Catalytic and kinetic studies of transition metal nanoparticles and reducible mesoporous transition metal oxide materials

Ph.D. (Chemistry)Abstract: The use of dendrimers as a template or stabilizer to synthesize stable and well-dispersed metal nanoparticles is a promising synthetic route. Dendrimers are three-dimensional polymers, which prevent Ostwald ripening of the metal nanoparticles. The dendrimer is an exceptional template for the synthesis of very small metal nanoparticles with dimensions in the range of 1-5 nm and large surface areas. For catalytic purposes, the large surface area of metal nanoparticles is beneficial for interfacial interactions. In our investigation, hydroxide-terminated dendrimers were applied as template for monometallic and bimetallic nanoparticles. All the colloidal metal nanoparticles were encapsulated inside the dendritic cavities and evaluated as nanocatalysts. Bimetallic nanoparticles were found to exhibit much higher catalytic activity compared to the monometallic nanoparticles. Thus, the synthesis of palladium-gold bimetallic nanoparticles was conducted in the presence of dendrimers as templates. Following the co-complexation method, bimetallic nanoparticles were synthesized which resulted in the formation of randomly dispersed alloy nanoparticles. A series of palladium-gold bimetallic nanoparticles were synthesized and their sizes were estimated in the range of 2-4 nm. The TEM analysis displayed well-dispersed spherical nanoparticles. The composition of the nano catalysts were quantified by ICP-OES analysis and their lifetime was estimated to more than two months. The synthesis of mesoporous metal oxide materials was conducted by adapting an inverse micelle sol-gel approach. The following mesoporous metal oxide materials were synthesized: SiO2, Fe2O3, MnO2, Co3O4, NiO, and CeO2. The final calcination temperature for all mesoporous metal oxide materials was 450 ºC for a total time of 2 hours. Some physicochemical techniques such as BET, XRD, and TPR were applied to study the porosity, crystallinity, and reducibility of each mesoporous materials, respectively. The results unveiled that all the mesoporous metal oxide materials were porous and JSCD number matched to the corresponding metal oxide crystallinity. All mesoporous metal oxide materials were reducible, which indicated the mobility of lattice oxygen. The mesoporous metal oxide materials served as supports to facilitate the recovery and reusability of the soluble nanocatalysts..