Search

Residual Macadamia F.Muell nutshell gasification assisted by CO2 was studied in this work. Monometallic Co, Na, and K and bimetallic CoNa and CoK catalysts were prepared and tested in the catalytic process. The idea of this research was to try to find any synergism between already known catalytically active components and to investigate possible ways to use mixed materials. All the materials under investigation were examined by SEM-EDX and XRD. The DTA-TG of the initial fresh macadamia nutshell was presented in this work. The synergism between the Co and K components was revealed in the CO2-assisted gasification process. The found optimal catalyst was 1.5 wt%K-1.5 wt% Co/PMNS. [ABSTRACT FROM AUTHOR]

While the attempts to find new energy sources have intensified, the interest in the use of biomass as a carbon-rich raw material still is increasing. In this work, we studied iron-, cobalt-, and nickel-based materials in the process of CO2-assisted gasification of sunflower husk. The materials with and without metal additives were examined by XRD, SEM, EDX, and TEM techniques and were tested in their gasification under the action of CO2. It was found that the Co-based material demonstrates the best activity among the studied ones (the CO2 conversion was up to 83%). The possible reason for such superiority may be related to the capability of Ni compounds to the formation of the metallic nickel phase and insufficient activity of iron species. [ABSTRACT FROM AUTHOR]

Glycerol is a major by-product in biodiesel manufacturing, which accounts for around 10% of the biodiesel volume. A surplus of glycerol has led to the development of technologies for production of value-added products using glycerol as a raw material, following the "waste as a resource" strategy. Various techniques are available to carry out glycerol transformation, viz. carrying out processes under thermal heating, application of ultrasonic or hydrodynamic cavitation, microchannel technologies, etc. Microwave-assisted organic synthesis (MAOS) is a simple and innovative technology, which can be considered as a means of intensifying these processes. This review describes microwave irradiation as a valuable energy-efficient alternative to conventional heating for the production of value-added chemicals from glycerol via dehydration, hydrogenolysis, esterification, transesterification, etherification, and oxidation. In general, innovative and potential catalysts, approaches, and technologies are discussed and critically evaluated in terms of the possibilities and potential for further industrial implementation [ABSTRACT FROM AUTHOR]

Triazine-based covalent organic framework CTF-1 was synthesized via polymerization of 1,4-dicyanobenzene in the presence of zinc chloride. Two different methods of the post-synthesis treatment of the obtained material were compared. It was demonstrated that ultrasonication effectively removes impurities from CTF-1. Adsorption of hydrocarbon gases (methane and ethane) and carbon dioxide was measured at 298 K in a wide pressure range for the first time. Ideal selectivity and IAST values for methane/ethane and methane/CO2 pairs were calculated from the obtained isotherms. [ABSTRACT FROM AUTHOR]

This review analyzes the use of magnetite-based catalysts in various oxidation reactions. It is shown that magnetite-based catalysts are the most promising candidates from the standpoint of easy separation from the reaction zone and reusability. Diverse examples of the use of magnetite-based composites are discussed, including the following reactions: partial oxidation of methane to formaldehyde; the oxidation of cycloalkanes into alcohols and ketones; the oxidation of alkenes and alcohols with the major focus made on benzylic alcohol oxidation; oxidative cracking of alkenes; Fenton-type reactions with H2O2 as a benign oxidant; the removal of dyestuff in water (including wastewater by oxidation); reactions of sulfides and thiols; the oxidation of 5-hydroxymethylfurfural as a platform chemical to 2,5-diformylfuran; the oxidation of D-glucose to D-gluconic acid; and the electrocatalytic oxidation of methanol and ethanol. The most important and best-studied applications of magnetic nanoparticles in the oxidation reactions are believed to be the oxidation of diverse benzylic alcohols and D-glucose, and Fenton-like reactions aiming at the removal of S- and N-compounds from ware and fuels. Magnetic nanocomposites are determined as the materials meeting a range of criteria: (1) they should be magnetic, (2) they contain nanoparticles, and (3) they consist of two (or more) nanocomponents. The core–shell materials with magnetic nanoparticles used as a core or as decorating nanoparticles are discussed in the review. Three main types of magnetic nanocomposites can be distinguished: (1) the systems where the magnetic phase is active in the considered reaction, for instance, Fenton-like oxidation; (2) the systems containing active metal nanoparticles supported onto the magnetic nanoparticles; and (3) materials with magnetic nanoparticles as a core coated with one or two shells (porous or non-porous), with the magnetic nanoparticles being active or not in the title reaction. Magnetic nanoparticles exhibit a number of advantages compared with supported non-magnetic catalysts of oxidation reactions. The advantages include the possibility of separation from the reaction medium (5–10 times) without a significant loss of the activity, their non-toxicity, low cost, and availability, and the easy preparation of these materials. The drawbacks may include the leaching of active components; a decrease in saturation magnetization in comparison with the bulk magnetite; a limited accessibility of active sites due to diffusion through the shells; the complicated composition and structure of the nanomaterials; a decrease in the activity and specific surface area; and a limited number of magnetic compounds with acceptable characteristics. Nevertheless, the advantages of magnetic nanocatalysts stimulate their wide use in liquid-phase oxidation reactions, which will be discussed in the review. Future perspectives on the use of magnetic composites are considered. [ABSTRACT FROM AUTHOR]

A series of 1%Rh/γ-Al2O3 catalysts was prepared using different Rh-containing precursors (chloride, nitrate, and complex [Rh(NH3)5Cl]Cl2). The catalysts prepared in this work were characterized by various physicochemical methods. Textural and acid–base properties, metal dispersion and metal charge state were characterized by nitrogen adsorption–desorption analysis, scanning electron microscopy with the energy dispersive X-ray analysis, diffuse-reflectance Fourier-transform infrared spectroscopy, transmission electron microscopy, CO chemisorption, X-ray photoelectron spectroscopy. The activity and selectivity of the catalysts were tested in the reaction of decalin ring opening under high pressures. The XPS study showed that rhodium in the surface layers of the samples is present in a metallic state. However, a small positive charge (δ+) is observed on the rhodium atoms due to the interaction of dispersed metal particles with the carrier. This effect is especially noticeable for the sample prepared using the Rh(NO3)3 precursor. According to the data, all studied catalysts allow one to obtain a similar set of reaction products, where C10 alkylcyclohexanes predominate. The catalyst activity decreases in the NO3− > Cl− > [Rh(NH3)5Cl]Cl2 series, that is in the inverse correlation with the rhodium particle size 1.5 nm < 2.2 nm < 17.2 nm (determined by the CO chemisorption method) and 1.7 nm < 2.3 nm < 6.6 nm (determined by TEM). The catalyst synthesized on the basis of rhodium nitrate demonstrates a reaction selectivity close to 74% for the partial ring opening at the total decalin conversion of 67%. The highest activity and selectivity for this catalyst are possibly accounted for by the relatively small size of metal particles formed on the alumina support. Also, some changes in the activity and selectivity of the catalysts observed with variation of the major reaction parameters, such as temperature, pressure, space velocity and H2/C10 molar ratio were determined. [ABSTRACT FROM AUTHOR]

The hydroconversion of asphaltenes into light hydrocarbons catalyzed by supported and free-standing non-noble metal nanoparticles was studied. The activity of Ni or Co immobilized on microspherical oxide carriers and Co nanoparticles dispersed in a hydrocarbon solution of asphaltene was found to be higher than that of a comparative Pt-Pd/Al2O3 catalyst. The yield of light products (C5+) reached up to 91% on cobalt nanoparticles supported onto alumina microspheres. [ABSTRACT FROM AUTHOR]

The trend today is transformation of traditional high-carbon fossil fuel energy to low-carbon clean energy. A promising energy carrier is hydrogen generated from renewable energy sources, providing that hydrogen storage and transportation are the primary important parts of hydrogen energy industrial chain. Efficient and reversible hydrogen storage is of crucial importance in the application of hydrogen energy, and the use of liquid organic hydrogen carriers (LOHC) for hydrogen storage is among technologies under development. Highly effective and low-cost catalysts are of prime importance in the LOHC technology. The present review elucidates the directions and advancements in the development of Pd catalysts for dehydrogenation/hydrogenation of heterocyclic LOHC compounds for the last few years including 2024. The review provides valuable insights into the design and preparation of efficient and durable heterogeneous Pd catalysts for the complete reversible dehydrogenation of hydrogen-rich heterocyclic molecules that are considered as LOHC, which can contribute to technologies based on hydrogen production and storage. Thermodynamic aspects of the use of N-heterocyclic compounds and results of theoretical studies of LOHC processing on Pd catalysts are considered. • Recent 5 years summary on Pd catalysts for H 2 release from heteroaromatic LOHC. • Variation in the catalyst efficiency depending on the Pd state and content is discussed. • Effect of the support nature and reducibility on the catalyst efficiency is analyzed. • Application of catalysts with a low Pd content for different LOHC was shown. • Pd clusters and nanoparticles of 1–4 nm on reducible supports are promising catalysts. [ABSTRACT FROM AUTHOR]

This work uses green sustainable reactions twice. Firstly, it is microwave synthesis: 2,4,6‐tribiphenyl‐4‐yl‐1,3,5‐triazine and similar compounds were prepared in a closed microwave reactor in n‐octane by the Friedel‐Crafts reaction. Second, a hybrid electrocatalyst for the highly demanded electrochemical reaction of nitrate reduction to ammonia (NO3RR) was prepared based on this material. This reaction has great potential to replace the energy‐intensive Haber‐Bosch process, and in addition, has independent value for the elimination of nitrate contamination of water resources. As shown in the work, microwave synthesis is an eco‐friendly method for the synthesis of complex organic compounds; fast, selective and with a high yield of the target product. The electrocatalyst deposited on the graphite electrode consisted of a layer of 2,4‐bis([1,1′‐biphenyl]‐4‐yl)‐6‐hydroxy‐1,3,5‐triazine and related compounds coated with cobalt oxide. The hybrid catalyst was firmly retained on the graphite electrode during NO3RR and the material showed impressive stability with almost no decrease in catalytic activity even after the fifth cycle. Both 2,4‐bis([1,1′‐biphenyl]‐4‐yl)‐6‐hydroxy‐1,3,5‐triazine and the catalyst based on this substance were characterized by SEM, XPS, XRD, UV‐vis spectra, cyclic (and linear) voltammetry, and chronoamperometry. This work can serve as a starting point for the development of stable and durable electrocatalysts for NO3RR using triazine derivatives. [ABSTRACT FROM AUTHOR]

The cheap non-noble Cu–SiO2-based nanocatalysts are under intensive study in different reactions resulting in useful chemicals, yet their application in environment protection is poorly studied. In the present work, the influence of the Cu loading (3–15 wt%) on the catalytic behavior of Cu/SiO2 materials was first precisely studied in the hydrogenation of hazardous trinitrobenzene to valuable aromatic amines with molecular hydrogen. The catalysts have been synthesized by the method of deposition–precipitation using urea. The catalyst characterization by XRD, TPR-H2, SEM, TEM, and N2 adsorption methods confirmed that they include nanoparticles of the micro-mesoporous chrysocolla-like phase supported in the mesopores of a commercial SiO2 carrier, as well as revealed formation of the highly dispersed CuO phase in the sample with the highest Cu loading. Variation in reaction conditions showed the optimal ones (170 °C, 1.3 MPa H2) resulting in complete trinitrobenzene conversion with a triaminobenzene yield of 65% for the catalyst with a 15% Cu loading, and the best yield of 82% was obtained over the catalyst with 10% Cu calcined at 600 °C. The results show the potential of Cu phyllosilicate-based catalysts for the utilization of trinitroaromatic compounds via catalytic hydrogenation to amines and their possible applications in a remediation treatment system. [ABSTRACT FROM AUTHOR]

Chromium-substituted aluminophosphate (CrAPO-5) with the AFI crystal structure was prepared for the first time by using microwave conditions at the stage of gel formation and crystallization. This approach allowed the reduction of the time required for the synthesis of CrAPO-5 from 60–70 h to 6 h. CrAPO-5 metal aluminophosphate prepared by microwave-assisted synthesis is studied by UV-visible and IR spectroscopy and X-ray photoelectron spectroscopy. The material is characterized by the presence of Cr3+ and Cr2+ ions in the framework with predominating Cr3+ ions introduced via isomorphous substitution, as well as some minor amounts of extra-framework Cr3+ species, which are present presumably in the state of α-Cr2O3. The latter species can be partially reduced to Cr2+ species in the presence of CO or H2. XPS study of CrAPO-5 revealed the presence of Cr3+ ions in the framework. A TPR experiment showed that the reduction of chromium starts at about 450–500 °C. [ABSTRACT FROM AUTHOR]