Papers by Keyword: Hydrogenation

Abstract: Hydrogenation of CO₂ provides an alternative route for methanol production and attractive option for CO₂ utilization. The present work investigates the synthesis of Cu-based catalyst on mesoporous silica (SBA-15) and promotion of the Cu-based catalyst with niobium (Nb). The addition of Nb promoter enhanced the reducibility and dispersion of the active sites as well as increased the BET and Cu surface areas. The performance of the synthesized catalyst in the hydrogenation of CO₂ was evaluated in a fixed-bed microreactor at 523K, 22.5bar and H₂/CO₂ of 3. The CO₂ conversion using the Cu/ZnO/SBA-15 catalyst was 14.2 % and increased to 17.1% on the Nb-promoted catalyst. The yield of methanol obtained using the un-promoted Cu-based catalyst was 51.4 g/h.gcat and it increased to 143 g/h.gcat over the Nb-promoted catalyst.

Abstract: Organic modification and surface functionalization of nanomaterials offers wide spectrum of materials which can be employed for several applications. Using this tool we have developed high performance recyclable nanocatalysts for several reactions such as transesterification, hydrogenation and oxidation. Using magnetic nanoparticles as a core, a few magnetically recoverable nanomaterials were also prepared. With suitable modifications these materials could be utilised for asymmetric synthesis as well as for drug delivery. Due to their interaction with magnetic field such hybrid nanomaterials can provide a strong platform for magnetic tumor targeting.

Abstract: In the paper catalytic hydrogenation of natural bitumen (NB) of Kazakhstan oil sands were investigated. The process provided under 350 bar of H₂ pressure and a temperature of 430 °C. At the experiment activated carbon supported catalyst was used. It has 699.807 m²/g of surface area and 0.0635 nm of medium pore size. In the processes the yield of hydrogenated natural bitumen was 91%, including 1st fraction is 13.12 wt.%; yield of 2nd fraction increased, that the temperature range from 216 to 316 °С formed in amount of 45.68 wt.%; vacuum residue of the distillation takes the 41.20 wt.% in natural bitumen.

Abstract: This paper presents the results of a defect structure investigation in commercially pure titanium alloy after hydrogen charging in a gaseous atmosphere at the temperature of 873 K up to the concentration of 5.1 at. %. Structure of samples was studied by positron lifetime, Doppler broadening and X-ray diffraction spectrometry. Several processes, corresponding to the different ranges of hydrogen concentrations were revealed. It was shown that hydrogen, penetrating in the material, expands its crystal lattice, initiates formation of vacancy-like defects of different dimensions and reacts with the last ones, forming the defect-hydrogen complexes.

Abstract: Silicene is a two-dimensional (2D) allotrope of silicon known to have a lower thermal conductivity than graphene; thus, more suitable for thermoelectric applications. This paper investigates the effect of hydrogenation on the thermal conductivity of silicene nanoribbon (SiNR) using equilibrium molecular dynamics (EMD) simulations. The simulations were carried out in Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) using a modified Tersoff potential that considers both Si-Si and Si-H interactions. The thermal conductivity of fully hydrogenated silicene nanoribbon (H-SiNR), also known as silicane nanoribbon, was found to be higher than that of pristine SiNR in all the temperatures and dimensions considered here. This anomalous enhancement in the thermal conductivity is similar to that found in hydrogenated silicon nanowires (H-SiNWs). A mechanism for this anomalous effect has been proposed relating the hydrogenation of SiNR with the stiffening and increase of the acoustic out-of-plane flexural (ZA) phonon modes. Also, for both SiNR and H-SiNR, the thermal conductivities generally increase as the dimensions are increased while they generally decrease as the temperatures are increased, in agreement to other reports.

Abstract: Two different polycarbosilane (PCS) fibers were prepared by a new oxygen-free curing method and Chemical Vapor Curing (CVC), respectively. Nearly stoichiometric SiC fiber was prepared via hydrogenation in H₂-N₂ mixture and subsequent sintering in inert gases. The green PCS fiber and nearly stoichiometric SiC fiber were characterized by FT-IR, XRD, SEM etc. Meanwhile, the effect of hydrogenation on the thermal stability of SiC fibres cured by CVC method was studied. It was found that the oxygen-free curing method can effectively decrease the content of oxygen in the final SiC fiber, while the hydrogenation treatment can dramatically diminish the content of free carbon, so the nearly stoichiometric SiC fiber with C/Si atomic ratio being 1.06 can be obtained. After the heat-treated at 1600°C in inert gases, the strength retaining ratio of the oxygen-free cured SiC achieved 68%, demonstrating that the nearly stoichiometric SiC fiber possesses excellent high-temperature stability and higher anti-oxidation property.

Abstract: With Raney nickel catalyst and aniline solvent, the reaction kinetics of catalytic hydrogenation of isophthalonitrile (IPN) for meta-xylenediamine (MXDA) preparation is studied in this paper. The experiment is conducted in a 1L büchiglas high-pressure hydrogenation reactor under the condition of the reaction temperature (100°C) and the reaction pressure (35 bar). The results shows that the kinetics equation proposed in this paper can be used to predict the response speed of IPN accurately.

Abstract: The study demonstrated that implementation of eddy currents of different frequencies enables identification of altered phase composition, diffusion properties and metal hydrogenation extent. Using the newly developed parameters of eddy current method sensitivity, we have established that the change of a metal structure from one layer to another is identified by the currents of different frequency according to the depth of their penetration into a metal.

Abstract: Ti-13Nb-13Zr alloy produced via powder metallurgy was submitted to heat treatment under various conditions and the effects on microstructure and elastic modulus were investigated. Heat treatment was performed using temperatures above and below α/β transus combined with different cooling rates – furnace cooling and water quenching. Microstructure and phases were analyzed employing scanning electron microscopy and X-ray diffraction. Elastic Modulus was determined using a dynamic mechanical analyzer (DMA). The results indicated that α phase precipitation and elastic modulus values increased after heat treatment performed using temperature below α/β transus. However, when it was performed above α/β transus and using higher cooling rate, a decrease in elastic modulus was observed despite higher α phase precipitation, indicating that the microstructural modifications observed via SEM, due to the presence of martensitic α phase, influenced on elastic modulus values.

Abstract: The research of recycling Ti-6Al-4V alloy industry scrap is conducting by hydrogenation and hydride sintering process. The Ti-6Al-4V alloy scrap was submitted to a activation treatment under vacuum atmosphere and hydrogenation process under pure H₂ gas, the hydrogenated product was attained. Sintering process used hydrogenated titanium alloy powder as a feedstock material. The oxygen content of raw scrap, hydrogenated Ti-6Al-4V alloy powder and as-sintered Ti-6Al-4V alloy was 0.107%, 0.256% and 0.117%, respectively. Compression and Vickers hardness tests were conducted on the as-received and as-sintered Ti-6Al-4V alloy to evaluate their mechanical properties.