New Approach to Synthesizing Cathode PtCo/C Catalysts for Low-Temperature Fuel Cells.

The presented study is concerned with a new multi-step method to synthesize PtCo/C materials based on composite CoxOy/C that combines the advantages of different liquid-phase synthesis methods. Based on the results of studying the materials at each stage of synthesis with the TG, XRD, TEM, SEI, TXRF, CV and LSV methods, a detailed overview of the sequential changes in catalyst composition and structure at each stage of the synthesis is presented. The PtCo/C catalyst synthesized with the multi-step method is characterized by a uniform distribution of bimetallic nanoparticles of about 3 nm in size over the surface of the support, which result in its high ESA and ORR activity. The activity study for the synthesized PtCo/C catalyst in an MEA showed better current-voltage characteristics and a higher maximum specific power compared with an MEA based on a commercial Pt/C catalyst. Therefore, the results of the presented study demonstrate high prospects for the developed approach to the multi-step synthesis of PtM/C catalysts, which may enhance the characteristics of proton-exchange membrane fuel cells (PEMFCs).

Insights on the Anion Effect in N-heterocyclic Carbene Based Dinuclear Gold(I) Catalysts.

Dinuclear bisNHC (bis(N-heterocyclic carbene)) gold(I) complexes 3 a and 4 a of general formula [Au2 Br2 (bisNHC)] were tested as catalysts in the cycloisomerization of N-(prop-2-yn-1-yl)benzamide and in the hydromethoxylation of 3-hexyne in the presence of silver(I) activators bearing different counteranions. The catalytic performance of mononuclear NHC complexes (1 a, 2 a) in the same reactions was also studied. The results highlighted the fundamental role of both NHC ligand and counterion in the catalytic cycles and activation process: dinuclear catalysts exhibit higher initial activity even under milder conditions but suffer in terms of stability with respect to mono NHCs. Furthermore, a new dinuclear bisNHC gold(I) complex 4 b of general formula [Au2 (OTs)2 (bisNHC)] (OTs=p-toluenesulfonate) was successfully synthesized and characterized by means of NMR and ESI-MS analyses.

Recent advances in electrospinning-nanofiber materials used in advanced oxidation processes for pollutant degradation.

Electrospun nanofiber membranes have emerged as a novel catalyst, demonstrating exceptional efficacy in advanced oxidation processes (AOPs) for the degradation of organic pollutants. Their superior performance can be attributed to their substantial specific surface area, high porosity, ease of modification, rapid recovery, and unparalleled chemical stability. This paper aims to comprehensively explore the progressive applications and underlying mechanisms of electrospun nanofibers in AOPs, which include Fenton-like processes, photocatalysis, catalytic ozonation, and persulfate oxidation. A detailed discussion on the mechanism and efficiency of the catalytic process, which is influenced by the primary components of the electrospun catalyst, is presented. Additionally, the paper examines how concentration, viscosity, and molecular weight affect the characteristics of the spinning materials and seeks to provide a thorough understanding of electrospinning technology to enhance water treatment methods. The review proposes that electrospun nanofiber membranes hold significant potential for enhancing water treatment processes using advanced oxidation methods. This is attributed to their advantageous properties and the tunable nature of the electrospinning process, paving the way for advancements in water treatment through AOPs.

Performance and emission characteristics of a diesel engine fuelled by biodiesel from black soldier fly larvae: Effects of synthesizing catalysts with citric acid.

Biodiesel has several environmental benefits, such as biodegradability, renewability and lower soot emissions. However, biodiesel has undesirable properties such as higher viscosity and density and low calorific value compared to petroleum diesel, resulting in high Brake Specific Fuel Consumption (BSFC), reduced Brake Power (BP) and increased NOX emissions creating an environmental concerns in biodiesel development. This study investigated the effects of synthesizing transesterification catalysts (CaO and NaOH) with Citric Acid (CA) on the quality of biodiesel and biodiesel blends produced from Black Soldier Fly Larvae (BSFL) (Hermetia Illucens). The quality of biodiesel and blends was determined based on fuel properties, engine performance and emission composition characteristics. The tests were performed on a single-cylinder, four-stroke, Compression Ignition (CI) diesel engine at five loads at a constant speed of 1500 rpm. The results showed that synthesizing the catalysts with CA significantly affected the fatty acid profile of the biodiesel compared to physical fuel properties. B100 (pure BSFL biodiesel) exhibited higher BSFC by 10.57-13.97 % and lower BP by 4.21-7.83 % than diesel fuel. However, the Brake Thermal Efficiency (BTE) of biodiesel was higher than that of diesel fuel by 0.82-4.34 % at maximum load. Synthesizing catalysts with CA improved the viscosity of biodiesel by 0.93-2.81 % and effectively reduced NOX, HC and Smoke opacity by 2.23-3.16 %, 4.95-5.83 % and 20.51-41.15 %, respectively.

A Highly Active Cobalt Catalyst for the General and Selective Hydrogenation of Aromatic Heterocycles.

Nanostructured earth abundant metal catalysts that mediate important chemical reactions with high efficiency and selectivity are of great interest. This study introduces a synthesis protocol for nanostructured earth abundant metal catalysts. Three components, an inexpensive metal precursor, an easy to synthesize N/C precursor, and a porous support material undergo pyrolysis to give the catalyst material in a simple, single synthesis step. By applying this catalyst synthesis, a highly active cobalt catalyst for the general and selective hydrogenation of aromatic heterocycles could be generated. The reaction is important with regard to organic synthesis and hydrogen storage. The mild reaction conditions observed for quinolines permit the selective hydrogenation of numerous classes of N-, O- and S-heterocyclic compounds such as: quinoxalines, pyridines, pyrroles, indoles, isoquinoline, aciridine amine, phenanthroline, benzofuranes, and benzothiophenes.

Green Recipes for Pyrimidine.

Pyrimidines serve as key structural components in chemical frameworks and biological processes. Several pyrimidine analogues have been produced over the years by means of traditional methods that necessitated large amounts of solvents, reagents, and, most importantly, additional time, which has led them to become prohibitive. These procedures are now being replaced with more cost-effective adaptive methodologies that incorporate one-pot synthesis and greener approaches involving various green solvents and catalysts. The current review covers a number of green synthetic techniques, including ultrasound-assisted synthesis, visible light irradiation synthesis, solvent-free synthesis, catalyst-free synthesis, microwave-assisted synthesis, and green catalyst synthesis for the synthesis of pyrimidine derivatives. Accordingly, it integrates different strategies to synthesize heterocyclic pyrimidine analogues in a well-organized manner.

Towards Heterogeneous Catalysis: A Review on Recent Advances of Depositing Nanocatalysts in Continuous-Flow Microreactors.

As a promising technology, microreactors have been regarded as a potential candidate for heterogeneous catalytic reactions as they inherently allow the superior advantages of precise flow control, efficient reactant transfer, flexible operation, etc. However, the wide market penetration of microreactors is still facing severe challenges. One of the most important reasons is the preparation of a high-performance catalytic layer in the microreactor because it can directly influence the catalytic activity and stability the reactor and thus the deployment the microreactor technology. Hence, significant progress in depositing nanocatalysts in microreactors has been made in the past decades. Herein, the methods, principles, recent advances, and challenges in the preparation of the catalyst layer in microreactors were presented. A general description of the physicochemical processes of heterogeneous catalytic reactions in microreactors were first introduced. Then, recent advances in catalyst layer preparation in microreactors were systematically summarized. Particular attention was focused on the most common sol-gel method and its latest developments. Some new strategies proposed recently, including bio-inspired electroless deposition and layer-by-layer self-assembly, were also comprehensively discussed. The remaining challenges and future directions of preparing the catalytic layer in microreactors with high performance and low cost were highlighted.

Use of X-Ray Photoelectron Spectroscopy as an analytical tool for the study of contamination by Teflon in the synthesis of Mo(VI)Cl2O2Bipy/ TiO2 catalysts

The preparation of catalysts can involve various sources of contamination, which can seriously affect the quality of the prepared materials. In the present work, a case of fluorine contamination in a set of catalyst samples was studied, in which using the X-Ray Photoelectron Spectroscopy (XPS) technique, it was evidenced by the F 1s signal that this element was present in the form of Teflon, since its binding energy corresponded mainly to the CF2 species. Furthermore, using the C 1s signal, it was also possible to corroborate the presence of the CF2 group, which is associated with the main component of the Teflon carbon chains. The use of this information made it possible to identify that the solvent dehydration procedure (previous step to obtaining the catalysts) could lead to contamination with Teflon since it involved various accessories with Teflon, organic solvents and high temperature; the Teflon tape and the magnetic stirrer being the possible sources of contamination.

La preparación de catalizadores puede contener diversas fuentes de contaminación, las cuales pueden afectar seriamente las propiedades de los materiales preparados. En este artículo se estudió un caso de contaminación con flúor en una serie de muestras de catalizadores. Empleando la técnica de espectroscopia fotoelectrónica de rayos X (XPS) se evidenció la presencia de flúor en la superficie de los materiales, el cual estaba asociado al polímero teflón, ya que su energía de enlace correspondía principalmente con la de la especie CF2. Además, empleando la señal C 1s, se logró corroborar la presencia de la especie CF2, el cual está asociado al componente principal de las cadenas carbonadas de teflón. El uso de la información obtenida por XPS permitió determinar que durante la deshidratación del solvente (paso previo para la obtención de los catalizadores en el cual se emplean solventes orgánicos y alta temperatura) se podría estar llevando a cabo la contaminación con teflón, ya que este componente está presente en diversos accesorios empleados en el proceso de deshidratación, siendo la cinta de teflón y el agitador magnético las posibles fuentes de contaminación.

A preparação de catalisadores pode conter diversas fontes de contaminação, as quais podem afeitar seriamente as propriedades dos materiais preparados. No presente trabalho estudou-se um caso de contaminação com flúor numa série de amostras de catalisadores. Usando a técnica da espectroscopia fotoeletrônica de raios X (XPS), evidenciou-se a presença de flúor na superfície dos materiais, o qual estava associado ao polímero Teflon, já que sua energia de ligação correspondia principalmente à da espécie CF2. Além disso, usando a sinal C 1s, foi possível corroborar a presença do grupo CF2, o qual está associado ao componente principal das cadeias carbônicas do Teflon. O uso da informação obtida por XPS permitiu determinar que durante a desidratação do solvente (passo prévio para a obtenção dos catalisadores no qual são usados solventes orgânicos e alta temperatura) tem-se a contaminação com Teflon, já que este componente está presente em diversos acessórios utilizados no processo de desidratação, sendo a fita do Teflon e o agitador magnético as possíveis fontes da contaminação.

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis.

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Improved direct synthesis of TiO2 catalyst using sonication and its application for the desulfurization of thiophene.

TiO2 catalyst was synthesized in the presence of ultrasound (ultrasonic horn at 20 kHz frequency and 70% duty cycle) at different power (80 W to 120 W) and durations as well as surfactant concentration with an objective of establishing best conditions for achieving lowest particle size of the photocatalyst. Detailed characterization in terms of crystal phase, crystallinity, functional groups and morphology of the photocatalyst has been performed using SEM, XRD and FTIR analysis. It was demonstrated that sonication significantly reduced the particle size with high degree of sphericity and homogeneity as compared to conventionally synthesized TiO2 with similar crystallinity in both cases. The catalytic performance was subsequently evaluated for the deep desulfurization of thiophene. Different desulfurization approaches including individual US (ultrasonic horn at 20 kHz frequency, 110 W power and 70% duty cycle) and UV irradiations, US/UV, US/UV/H2O2, US/UV/TiO2 and US/UV/H2O2/TiO2 were applied to evaluate the catalytic activity. The best approach was demonstrated as US/UV/H2O2/TiO2 and also activity of catalyst synthesized using ultrasound was much better compared to conventionally synthesized catalyst. The studies related to different model solvents demonstrated lowest reactivity for toluene whereas n-hexane and n-octane resulted in complete desulfurization in 60 min and 50 min treatment respectively. The desulfurization followed pseudo first order reaction kinetics irrespective of the solvent used. Overall the work clearly demonstrated the efficacy of ultrasound in improving the catalyst synthesis as well as desulfurization of thiophene.

Ultrasound-assisted sequentially precipitated nickel-silica catalysts and its application in the partial hydrogenation of edible oil.

Sequentially precipitated Mg-promoted nickel-silica catalysts with ageing performed under various ultrasonic intensities were employed to study the catalyst performance in the partial hydrogenation of sunflower oil. Results from various characterisation studies showed that increasing ultrasonic intensity caused a higher degree of hydroxycarbonate erosion and suppressed the formation of Ni silicates and silica support, which improved Ni dispersion, BET surface area and catalyst reducibility. Growth of silica clusters on the catalyst aggregates were observed in the absence of ultrasonication, which explained the higher silica and nickel silicate content on the outer surface of the catalyst particle. Application of ultrasound also altered the electron density of the Ni species, which led to higher activity and enhanced product selectivity for sonicated catalysts. The catalyst synthesised with ultrasonic intensity of 20.78 Wcm-2 achieved 22.6% increase in hydrogenation activity, along with 28.5% decrease in trans-C18:1 yield at IV = 70, thus supporting the feasibility of such technique.

Mechanochemical Synthesis of Catalytic Materials.

The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route-in contrast to more conventional synthesis-in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance.

A state-of-the-art review on emission characteristics of SI and CI engines fueled with 2,5-dimethylfuran biofuel.

Currently, the considerable decline in fossil fuel resources and the high rise in vehicle emissions have prompted researchers and governments to formulate strategies for sustainable energy development. In addition to imposing strict laws, promoting sustainable energy sources such as the development of new types of non-fossil fuels has been considered a suitable direction for the roadmap to healing the Earth's environment. Biomass sources have affirmed huge potentials in the production of biofuels. In the pathway of searching renewable biofuels, it is found that that 2,5-dimethylfuran (DMF) can become a promising fuel because it is synthesized from lignocellulose biomass, which is an available feedstock for the production of prospective fuels. Indeed, recent review studies have focused in great detail on engine performance evaluation using DMF but seemed to have gaps in emission characteristics. In this work, the controversial issues of emissions from spark and compression ignition engines during the DMF combustion were completely assessed. Indeed, the mechanism of formation and oxidation of DMF compounds during combustion was clearly described to serve as the basis for analyzing and comparing the pollution emission behavior of different fuels. More importantly, gaseous emissions, PM characteristics, and soot tendency from spark and compression ignition engines were thoroughly evaluated on the basis of the experimental and numerical data. In general, DMF has shown outstanding advantages upon emissions compared to fossil fuels; however, the impacts of DMF on the engine durability and fuel system should be further investigated to have a comprehensive analysis of this biofuel class.

Synthesis and catalytic utilization of bimetallic systems for wastewater remediation: A review.

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies (physicochemical processes, biological degradation, and oxidative processes) have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. This study reviews existing research on various synthesis methods for the preparation of bimetallic catalysts and their catalytic application to the treatment of organic (dyes, phenol and its derivatives, and chlorinated organic compounds) and inorganic pollutants (nitrate and hexavalent chromium) from water and wastewater. The reaction mechanisms, removal efficiencies, operating conditions, and research progress are also presented. The results reveal that Fe-based bimetallic catalysts are one of the most efficient heterogeneous catalysts for the treatment of organic and inorganic contamination. Furthermore, the roles and performances of bimetallic catalysts in the removal of these environmental contaminants are different.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition.

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Superficial properties of activated carbon fiber catalysts produced by green synthesis and their application in water purification.

Catalysts of Pd-In supported on activated carbon fiber were synthesized, characterized, and evaluated for the removal of nitrogen oxyanions from water. The work was carried out aiming the development of a green synthesis process, and the studies were accomplished with the following objectives: (a) to evaluate whether catalysts produced by wet impregnation (WI) and autocatalytic deposition (AD) have enough catalytic activity for the removal of oxyanions in water; (b) to determine the efficiency of ion removal using formic acid as a reducing agent; (c) to determine which synthesis method produces less waste. It was found that the two synthesis processes modified the properties of the support and that the distribution of the particles of the metallic phase was of the nanometric order, being these particles found predominantly at the support surface. By using formic acid as a reducing agent, although low nitrate conversions were obtained (32%), a selectivity to N2 higher than 99% was achieved. These findings were attributed to the low decomposition of formic acid on the catalyst surface. The Pd:In (0.45:0.2) catalyst prepared by WI was the most suitable for the catalytic reduction of both nitrate and nitrite oxyanions. Regarding the green point of view of the synthesis method, catalysts prepared by WI generated less waste. Graphical abstract.

Improved Access to Chiral Tetranaphthoazepinium-Based Organocatalysts Using Aqueous Ammonia as Nitrogen Source.

The class of 3,3'-diaryl substituted tetranaphthobisazepinium bromides has found wide application as highly efficient C2-symmetrical phase-transfer catalysts (PTCs, Maruoka type catalysts). Unfortunately, the synthesis requires a large number of steps and hampers the build-up of catalyst libraries which are often desired for screening experiments. Here, we present a more economic strategy using dinaphthoazepine 7 as the common key intermediate. Only at this stage various aryl substituents are introduced, and only two individual steps are required to access target structures. This protocol was applied to synthesize ten tetranaphthobisazepinium compounds 1a-1j. Their efficiency as PTCs was tested in the asymmetric substitution of tert-butyl 2-((diphenylmethylene)amino)acetate. Enantioselectivities up to 92% have been observed with new catalysts.

Ultrasound-assisted impregnation for high temperature Fischer-Tropsch catalysts.

A fraction of the petroleum extracted from oil reservoirs contains associated natural gas. Rather than building infrastructure to recover low volumes of this natural gas, the industry flares or vents it to the atmosphere, which contributes to atmospheric greenhouse gas emissions but also reduces the air quality locally because it contains gaseous sulphur and nitrogen compounds. Converting the natural gas (NG) to hydrocarbons with a small-scale two-step gas-to-liquids process, is an alternative to flaring and venting. In the first step, NG reacts with oxygen to form syngas (Catalytic Partial Oxidation) and in the second step the syngas reacts over metallic catalysts to form higher paraffins at 210 °C to 300 °C-Fischer Tropsch synthesis (FT). For the first time, we synthesize bimetallic FeCo FT catalysts with ultrasound. An ultrasonic horn agitates the solution during the entire impregnation process. The active phase dispersion of the sonicated catalysts was superior to the catalyst synthesized without ultrasound, while reducing the impregnation time by a factor of three. We tested our catalysts in a lab-scale, fixed-bed reactor at 270 °C and 300 °C, and achieved 80% conversion over 3-days on stream and a 40% yield of C2+.

Sulfur resistance of Ce-Mn/TiO2 catalysts for low-temperature NH3-SCR.

Ce-Mn/TiO2 catalyst prepared using a simple impregnation method demonstrated a better low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) activity in comparison with the sol-gel method. The Ce-Mn/TiO2 catalyst loading with 20% Ce had the best low-temperature activity and achieved a NO conversion rate higher than 90% at 140-260°C with a 99.7% NO conversion rate at 180°C. The Ce-Mn/TiO2 catalyst only had a 6% NO conversion rate decrease after 100 ppm of SO2 was added to the stream. When SO2 was removed from the stream, the catalyst was able to recover completely. The crystal structure, morphology, textural properties and valence state of the metals involving the novel catalysts were investigated using X-ray diffraction, N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy, respectively. The decrease of NH3-SCR performance in the presence of 100 ppm SO2 was due to the decrease of the surface area, change of the pore structure, the decrease of Ce4+ and Mn4+ concentration and the formation of the sulfur phase chemicals which blocked the active sites and changed the valence status of the elements.

High-performance bimetallic alloy catalyst using Ni and N co-doped composite carbon for the oxygen electro-reduction.

In this study, a novel synthesis method for the bimetallic alloy catalyst is reported, which is subsequently used as an oxygen reduction catalyst in polymer electrolyte membrane fuel cells (PEMFCs). The support prepared from the Ni-chelate complex shows a mesoporous structure with a specific surface area of ca. 400 m2 g-1 indicating the suitable support for PEMFC applications. Ethylenediamine is converted to the nitrogen and carbon layers to protect the Ni particles which will diffuse into the Pt lattice at 800 °C. The PtNi/NCC catalyst with PtNi cores and Pt-rich shells is successfully formed when acid-treated as evidenced by line scan profiles. The catalyst particles thus synthesized are well-dispersed on the N-doped carbon support, while the average particle size is ca. 3 nm. In the PEMFC test, the maximum power density of the PtNi/NCC catalyst shows approximately 25% higher than that of the commercial Pt/C catalyst. The mass activity of the PtNi/NCC catalyst showed approximately 3-fold higher than that of the commercial Pt/C catalyst. The mass activity strongly depends on the ratio of Pt to Ni since the strain effect can be strong for catalysts due to the mismatch of lattice parameters of the Ni and Pt.