A comparative study of the performance of Pt/MgF2, Ir/MgF2 and Ru/MgF2 catalysts in hydrogenation reactions

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.

Antioxidant, Antimicrobial, and Photocatalytic Potential of Cobalt Fluoride (CoF2) Nanoparticles

Herein, CoF2 nanoparticles (NPs) are prepared by simple coprecipitation method and are characterized by various techniques, i.e., XRD, SEM/EDX, FTIR, and UV/Vis, for their structure identification. As-prepared nanostructures were used as photocatalyst, as antioxidant, and as antimicrobial agent. The degradation studies of the prepared samples were carried out for specific time for the degradation of methylene blue (MLB) dye under a UV/visible spectrophotometer to determine decolorization and change in concentration of MLB with respect to time. The antibacterial activity against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) was measured by well diffusion and serial dilution method to determine their efficiency against these two bacteria, through a dose-dependent method. The antibacterial activity was further confirmed against the experimental bacteria through calculation of minimum inhibition concentration (MIC). The antioxidant activity (radical scavenging activity) of the prepared CoF2 NPs was also assessed.

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.

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.

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_xCo_1−xF₂ 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_xCo_1−xF₂ 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_xCo_1−xF₂ 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.

Results of the first research on structural and surface properties of binary fluorides MgF₂–CoF₂ are presented.