Integrating PET chemical recycling with pyrolysis of mixed plastic waste via pressureless alkaline depolymerization in a hydrocarbon solvent

This study presents a proof of concept for a technology train that integrates polyethylene terephthalate (PET) recovery from mixed plastic waste and plastic pyrolysis. PET is depolymerized into terephthalic acid (TPA) by hydrolysis using a low volatility oil as medium, which enables (i) low-pressure operation, and (ii) a selective separation and recovery of TPA from the product mix by a simple process of filtration, washing, and precipitation. Full PET conversion and high TPA recovery (>98 %) were achieved at 260 °C. This technology train is demonstrated to be effective for processing mixed waste streams, leading to higher yield and quality of liquid product from thermal pyrolysis when compared with feedstock that has not been pre-treated. Further, the technology could be readily integrated with a plastics pyrolysis process, whereby a by-product from the pyrolysis could be used as the low-volatility oil.

Nanosphere Lithography: A Versatile Approach to Develop Transparent Conductive Films for Optoelectronic Applications

Transparent conductive films (TCFs) are irreplaceable components in most optoelectronic applications such as solar cells, organic light-emitting diodes, sensors, smart windows, and bioelectronics. The shortcomings of existing traditional transparent conductors demand the development of new material systems that are both transparent and electrically conductive, with variable functionality to meet the requirements of new generation optoelectronic devices. In this respect, TCFs with periodic or irregular nanomesh structures have recently emerged as promising candidates, which possess superior mechanical properties in comparison with conventional metal oxide TCFs. Among the methods for nanomesh TCFs fabrication, nanosphere lithography (NSL) has proven to be a versatile platform, with which a wide range of morphologically distinct nanomesh TCFs have been demonstrated. These materials are not only functionally diverse, but also have advantages in terms of device compatibility. This review provides a comprehensive description of the NSL process and its most relevant derivatives to fabricate nanomesh TCFs. The structure-property relationships of these materials are elaborated and an overview of their application in different technologies across disciplines related to optoelectronics is given. It is concluded with a perspective on current shortcomings and future directions to further advance the field.

Conversion of agricultural waste into stable biocrude using spinel oxide catalysts

Biomass, the feedstock for biocrude and ultimately renewable diesel is a low energy density feedstock. The transport of this feedstock over long distance has been proven to be a major burden on the commercialisation of biorefining. Therefore, it has been generally accepted that biomass should be upgraded to biocrude (a relatively high energy density liquid) in close proximity to the biomass sources. The biocrude liquid would then be transported to a biorefinery. Biocrude contains large amounts of oxygen (generally up to 38 wt%) that is removed from the crude in the refining process. In this study, we have synthesised a range of spinel oxide based catalysts to remove oxygen from the biocrude during the catalytic fast pyrolysis. The activity of spinel oxide (MgB₂O₄ where B = Fe, Al, Cr, Ga, La, Y, In) catalysts were screened for the pyrolysis reaction. While all the tested spinel oxides deoxygenated the pyrolysis vapour, MgCr₂O₄ was found to be effective in terms of oxygen removal efficiency relative to the quantity of bio oil produced.

Metal-incorporated mesoporous oxides: Synthesis and applications

Mesoporous oxides are outstanding metal nanoparticle catalyst supports owing to their well-defined porous structures. Such mesoporous architectures not only prevent the aggregation of metal nanoparticles but also enhance their catalytic performance. Metal/metal oxide heterojunctions exhibit unique chemical and physical properties because of the surface reconstruction around the junction and electron transfer/interaction across the interface. This article reviews the methods used for synthesizing metal-supported hybrid nanostructures and their applications as catalysts for environmental remediation and sensors for detecting hazardous materials.

Red-mud based porous nanocatalysts for valorisation of municipal solid waste

Red mud samples were used to catalyse in-situ co-pyrolysis of pinewood and low-density polyethylene for the production of high-quality bio-oil. The sodium cation in the crude red-mud was exchanged with barium and calcium cations and further tested to explore their role in oil upgrading. The relationship between red-mud catalytic activity and its constituents was explored using synthetic sodalite. The red-mud catalysts exhibited a considerable aromatisation capacity compared to the thermal co-pyrolysis, as the selectivity towards monocyclic aromatic hydrocarbons increased from 12.7 to 19.6%, respectively. Long-chain molecules cracking was more significant in synthetic sodalite associated with their acidic active sites. The addition of barium and calcium cations to the red-mud largely improved oxygen elimination as a result of the enhanced catalyst basicity. In contrast, the aromatisation ability of red-mud significantly impeded by the large cation size (Ba²⁺ and Ca²⁺) due to the limited diffusion of pyrolysis vapours to the active sites. Ba-exchanged red-mud catalysts reduced the content of carboxylic acids in the bio-oil to 1.8 % while maintained a high yield of the organic fraction (34 %). Ca-exchanged red-mud catalysts produced the lowest fraction of oxygenated compounds (35.1 %); however, the organic phase yield was as low as 23.6 %. The modified red-mud catalysts reduced the fraction of oxygenated compounds from 69.9-35.1% during the biomass-plastic co-pyrolysis.

Nanostructured NiMoS₂/Carbon Catalysts for Syngas Conversion to Higher Alcohols

Syngas conversion to higher alcohols remains a very attractive alternative due to the abundance of syngas feedstock, such as renewable carbon and waste-carbon resources. Catalysts suitable for syngas conversion still show low selectivity to alcohols. In this article, we present nanostructured NiMoS₂ and CoMoS₂ catalysts supported on activated carbon pellets and design strategies to improve its selectivity towards higher alcohols. Activated carbon pellets were treated with concentrated HNO₃ to enlarge porous channels and enable better dispersion of NiMoS₂ and CoMoS₂. These treatment steps lead to a formation of nanostructured NiMoS₂ and CoMoS₂ catalysts and promoted higher selectivity to ethanol, propanol and butanol. BET surface area of 532 m² g^-1 was obtained for NiMoS₂/Carbon catalysts from the nitrogen physisorption analysis. In catalytic tests, the highest CO conversion (39.1%) was achieved by the NiMoS₂/Carbon, whereas the CoMoS₂/Carbon showed the highest alcohol selectivity (74.4%). CoMoS₂ catalysts supported on activated carbon pellets proved to be highly active towards undesired by-product "filamentous carbon."

A review on advanced catalytic co-pyrolysis of biomass and hydrogen-rich feedstock: Insights into synergistic effect, catalyst development and reaction mechanism

The depletion of fossil fuel reserves and the growing demand for alternative energy sources are the main drivers of biomass and carbonaceous waste utilization. Particularly, non-edible lignocellulosic biomass is the most attractive renewable feedstock due to its abundance. Pyrolysis of biomass produces highly oxygenated compounds with oxygen content >35 wt%. The cost-effective elimination of oxygen from the pyrolysis oil is the most challenging task impeding the commercialization of biomass to biofuel processes. The effective hydrogen/carbon ratio in biomass pyrolysis oil is low (0.3), requiring external hydrogen supply to produce hydrocarbon-rich oils. Exploiting hydrogen-rich feedstock particularly, solid waste (plastic, tyre and scum) and other low-cost feedstock (lubricant oil, methane, methanol, and ethanol) offer an eco-friendly solution to upgrade the produced bio-oil. Multi-functional catalysts that are capable of cleaving oxygen, promoting hydrogen transfer and depolymerisation must be developed to produce hydrocarbon-rich oil from biomass. This review compares catalytic co-pyrolysis studies based on zeolites, mesoporous silica and metal oxides. Furthermore, a wide range of catalyst modifications and the role of each feedstock were summarised to give a complete picture of the progress made on biomass co-pyrolysis research and development.

Tailored Nanoarchitecturing of Microporous ZIF-8 to Hierarchically Porous Double-Shell Carbons and Their Intrinsic Electrochemical Property

Mesostructured polydopamine (PDA) coating has been successfully achieved on the surface of zeolitic imidazolate framework-8 (ZIF-8) particles by incorporating Pluronic F127 (with a pore-expanding agent, 1,3,5-trimethylbenzene) as a pore-directing agent during dopamine polymerization. Upon pyrolysis at high temperatures, mesostructured PDA-coated ZIF-8 particles become hierarchically porous double-shell carbons (HPDCs) with a wide pore size distribution ranging from micro- and meso- to macropores. The formation of a hollow inner shell progresses initially with the shrinkage of ZIF-8 at the periphery where the interface interactions with mesostructured PDA exist, and then the subsequent disintegration of the ZIF-8 core at higher temperatures occurs. Our HPDCs prepared in this study feature physical and electrochemical advantages of hierarchically porous carbons such as high electrochemically accessible surface area, short diffusion distance, and high mass-transfer rate, thus demonstrating significantly improved ion diffusion and surface-enhanced high specific capacitance at high charge-discharge rates. HPDC_5.0 therefore exhibits the capacitance retention of up to 76.7% from 1 to 10 A g^-1 and maximum specific capacitance of 344.7 F g^-1 at 1 mV s^-1. It also possesses superior electrochemical stability with about 108% capacitance retention even after 10,000 consecutive cycles of galvanostatic charge-discharge at 10 A g^-1.

Magnetic nanocellulose: A potential material for removal of dye from water

In this study, cellulose nanofibers are used as a template to synthesise magnetic nanoparticles with a uniform size distribution. Magnetic nanoparticles are grafted on the surface of nanofibers via in situ hydrolysis of metal precursors at room temperature. Effects of different concentrations of nanofibers on the morphology, the crystallite size of magnetic nanoparticles, and the thermal and magnetic properties of the membrane produced from the cellulose nanofibers decorated with magnetic nanoparticles are examined. The sizes of magnetic nanoparticles produced in this study are below 20 nm, and the crystallite size of the nanoparticles is in the range of 96-130 Å. The flexible magnetic membranes containing a high concentration of magnetic nanoparticles (83-60 wt%) showed superparamagnetic behaviour with very high magnetic properties (67.4-38.5 emu g^-1). The magnetic membrane was then used as an environmentally friendly, low-cost catalyst in a sulphate radical-based advanced oxidation process. The membranes successfully activated peroxymonosulphate (PMS) to remove Rhodamine B (RhB), a common hydrophilic organic dye applied in industry. 94.9 % of the Rhodamine B was degraded in 300 min at room temperature, indicating that the magnetic nanocellulose membrane is highly effective for catalyzing PMS to remove RhB.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction

Achieving high product selectivities is one challenge that limits viability of electrochemical CO₂ reduction (CO₂ R) to chemical feedstocks. Here, it was demonstrated how interactions between Ag foil cathodes and reline (choline chloride + urea) led to highly selective CO₂ R to CO with a faradaic efficiency of (96±8) % in 50 wt % aqueous reline at -0.884 V vs. the reversible hydrogen electrode (RHE), which is a 1.5-fold improvement over CO₂ R in KHCO₃ . In reline the Ag foil was roughened by (i) dissolution of oxide layers followed by (ii) electrodeposition of Ag nanoparticles back on cathode. This surface restructuring exposed low-coordinated Ag atoms, and subsequent adsorption of choline ions and urea at the catalyst surface limited proton availability in the double layer and stabilized key intermediates such as *COOH. These approaches could potentially be extended to other electrocatalytic metals and lower-viscosity deep eutectic solvents to achieve higher-current-density CO₂ R in continuous-flow cell electrolyzers.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction

Invited for this month's cover is the group of Tom Rufford at the University of Queensland. The image shows how choline chloride and urea in a reline solution interact with the surface of a silver cathode to enhance the selectivity of electrochemical CO₂ reduction to CO. The Full Paper itself is available at 10.1002/cssc.201902433.

Highly active and robust Ni–MoS2supported on mesoporous carbon: a nanocatalyst for hydrodeoxygenation reactions

NiMoS₂ nanoparticles supported on carbon, synthesized by a microemulsion method were used as a nanocatalyst for hydrodeoxygenation (HDO) of a lignin model compound – guaiacol. Two types of carbon supports – mesoporous carbon (CMK-3) and activated carbon (AC) with a predominantly microporous structure, were studied to investigate the role of porosity and nature of the porous structure in catalyst activity. The activity of NiMoS₂/AC resulted in the complete guaiacol conversion at 13 h of reaction time to produce phenol (31.5 mol%) and cyclohexane (35.7 mol%) as the two main products. Contrastingly, NiMoS₂/CMK-3 needed a much lesser reaction time (6 h) to attain a similar conversion of guaiacol but gave different selectivities of phenol (25 mol%) and cyclohexane (55.5 mol%). Increased cyclohexane production with NiMoS₂/CMK-3 implied better deoxygenation of MoS₂ and enhanced hydrogenation capacity of Ni since phenol is a partially deoxygenated product of guaiacol while cyclohexane is a completely deoxygenated and hydrogenated product. The superior catalytic activity and deoxygenating behavior of NiMoS₂/CMK-3 catalysts could be attributed to the organized mesoporosity of the CMK-3 support in relation to the improved active phase distribution and access to active sites that facilitate the conversion of the reaction's product. Recyclability study implied NiMoS₂/CMK-3 was more stable without significant changes in the catalytic activity even after three reaction cycles.

NiMoS₂ nanoparticles supported on carbon, synthesized by a microemulsion method were used as a nanocatalyst for hydrodeoxygenation (HDO) of a lignin model compound – guaiacol.

High yield conversion of cellulosic biomass into 5-hydroxymethylfurfural and a study of the reaction kinetics of cellulose to HMF conversion in a biphasic system

Biphasic dehydration of cellulosic biomass into remarkable yield of HMF can be achieved via mechanocatalysis and fractionation treatment.

C–H bond cyanation of arenes using N,N-dimethylformamide and NH4HCO3 as a CN source over a hydroxyapatite supported copper catalyst

Copper dispersed on Ca₅(PO₄)₃OH has been identified as an excellent heterogeneous catalyst for the in situ generation of ‘CN’ from NH₄HCO₃ and N,N-dimethylformamide, in the C–H bond activation of 2-phenylpyridine.

Direct Production of 5-Hydroxymethylfurfural via Catalytic Conversion of Simple and Complex Sugars over Phosphated TiO2

A water-THF biphasic system containing N-methyl-2-pyrrolidone (NMP) was found to enable the efficient synthesis of 5-hydroxymethylfurfural (HMF) from a variety of sugars (simple to complex) using phosphated TiO2 as a catalyst. Fructose and glucose were selectively converted to HMF resulting in 98 % and 90 % yield, respectively, at 175 °C. Cellobiose and sucrose also gave rise to high HMF yields of 94 % and 98 %, respectively, at 180 °C. Other sugar variants such as starch (potato and rice) and cellulose were also investigated. The yields of HMF from starch (80-85 %) were high, whereas cellulose resulted in a modest yield of 33 %. Direct transformation of cellulose to HMF in significant yield (86 %) was assisted by mechanocatalytic depolymerization-ball milling of acid-impregnated cellulose. This effectively reduced cellulose crystallinity and particle size, forming soluble cello-oligomers; this is responsible for the enhanced substrate-catalytic sites contact and subsequent rate of HMF formation. During catalyst recyclability, P-TiO2 was observed to be reusable for four cycles without any loss in activity. We also investigated the conversion of the cello-oligomers to HMF in a continuous flow reactor. Good HMF yield (53 %) was achieved using a water-methyl isobutyl ketone+NMP biphasic system.

Guaiacol hydrodeoxygenation reaction catalyzed by highly dispersed, single layered MoS2/C

Single layered MoS₂ supported on activated carbon prepared by a microemulsion technique with good catalyst stability even after 4 uses.