Methanation of CO2 over Ruthenium Supported on Alkali-Modified Silicalite-1 Catalysts.

This study focuses on the catalytic properties of ruthenium catalysts supported on modified silicalite-1 (with an MFI structure). By post-synthesis modification of silicalite-1 with solutions of alkali metal compound, a novel and cost-effective method was discovered to create basic centers on the surface of silicalite-1 supports. The modification not only affected the basicity of the supports but also their porosity. The influence of the type of alkali solution (KOH or NaOH) and its concentration (0.1 M or 1.0 M) on both the basicity and porosity was investigated. The modified silicalite-1 materials were employed as supports for ruthenium catalysts (1 wt.% Ru) and evaluated for their CO2 methanation activity. The results were compared with the hydrogenation performance of ruthenium catalysts supported on unmodified silicalite-1. Characterization of the supports and catalysts was conducted using techniques such as BET, XRD, FT-IR, ICP-OES, TPR-H2, H2 chemisorption, TPD-CO2, SEM, and TEM. Remarkably, the catalytic activity of ruthenium supported on silicalite-1 treated with 1.0 M NaOH (exhibiting selectivity toward methane above 90% in a reaction temperature range of 250-450 °C) outperformed both unmodified and KOH-modified silicalite-1 supported Ru catalysts.

In situ growth of N-doped carbon nanotubes from the products of graphitic carbon nitride etching by nickel nanoparticles.

The in situ growth of N-doped multi-walled carbon nanotubes (N-MWCNTs) from the products of graphitic carbon nitride (g-C3N4) etching by Ni nanoparticles in a hydrogen atmosphere has been confirmed for the first time. During the etching process of g-C3N4, the building blocks, notably methane, ammonia, and hydrogen cyanide, are formed. The formation of N-MWCNTs was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning (SEM) and transmission electron microscopy (TEM). A sponge-like carbonaceous structure was obtained with a specific surface area of 384 m2 g-1 from initial g-C3N4 (32 m2 g-1).

Supported Ionic Liquid-Phase Materials (SILP) as a Multifunctional Group of Highly Stable Modifiers and Hardeners for Carbon and Flax Epoxy Composites.

This paper introduces a novel approach to enhance epoxy resin formulations by using SILP materials as multifunctional hardeners and fillers in composite structures reinforced with carbon and flax fibers. This study explores the integration of ionic liquids (ILs) onto a silica support structure, presenting various permutations involving silica selection, ionic liquid choice, and concentration. The focus of this study was to elucidate the influence of SILP on resin curing ability and the mechanical properties of the resulting composites. Detailed research was conducted, including Brunauer-Emmett-Teller analysis (BET) for SILP materials and curing characterization for epoxy resin formulations with different SILP materials. Furthermore, the mechanical properties of the obtained composites were determined by Scanning Electron Microscopy analysis (SEM) (the force at break, the maximum elongation at break, tensile strength, and modulus of elasticity). Through SILP incorporation, the mechanical properties of composites, including the modulus of elasticity and tensile strength, are substantially improved, a phenomenon akin to traditional filler effects. The findings highlight SILP materials as prospective candidates for concurrent hardening and filling roles within composites (through a single-step procedure, with prolonged storage stability and controlled processing conditions), particularly pertinent as the composite industry veers toward epoxy bioresins necessitating liquefaction via temperature application.

Supported Gold Catalysts for Base-Free Furfural Oxidation: The State of the Art and Machine-Learning-Enabled Optimization.

Supported gold nanoparticles have proven to be highly effective catalysts for the base-free oxidation of furfural, a compound derived from biomass. Their small size enables a high surface-area-to-volume ratio, providing abundant active sites for the reaction to take place. These gold nanoparticles serve as catalysts by providing surfaces for furfural molecules to adsorb onto and facilitating electron transfer between the substrate and the oxidizing agent. The role of the support in this reaction has been widely studied, and gold-support interactions have been found to be beneficial. However, the exact mechanism of furfural oxidation under base-free conditions remains an active area of research and is not yet fully understood. In this review, we delve into the essential factors that influence the selectivity of furfural oxidation. We present an optimization process that highlights the significant role of machine learning in identifying the best catalyst for this reaction. The principal objective of this study is to provide a comprehensive review of research conducted over the past five years concerning the catalytic oxidation of furfural under base-free conditions. By conducting tree decision making on experimental data from recent articles, a total of 93 gold-based catalysts are compared. The relative variable importance chart analysis reveals that the support preparation method and the pH of the solution are the most crucial factors determining the yield of furoic acid in this oxidation process.

Reductive Modification of Carbon Nitride Structure by Metals-The Influence on Structure and Photocatalytic Hydrogen Evolution.

Pt, Ru, and Ir were introduced onto the surface of graphitic carbon nitride (g-C3N4) using the wet impregnation method. A reduction of these photocatalysts with hydrogen causes several changes, such as a significant increase in the specific surface area, a C/N atomic ratio, a number of defects in the crystalline structure of g-C3N4, and the contribution of nitrogen bound to the amino and imino groups. According to the X-ray photoelectron spectroscopy results, a transition layer is formed at the g-C3N4/metal nanoparticle interphase, which contains metal at a positive degree of oxidation bonded to nitrogen. These structural changes significantly enhanced the photocatalytic activity in the production of hydrogen through the water-splitting reaction. The activity of the platinum photocatalyst was 24 times greater than that of pristine g-C3N4. Moreover, the enhanced activity was attributed to significantly better separation of photogenerated electron-hole pairs on metal nanoparticles and structural distortions of g-C3N4.

Phosphate doping as a promising approach to improve reactivity of Nb2O5 in catalytic activation of hydrogen peroxide and removal of methylene blue via adsorption and oxidative degradation.

This study is devoted to the evaluation of the influence of phosphate dopants on the reactivity of Nb2O5-based nanomaterials in the combined catalytic activation of H2O2 and the elimination of methylene blue (MB) from an aqueous solution via adsorption and chemical degradation. For this purpose, several niobia-based catalysts doped with various amounts of phosphate were prepared by a facile hydrothermal method and subsequent calcination. Phosphate doping was shown to strongly enhance the ability of Nb2O5 to activate H2O2, as well as to adsorb and degrade MB. The most pronounced differences in the reactivity of the parent Nb2O5 and phosphate-doped samples were observed under strongly acidic conditions (pH ~ 2.4), at which the most active modified catalysts (Nb/P molar ratio = 5/1) was approximately 6 times more efficient in the removal of MB. The observed enhancement of reactivity was attributed to the increased generation of singlet oxygen 1O2, which was identified as the main oxidizing agent responsible for efficient degradation of MB. To our knowledge, it is the first report revealing that phosphate doping of Nb2O5 resulted in an improved activity of niobia in the adsorption and degradation of organic pollutants.

SILP materials based on TiO2-SiO2 and TiO2-SiO2/lignin supports as new catalytic materials for hydrosilylation reaction - synthesis, physicochemical characterization and catalysis.

The oxide system TiO2-SiO2 as well as a TiO2-SiO2/lignin system have been obtained by the sol-gel synthesis method and applied as supports in Supported Ionic Liquid Phase (SILP) materials. In total 24 SILP systems were obtained with ionic liquids containing imidazolium, pyridinium, phosphonium or sulfonic cations and bis(trifluoromethylsulfonyl)imide or methylsulfate anions, and homogeneous complexes of rhodium or platinum as the active phase. The supports and catalytic materials were subjected to thorough characterization by elemental analysis, XRD, SEM-EDX, IR, and TGA, and their particle size distribution and porous properties were assessed. The new SILP materials were used in hydrosilylation of 1-octene with 1,1,1,3,5,5,5-heptamethyltrisiloxane. The effectiveness of hydrosilylation reaction catalyzed by the obtained SILP materials for the polar and nonpolar reagents was assessed. All the catalytically active materials were proved to be easy to isolate and reuse, and the best SILP systems have been shown to be active in 10 or more subsequent catalytic cycles.

Effect of Modification of Amorphous Silica with Ammonium Agents on the Physicochemical Properties and Hydrogenation Activity of Ir/SiO2 Catalysts.

The modification of commercial silica with solutions of NH4F or NH4Cl salts, followed by thermal treatment, enabled generation of the acidic sites in SiO2 and changed its textural properties. The use of ammonium salts solution also caused the generation of additional porosity. Using NH4F solution caused significant decrease in the specific surface area and the increase in the average pore diameter. The number and strength of resulting acid sites depend on the nature of anion in the applied ammonium salt and the concentration of salt solution. It has been found that the sample treated with NH4F presented higher total acidity (TPD-NH3) and the amount as well as the strength of acid sites increased with the concentration of the used modifier. As modified amorphous SiO2 materials used as a support for iridium (1 wt %, Ir(acac)3) nanoparticles permitted to obtain highly active catalysts for toluene hydrogenation under atmospheric pressure. The highest activity (expressed as the apparent rate and TOF) was obtained for iridium catalysts supported on silica modified by NH4F with the highest acidity. The modification of silica with NH4F favors the generation of centers able to adsorb toluene, which results in higher activity of this catalyst.

Studies of New Iridium Catalysts Supported on Modified Silicalite-1-Their Structure and Hydrogenating Properties.

This paper investigates the catalytic properties of the iridium catalysts supported on modified silicalite-1. Post-synthesis modification of silicalite-1, with solutions of ammonium compounds (NH4F and NH4OH), appeared to be an efficient method to generate the acidic sites in starting support. The modification of support led not only to changes in its acidity but also its porosity-formation of additional micro- and mesopores. The novel materials were used as supports for iridium. The iridium catalysts (1 wt.% Ir) were characterized by N2 adsorption/desorption measurements, temperature-programmed reduction with hydrogen (TPR-H2), H2 chemisorption, transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH3), X-ray photoelectron spectroscopy (XPS) and tested in the hydrogenation of toluene reaction. The catalytic activity of iridium supported on silicalite-1 treated with NH4OH (higher porosity of support, better dispersion of active phase) was much higher than that of Ir supported on unmodified and modified with NH4F silicalite-1.

Elucidating the structure of the graphitic carbon nitride nanomaterials via X-ray photoelectron spectroscopy and X-ray powder diffraction techniques.

By using the most popular method of thermal condensation of dicyandiamide in a semi-closed system, graphitic carbon nitrides (gCNs) were synthesized at 500, 550, and 600 °C. The resulting materials were comprehensively analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD)techniques. We show that the use of routine analytical methods provides an insight into the structure of the carbon nitride materials. The analysis of geometric linear structures and fully condensed structure of polymeric carbon nitrides was performed and the ranges within which the contents of different nitrogen species (pyridine, amine, imine and quaternary nitrogen) can change were determined. This analysis, in combination with quantitative XPS studies, permits to state that the carbon nitride structure prepared by the thermal condensation of dicyandiamide is closer to the structure in which poly(aminoimino)heptazine subunits are linked into chains rather than the structure involving fully-condensed polyheptazine network. The XRD analysis proved that the 3D crystal structure of carbon nitride is described more correctly by the orthorhombic cell and space group P21212 applied to condensed chains of poly(aminoimino)heptazine (melon) and not by the hexagonal cell with the space group P6m2.

Influence of High Temperature Synthesis on the Structure of Graphitic Carbon Nitride and Its Hydrogen Generation Ability.

Graphitic carbon nitride (g-C3N4) was obtained by thermal polymerization of dicyandiamide, thiourea or melamine at high temperatures (550 and 600 °C), using different heating rates (2 or 10 °C min-1) and synthesis times (0 or 4 h). The effects of the synthesis conditions and type of the precursor on the efficiency of g-C3N4 were studied. The most efficient was the synthesis from dicyandiamide, 53%, while the efficiency in the process of synthesis from melamine and thiourea were much smaller, 26% and 11%, respectively. On the basis of the results provided by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), thermogravimetric analysis (TGA), elemental analysis (EA), the best precursor and the optimum conditions of synthesis of g-C3N4 were identified to get the product of the most stable structure, the highest degree of ordering and condensation of structure and finally the highest photocatalytic activity. It was found that as the proton concentration decreased and the degree of condensation increased, the hydrogen yields during the photocatalytic decomposition of water-methanol solution were significantly enhanced. The generation of hydrogen was 1200 µmol g-1 and the selectivity towards hydrogen of more than 98%.

Synthesis and characterization of MgF2-CoF2 binary fluorides. Influence of the treatment atmosphere and temperature on the structure and surface properties.

Research was carried out on the incorporation of divalent cobalt cations into the crystalline structure of MgF2 to form Mg x Co1-x F2 binary fluorides, which had not been investigated before. The above fluorides were obtained by the precipitation from aqueous solution of magnesium and cobalt nitrates with ammonium fluoride. Binary fluorides containing 0.6, 7.5 and 37.7 mol% CoF2 were prepared. The effects of treatment temperature (300, 400 °C) and atmosphere (oxidizing or reducing) on the structure (XRD, TPR-H2, UV-Vis), texture (low-temperature N2 adsorption), surface composition (XPS) and surface acidity (NH3-TPD) of the binary fluorides were determined. It has been found that in Mg x Co1-x F2 an isomorphic substitution occurs of Mg2+ cations by Co2+ cations which results in the formation of a rutile-type solid solution. The obtained binary fluorides are characterized by a mesoporous structure and relatively large surface area. It has been found that thermal treatment of the binary fluorides in oxidizing conditions results in the oxidation of CoF2 to Co3O4 even at 300 °C; therefore it is not possible to obtain pure Mg x Co1-x F2 binary fluorides in the presence of air. The preparation of the latter requires reducing conditions, namely thermal treatment of dry precipitate at 300 °C in an atmosphere of hydrogen. If the treatment is conducted at a higher temperature (400 °C), CoF2 undergoes a partial reduction to metallic cobalt. An XPS study has shown the presence of hydroxyl groups in the investigated samples. However, these are solely surface groups because their presence was not detected by XRD measurements. The binary fluorides obtained by our method are characterized by a very narrow optical energy gap (5.31-3.50 eV), considerably narrower than that recorded for bulk fluorides. Measurements of temperature-programmed desorption of ammonia have shown that the incorporation of cobalt cations into the crystal structure of MgF2 results in a decrease in the surface acidity of the binary fluorides.