catalysts made directly from CO2 for fuel cells and zinc-air batteries. The molten salt electrolysis process is used to electrodeposit solid carbon from CO2 in two mixtures, a known eutectic mixture of Li2CO3, Na2CO3, K2CO3 and a new mixture containing 0.1 mol of LiOH in addition. The effects of the electrolyte towards the final carbon product and its electrocatalytic activity are analysed using the rotating disk electrode method, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The porosity of the materials is described by N2 adsorption and the best performing catalyst is compared to the activity of a commercial 20 wt% PtRu/C material in a zinc-air battery.

Thermal degradation of nanoporous Si-containing hybrid terpolymer

AbstractIn this work development of structural and chemical properties of four nanoporous hybrid carbons has been presented. The carbons were synthesized by direct carbonization at 450, 600, 750 and 900 °C of the terpolymeric hybrid precursor composed of methacrylamide, divinylbenzene and trimethoxyvinylsilane and impregnated with sulfanilic acid (SA) as the surface modifier. The conditions of the carbonization process were set on the basis of the thermogravimetric analysis combined with FTIR analysis of the evolved gases (TGA-EGA). The use of SA contributed to the reduction of the carbonization temperature by about 100 °C and resulted in carbons with very uniform and bimodal porosity with the width range of about 1 and 14–28 nm. Spectral (ATR, Raman, XPS) and X-ray diffraction methods used to characterize the resulting carbon products allowed to define the gradual changes taking place in the morphological and chemical structure of the prepared materials. Cyclic and symmetrical structures of silicates species were gradually replaced by amorphous arrangements. At the same time, the increase in the sp2/sp3 carbon ratio from 1 to 65% proved progressive ordering and aromatization of the carbonized polymeric hybrid precursor. Some functional groups (e.g., N-containing) were built into carbon clusters forming pyridinic, pyrrolic and N-graphitic like structures, while others (e.g., carbonyls) were removed from the surface.

Anionic Surfactant-Tailored Interfacial Microenvironment for Boosting Electrochemical CO2 Reduction.

Both the catalyst and electrolyte deeply impact the performance of the carbon dioxide reduction reaction (CO2RR). It remains a challenge to design the electrolyte compositions for promoting the CO2RR. Here, typical anionic surfactants, dodecylphosphonic acid (DDPA) and its analogues, are employed as electrolyte additives to tune the catalysis interface where the CO2RR occurs. Surprisingly, the anionic surfactant-tailored interfacial microenvironment enables a set of typical commercial catalysts for the CO2RR to deliver a significantly enhanced selectivity of carbon products in both neutral and acidic electrolytes. Mechanistic studies disclose that the DDPA addition restructures the interfacial hydrogen-bond environment via increasing the weak H-bonded water, thus promoting the CO2 protonation to CO. Specifically, in an H-type cell, the Faradaic efficiency of CO increases from 70 to 98% at -1.0 V versus the reversible hydrogen electrode. Furthermore, in a flow cell, the DDPA-containing electrolyte maintains over 90% FECO from 50-400 mA cm-2. Additionally, this electrolyte modulation strategy can be extended to acidic CO2RR with a pH of 1.5-3.5.

Electrotribochemical formation of abrasive nano-carbon particles under electrified conditions on lubricated sliding contacts

Electric vehicle (EV) mobility represents a transformative shift in achieving better energy security, environmental cleanliness, and economic prosperity. Despite recent advancements in EV technology, several challenges persist in tribology and lubrication fronts that can hamper their long-term reliability, performance, and efficiency. In this work, we explored the tribological performance of four commercially available driveline lubricants under non-electrified and electrified sliding conditions using AISI 52100 bearing steel. The results confirmed that passing of electricity through the contact interface exacerbate the wear damage (causing as much as a 5-fold increase in wear volume). Using Raman Spectroscopy, XPS, SEM, ToF-SIMS, and HRTEM, we confirmed that such accelerated wear primarily results from the formation of highly abrasive soot-like amorphous carbon, iron carbide, and other carbonaceous products which result from the decomposition of long-chain hydrocarbon molecules of lubricating oils under electrification. These findings confirm the existence of very complex wear mechanisms in electrified contacts and suggest the need for much improved lubricants and/or materials for future EV applications.

Pyrolysis of high-density polyethylene: Degradation behaviors, kinetics, and product characteristics

Pyrolysis is a promising technology for converting plastic waste into valuable raw materials while offering a potential solution to the global plastic pollution crisis. In this study, the thermal pyrolysis of high-density polyethylene (HDPE) is investigated in a drop tube reactor under nearly isothermal conditions. The impact of reaction temperature and gas/volatile residence time on carbon conversion and product distribution is examined across a range of 500–900 °C and 3.6–32.2 s, respectively. Non-condensable gas products detected by online mass spectrometry are H2, CH4, C2H4, C2H6, C3H6, and C3H8. At elevated temperatures and prolonged residence time, H2 yield reaches as high as 8.6 wt% of the initial HDPE mass due to intensified cracking reactions of C2–C3 hydrocarbons and long-chain aliphatic compounds. Consequently, pyrolysis tars consist mainly of polycyclic aromatic hydrocarbons (PAHs) with 5–7 rings, accompanied by visible coke deposition within the reactor. HDPE decomposition to volatiles is an endothermic process and it is complete at a temperature between 492 °C and 525 °C, depending on the heating rate employed, from non-isothermal thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) measurements. The thermal degradation of HDPE pellets follows the two-dimensional nucleation growth model for conversion levels up to 0.8 with an apparent activation energy of 259–270 kJ/mol and a pre-exponential factor of 4.83 × 1017–1.37 × 1019 min−1, determined from various isoconversional methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, along with Criado's master plots. These findings provide valuable insights into optimizing process parameters and refining reactor design for pyrolysis, which can be integrated with gasification and reforming processes to enhance hydrogen production on a larger scale.

Synthesis, Characterization and Application of New Polymers Imprinted with Zinc (II) Ions

In this work, molecularly imprinted polymers with zinc imprints and their comparison polymers without imprints were synthesized. A comparative characterization of the physical parameters of the synthesized zinc-imprinted (ZnIP) and non-imprinted (NIP) polymers was carried out using the methods of elemental analysis, conductometry, scanning electron microscopy, and IR-Fourier spectroscopy. The ability of the resulting polymers to molecularly recognize zinc was evaluated. Based on experimental data on static adsorption, the adsorption capacity of ZnIP and NIP was determined using an atomic emission spectrometer. It was found that ZnIP is characterized by better physical parameters and a higher ability for molecular recognition of zinc compared to NIP. ZnIP with zinc imprints were found to have better sorption capacity for zinc than their reference polymers. The sorption of zinc by molecular imprinted ZnIP is mainly due to the complex formation and pores of the initial carbon product. The synthesized ZnIP have increased porosity. The presence of pores with a diameter <50 nm in ZnIP is associated with voids formed after acid hydrolysis, which is clearly visible in images recorded by scanning electron microscopy. Thus, the possibility of using ZnIP as a selective sorbent has been established.

Carbon footprint accounting method based on dynamic allocation of multi-level carbon data from manufacturing organizations to products

In the process of accounting for product carbon footprints, data quality is a key requirement. To mitigate the impacts of uncertainty, dynamism, and coupling in carbon data during product carbon footprint accounting, a method based on multi-level dynamic allocation of carbon data between organizations and products is proposed. First, considering the complex distribution and merging relationships between organizational carbon emissions and product carbon footprints, an AAC (Accounting Allocation Correlation) model between the two is constructed. Then, through EIS (Enterprise Information System), carbon data is obtained, and a multi-level dynamic allocation method for carbon data, as well as a Monte Carlo-based method for merging carbon data, is proposed for the dynamic accounting of product carbon footprints. Finally, using high-voltage switchgear as a case study, the feasibility and effectiveness of the proposed method are validated.

Ethylene Electrosynthesis via Selective CO2 Reduction: Fundamental Considerations, Strategies, and Challenges

AbstractThe electrochemical carbon dioxide reduction reaction (CO2RR) is a promising approach for reducing atmospheric carbon dioxide (CO2) emissions, allowing harmful CO2 to be converted into more valuable carbon‐based products. On one hand, single carbon (C1) products have been obtained with high efficiency and show great promise for industrial CO2 capture. However, multi‐carbon (C2+) products possess high market value and have demonstrated significant promise as potential products for CO2RR. Due to CO2RR's multiple pathways with similar equilibrium potentials, the extended reaction mechanisms necessary to form C2+ products continue to reduce the overall selectivity of CO2‐to‐C2+ electroconversion. Meanwhile, CO2RR as a whole faces many challenges relating to system optimization, owing to an intolerance for low surface pH, systemic stability and utilization issues, and a competing side reaction in the form of the H2 evolution reaction (HER). Ethylene (C2H4) remains incredibly valuable within the chemical industry; however, the current established method for producing ethylene (steam cracking) contributes to the emission of CO2 into the atmosphere. Thus, strategies to significantly increase the efficiency of this technology are essential. This review will discuss the vital factors influencing CO2RR in forming C2H4 products and summarize the recent advancements in ethylene electrosynthesis.

Effect of mixed carbon phase state on detonation parameters and reaction zone of explosives under extreme condition

A precise description of the thermodynamic states of gaseous and solid detonation products is essential when using thermodynamic calculations to determine the detonation performance and destructive power of explosives. For high oxygen-lean explosives (the oxygen contained in explosives is insufficient to completely oxidize combustible elements and excess solid carbon will be generated in the detonation products), the phase state of solid carbon product affects the Chapman–Jouguet (CJ) detonation performance parameters, reaction zone, and energy release process. However, the recovery of detonation products demonstrates that the actual detonation carbon product is primarily a mixed state of diamond/graphite stack, as opposed to the existing thermodynamic codes, which essentially treat detonation carbon as single-phase carbon. To understand the thermodynamic effect of the mixed carbon phase state on the non-ideal detonation behavior, in this work, the matching relationship among the VINET equation of state parameters, thermodynamic potential parameters of the solid products of the equivalent system and the phase mixed system was constructed by using the nonlinear fitting method. The relationship between the carbon phase composition at the CJ point and the explosive composition structure was researched. Investigations were conducted into how the mixed carbon phase affected the volume and content of gas products as well as the composition at CJ points. Diamond formation in products is good for enhancing explosive's working capacity. Based on mixed-state potential parameters, the correlation mechanism between the mixed carbon phase and the chemical reaction zone was investigated, and it was found that intramolecular carbon/intermolecular carbon and more detonation graphite/diamond products all would lead to the extension of the reaction zone.

Deep Desulfurization of High-Sulfur Petroleum Coke via Alkali Catalytic Roasting Combined with Ultrasonic Oxidation.

The sulfur in petroleum coke is harmful to carbon products, underscoring the importance of desulfurization for high-sulfur petroleum coke. This paper proposes a method combining alkaline catalytic roasting with ultrasonic oxidation for the deep desulfurization of high-sulfur petroleum coke. The results show that the desulfurization rate reaches 88.99% and the sulfur content is reduced to 0.83 wt.% under a coke particle size of 96-75 μm, sodium-hydroxide-to-petroleum-coke ratio of 50%, roasting temperature of 700 °C, and holding time of 2 h. The alkali-calcined petroleum coke is ultrasonically oxidized and desulfurized in peracetic acid. The results show that, under a hydrogen peroxide content of 10%, hydrogen-peroxide-(liquid)-to-petroleum-coke (solid) ratio of 20 mL/g, acetic acid content of 5 mL, ultrasonic power of 300 W, reaction temperature of 60 °C, and reaction duration of 4 h, the sulfur content is reduced to 0.15 wt.% and the total desulfurization reaches 98.01%. Through a series of characterizations, the proposed desulfurization mechanism is verified. Alkali roasting effectively removes a significant portion of sulfur in petroleum coke. However, the elimination of certain sulfur compounds, such as the more complex thiophene, presents challenges. The thiophene content is subsequently removed via ultrasonic oxidation.

Influence of pyrolysis temperature on carbon deposition from the perspective of volatile evolution during the ex-situ pyrolysis-catalysis of plastic

To better understand the mechanism of carbon deposition, the ex-situ catalytic pyrolysis of polyethylene (PE) was explored over a FeNi/Al2O3 catalyst, and the evolution of volatiles as well as the yield and structure of carbon products at different temperatures were analyzed in depth by an in-situ atmospheric pressure photoionization high-resolution mass spectrometry (APPI HRMS) combined with a fixed-bed reactor. The results show that raising the pyrolysis temperature (from 500 to 800 °C) reduces carbon product yield and H2 production, and the proportion of carbon nanotubes (CNTs) in the carbon products decreases. The source of carbon products gradually shifts from liquid-phase carbon sources to gaseous-phase carbon sources. Below 700 °C, both the outer diameter and carbon interlayer spacing of CNTs decrease, while above 700 °C, they both increase along with increased distortion of carbon layers. It is also observed that the carbon layers are connected to the catalyst lattice stripes, and the interlayer spacing of carbon layers is greater than the catalyst lattice spacing. In situ mass spectrometry reveals a significant increase in the carbon number and double bond equivalent (DBE) values of volatiles with increasing pyrolysis temperature, but the rate of increase slows down after 700 °C. Volatiles from lower pyrolysis temperatures undergo severe polymerization, upon entering the catalytic zone at higher temperatures, minimizing temperature-induced distinctions. Nevertheless, it remains evident that volatiles from lower pyrolysis temperatures exhibit less pronounced polymerization when exposed to higher catalytic temperatures.