Search Results (150)

This review thoroughly evaluates gasification as a transformative alternative to conventional methods for managing municipal solid waste (MSW), highlighting its potential to convert carbonaceous materials into syngas for energy and chemical synthesis. A comparative evaluation of more than 350 papers and documents demonstrated that gasification is superior to incineration and pyrolysis, resulting in lower harmful emissions and improved energy efficiency, which aligns with sustainability goals. Key operational findings indicate that adjusting the temperature to 800–900 °C leads to the consumption of CO₂ and the production of CO via the Boudouard reaction. Air gasification produces syngas yields of up to 76.99 wt% at 703 °C, while oxygen gasification demonstrates a carbon conversion efficiency of 80.2%. Steam and CO₂ gasification prove to be effective for producing H₂ and CO, respectively. Catalysts, especially nickel-based ones, are effective in reducing tar and enhancing syngas quality. Innovative approaches, such as co-gasification, plasma and solar-assisted gasification, chemical looping, and integration with carbon capture, artificial intelligence (AI), and the Internet of Things (IoT), show promise in improving process performance and reducing technical and economic hurdles. The review identifies research gaps in catalyst development, feedstock variability, and system integration, emphasizing the need for integrated research, policy, and investment to fully realize the potential of gasification in the clean energy transition and sustainable MSW management. Full article

This study explores a series of eco-compatible, safe, inexpensive, and recyclable catalysts for the aza-Michael reaction, an essential transformation for constructing C-N bonds. In particular, we focus on hydrothermal carbons (HCB and HCC) prepared from chestnut cupule waste under mild, aqueous conditions, offering a sustainable alternative to traditional pyrolytic methods. These carbonaceous solids, thoroughly characterized by physicochemical techniques, exhibit notable catalytic activity, completing aza-Michael reactions in as little as 5–30 min for various model substrates. Their performance was benchmarked against Montmorillonite K10, [Cho][Pro] ionic liquid, and K10+[Cho][Pro], with the latter combination and [Cho][Pro] alone giving the fastest conversions. For example, the reaction of benzylamine with acrylonitrile reached complete conversion (typically 95% yield) in five minutes using [Cho][Pro], K10+[Cho][Pro], or likewise with HCB and HCC. Although the reactions catalyzed by hydrothermal carbons did not outperform in general those using K10-[Cho][Pro] or [Cho][Pro], they proceeded rapidly and afforded good to excellent yields. Furthermore, the HCC catalyst demonstrated excellent recyclability, maintaining its activity and yield over at least five cycles. These findings underscore the potential of hydrothermal carbons as efficient green heterogeneous catalysts, combining high surface area, porosity, and reusability with strong catalytic performance and scalability, in alignment with the principles of the circular economy. Full article

This study focuses on the production and characterization of activated carbons derived from the carbonaceous residue obtained through the catalytic pyrolysis of waste tires. A catalytic pyrolysis process was conducted at 450 °C and 575 °C, employing two zeolitic catalysts, the commercial ZSM-5 and a synthesized zeolite (PZ2), developed from natural pozzolan, which played a key role in the pyrolysis performance and the quality of the resulting carbons. After pyrolysis, the solid residues were chemically activated using KOH to improve their porous structure and surface characteristics. Comprehensive characterization was carried out, including textural properties (BET surface area and porosity) and morphological (SEM) analysis of the activated carbons, as well as crystallinity evaluation (XRD) of the zeolitic catalysts. The BET surface areas of activated carbons PZ2-T1-AK and PZ2-T2-AK reached 608.65 m²/g and 624.37 m²/g, respectively, values that surpass those reported for similar materials under comparable activation conditions. The developed porous structure suggests strong potential for applications in adsorption processes, including pollutant removal. These findings demonstrate the effectiveness of zeolite-catalyzed pyrolysis, particularly using PZ2, as a sustainable strategy for transforming tire waste into high-performance adsorbent materials. This approach supports circular economy principles through innovative waste valorization and offers a promising solution to an environmental challenge. Full article

Carbonaceous materials (CMs) have gained great attention as heterogeneous catalysts in water treatment because of their high efficiency and potential contribution to achieving carbon neutrality. Expanded graphite (EG) is ideal for studying CMs because the reactivity in CMs largely depends on graphitic structures, and most surface of EG is exposed, minimizing mass transfer resistance. However, EG is poor in adsorption and catalysis. In this study, EG was modified by simple thermal treatment to investigate the effects of characteristics of graphitic structures on reactivity. Tetracycline (TC) removal rate via activating peroxydisulfate (PDS) by the EG treated at 550 °C (EG550) was more than 10 times that of EG. The thermal modification did not significantly increase surfaces but led to increases in damaged, rough surfaces, graphitization degree, C content, defects, and C=O. Radical and non-radical pathways, such as SO₄^•−, O₂^•−, ¹O₂, and electron transfer, were involved in TC removal in EG550+PDS. TC degradation in EG550+PDS was initiated by hydroxylation, followed by demethylation, dehydroxylation, decarbonylation, and ring-opening. The ions ubiquitous in water systems did not significantly affect the performance of EG550+PDS, except for H₂PO₄⁻ and HCO₃⁻, suggesting the high potential of practical applications. This study demonstrated that graphitic structure itself and surface area are not detrimental in the catalytic reactivity of CMs, which is different from previous studies. Rather, the reactivity is governed by the characteristics, i.e., defects and functional groups of the graphitic structure. It is thought that this study provides valuable insights into the development of highly reactive CMs and the catalytic systems using them. Full article

The exploration of high-performance, low-cost, and dual-function electrodes is crucial for anion exchange membrane water electrolysis (AEMWE) to meet the relentless demand for green H₂ production. In this study, a heteroatom-doped carbon-cage-supported CoSe₂@MoSe₂@NC catalyst with a formicarium structure has been fabricated using a scalable one-step selenization strategy. The component-refined bifunctional catalyst exhibited minimal overpotential values of 116 mV and 283 mV at 10 mA cm⁻² in 1 M KOH for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. Specifically, rationally designed heterostructures and flexible carbonaceous sponges facilitate interfacial reaction equalization, modulate local electronic distributions, and establish efficient electron transport pathways, thereby enhancing catalytic activity and durability. Furthermore, the assembled AEMWE based on the CoSe₂@MoSe₂@NC bifunctional catalysts can achieve a current density of 106 mA cm⁻² at 1.9 V and maintain a favorable durability after running for 100 h (a retention of 95%). This work highlights a new insight into the development of advanced bifunctional catalysts with enhanced activity and durability for AEMWE. Full article

With the annual increase in carbon emissions and the warming of the global temperature, it is imperative to accelerate the construction of a green, low-carbon, circular economic system. The photocatalytic reduction of CO₂ can convert the emitted CO₂ into valuable carbonaceous products, which is of great significance for alleviating the global CO₂ emission problem. In this study, the literature on the “photocatalytic reduction of CO₂” from two Chinese and foreign databases was used as the analysis sample. From the perspective of net present value, nitride-based catalysts were selected as the research object. An in-depth analysis of the costs and economic benefits of the nitride-based photocatalytic reduction of CO₂ was carried out, considering four factors: catalyst efficiency, light conditions, discount rate, and depreciation period. The analysis results show that with a project duration of 10 years and a discount rate of 10%, the net present values of all the catalysts are negative, indicating that from an economic perspective, investment projects using general catalysts to reduce CO₂ are not feasible under current conditions. However, it is worth noting that when the light conditions are changed and sunlight is used as the light source, the net present values corresponding to the Ta₃N₅/Bi and NiOx/Ta₃N₅ catalysts have turned positive, showing a certain economic feasibility. When the yield is increased to 2.64 times and 6.15 times of the original values, the net present values corresponding to the T-CN/ZIS (refers to ZnIn₂S₄ (ZIS) nanosheets grown in situ on tubular g-C₃N₄ microtubes (T-CNs)) catalyst and the Ta₃N₅ cuboid catalyst turn positive, and only the net present value of the g-C₃N₄/Bi₂O₂[BO₂(OH)] catalyst remains negative. Full article

This review provides an exploration of various catalytic pyrolysis techniques for bio-oil production, focusing on the effects of different pyrolysis methods (slow, fast, and flash pyrolysis) on bio-oil yield and composition. The review also discusses key factors influencing bio-oil production, including feedstock composition (cellulose, hemicellulose, and lignin), and the role of catalytic materials in enhancing yield and product selectivity. Three primary classes of catalysts—zeolites, carbonaceous materials, and metal oxides—are thoroughly examined, with a discussion on the differences between bulk catalysts and nanocatalysts. The paper highlights how these catalysts influence the formation of bio-oil components such as phenols, hydrocarbons, and oxygenated compounds. Furthermore, this review discusses recent advancements in catalyst design and modifications to optimize bio-oil production. This review provides the latest advancements in catalytic pyrolysis, emphasizing the correlation between catalyst properties and the resulting products. It aims to offer valuable insights into the future potential of catalytic pyrolysis for efficient biomass conversion and sustainable biofuel production. Full article

In this study, a millimeter-scale N/P-doped carbonaceous catalyst was synthesized via facile carbonization of the N/P-doped resin at 800 °C (NPCR-800). This work aimed to investigate the performance of the NPCR-800 catalyst in heterogeneous catalytic ozonation and the mechanism of reactive oxygen species (ROS) generation. The NPCR-800 achieved the highest oxalic acid (OA) degradation efficiency of 91% within 40 min. The first-order kinetics of OA degradation in the NPCR-800/O₃ system was approximately twelve and three times higher than that in the O₃ and O₃/GAC system, respectively. In addition to excellent catalytic ozonation performance, the NPCR catalyst also exhibited good reusability and salt tolerance. The dominant ROS were identified by the electronic spin response and free radical quantitative experiments, being responsible for oxalic acid degradation in NPCR-800/O₃ system. The effect of the doped N and P elements on enhancing the catalytic activity was understood, what was ascribed to the efficient reaction of the O₃ molecule with the active site of the graphitic N, defect site and carbonyl/carboxyl groups of NPCR to generate the hydroxyl radical and singlet oxygen. A type of metal-free catalytic ozonation strategy was developed in this work, which is promising in the practical treatment of the refractory organic pollutants. Full article

The end-of-life management of plastic represents a significant environmental challenge, largely due to its limited use, low biodegradability, and high volume of disposed material, in the order of 400 million tonnes by 2019. Several types of polymers can be recycled by mechanical means, but some others, like plastics, sometimes require chemical methods for their reuse. In this context, gasification is one of the most promising chemical recycling techniques. Gasification is a thermochemical process performed at moderate temperatures of work (800–1100 °C) that converts carbonaceous materials into rich hydrogen gas, which can be used for energy obtention or the Fisher–Tropsch process. However, this procedure can also produce undesirable by-products like tar and char. The products’ composition and relative quantities are highly dependent on the overall process configuration and the input fuel. The current study evaluates the catalytic gasification of the most common plastic waste, seeking to obtain higher gas yields and syngas with high energy. The text focuses on the current state of development and recent advances in various publications over the last fifteen years, with emphasis on thermoplastics and thermosets. The search showed that temperatures, the type of fluidizing gas, and the catalyst have a major influence on the quality of the obtained gas. Optimal gasification conditions, such as temperatures between 600 and 900 °C, depending on the plastic feedstock, steam-to-feedstock ratios > 1, the appropriate selection of a gasifying agent according to gas requirements and energy optimization, and the composition and location of the catalyst in the system (in situ, in the reactor, or ex situ), are identified as critical for maximizing H₂ and CO production and minimizing tar. Finally, we provide summaries of the last advanced patent in the field, where the main focus appears to be feedstock pretreatment intended to ensure handling feasibility due to the variety of plastic wastes. Full article

This study investigated the production of high-performance biochar from swine manure using a sequential carbonization process combining hydrothermal carbonization (HTC) and pyrolysis. Biochar produced through HCl-assisted sequential carbonization exhibited superior properties, including the highest fixed carbon (70.0%), higher heating value (28.48 MJ/kg, ~18.8% increase over HTC-Py), and BET surface area (279.66 m²/g, ~17 times higher than other biochars). These improvements were attributed to the catalytic role of HCl in promoting dehydration, hydrolysis, and decarboxylation, leading to a more condensed and stabilized carbon structure. Furthermore, HCl significantly enhanced heavy metal removal, reducing Zn to 343.17 mg/kg (compared to HTC-Py 1324.15 mg/kg) and lowering Cd, As, Cu, Pb, Ni, and Cr by 70–80%, demonstrating effective demineralization. This approach presents a practical strategy for producing high-quality biochar with improved carbonization, energy properties, and pollutant removal, offering potential applications in environmental and agricultural fields. Full article

The shift toward sustainable energy sources is essential to curb greenhouse gas emissions and satisfy energy demands. Among renewable options, carbon-based materials—such as agricultural residues and municipal solid waste—provide a dual advantage by generating energy and fuels while also reducing landfill waste. A notable innovation is transforming plastic waste into methane-rich streams via catalytic hydrogasification, a process in which carbon-based feedstocks interact with hydrogen using a selective catalyst. In this study, a structured catalyst was developed, characterized, and tested for converting plastic waste samples. The thermal degradation properties of plastic waste were first studied using thermogravimetric analysis. The catalyst was prepared using an Oxygen Bonded Silicon Carbide (OBSiC) open-cell foam as the carrier, coated with γ-Al₂O₃-based washcoat, CeO₂, and Ni layers. It was characterized in terms of specific surface area, coating adhesion, pore distribution, acidity, and the strength of its active sites. Experimental tests revealed that a hydrogen-enriched atmosphere significantly enhances CH₄ formation. Specifically, during catalytic hydrogasification, methane selectivity reached approximately 59%, compared to 6.7%, 13.7%, and 7.8% observed during pyrolysis, catalyzed pyrolysis, and non-catalyzed hydrogasification tests, respectively. This study presents a novel and effective approach for converting plastic waste using a structured catalyst, a method rarely explored in literature. Full article

Carbonaceous-based metal-free catalysts are promising aspirants for effective electrocatalytic hydrogen generation. Herein, we synthesized mesoporous-activated carbon nanosheets (ELC) from biomass eucalyptus leaves through KOH activation. The microstructure, structural, and textural characteristics of the prepared materials were characterized by FE-SEM, Raman, XRD, and BET measurements. The high temperature (700 °C) KOH-activated ELC nanosheets exhibited an interconnected nanosheet morphology with a large specific surface area (1436 m²/g) and high mesoporosity. The ELC-700 catalyst exhibited an excellent electrocatalytic HER performance with a low overpotential (39 mV at 10 mA/cm²), excellent durability, and a Trivial Tafel slope (36 mV/dec) in 0.5 M H₂SO₄ electrolyte. These findings indicate a new approach for developing excellent biomass-derived electrocatalysts for substantially efficient green hydrogen production. Full article

Lignin is one of the main structural components of lignocellulosic biomass and can be utilized to produce phenolic compounds that can be converted downstream to cycloalkanes and aromatics, which are useful as drop-in road or aviation biofuels. Within this study, the hydrodeoxygenation of model phenolic/aromatic compounds and surrogate mixture simulating the light fraction of lignin fast-pyrolysis bio-oil was performed under mild reaction conditions. Ni/BEA zeolite was selected as a catalyst to investigate the conversion and the product selectivity of alkyl phenols (phenol, catechol, cresols), methoxy-phenols (guaiacol, syringol, creosol), aromatics (anisole, 1,2,3-trimethoxybenzene) and dimer (2-phenoxy-1-phenyl ethanol) compounds towards (alkyl)cycloalkanes. The hydrodeoxygenation of a surrogate mixture of eleven phenolic and aromatic compounds was then studied by investigating the effect of reaction conditions (temperature, time, H₂ pressure, surrogate mixture concentration, and catalyst-to-feed ratio). The conversion of model compounds was in the range of 80–100%, towards a 37–81% (alkyl)cycloalkane yield, being strongly dependent on the complexity/side-chain group of the phenolic/aromatic ring. Regarding the hydrodeoxygenation of the surrogate mixture, 59–100% conversion was achieved, with up to a 72% yield of C₆–C₉ cycloalkanes. Characterization of spent catalysts showed that the hydrodeoxygenation of surrogate mixture led to carbonaceous depositions on the catalyst, which can be limited under lower temperatures and longer reaction conditions, while after regeneration, the physicochemical properties of catalysts can be partially recovered. Full article

This study delves into the distinctive selective property exhibited by a non-conjugated cholesterol-based polymer, poly(CEM₁₁-b-EHA₇), in sorting semiconducting single-walled carbon nanotubes (s-SWCNTs) within isooctane. Comprised of 11 repeating units of cholesteryloxycarbonyl-2-hydroxy methacrylate (CEM) and 7 repeating units of 2-ethylhexyl acrylate (EHA), this non-conjugated polymer demonstrates robust supramolecular interactions across the sp² surface structure of carbon nanotubes and graphene. When coupled with the Double Liquid-Phase Extraction (DLPE) technology, the polymer effectively segregates s-SWCNTs into the isooctane phase (nonpolar) while excluding metallic SWCNTs (m-SWCNTs) in the water phase (polar). DLPE proves particularly efficient in partitioning larger-diameter s-SWCNTs (0.85–1.0 nm) compared to those dispersed directly in isooctane by poly(CEM₁₁-b-EHA₇) using direct liquid-phase exfoliation (LPE) techniques for diameters ranging from 0.75 to 0.95 nm. The DLPE method, bolstered by poly(CEM₁₁-b-EHA₇), successfully eliminates impurities from s-SWCNT extraction, including residual metallic catalysts and carbonaceous substances, which constitute up to 20% of raw HiPCO SWCNTs. DLPE emerges as a scalable and straightforward approach for selectively extracting s-SWCNTs in nonpolar, low-boiling-point solvents like alkanes. These dispersions hold promise for fabricating fast-drying s-SWCNT inks, which are ideal for printed and flexible thin-film transistors. Full article

The presence of pharmaceuticals in aquatic ecosystems is an issue of increasing concern. Regardless of the low concentration of pharmaceuticals in water, they can have a toxic effect on both humans and aquatic organisms. Advanced oxidation processes (AOPs) have been described as a promising technique for eliminating pharmaceuticals due to their high efficiency. However, the cost associated with the application of these processes and their high reagents and energy requirements have affected the implementation of AOPs at large scales. Biochar has been suggested to be used as a catalyst in AOPs to overcome these limitations. Biochar is considered as an alternative heterogeneous catalyst thanks to its physicochemical characteristics like its specific surface area, porous structure, oxygen-containing functional groups, electrical conductivity, persistent free radicals (PFRs), modifiable properties, and structure defects. This carbonaceous material presents the capacity to activate oxidizing agents leading to the formation of radical species, which are needed to degrade pharmaceuticals. Additionally, AOP/biochar systems can destroy pharmaceutical molecules following a non-radical pathway. To enhance biochar catalytic performance, modifications have been suggested such as iron (Fe) impregnation, heteroatom doping, and supporting semiconductors on the biochar surface. Although biochar has been efficiently used in combination with several AOPs for the mineralization of pharmaceuticals from water, further research must be conducted to evaluate different regeneration techniques to increase biochar’s sustainable applicability and reduce the operational cost of the combined process. Moreover, operational conditions influencing the combined system are required to be evaluated to discern their effect and find conditions that maximize the degradation of pharmaceuticals by AOP/biochar systems. Full article