Preparation Of Rhodium Nanoparticle Catalysts For Hydrogenation Applications

Along with the advent and development of nanoscience, the preparation and application of nanoparticles have been widely studied, and catalysis is one of the most important applications. Therefore, nanoparticle catalyst has been developed as a new kind of catalysts. On one hand, noble metal nanoparticles can be stabilized by stabilizers such as surfactants or polymers to be soluble nanoparticle catalysts; on the other hand, noble metal nanopartilces can also be supported on inorganic supports to be supported nanoparticle catalysts. Thus, nanoparticle catalysts involve both homogeneous and heterogeneous catalysts, and these catalysts are vividly called as "semi-homogeneous catalysts". In this dissertation, rhodium (Rh) nanoparticle catalysts with different structures and characteristics were prepared by different methods such as sonication, microwave-assisted reduction, and electrospinning, and were applied in the hydrogenation of alkenes and nitrile butadiene rubber (NBR). This dissertation consists of the following five parts:1. A water soluble poly (ethylene oxide)-block-poly (acrylic acid)-Rh (PEO-b-PAA-Rh) nanoparticle catalyst was prepared by microwave-assisted hydrothermal method with a double hydrophilic block copolymer PEO-b-PAA as stabilizer and L-ascorbic acid as reductant. The prepared PEO-b-PAA-Rh nanoparticle catalyst was characterized by XPS, XRD, TEM, EDS, and ICP-MS. The results indicate that the PEO-b-PAA-Rh nanoparticles were spherical with a mean size of about 27 nm. The PEO-b-PAA-Rh nanoparticle catalyst was applied in the hydrogenation of alkenes with different structures and exhibited excellent catalytic activity at room temperature. The catalyst was easy to be separated from the product, and the activity of the catalyst increased with the increase of the hydrogenation temperature. The PEO-b-PAA-Rh nanoparticles were also prepared at different temperatures. The size of the PEO-b-PAA-Rh nanoparticles decreased with the increase of temperature, and the catalytic activity of the PEO-b-PAA-Rh nanoparticles decreased with the decrease of the size of the PEO-b-PAA-Rh nanoparticles.2. A Rh-SiO2 fiber catalyst was prepared by electrospinning, calcination, and reduction in that order. The as-prepared Rh-SiO2 fiber catalyst was applied in the catalytic hydrogenation of alkenes. This catalyst allowed the hydrogenation reaction to be carried out at room temperature with excellent catalytic activity and could be reused nine times without obvious loss of catalytic activity. The excellent mechanical strength, thermal stability, and chemical stability of SiO2 and the uniform dispersion of the Rh nanoparticles in the fibers are the reasons for the superior activity and reusability of the catalyst.3. For the first time, a carbon-nanotubes (CNTs)-supported Rh nanoparticle catalyst was prepared by sequential sonication-assisted liquid phase exfoliation of multi-walled CNTs (MWCNTs) in the presence of polyvinylpyrrolidone (PVP), followed by microwave-assisted hydrothermal reduction of the supported Rh. The as-prepared Rh-PVP-MWCNT catalyst was applied in the selective hydrogenation of NBR. The catalyst exhibited excellent activity even at room temperature and can be easily separated from the product.4. Rh nanoparticles were prepared by microwave-assisted hydrothermal method and applied in the hydrogenation of NBR for the first time. The as-prepared Rh nanoparticles allowed the hydrogenation reaction to be carried out at 50℃ with excellent activity and can be easily separated from the product. A negative size effect was observed for the catalytic activity of the Rh nanoparticles, suggesting that the hydrogenation of NBR takes place at face atoms (C8 and C9) of Rh nanoparticles, and the size dependent chemical composition of the Rh nanoparticles also contributes to the negative size effect of the catalytic activity of the Rh nanoparticles. The temperature of microwave-assisted hydrothermal reduction has no obvious influence on the size of Rh nanoparticles while the content of the inactive Rh+3 decreases with the increase of the reduction temperature, leading to the increase of catalytic activity of the Rh nanoparticles with the increase of reduction temperature.5. A polyurethane elastomer (PUE) with hydrogenated hydroxy-terminated butadiene-acrylonitrile copolymer (HHTBN) as soft segments and 2,4-tolylene diisocyanate (TDI) and 3,5-dimethylthio-2,4-toluenediamine (DMTDA) as hard segments was synthesized by casting method. The HHTBN-based PUEs exhibited better mechanical properties, thermal oxidative and ozone aging resistance than those of the HTBN-based PUEs. The results show that hydrogenation modification is an effective method to prepare HHTBN-based PUEs, expanding the applications of PUEs.