Karbon destekli tek metalli Pd, Pt ve iki metalli Pd-Pt nanoparçacıkların süperkritik CO2 depozisyon yöntemiyle hazırlanması

Metal nanoparticles supported on high surface area carbon substrates are used extensively as catalysts for a wide variety of reactions. Among these catalysts, carbon supported single Pd and bimetallic Pd-Pt catalysts are commonly used for hydrogenation reactions in the fine chemical industry. In order to prepare carbon supported catalysts, the supercritical fluid deposition technique has recently been receiving increased attention. This process involves the dissolution of an organometallic precursor (OM) in a supercritical fluid and the exposure of the carbon support to the solution. After adsorption of the precursor onto the support, the metallic precursor is converted to its metal form by chemical or thermal reduction. Although many studies have been conducted in order to prepare supported single metallic nanoparticles so far; there are very few studies regarding the preparation of supported bimetallic nanoparticles by scCO2 deposition in the literature.In this thesis the preparation of carbon black (Black Pearl 2000) supported single Pd and Pt nanoparticles by supercritical CO2 deposition was investigated. The scCO2 depostion was utilized also for the preparation of carbon supported bimetallic Pt-Pd by introduing two different deposition alternatives consisting of the preparation starting from the formation of carbon supported platinum (Pt/C) followed by deposition of Pd precursor and reduction; and the simultaneous adsorption and subsequent reduction of the precursors. Palladium (II) acetylacetonate (Pd(acac)2) and dimethyl (cyclooctadiene) platinum (II) (PtMe2COD) were utilized as metallic precursors. The adsorption isotherms of Pd(acac)2 and PtMe2COD on BP2000 in scCO2 at the experimental conditions; 20 MPa and 60 degrees centigrate was determined in order to understand the correlation between the concentration of the OMs in the supercritical phase and the uptake amount of the OMs on the substrate at the given experimental conditions. A mass transfer model was found to represent the experimental data on the kinetics of adsorption of Pd(acac)2 onto BP2000 in scCO2 fairly well with a fitting error of 5.6 %. With the help of the model obtained, the effect or process parameters like the tortuosity and particle size of support and isotherm constants on the adsorption kinetics was investigated. In order to reduce the OMs adsorbed on the substrate, chemical reduction with H2 in scCO2 was utilized. Increasing reduction temperature and metal loading caused an increase in Pd particle size. From the TEM image, it was seen that the Pd particles were irregularly distributed and the size range of the particles was 3-100 nm, whereas Pt nanoparticles were homogeneously distributed with a size range of 2-4 nm. From the TEM image of the supported bimetallic Pt-Pd nanoparticles, it was found that addition of Pt increased the homogeneity and reduced the particle size on the support compared to single Pd nanoparticles. From the EDS results, it was seen that there was a heterogeneous mixture of the bimetallic nanoparticles. Pt-rich nanoparticles had diameters of between 3-5 nm, whereas Pd-rich nanoparticles were larger with diameters of around 10 nm.Keywords: supercritical deposition, carbon, nanoparticles, platinum, palladium, organometallic.