Preparation And Characterization Of Carbon Nanotubes Supported Palladium And Ruthenium Nanoparticles

Compared with other carbon materials and traditional catalyst carriers, carbon nanotubes has unique physical and chemical properties, such as excellent conductivity and chemical stability. The current problem is how to improve hydrophobicity of carbon nanotubes and the dispersion of the load of precious metal nanoparticles,which is closely related to the catalytic activity. In this paper, we attempted to modify carbon nanotubes by several methods, and synthesized the controllable precious metal nanoparticles, and set the control experiment to explore the best method of loading precious metal nanoparticles on carbon nanotubes. At last, the acitivity of CNTs catalysts were tested by hydrogenation of p-chloronitrobenzene under mild conditions.The main findings are summarized as follows:The carbon nanotubes were pretreated by H2SO4-HNO3 and HNO3 respectively in high tempurature. From infrared characterization, we found that CNTs with two pretreatment were both chemically modified. The oxygen-containing functional groups such as hydroxyl group and carboxyl group were successfully introduced,which is useful to improve hydrophobicity, while providing the anchor position for the precious metal particles's loading. The latter pretreatment had a certain impact on the structure of carbon nanotubes, and increased the surface area and pore volunme while provided a new location to load the precious metal nanoparticle.Pd/CNTs and Ru/CNTs nanocatalyst was prepared by pretreatment of carbon nanotubes (CNTs) followed with liquid phase reduction method. The small size Pd and Ru nanoparticles (particle sizes of 5 nm and 2 nm, respectively) were synthesized by reduction of ethylene glycol and sodium borohydride solution, respectively. We also prepared catalsys loading the same active components (7 nm and 5 nm in particle size) by calcination reduction on different pretreated carbon nanotubes.The catalyst was characterized by XRD, TEM, BET, Raman spectra, ICP and gas chromatography method. The results showed that the average loading of palladium and ruthenium on CNTs catalyst was 0.95% (1% theoretical loading), palladium and ruthenium nanoparticles highly dispersed on the surface of CNTs. The catalysts were used for selective hydrogenation of chloronitrobenzene, and the Pd/CNTs hydrogenation conversion was 94.7% and the selectivity was 89.2%, the Ru/CNTs hydrogenation conversion was 96.6% and the selectivity was 74.2%. After recycling 5 times, the conversion rate and selectivity decreased slightly. By comparison, we found the catalyst prepared by HNO3 pretreatment and liquid phase reduction method shows higher catalytic performances in selective hydrogenation of chloronitrobenzene.