Pd/Fe3O4 Nanofibers for the Catalytic Conversion of Lignin-Derived Benzyl Phenyl Ether under Transfer Hydrogenolysis Conditions

Water-Resistant Photo-Crosslinked PEO/PEGDA Electrospun Nanofibers for Application in Catalysis

Catalysts are used for producing the vast majority of chemical products. Usually, catalytic membranes are inorganic. However, when dealing with reactions conducted at low temperatures, such as in the production of fine chemicals, polymeric catalytic membranes are preferred due to a more competitive cost and easier tunability compared to inorganic ones. In the present work, nanofibrous mats made of poly(ethylene oxide), PEO, and poly(ethylene glycol) diacrylate, PEGDA, blends with the Au/Pd catalyst are proposed as catalytic membranes for water phase and low-temperature reactions. While PEO is a water-soluble polymer, its blending with PEGDA can be exploited to make the overall PEO/PEGDA blend nanofibers water-resistant upon photo-crosslinking. Thus, after the optimization of the blend solution (PEO molecular weight, PEO/PEGDA ratio, photoinitiator amount), electrospinning process, and UV irradiation time, the resulting nanofibrous mat is able to maintain the nanostructure in water. The addition of the Au₆/Pd₁ catalyst (supported on TiO₂) in the PEO/PEGDA blend allows the production of a catalytic nanofibrous membrane. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), taken as a water phase model reaction, demonstrates the potential usage of PEO-based membranes in catalysis.

Is Graphene Always Effective in Reinforcing Composites? The Case of Highly Graphene-Modified Thermoplastic Nanofibers and Their Unfortunate Application in CFRP Laminates

Graphene (G) can effectively enhance polymers' and polymer composites' electric, thermal, and mechanical properties. Nanofibrous mats have been demonstrated to significantly increase the interlaminar fracture toughness of composite laminates, hindering delamination and, consequently, making such materials safer and more sustainable thanks to increased service life. In the present paper, poly(ethylene oxide) (PEO), polycaprolactone (PCL), and Nylon 66 nanofibers, plain or reinforced with G, were integrated into epoxy-matrix Carbon Fiber Reinforced Polymers (CFRPs) to evaluate the effect of polymers and polymers + G on the laminate mechanical properties. The main aim of this work is to compare the reinforcing action of the different nanofibers (polyether, polyester, and polyamide) and to disclose the effect of G addition. The polymers were chosen considering their thermal properties and, consequently, their mechanism of action against delamination. PEO and PCL, displaying a low melting temperature, melt, and mix during the curing cycle, act via matrix toughening; in this context, they are also used as tools to deploy G specifically in the interlaminar region when melting and mixing with epoxy resin. The high extent of modification stems from an attempt to deploy it in the interlaminar layer, thus diluting further in the resin. In contrast, Nylon 66 does not melt and maintain the nanostructure, allowing laminate toughening via nanofiber bridging. The flexural properties of the nanomodifed CFRPs were determined via a three-point bending (3PB) test, while delamination behavior in Mode I and Mode II was carried out using Double Cantilever Beam (DCB) and End-Notched Flexture (ENF) tests, respectively. The lack of a positive contribution of G in this context is an interesting point to raise in the field of nanoreinforced CFRP.

Hydrothermal Carbonization as Sustainable Process for the Complete Upgrading of Orange Peel Waste into Value-Added Chemicals and Bio-Carbon Materials

In this study, a simple and green protocol to obtain hydrochar and high-added value products, mainly 5-hydroxymethylfurfural (5-HMF), furfural (FU), levulinic acid (LA) and alkyl levulinates, by using the hydrothermal carbonization (HTC) of orange peel waste (OPW) is presented. Process variables, such as reaction temperature (180–300 °C), reaction time (60–300 min), biomass:water ratio and initial pH were investigated in order to find the optimum conditions that maximize both the yields of solid hydrochar and 5-HMF and levulinates in the bio-oil. Data obtained evidence that the highest yield of hydrochar is obtained at a 210 °C reaction temperature, 180 min residence time, 6/1 w/w orange peel waste to water ratio and a 3.6 initial pH. The bio-products distribution strongly depends on the applied reaction conditions. Overall, 180 °C was found to be the best reaction temperature that maximizes the production of furfural and 5-HMF in the presence of pure water as a reaction medium.

Investigation on the Suitability of Engelhard Titanium Silicate as a Support for Ni-Catalysts in the Methanation Reaction

Methanation reaction of carbon dioxide is currently envisaged as a facile solution for the storage and transportation of low-grade energies, contributing at the same time to the mitigation of CO2 emissions. In this work, a nickel catalyst impregnated onto a new support, Engelhard Titanium Silicates (ETS), is proposed, and its catalytic performance was tested toward the CO2 methanation reaction. Two types of ETS material were investigated, ETS-4 and ETS-10, that differ from each other in the titanium content, with Si/Ti around 2 and 3% by weight, respectively. Catalysts, loaded with 5% of nickel, were tested in the CO2 methanation reaction in the temperature range of 300–500 °C and were characterized by XRD, SEM–EDX, N2 adsorption–desorption and H2-TPR. Results showed an interesting catalytic activity of the Ni/ETS catalysts. Particularly, the best catalytic performances are showed by Ni/ETS-10: 68% CO2 conversion and 98% CH4 selectivity at T = 400 °C. The comparison of catalytic performance of Ni/ETS-10 with those obtained by other Ni-zeolites catalysts confirms that Ni/ETS-10 catalyst is a promising one for the CO2 methanation reaction.

Ru-gC3N4 Catalyzed Hydrodebenzylation of Benzyl Protected Alcohol and Acid Groups Using Sodium Hypophosphite as a Hydrogen Source

A straightforward process for hydrodebenzylation of benzyl protected acid and alcohol derivatives to the corresponding acids and alcohols using sodium hypophosphite in the presence of Ru-GCN catalyst is reported. The developed Ru-GCN catalyst is cost effective compared to other noble metal-based catalysts and has been explored to exhibit excellent activity for catalytic hydrodebenzylation reactions under moderate reaction conditions. The non-corrosive sodium hypophosphite has been found as a better hydrogen donor compared to alkali metal formats in presence of Ru-GCN catalyst. The stated catalyst was characterized using several spectrometric and material characterization methods such as PXRD, IR, SEM, TEM, XPS, and TGA. The Ru-GCN catalyst corroborated good reusability and stability for multiple cycles. The catalyst preparation is facile and the developed process is simple and safe as it avoids use of high hydrogen pressure. The developed protocol can also be replicated on industrial scale on account of excellent recyclability and retained activity after multiple cycles and makes the process sustainable. Gram scale reaction was performed to verify the industrial potential of reported catalyst.

Focus on Materials for Sulfur-Resistant Catalysts in the Reforming of Biofuels

The reforming of biofuels represents a promising technology for low carbon and renewable hydrogen production today. The core of the process is an active and stable catalyst, which can help to improve this technology and its efficiency. With this review, we aim to survey the more relevant literature on heterogeneous catalysts for the reforming of biofuels with improved sulfur tolerance. The review is structured into four main sections. Following the introduction, the fundamental aspects of sulfur poisoning are discussed. In the third section, the basic principles of the reforming of biofuels are reported, and finally, in the fourth section—the core of the review—recent progresses in the development of sulfur resistant catalysts are discussed, distinguishing the role of the metal (noble and non-noble) from that of the support.

Electrospun Nanofibers and Electrochemical Techniques for the Detection of Heavy Metal Ions

Contamination by heavy metals is currently one of the most environmental concerns especially due to the toxicity, pervasiveness, and persistence of these substances. As they are not biodegradable, heavy metals are harmful not only for water, air, and soil but also for human health, even in very low traces. There is therefore a pressing need to develop an efficient, economic, and rapid analysis method to be applied in a wide range of conditions and able to detect very low contaminants concentrations. Currently, the most novel solution in this field is represented by the combination of electrospun nanofibers and highly sensitive electrochemical techniques. It has been proved that nanofibers, due to their outstanding properties, perfectly fit as sensing material when trace concentrations of heavy metals were investigated by anodic stripping voltammetry, envisaged as the most sensitive electrochemical technique for this kind of measurements. This work aims to provide an overview of the latest trends in the detection of contaminants by the simultaneous use of electrospun fibers and anodic stripping voltammetry. Indeed, a clear and comprehensive vision of the current status of this research may drive future improvements and new challenges.

Self Standing Mats of Blended Polyaniline Produced by Electrospinning

Conducting nanofibers of polyaniline (PANI) doped with camphor-10-sulfonic acid (HCSA) and blended with different polymers, such as polymethyl methacrylate (PMMA) and polyvinyl acetate (PVAc), have been fabricated using the electrospinning technique. Scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) were utilized to characterize the morphology and the thermal stability of PANI-blended fibers. An extensive study was performed to understand the copolymer influence on both the structural and surface properties of the realized conductive thin films. Samples main electrical characteristics, as conductivity, specific capacitance and electrochemical performances were tested. The better mats were obtained with the use of PVAc copolymer, which showed a conductivity value two orders of magnitude higher than the PMMA system. Aiming at further improving the electrochemical features of these blended mats, hybrid fibers based on PANI/PVAc/graphene oxide and PANI/PVAc/iron oxide were also produced and characterized. The obtained mats were potentially addressed to numerous practical fields, including sensors, health applications, smart devices and multifunctional textile materials.

Recovery/Reuse of Heterogeneous Supported Spent Catalysts

The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

The Limonene Biorefinery: From Extractive Technologies to Its Catalytic Upgrading into p-Cymene

Limonene is a renewable cyclic monoterpene that is easily obtainable from citrus peel and it is commonly used as a nutraceutical ingredient, antibacterial, biopesticide and green extraction solvent as well as additive in healthcare, fragrance and food and beverage industries for its characteristic lemon-like smell. Indeed, the lack of toxicity makes limonene a promising bio-alternative for the development of a wide range of effective products in modern biorefineries. As a consequence, industrial demand largely exceeds supply by now. Limonene can be also used as starting substrate for the preparation of building block chemicals, including p-cymene that is an important intermediate in several industrial catalytic processes. In this contribution, after reviewing recent advances in the recovery of limonene from citrus peel and residues with particular attention to benign-by-design extractive processes, we focus on the latest results in its dehydrogenation to p-cymene via heterogeneous catalysis. Indeed, the latest reports evidence that the selective production of p-cymene still remains a scientific and technological challenge since, in order to drive the isomerization and dehydrogenation of limonene, an optimal balance between the catalyst nature/content and the reaction conditions is needed.

Recent Catalytic Advances in Hydrotreatment Processes of Pyrolysis Bio-Oil

Catalytic hydrotreatment (HT) is one of the most important refining steps in the actual petroleum-based refineries for the production of fuels and chemicals, and it will play also a crucial role for the development of biomass-based refineries. In fact, the utilization of HT processes for the upgrading of biomass and/or lignocellulosic residues aimed to the production of synthetic fuels and chemical intermediates represents a reliable strategy to reduce both carbon dioxide emissions and fossil fuels dependence. At this regard, the catalytic hydrotreatment of oils obtained from either thermochemical (e.g., pyrolysis) or physical (e.g., vegetable seeds pressing) processes allows to convert biomass-derived oils into a biofuel with properties very similar to conventional ones (so-called drop-in biofuels). Similarly, catalytic hydro-processing also may have a key role in the valorization of other biorefinery streams, such as lignocellulose, for the production of high-added value chemicals. This review is focused on recent hydrotreatment developments aimed to stabilizing the pyrolytic oil from biomasses. A particular emphasis is devoted on the catalyst formulation, reaction pathways, and technologies.

Biofuels of Green Diesel–Kerosene–Gasoline Production from Palm Oil: Effect of Palladium Cooperated with Second Metal on Hydrocracking Reaction

In this work, two kinds of catalyst called monometallic Palladium (Pd) and a bimetallic of Pd-Iron (Fe) were synthesised using aluminum oxide (Al2O3) as the supported material via the wet impregnate method. A monometallic catalyst (0.5% Pd/Al2O3) named Pd cat was used as control. For the bimetallic catalyst, ratios of Pd to Fe were varied, and included 0.38% Pd–0.12% Fe (PF1), 0.25% Pd–0.25% Fe (PF2), and 0.12% Pd–0.38% Fe (PF3). The catalysts were characterised to investigate physical properties such as the surface area, pore size, porosity, and pore size distribution including their composition by Brunauer–Emmett–Teller (BET) surface area, Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD). Subsequently, all catalysts were applied for biofuels production in terms of green diesel/kerosene/gasoline from palm oil via a hydrocracking reaction. The results showed that the loading of Fe to Pd/Al2O3 could improve the active surface area, porosity, and pore diameter. Considering the catalytic efficiency for the hydrocracking reaction, the highest crude biofuel yield (94.00%) was obtained in the presence of PF3 catalyst, while Pd cat provided the highest refined biofuel yield (86.00%). The largest proportion of biofuel production was green diesel (50.00–62.02%) followed by green kerosene (31.71–43.02%) and green gasoline (6.10–8.11%), respectively. It was clearly shown that the Pd-Fe bimetallic and Pd monometallic catalysts showed potential for use as chemical catalysts in hydrocracking reactions for biofuel production.