Highly Porous Para-Aramid Aerogel as a Heterogeneous Catalyst for Selective Hydrogenation of Unsaturated Organic Compounds.

A new para-aramid aerogel based on a polymer made by the reaction of terephthaloyl dichloride with 2-(4-aminophenyl)-1H-benzimidazol-5-amine (PABI) is introduced. The aerogel readily bound Pd (+2) ions and was used as a hydrogenation catalyst in some industrially actual reactions. The new material, which did not contain p-phenylenediamine moieties, was prepared in two form factors: bulk samples and spherical pellets of 700-900 µm in diameter. Aerogels were synthesized from 1% or 5% solutions of PABI in N,N-dimethylacetamide via gelation with acetone or isopropanol and had a density of 0.057 or 0.375 g/cm3 depending on the concentration of the starting PABI solution. The specific surface area of the obtained samples was 470 or 320 m2/g. Spherical pellets containing Pd were prepared from a solution of PdCl2 in PABI and were used as heterogeneous catalysts for the gas-phase hydrogenation of unsaturated organic compounds presenting the main types of industrially important substrates: olefins, acetylenes, aromatics, carbonyls, and nitriles. Catalytic hydrogenation of gaseous hexene-1, hexyne-3, cyclohexene, and acrylonitrile C=C bond proceeded with a 99% conversion at ambient pressure, but the catalyst failed to reduce acetone at 150 °C and benzene and ethyl acetate even at 200 °C. The only product of acrylonitrile hydrogenation was propionitrile. The prepared catalysts showed high selectivity, which is important for the chemistry of complex organic compounds.

NiO-Based Aerogels-Unexpected Formation of Metallic Nickel Nanoparticles during Supercritical Drying Process.

The aim of the study is to investigate the influence of the solvents applied both in sol-gel process and for supercritical drying (SCD) on NiO aerogels' properties. NiO aerogels were synthesized using methanol and 2-methoxy-ethanol (MeGl) as sol solvents. SCD was performed using iso-propanol, methanol and tert-butyl-methyl ether as supercritical fluids. The obtained samples were characterized using low-temperature nitrogen adsorption, X-ray diffraction analysis, mass-spectra analysis and STEM and TEM methods. It was found that specific surface area and the phase and chemical composition strongly depend on the synthesis conditions. We revealed that Ni2+ cations were reduced into Ni0 when 2-methoxy-ethanol was applied as a sol solvent. The mechanism of the Ni2+ cations reduction is proposed. We consider that at the stage of sol preparation, the Ni2+-MeGl chelate was formed. This chelate decomposes at the SCD stage with the release of MeGl, which, in turn, eliminates methanol and leads to the formation of aldehyde. The latter is responsible for the nickel reduction. The proposed mechanism was confirmed experimentally.

Electrochemical Properties of Carbon Aerogel Electrodes: Dependence on Synthesis Temperature.

A series of carbon aerogels (C-AGs) were prepared by the pyrolysis of resorcinol-formaldehyde aerogels at 700-1100 °C as potential supercapacitor electrodes, and their texture and electrochemical properties were determined. The specific surface area of all C-AGs was in the range of 700-760 m2/g, their electron conductivity increased linearly from 0.4 to 4.46 S/cm with an increase of the pyrolysis temperature. The specific capacitance of electrode material based on C-AGs reached 100 F/g in sulfuric acid and could be realized at a 2 A/g charge-discharge current, which makes it possible to use carbon aerogels as electrode materials.