Catalytic oxidation of polystyrene to aromatic oxygenates over a graphitic carbon nitride catalyst

Paired Chemical Upgrading in Photoelectrochemical Cells

Photoelectrochemical (PEC) technology has emerged as a promising platform for sustainable energy conversion and chemical synthesis, utilizing solar energy to facilitate redox reactions. While PEC systems have been extensively studied for water splitting, CO2 reduction, nitrogen reduction for value-added compounds synthesis, the sluggish oxygen evolution reaction (OER) on the anode side and the less economic value of O2 limit system efficiency. To address this, researchers have explored paired chemical upgrading strategies, coupling selective anodic organic oxidation reactions (OORs) with cathodic reduction reactions. This approach enabled the simultaneous production of high-value chemicals and fuels, enhancing the PEC system efficiency and economic viability. In this Perspective, we highlight the latest advancements and milestones in coupling anode OORs and cathode reduction reactions within PEC cells. Particular emphasis is placed on the key design principles, catalyst development, reaction mechanisms, and the performance of paired PEC cells. In addition, challenges and perspectives are provided for the future development of this emerging and sustainable technology.

Rapid degradation of microplastics by catalyst-free gliding arc plasmatron

A gliding arc plasmatron (GAP) was proposed for efficient degradation of mixed microplastics (MPs) under simplified and adaptable conditions. Complete degradation of MPs can be achieved within 2-4 minutes, with non-hazardous CO2 as nearly the only gas product. The catalyst-free GAP system, with its simplicity and compatibility with distributed renewable energy supply, offers a sustainable solution for MP treatment.

Facile visible-light upcycling of diverse waste plastics using a single organocatalyst with minimal loadings

The escalating plastic waste crisis stems from limitations in conventional recycling methods, which are energy-intensive and produce lower-quality materials, leaving a substantial portion unrecycled. Here, we report a versatile organo-photocatalytic upcycling method employing an easily accessible phenothiazine derivative, PTH-3CN, to selectively deconstruct a wide array of commodity polymers-including polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyurethanes (PU), polycarbonates (PC), and other vinyl polymers-into valuable small molecules with minimal catalyst loading (as low as 500 ppm). Operating under mild conditions with visible light and ambient air, this protocol requires no additional acids or metals and adapts effectively to mixed and post-consumer plastic waste. Mechanistic analysis reveals that PTH-3CN serves as a precatalyst, decomposing into active triarylamine species that drive efficient degradation likely through a consecutive photoinduced electron transfer mechanism. This approach offers a promising, scalable route for sustainable plastic upcycling with broad applicability.

A Mind Map to Address the Next Generation of Artificial Photosynthesis Experiments

Artificial photosynthesis (APS) is using light for uphill chemical reactions that converts light energy into chemical energy. It follows the example of natural photosynthesis, but offers a broader choice of materials and components, which can enhance its performance it terms of application conditions, stability, efficiency, and uphill reactions to be carried out. This work presents here first the status of the field, just to focus afterward on the current problems seen at the forefront of the field, as well as discussing some general misunderstandings, which are often repeated in the primary literature. Finally, this perspective article is daring to define some grand challenges, which have to be tackled for the translation of APS into society.

Oxygen-Mediated Hydrogen Spillover Promotes Stable Synthesis of Vinyl Chloride on Ru Single-Atom Catalysts

Ru single-atom catalysts hold great promise for the robust synthesis of vinyl chloride through acetylene hydrochlorination. However, the easy over-chlorination of Ru atoms during reaction suppress the catalytic activity and stability. Herein, we have synthesized an oxygen doped Ru single-atom catalyst by a sequential oxygen etching strategy, which delivers the remarkable yield of vinyl chloride monomer (>99.38 %) and stability (>900 h, 180 h-1), far beyond those reported Ru counterparts. Experimental results and theoretical calculations reveal that the asymmetric structure of single-atom Ru promotes an unconventional oxygen-mediated hydrogen spillover after the activation of hydrogen chloride, which enables the reaction to proceed through Eley-Rideal mechanism with a reduced energy barrier of acetylene hydrochlorination compared to the traditional Langmuir-Hinshelwood pathway. As a result, the enhanced reaction kinetics further restrict over-chlorination of single-atom Ru, thereby ensuring the excellent durability. This work offers a strategy for designing multifunctional catalysts with enhanced performances for acetylene hydrochlorination.

Cytocompatible 2D Graphitic Carbon Nitride-Modified Polybutylene Adipate Terephthalate/Polylactic Acid Hybrid Nanobiocomposites

Polymer nanobiocomposites (PNCs) prepared with graphitic carbon nitride (GCN) nanosheets in polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA) bioblends were processed using a three-step processing technique that involved: (1) a solution-based GCN exfoliation step; (2) a masterbatching step of GCN in PBAT by solution processing; and (3) a melt-compounding step where the masterbatch was mixed with pristine PLA to delaminate the 2D GCN layers by extrusion high-shear mixing and to deposit them onto the biphasic PLA/PBAT morphology. Due to the partial exfoliation of GCN, this process led to a concurrent presence of three distinct morphologies within the PNCs' microstructure: (1) Type 1, characterized by an unaltered interface and PLA matrix, with minimal GCN deposition within the PBAT phase; (2) Type 2, distinguished by a diffused and stiff interface with GCN distribution in both the dispersed (PBAT) and matrix (PLA) phases; and (3) Type 3, featuring unmodified interfaces and GCN localization across both PLA and PBAT phases with a stair-like morphological texture. Such a morphological combination generates distinct crack propagation micromechanics, thereby influencing the variability of the plastic deformational behavior of their PNCs. Particularly, the Type 1 morphology enables GCN to act as a secondary stress-dissipating agent, whereas the PBAT domains serve as the primary stress-absorbing sites, contributing to enhanced crack propagation energy requirements. Contrarily, Type 3 (slightly) and Type 2 (predominantly) morphologies invert GCN's role from stress dissipation to stress concentration due to its localization within the PLA matrix. Differential scanning calorimetry revealed a crystallinity increase in the PNCs until 0.1 wt % GCN, followed by a decline, likely due to agglomeration at higher contents. Thermogravimetric analysis showed that GCN addition improved the thermostability of the bioblends, attributed to the GCN's nanophysical and pyrolytic barrier effect. Moreover, using both direct and indirect methods, GCN did not impair the biocompatibility of the bioblends as confirmed via cytocompatibility assays.

Synergistic Co-Recycling: Selective Oxidation of Polyethylene to Dicarboxylic Acids over Spent LiCoO2 Cathodes

The escalating production of lithium-ion batteries and plastics poses critical challenges to environmental integrity and resource sustainability. Here, we report a synergistic co-recycling strategy for spent lithium cobalt oxide (LCO) cathodes and waste polyethylene (PE), leveraging the catalytic properties of LCO to oxidize PE into high-value dicarboxylic acids. Through a combination of density functional theory calculations, electron spin resonance, and in situ infrared spectroscopy, we reveal that lithium-deficient LCO undergoes a spin-state transition of Co3+ to a high-spin state, facilitating the activation of oxygen and the generation of singlet oxygen. This reactive oxygen species drives the selective oxidation of PE via hydrogen atom transfer, achieving dicarboxylic acid yields of up to 77.5 wt%, markedly exceeding previous benchmarks. Validation with real-world plastic waste and spent batteries underscores the feasibility of this approach, presenting a sustainable paradigm-shift solution for the efficient management of lithium-ion batteries and plastic waste in a circular economy.

Current Advances in the Photoconversion of Plastics: the Catalysts and Reaction Pathways

Plastic waste has caused severe global environmental pollution and health issues due to the high production rate and lack of proper disposal technology. Traditional methods to deal with plastic waste, such as incineration and landfilling, are deemed unsustainable and energy-intensive. A promising alternative is the photocatalytic conversion of plastic waste, using sunlight as a sustainable and carbon-neutral energy source to break down plastic waste under ambient pressure and low temperatures. This review aims to provide a comprehensive summary of recent advancements in plastic photoconversion, with an emphasis on the catalysts and reaction pathways. The mechanisms and reaction routes are first reviewed, followed by a detailed discussion of strategies to design catalysts for improved performance in photoconversion. Then, examples of photothermal degradation processes are presented. Finally, current strategies, challenges, and possible future directions of plastic photoconversion are summarized and discussed.

Can the Hock Process Be Used to Produce Phenol from Polystyrene?

Polystyrene (PS) is a widely used thermoplastic polymer, but its very low recycling rate has motivated consideration of chemical conversion strategies to convert waste PS into value-added products. Oxidation methods have been widely studied, but they typically generate benzoic acid, a product with a relatively low market demand. Phenol is a higher volume chemical that would be an appealing target, but no methods currently exist for the conversion of PS into phenol. The repeat unit in PS closely resembles cumene, the primary feedstock used to produce phenol through the Hock process. Here, we investigate prospects for adapting the Hock process to PS, generating hydroperoxides through the autoxidation of benzylic C-H bonds followed by the acid-promoted rearrangement of the hydroperoxides to afford phenol and a partially oxygenated polymer. Experimental and computational studies of dimeric and trimeric PS model compounds show that neighboring phenyl rings impose conformational constraints that raise the barrier to hydrogen-atom transfer from the tertiary benzylic C-H bond. These effects are also evident with PS and contribute to lower yields of phenol when PS is subjected to Hock process conditions. These results provide valuable insights that have important implications for other efforts that seek to adapt small-molecule reactivity to polymeric feedstocks.

Selective Liquid Chemical Production in Waste Polyolefin Photorefinery by Controlling Reactive Species

Photocatalytic upcycling of waste polyolefins into value-added chemicals provides promise in plastic waste management and resource utilization. Previous works demonstrate that polyolefins can be converted into carboxylic acids, with CO2 as the final oxidation product. It is still challenging to explore more transformation products, particularly mild-oxidation products such as alcohols, because of their instability compared with polymer substrates, which are prone to oxidation during catalytic reactions. In this work, we propose an efficient strategy to regulate the product type through precise control of radicals, intermediates, and reaction paths. Taking the commonly used photocatalyst C3N4 as an example, its major products are carboxylic acids and CO2. When MoS2 is introduced to construct a Z-scheme heterostructure, gas products are significantly reduced and alcohols appear with a high yield of 1358.8 μmol gcat-1 and a high selectivity up to 80.3%. This is primarily attributed to the presence of •OH radicals from oxygen reduction, acting a key role in alcohol formation while simultaneously suppressing the competing pathways oxygen to •O2- and 1O2, thus reducing the overoxidation products. The β-scission of the C-C bonds in the polymer chains generates intermediate alkyl species, followed by the combination with •OH to produce methanol, which is more energetically favorable for MoS2/C3N4. In contrast, alkyl species couple with oxygen species to form formic acid, which is favorable for C3N4. This work provides new approaches for controlling the product types and offers new insights into the reaction pathways involved in polyolefin photorefinery.

Reassessing the Photochemical Upcycling of Polystyrene Using Acridinium Salts

Polystyrene (PS) is a commodity plastic recalcitrant to chemical recycling or upcycling processes. Approaches aimed at deconstructing PS by photocatalytic means struggle to generate high-energy species capable of cleaving the robust C-H and C-C bonds of PS. We show that 9-mesityl-10-methylacridinium perchlorate (MA) is capable of upcycling various grades of PS substrates into up to 40 % benzoic acid (BAc), formic acid (FA) and small proportions of acetophenone (ACP), under visible light (456 nm) or through solar radiation. Time-resolved emission and absorption spectroscopy evidence that a reaction with oxygen is the primary photochemical step in oxygen-saturated solutions, accounting for 77 % of the photons absorbed vs. 1 % for the direct reaction with PS (0.303 M in repeating units). These results are in agreement with a mechanism in which MA-mediated photo upcycling of PS to BAc occurs through the abstraction of benzylic H atoms by reactive oxygen species generated by energy or electron transfer from the excited state of MA. Addition of triplet O2 to these radicals, followed by intra- or inter-molecular hydrogen atom transfer (HAT) generates C- or O-centered radicals then undergoing β-scission or hydroperoxide fragmentation. The formation of intermediate oligomers functionalized by terminal carbonyl groups is demonstrated by both infrared analysis and MALDI TOF mass spectrometry. These oligomers undergo further photoinduced conversion even in the absence of MA, as evidenced by size exclusion chromatography analysis of the irradiated samples.

Nitrogenative Degradation of Polystyrene Waste

Owing to massive production and poor end-of-life management, plastic waste pollution has become one of the most pressing environmental crises. In response to the mounting crisis, the past several decades have witnessed the development of numerous methods and technologies for plastic recycling. However, most of the current recycling technologies often produce low-quality or low-value products, making it difficult to recover the operating costs. To this end, we report a novel preoxygenation-induced strategy for the nitrogenative degradation of real-life polystyrene plastics into high-value aromatic nitrogen compounds in a cost-effective manner. Thus, expensive and highly demanding benzonitrile as well as benzamide were obtained in up to 74% overall isolated yield from polystyrene waste by using CuBr as the catalyst, O2 as the oxidant, and CH3CN as the nitrogen source. Detailed mechanistic investigations indicate that hydroxyl radicals from O2 activation play a role in this selective aerobic degradation process. Furthermore, multiple reaction pathways contribute to the formation of benzonitrile and benzamide.

Aerobic oxidation of alkylarenes and polystyrene waste to benzoic acids via a copper-based catalyst

The chemical recycling of polystyrene (PS) waste to value-added aromatic compounds is an attractive but formidable challenge due to the inertness of the C-C bonds in the polymer backbone. Here we develop a light-driven, copper-catalyzed protocol to achieve aerobic oxidation of various alkylarenes or real-life PS waste to benzoic acid and oxidized styrene oligomers. The resulting oligomers can be further transformed under heating conditions, thus achieving benzoic acid in up to 65% total yield through an integrated one-pot two-step procedure. Mechanistic studies show that the CuCl2 catalyst undergoes Ligand-to-Metal Charge Transfer (LMCT) to generate a chlorine radical, which triggers activation of the C-H bond and subsequent oxidative cleavage of C-C bonds. The practicality and scalability of this strategy are demonstrated by depolymerization of real-life PS foam on a gram scale, thus showing promising application potential in chemical recycling of PS waste.

Advanced Catalysts for the Chemical Recycling of Plastic Waste

Plastic products bring convenience to various aspects of the daily lives due to their lightweight, durability and versatility, but the massive accumulation of post-consumer plastic waste is posing significant environmental challenges. Catalytic methods can effectively convert plastic waste into value-added feedstocks, with catalysts playing an important role in regulating the yield and selectivity of products. This review explores the latest advancements in advanced catalysts applied in thermal catalysis, microwave-assisted catalysis, photocatalysis, electrocatalysis, and enzymatic catalysis reaction systems for the chemical recycling of plastic waste into valuable feedstocks. Specifically, the pathways and mechanisms involved in the plastics recycling process are analyzed and presented, and the strengths and weaknesses of various catalysts employed across different reaction systems are described. In addition, the structure-function relationship of these catalysts is discussed. Herein, it is provided insights into the design of novel catalysts applied for the chemical recycling of plastic waste and outline challenges and future opportunities in terms of developing advanced catalysts to tackle the "white pollution" crisis.

Upcycling of Polystyrene to Aromatic Polyacids by Tandem Friedel-Crafts and Oxidation Reactions

Due to the high demand and the increasing production rate of plastic materials, vast amounts of wastes are generated every year. An important fraction of these wastes contain polystyrene (PS), which is seldom recycled, neither mechanically nor chemically. While several chemical recycling strategies have been developed, they are either very energy-demanding or produce chemicals that can hardly be employed in the synthesis of plastics (e.g., benzene and benzoic acid). Here, we report the upcycling of PS waste into aromatic polyacids, useful in polyester synthesis, such as polyethylene terephthalate (PET). To this end, a conventional Friedel-Crafts acylation was first investigated, to produce an acylated PS chain, using acetic anhydride and stoichiometric amounts of AlCl3. As a catalytic alternative, the alkylation of PS was studied, using InCl3 and isopropyl acetate. The acylated and alkylated PS samples were then oxidized to produce terephthalic (TA), isophthalic (IPTA), benzoic (BA), and trimesic (TMA) acid.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

Upconversion Phosphor-Driven Photodegradation of Plastics

Plastic waste poses a profound threat to ecosystems and human health, necessitating novel strategies for effective degradation in nature. Here, we present a novel approach utilizing upconversion phosphors as additives to significantly accelerate plastic photodegradation in nature via enhancing ultraviolet (UV) radiation. Pr-doped Li2CaGeO4 (LCGO:Pr) upconversion phosphors readily converting blue light into deep-UV radiation, dramatically improve photodegradation rates for polyethylene (PE) and polyethylene terephthalate (PET) microplastics. In situ spectroscopic studies show that upconversion fluorescence initiates the photophysical cleavage of C-C and C-O bonds in the backbones of PE and PET, resulting in plastic degradation. Moreover, incorporating LCGO:Pr into polypropylene (PP) sheets realizes markedly enhanced photodamage, with the cracking area increasing by nearly 38-fold under simulated sunlight for 10 days. This underscores the potential of employing this approach for the construction of light-driven destructible polymers. Further optimization and exploration of material compatibility hold promise for developing sustainable photodegradable plastics.

Photocatalytic Upcycling of Different Types of Plastic Wastes: A Mini Review

With the escalating demand and utilization of plastics, considerable attention has been given to controlling plastic pollution. Among these methodologies, photocatalytic upcycling of plastic has emerged as a promising method for plastic management due to its energy-saving and eco-friendly properties. In the past several years, great efforts have been devoted to the photocatalytic conversion of a variety of commercial plastic types. These encouraging endeavors foreshadow the continued progression and application in this field. In this review, recent advancements in the photocatalytic upcycling of plastics are reviewed. The fundamentals and principles of photocatalytic deconstruction of plastics are first introduced. Then, we summarize the works on the reforming of different types of plastic, including polyolefins, polyesters, and other types. Finally, some challenges and possible solutions are provided for the development of photocatalytic upcycling of plastics.

Revealing OH species in situ generated on low-valence Cu sites for selective carbonyl oxidation

Catalytic oxidation through the transfer of lattice oxygen from metal oxides to reactants, namely the Mars-van Krevelen mechanism, has been widely reported. In this study, we evidence the overlooked oxidation route that features the in situ formation of surface OH species on Cu catalysts and its selective addition to the reactant carbonyl group. We observed that glucose oxidation to gluconic acid in air (21% O2) was favored on low-valence Cu sites according to X-ray spectroscopic analyses. Molecular O2 was activated in situ on Cu0/Cu+ forming localized, adsorbed hydroxyl radicals (*OH) which played the primary reactive oxygen species as confirmed by the kinetic isotope effect (KIE) study in D2O and in situ Raman experiments. Combined with DFT calculations, we proposed a mechanism of O2-to-*OH activation through the *OOH intermediate. The localized *OH exhibited higher selectivity toward glucose oxidation at C1HO to form gluconic acid (up to 91% selectivity), in comparison with free radicals in bulk environment that emerged from thermal, noncatalytic hydrogen peroxide decomposition (40% selectivity). The KIE measurements revealed a lower glucose oxidation rate in D2O than in H2O, highlighting the role of water (H2O/D2O) or its derivatives (e.g., *OH/*OD) in the rate-determining step. After proving the C1-H activation step kinetically irrelevant, we proposed the oxidation mechanism that was characterized by the rate-limiting addition of *OH to C1=O in glucose. Our findings advocate that by maneuvering the coverage and activity of surface *OH, high-performance oxidation of carbonyl compounds beyond biomass molecules can be achieved in water and air using nonprecious metal catalysts.

Tandem microplastic degradation and hydrogen production by hierarchical carbon nitride-supported single-atom iron catalysts

Microplastic pollution, an emerging environmental issue, poses significant threats to aquatic ecosystems and human health. In tackling microplastic pollution and advancing green hydrogen production, this study reveals a tandem catalytic microplastic degradation-hydrogen evolution reaction (MPD-HER) process using hierarchical porous carbon nitride-supported single-atom iron catalysts (FeSA-hCN). Through hydrothermal-assisted Fenton-like reactions, we accomplish near-total ultrahigh-molecular-weight-polyethylene degradation into C3-C20 organics with 64% selectivity of carboxylic acid under neutral pH, a leap beyond current capabilities in efficiency, selectivity, eco-friendliness, and stability over six cycles. The system demonstrates versatility by degrading various daily-use plastics across different aquatic settings. The mixture of FeSA-hCN and plastic degradation products further achieves a hydrogen evolution of 42 μmol h‒1 under illumination, outperforming most existing plastic photoreforming methods. This tandem MPD-HER process not only provides a scalable and economically feasible strategy to combat plastic pollution but also contributes to the hydrogen economy, with far-reaching implications for global sustainability initiatives.

Degradation of Polymer Materials in the Environment and Its Impact on the Health of Experimental Animals: A Review

The extensive use of polymeric materials has resulted in significant environmental pollution, prompting the need for a deeper understanding of their degradation processes and impacts. This review provides a comprehensive analysis of the degradation of polymeric materials in the environment and their impact on the health of experimental animals. It identifies common polymers, delineates their degradation pathways, and describes the resulting products under different environmental conditions. The review covers physical, chemical, and biological degradation mechanisms, highlighting the complex interplay of factors influencing these processes. Furthermore, it examines the health implications of degradation products, using experimental animals as proxies for assessing potential risks to human health. By synthesizing current research, the review focuses on studies related to small organisms (primarily rodents and invertebrates, supplemented by fish and mollusks) to explore the effects of polymer materials on living organisms and underscores the urgency of developing and implementing effective polymer waste management strategies. These strategies are crucial for mitigating the adverse environmental and health impacts of polymer degradation, thus promoting a more sustainable interaction between human activities and the natural environment.

Photorefinery of Biomass and Plastics to Renewable Chemicals using Heterogeneous Catalysts

The photocatalytic conversion of biomass and plastic waste provides opportunities for sustainable fuel and chemical production. Heterogeneous photocatalysts, typically composed of semiconductors with distinctive redox properties in their conduction band (CB) and valence band (VB), facilitate both the oxidative and reductive valorization of organic feedstocks. This article provides a comprehensive overview of recent advancements in the photorefinery of biomass and plastics from the perspective of the redox properties of photocatalysts. We explore the roles of the VB and CB in enhancing the value-added conversion of biomass and plastics via various pathways. Our aim is to bridge the gap between photocatalytic mechanisms and renewable carbon feedstock valorization, inspiring further development in photocatalytic refinery of biomass and plastics.

Progress and Challenges in Polystyrene Recycling and Upcycling

Polystyrene is a staple plastic in the packaging and insulation market. Despite its good recyclability, the willingness of PS recycling remains low, largely due to the high recycling cost and limited profitability. This review examines the research progresses, gaps, and challenges in areas that affect the recycling costs, including but not limited to logistics, packaging design, and policymaking. We critically evaluate the recent developments in upcycling strategies, and we particularly focus on tandem and hydrogen-atom transfer (HAT) upcycling strategies. We conclude that future upcycling studies should focus on not only reaction chemistry and mechanisms but also economic viability of the processes. The goal of this review is to stimulate the development of innovative recycling strategies with low recycling costs and high economic output values. We hope to stimulate the economic and technological momentum of PS recycling towards a sustainable and circular economy.

Catalytic Upcycling of Polyolefins

The large production volumes of commodity polyolefins (specifically, polyethylene, polypropylene, polystyrene, and poly(vinyl chloride)), in conjunction with their low unit values and multitude of short-term uses, have resulted in a significant and pressing waste management challenge. Only a small fraction of these polyolefins is currently mechanically recycled, with the rest being incinerated, accumulating in landfills, or leaking into the natural environment. Since polyolefins are energy-rich materials, there is considerable interest in recouping some of their chemical value while simultaneously motivating more responsible end-of-life management. An emerging strategy is catalytic depolymerization, in which a portion of the C-C bonds in the polyolefin backbone is broken with the assistance of a catalyst and, in some cases, additional small molecule reagents. When the products are small molecules or materials with higher value in their own right, or as chemical feedstocks, the process is called upcycling. This review summarizes recent progress for four major catalytic upcycling strategies: hydrogenolysis, (hydro)cracking, tandem processes involving metathesis, and selective oxidation. Key considerations include macromolecular reaction mechanisms relative to small molecule mechanisms, catalyst design for macromolecular transformations, and the effect of process conditions on product selectivity. Metrics for describing polyolefin upcycling are critically evaluated, and an outlook for future advances is described.

Challenges and Future Perspectives in Photocatalysis: Conclusions from an Interdisciplinary Workshop

Photocatalysis is a versatile and rapidly developing field with applications spanning artificial photosynthesis, photo-biocatalysis, photoredox catalysis in solution or supramolecular structures, utilization of abundant metals and organocatalysts, sustainable synthesis, and plastic degradation. In this Perspective, we summarize conclusions from an interdisciplinary workshop of young principal investigators held at the Lorentz Center in Leiden in March 2023. We explore how diverse fields within photocatalysis can benefit from one another. We delve into the intricate interplay between these subdisciplines, by highlighting the unique challenges and opportunities presented by each field and how a multidisciplinary approach can drive innovation and lead to sustainable solutions for the future. Advanced collaboration and knowledge exchange across these domains can further enhance the potential of photocatalysis. Artificial photosynthesis has become a promising technology for solar fuel generation, for instance, via water splitting or CO2 reduction, while photocatalysis has revolutionized the way we think about assembling molecular building blocks. Merging such powerful disciplines may give rise to efficient and sustainable protocols across different technologies. While photocatalysis has matured and can be applied in industrial processes, a deeper understanding of complex mechanisms is of great importance to improve reaction quantum yields and to sustain continuous development. Photocatalysis is in the perfect position to play an important role in the synthesis, deconstruction, and reuse of molecules and materials impacting a sustainable future. To exploit the full potential of photocatalysis, a fundamental understanding of underlying processes within different subfields is necessary to close the cycle of use and reuse most efficiently. Following the initial interactions at the Lorentz Center Workshop in 2023, we aim to stimulate discussions and interdisciplinary approaches to tackle these challenges in diverse future teams.

Photocatalytic Cracking of non-Biodegradable Plastics to Chemicals and Fuels

Plastic pollution is worsening the living conditions on Earth, primarily due to the toxicity and stability of non-biodegradable plastics (NBPs). Photocatalytic cracking of NBPs is emerging as a promising way to cleave inert C-C bonds and abstract the carbon atoms from these wastes into valuable chemicals and fuels. However, controlling these processes is a huge challenge, ascribed to the complicated reactions of various NBPs. Herein, we summarize recent advances in the CO2 and carbon-radical-mediated photocatalytic cracking of NBPs, with an emphasis on the pivotal intermediates. The CO2-mediated cracking proceeded with indiscriminate C-H/C-C bond cleavage of NBPs and tandem photoreduction of CO2, while carbon-radical-mediated cracking was realized by the prior activation of C-H bonds for selective C-C bond cleavage of NBPs. Catalytic generation and conversion of different intermediates greatly depend on the kinds of active species and the structure of photocatalysts under irradiation. Meanwhile, the fate of a specific intermediate is compared with small molecule activation to reveal the key problems in the cracking of NBPs. Finally, the challenges and potential directions are discussed to improve the overall efficiency in the photocatalytic cracking of NBPs.

Asymmetric Ru-In atomic pairs promote highly active and stable acetylene hydrochlorination

Ru single-atom catalysts have great potential to replace toxic mercuric chloride in acetylene hydrochlorination. However, long-term catalytic stability remains a grand challenge due to the aggregation of Ru atoms caused by over-chlorination. Herein, we synthesize an asymmetric Ru-In atomic pair with vinyl chloride monomer yield (>99.5%) and stability (>600 h) at a gas hourly space velocity of 180 h-1, far surpassing those of the Ru single-atom counterparts. A combination of experimental and theoretical techniques reveals that there is a strong d-p orbital interaction between Ru and In atoms, which not only enables the selective adsorption of acetylene and hydrogen chloride at different atomic sites but also optimizes the electron configuration of Ru. As a result, the intrinsic energy barrier for vinyl chloride generation is lowered, and the thermodynamics of the chlorination process at the Ru site is switched from exothermal to endothermal due to the change of orbital couplings. This work provides a strategy to prevent the deactivation and depletion of active Ru centers during acetylene hydrochlorination.

Recent advances in oxidative degradation of plastics

Oxidative degradation is a powerful method to degrade plastics into oligomers and small oxidized products. While thermal energy has been conventionally employed as an external stimulus, recent advances in photochemistry have enabled photocatalytic oxidative degradation of polymers under mild conditions. This tutorial review presents an overview of oxidative degradation, from its earliest examples to emerging strategies. This review briefly discusses the motivation and the development of thermal oxidative degradation of polymers with a focus on underlying mechanisms. Then, we will examine modern studies primarily relevant to catalytic thermal oxidative degradation and photocatalytic oxidative degradation. Lastly, we highlight some unique studies using unconventional approaches for oxidative polymer degradation, such as electrochemistry.

Chemical Upcycling of Polyolefin Plastics Using Structurally Well-defined Catalysts

Single-use polyolefins are widely used in our daily life and industrial production due to their light weight, low cost, superior stability, and durability. However, the rapid accumulation of plastic waste and low-profit recycling methods resulted in a global plastic crisis. Catalytic hydrogenolysis is regarded as a promising technique, which can effectively and selectively convert polyolefin plastic waste to value-added products. In this perspective, we focus on the design and synthesis of structurally well-defined hydrogenolysis catalysts across mesoscopic, nanoscopic, and atomic scales, accompanied by our insights into future directions in catalyst design for further enhancing catalytic performance. These design principles can also be applied to the depolymerization of other polymers and ultimately realize the chemical upcycling of waste plastics.

Recycling Valuable Alkylbenzenes from Polystyrene through Methanol-Assisted Depolymerization

The vast bulk of polystyrene (PS), a major type of plastic polymers, ends up in landfills, which takes up to thousands of years to decompose in nature. Chemical recycling promises to enable lower-energy pathways and minimal environmental impacts compared with traditional incineration and mechanical recycling. Herein, we demonstrated that methanol as a hydrogen supplier assisted the depolymerization of PS (denoted as PS-MAD) into alkylbenzenes over a heterogeneous catalyst composed of Ru nanoparticles on SiO2. PS-MAD achieved a high yield of liquid products which accounted for 93.2 wt % of virgin PS at 280 °C for 6 h with the production rate of 118.1 mmolcarbon gcatal. -1 h-1. The major components were valuable alkylbenzenes (monocyclic aromatics and diphenyl alkanes), the sum of which occupied 84.3 wt % of liquid products. According to mechanistic studies, methanol decomposition dominates the hydrogen supply during PS-MAD, thereby restraining PS aromatization which generates by-products of fused polycyclic arenes and polyphenylenes.

Photocatalytic Upcycling and Depolymerization of Vinyl Polymers

Photocatalytic upcycling and depolymerization of vinyl polymers have emerged as promising strategies to combat plastic pollution and promote a circular economy. This mini review critically summarizes current developments in the upcycling and degradation of vinyl polymers including polystyrene and poly(meth)acrylates. Of these material classes, polymethacrylates possess the unique possibility to undergo a photocatalytic depolymerization back to monomer under thermodynamically favourable conditions, thus presenting significant advantages over traditional thermal strategies. Our perspective on current formidable challenges and potential future directions are also discussed.

Light-driven polymer recycling to monomers and small molecules

Only a small proportion of global plastic waste is recycled, of which most is mechanically recycled into lower quality materials. The alternative, chemical recycling, enables renewed production of pristine materials, but generally comes at a high energy cost, particularly for processes like pyrolysis. This review focuses on light-driven approaches for chemically recycling and upcycling plastic waste, with emphasis on reduced energy consumption and selective transformations not achievable with heat-driven methods. We focus on challenging to recycle backbone structures composed of mainly C‒C bonds, which lack functional groups i.e., esters or amides, that facilitate chemical recycling e.g., by solvolysis. We discuss the use of light, either in conjunction with heat to drive depolymerization to monomers or via photocatalysis to transform polymers into valuable small molecules. The structural prerequisites for these approaches are outlined, highlighting their advantages as well as limitations. We conclude with an outlook, addressing key challenges, opportunities, and provide guidelines for future photocatalyst (PC) development.

Protocol for the preparation and application of CeO2-CuO catalysts in the decarboxylative oxidation reaction of benzoic acids to phenols

Phenolic chemicals are important building blocks in chemical and material industries. In this protocol, we describe the preparation of CeO2-CuO catalysts and the application in the decarboxylative oxidation reaction of benzoic acids to phenols. Furthermore, we describe how to modify the basic sites of CeO2-CuO catalysts by CO2 treatment to increase the selectivity of phenol and the regeneration process of used catalyst. For complete details on the use and execution of this protocol, please refer to Du et al. (2023).1.

Upcycling Waste Plastics with a C-C Backbone by Heterogeneous Catalysis

Plastics with an inert carbon-carbon (C-C) backbone, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), are the most widely used types of plastic in human activities. However, many of these polymers were directly discarded in nature after use, and few were appropriately recycled. This not only threatens the natural environment but also leads to the waste of carbon resources. Conventional chemical recycling of these plastics, including pyrolysis and catalytic cracking, requires a high energy input due to the chemical inertness of C-C bonds and C-H bonds and leads to complex product distribution. In recent years, significant progress has been made in the development of catalysts and the introduction of small molecules as additional coreactants, which could potentially overcome these challenges. In this Review, we summarize and highlight catalytic strategies that address these issues in upcycling C-C backbone plastics with small molecules, particularly in heterogeneous catalysis. We believe that this review will inspire the development of upcycling methods for C-C backbone plastics using small molecules and heterogeneous catalysis.

Catalytic conversion of mixed polyolefins under mild atmospheric pressure

The chemical recycling of polyolefin presents a considerable challenge, especially as upcycling methods struggle with the reality that plastic wastes typically consist of mixtures of polyethylene (PE), polystyrene (PS), and polypropylene (PP). We report a catalytic aerobic oxidative approach for polyolefins upcycling with the corresponding carboxylic acids as the product. This method encompasses three key innovations. First, it operates under atmospheric pressure and mild conditions, using O2 or air as the oxidant. Second, it is compatible with high-density polyethylene, low-density polyethylene, PS, PP, and their blends. Third, it uses an economical and recoverable metal catalyst. It has been demonstrated that this approach can efficiently degrade mixed wastes of plastic bags, bottles, masks, and foam boxes.

Innovations in chemical degradation technologies for the removal of micro/nano-plastics in water: A comprehensive review

Micro/nanoplastics (M/NPs) in water have raised global concern due to their potential environmental risks. To reestablish a M/NPs free world, enormous attempts have been made toward employing chemical technologies for their removal in water. This review comprehensively summarizes the advances in chemical degradation approaches for M/NPs elimination. It details and discusses promising techniques, including photo-based technologies, Fenton-based reaction, electrochemical oxidation, and novel micro/nanomotors approaches. Subsequently, critical influence factors, such as properties of M/NPs and operating factors, are analyzed in this review specifically. Finally, it concludes by addressing the current challenges and future perspectives in chemical degradation. This review will provide guidance for scientists to further explore novel strategies and develop feasible chemical methods for the improved control and remediation of M/NPs in the future.

Recent advancement on photocatalytic plastic upcycling

More than 8 billion tons of plastics have been generated since 1950. About 80% of these plastics have been dumped in landfills or went into natural environments, resulting in ever-worsening contamination. Among various strategies for waste plastics processing (e.g., incineration, mechanical recycling, thermochemical conversion and electrocatalytic/photocatalytic techniques), photocatalysis stands out as a cost-effective, environmentally benign and clean technique to upcycle plastic waste at ambient temperature and pressure using solar light. The mild reaction conditions for photocatalysis enable the highly selective conversion of plastic waste into targeted value-added chemicals/fuels. Here, we for the first time summarize the recent development of photocatalytic plastic upcycling based on the chemical composition of photocatalysts (e.g., metal oxides, metal sulfides, non-metals and composites). The pros and cons of various photocatalysts have been critically discussed and summarized. At last, the future challenges and opportunities in this area are presented in this review.

Precise activation of C-C bonds for recycling and upcycling of plastics

The rapid accumulation of plastic waste has led to a severe environmental crisis and a noticeable imbalance between manufacturing and recycling. Fortunately, chemical upgradation of plastic waste holds substantial promise for addressing these challenges posed by white pollution. During plastic upcycling and recycling, the key challenge is to activate and cleave the inert C-C bonds in plastic waste. Therefore, this perspective delves deeper into the upcycling and recycling of polyolefins from the angle of C-C activation-cleavage. We illustrate the importance of C-C bond activation in polyolefin depolymerization and integrate molecular-level catalysis, active site modulation, reaction networks and mechanisms to achieve precise activation-cleavage of C-C bonds. Notably, we draw potential inspiration from the accumulated wisdom of related fields, such as C-C bond activation in lignin chemistry, alkane dehydrogenation chemistry, C-Cl bond activation in CVOC removal, and C-H bond activation, to influence the landscape of plastic degradation through cross-disciplinary perspectives. Consequently, this perspective offers better insights into existing catalytic technologies and unveils new prospects for future advancements in recycling and upcycling of plastic.

Enhancing the photocatalytic upcycling of polystyrene to benzoic acid: a combined computational-experimental approach for acridinium catalyst design

Converting polystyrene into value-added oxygenated aromatic compounds is an attractive end-of-life upcycling strategy. However, identification of appropriate catalysts often involves laborious and time-consuming empirical screening. Herein, after demonstrating the feasibility of using acridinium salts for upcycling polystyrene into benzoic acid by photoredox catalysis for the first time, we applied low-cost descriptor-based combinatorial in silico screening to predict the photocatalytic performance of a family of potential candidates. Through this approach, we identified a non-intuitive fluorinated acridinium catalyst that outperforms other candidates for converting polystyrene to benzoic acid in useful yields at low catalyst loadings (≤5 mol%). In addition, this catalyst also proved effective with real-life polystyrene waste containing dyes and additives. Our study underscores the potential of computer-aided catalyst design for valorizing polymeric waste into essential chemical feedstock for a more sustainable future.

Selective Electrocatalytic Degradation of Ether-Containing Polymers

Leveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron-rich C-H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether-based polyurethane in a green solvent. This work demonstrates a facile, electrochemically-driven route to degrade polymers containing ether functionalities.

Photocatalytic production of ethylene and propionic acid from plastic waste by titania-supported atomically dispersed Pd species

Current chemical recycling of bulk synthetic plastic, polyethylene (PE), operates at high temperature/pressure and yields a complex mixture of products. PE conversion under mild conditions and with good selectivity toward value-added chemicals remains a practical challenge. Here, we demonstrate an atomic engineering strategy to modify a TiO2 photocatalyst with reversible Pd species for the selective conversion of PE to ethylene (C2H4) and propionic acid via dicarboxylic acid intermediates under moderate conditions. TiO2-supported atomically dispersed Pd species exhibits C2H4 evolution of 531.2 μmol gcat-1 hour-1, 408 times that of pristine TiO2. The liquid product is a valuable chemical propanoic acid with 98.8% selectivity. Plastic conversion with a C2 hydrocarbon yield of 0.9% and a propionic acid yield of 6.3% was achieved in oxidation coupled with 3 hours of photoreaction. In situ spectroscopic studies confirm a dual role of atomic Pd species: an electron acceptor to boost charge separation/transfer for efficient photoredox, and a mediator to stabilize reaction intermediates for selective decarboxylation.

Novel and Accessible Physical Recycling for Expanded Polystyrene Waste with the Use of Acetone as a Solvent and Additive Manufacturing (Direct Ink-Write 3D Printing)

The current high production of plastics has prompted the exploration of alternative pathways to facilitate recycling, aiming for a progressively sustainable society. This paper presents an alternative and affordable technology for treating waste expanded polystyrene (EPS) mixed with acetone in a 100:1 volume ratio to be used as 3D printing ink for Direct Ink Write technology. In order to optimize the printing parameters, a comprehensive study was conducted, evaluating different needle diameters, printing speeds, and bed temperature values to achieve homogenous pieces and a highly repeatable 3D printing process. Results showed that the main optimum printing parameters were using needles with diameters of 14 to 16 G and printing speeds ranging from 2 to 12 mm/s, which were found to yield the most uniform ribbons. Increasing the bed temperature, despite favoring acetone evaporation, led to the generation of more heterogeneous structures due to void growth inside the printed ribbons. Thus, employing room temperature for the bed proved to be the optimal value. Lastly, a comparative study between the starting material and the EPS after the printing process was conducted using FTIR-ATR and GPC analyses, ensuring the preservation of the original polymer's integrity during physical recycling.

Highly efficient degradation of polyesters and polyethers by decatungstate photocatalysis

Photocatalytic polymer degradation has been recognized as a promising solution to the global disposal of waste plastics. In this work, we revealed that various polyesters and polyethers were efficiently degraded in the presence of a polyoxometalate photocatalyst, specifically, decatungstate ([W10O32]4-, W10). A catalytic amount of W10 initiated the degradation of various polyesters and polyethers under photo-irradiation with a xenon lamp (λ > 350 nm) using O2 (1 atm) as the oxidant in acetonitrile or water. Moreover, this system can promote polymer degradation even under sunlight. The degradation efficiency, assessed from the degradation rate (Mw0 - Mw)/Mw0 (%) (where Mw0 is the Mw before the reaction), of W10 was notably higher than those of previously reported photocatalysts such as titanium oxide, other polyoxometalates, organometallic compounds, and organic dyes.

Integrated Photochromic-Photothermal Processes for Catalytic Plastic Upcycling

Incorporating high-energy ultraviolet (UV) photons into photothermal catalytic processes may enable photothermal-photochemical synergistic catalysis, which represents a transformative technology for waste plastic recycling. The major challenge is avoiding side reactions and by-products caused by these energetic photons. Here, we break through the limitation of the existing photothermal conversion mechanism and propose a photochromic-photothermal catalytic system based on polyol-ligated TiO2 nanocrystals. Upon UV or sunlight irradiation, the chemically bonded polyols can rapidly capture holes generated by TiO2 , enabling photogenerated electrons to reduce Ti4+ to Ti3+ and produce oxygen vacancies. The resulting abundant defect energy levels boost sunlight-to-heat conversion efficiency, and simultaneously the oxygen vacancies facilitate polyester glycolysis by activating the nucleophilic addition-elimination process. As a result, compared to commercial TiO2 (P25), we achieve 6-fold and 12.2-fold performance enhancements under thermal and photothermal conditions, respectively, while maintaining high selectivity to high-valued monomers. This paradigm-shift strategy directs energetic UV photons for activating catalysts and avoids their interaction with reactants, opening the possibility of substantially elevating the efficiency of more solar-driven catalysis.

A Generic Platform for Upcycling Polystyrene to Aryl Ketones and Organosulfur Compounds

Polystyrene (PS) is one of the least recycled large-volume commodity plastics due to bulkiness of foam products and associated contaminants. PS recycling is also severely hampered by the lack of financial incentive, limited versatility, and poor selectivity of existing methods. To this end, herein we report a thermochemical recycling strategy of "degradation-upcycling" to synthesize a library of high-value aromatic chemicals from PS wastes with high versatility and selectivity. Two cascade reactions are selected to first degrade PS to benzene under mild temperatures, followed by the derivatization thereof utilizing a variety of acyl/alkyl and sulfinyl chloride additives. To demonstrate the versatility, nine ketones and sulfides of cosmetic and pharmaceutical relevance were prepared, including propiophenone, benzophenone, and diphenyl sulfide. The approach is also amenable to sophisticated upcycling reaction designs and can produce desired products stepwise. The facile and versatile approach will provide a scalable and profitable methodology for upcycling PS waste into value-added chemicals.

Electrochemical Production of Glycolate Fuelled By Polyethylene Terephthalate Plastics with Improved Techno-Economics

Electrochemical valorization of polyethylene terephthalate (PET) waste streams into commodity chemicals offers a potentially sustainable route for creating a circular plastic economy. However, PET wastes upcycling into valuable C2 product remains a huge challenge by the lack of an electrocatalyst that can steer the oxidation economically and selectively. Here, it is reported a catalyst comprising Pt nanoparticles hybridized with γ-NiOOH nanosheets supported on Ni foam (Pt/γ-NiOOH/NF) that favors electrochemical transformation of real-word PET hydrolysate into glycolate with high Faradaic efficiency (> 90%) and selectivity (> 90%) across wide reactant (ethylene glycol, EG) concentration ranges under a marginal applied voltage of 0.55 V, which can be paired with cathodic hydrogen production. Computational studies combined with experimental characterizations elucidate that the Pt/γ-NiOOH interface with substantial charge accumulation gives rise to an optimized adsorption energy of EG and a decreased energy barrier of potential determining step. A techno-economic analysis demonstrates that, with the nearly same amount of resource investment, the electroreforming strategy towards glycolate production can raise revenue by up to 2.2 times relative to conventional chemical process. This work may thus serve as a framework for PET wastes valorization process with net-zero carbon footprint and high economic viability.

Chemical upcycling of polyethylene, polypropylene, and mixtures to high-value surfactants

Conversion of plastic wastes to fatty acids is an attractive means to supplement the sourcing of these high-value, high-volume chemicals. We report a method for transforming polyethylene (PE) and polypropylene (PP) at ~80% conversion to fatty acids with number-average molar masses of up to ~700 and 670 daltons, respectively. The process is applicable to municipal PE and PP wastes and their mixtures. Temperature-gradient thermolysis is the key to controllably degrading PE and PP into waxes and inhibiting the production of small molecules. The waxes are upcycled to fatty acids by oxidation over manganese stearate and subsequent processing. PP ꞵ-scission produces more olefin wax and yields higher acid-number fatty acids than does PE ꞵ-scission. We further convert the fatty acids to high-value, large-market-volume surfactants. Industrial-scale technoeconomic analysis suggests economic viability without the need for subsidies.

Circular Design and Functionalized Upcycling of Waste Commodity Polystyrene via C-H Activation Using Microwave-Assisted Multicomponent Synthesis

The inefficient reuse and recycling of plastics-and the current surge of medical and take-out food packaging use during the pandemic-have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich three-component coupling reaction for the modification of polystyrene (PS) recovered with a 99.1% yield from waste food containers to form functionalized nitrogen and oxygen-rich PS derivatives. A series of functionalized PS with increasing moles of formaldehyde (F) and morpholine (M) (0.5 × 10^-2, 1.0 × 10^-2, and 2.0 × 10^-2 mol) was achieved using a sol-gel-derived Fe-TiO₂ catalyst in a solvent-free, microwave-assisted synthesis. Modified polymers were characterized with viscometry, ¹H NMR, ¹³CNMR (DEPT) FTIR, XPS, UV, and TGA. Functionalization scaled with an increasing ratio, validating the 3CR approach. Further functionalization was constrained by a competing oxidative degradation; however, the varying hydrogen bond density due to nitrogen and oxygen-rich species at higher ratios was shown to compensate for molecular weight loss. The integration of the N-cyclic quaternary ammonium cations exhibited the potential of functionalized polymers for ion-exchange membrane applications.

Polystyrene Waste Thermochemical Hydrogenation to Ethylbenzene by a N-Bridged Co, Ni Dual-Atom Catalyst

Recycling waste plastics requires the degradation of plastics into small molecules. However, various products are widely distributed using traditional methods of depolymerizing polystyrene (PS) such as catalytic pyrolysis and hydrogenolysis. Here, we creatively report a N-bridged Co, Ni dual-atom (Co-N-Ni) catalyst for the targeted conversion of waste PS plastics to ethylbenzene via a pressurized tandem fixed-bed reactor where hydropyrolysis is coupled with downstream vapor-phase hydrotreatment. The Co-N-Ni catalyst achieves 95 wt % PS conversion with 92 wt % ethylbenzene yield, significantly superior to the corresponding single-atom catalysts, and enables degradation of real PS plastics. Theoretical calculations and experimental results demonstrate that the d-band center of metal atoms is well regulated in the Co-N-Ni catalyst. The Co site activates the C═C bond more easily, while the Ni site spatially optimizes the adsorption configuration of the styrene molecule due to the electronic interaction. This Co-N-Ni catalyst in the tandem reactor also shows excellent durability and provides a new direction for real plastic degradation.