The Study Of Preparation Of Supported Catalysts In The Supercritical Fluid

Catalysis is important in fine chemical industry. There are only a small number of chemistry processed are still conducted without the addition of a catalyst. Supported catalysts are of special interest, for they allow for the dispersion and stabilization of small metallic particles. They provide access to a much large number of catalytically active atoms than in the corresponding bulk metal, even when the latter is ground to a fine powder.Compared with conventional liquid solvents, high diffusivities in supercritical fluids(SCFs) combined with their low viscosities result in enhanced mass-transfer characteristics. Properties of a SCF are different from those of ordinary liquids and gases and tunable simply by changing the pressure and the temperature. The low surface tension of SCFs not only permit better penetration and wetting pores than liquid solvents do, but also avoid the pore collapse which can occur on certain structures such as organic and silica aerogels with liquid solvents. Among the SCFs, supercritical carbon dioxide(scCO2), readily accessible with a Tc of 31℃and a Pc of 7.38 MPa, is particularly attractive since it is abundant, inexpensive, non-flammable, non-toxic, environmentally benign and leaves no residue in the treated medium.Ru/C catalysts was prepared by supercritical fluid deposition, with the precursor of RuCl3·nH2O, which was impregnated into activated carbon in methanol by supercritical fluid method, followed by calcinations and hydrogen reduction. The L9(34) orthogonal test was used to obtain optimum technological parameters. The influencing factors were supercritical temperature,supercritical pressure,the amount of methanol,time of deposition. The catalyst was prepared in 40℃,8 MPa,with 4ml methanol,9 hours depositing time, which have the best catalytic activities in the hydrogenation of glucose.Ru particles was characterized by transmission electron microscope(TEM),X-ray diffraction(XRD), Temperature Programmed Desorption (TPD), Temperature Programmed Reduction(TPR), N2 adsorption-desorption。TEM images show that the Ru particles which was prepared in the optimization dispersed on the surface of carbon uniformly and the size of the Ru particles is in the range of 1-2 nm, Compared with Ru/C catalysts which was prepared in the traditional conditions, TPR results showed that the initial temperature was higher, which indicates that there was strong interaction between the Ru particles and the carbon supports, the diameter of the Ru particles was larger which facilitate the approaching of the glucose and the sorption of the product to the carbon surface.The deposition conditions which influence the catalysts properties were studied separately, such as supercritical temperature,supercritical pressure,the amount of methanol,time of deposition. The initial temperature (TPR) decreased with the increasing depositing temperature, along with the catalytic activities. When the pressure was beyond 8MPa, the initial temperature (TPR) and the catalytic activities decreased with the increasing depositing pressure. The increasing amount of methanol and increasing depositing time were benefit to the catalytic activities.Adsorbed amount of RuCl3 on the supported carbon which was prepared by the supercritical deposition was more than by traditional deposition.along with the supercritical CO2 rised, the amount of RuCl3 on the supported carbon increased significantly,then decreased slowly. When the amount of RuCl3 in the supercritical CO2 was above 0.2g, adsorption model of RuCl3 on the supported carbon basically meet the Freundlich adsorption model by supercritical deposition, the correlation coefficient r=0.952, close to the test level equal to 1% critical value of 0.959. Under the traditional conditions, adsorption model of RuCl3 on the supported carbon was consistant with Langmuir model by traditional deposition, the correlation coefficient r = 0.925, close to the test level is equal to 1% critical value 0.874.A rapid,convenient and environmentally benign method has been developed for the fabrication of metal nanoparticle-multiwall carbon nanotube (MWCNT) composites. Nanoparticles ruthenium are deposited onto MWCNTs of RuCl2·nH2O precursors in supercritical carbon dioxide, followed by calcinations and hydrogen reduction. The catalysts were used in the hydrogenation of the glucose and are characterized by transmission electron microscopy. These highly dispersed nanoparticles, with a narrow range of size distribution and good adhesion on MWCNT surfaces, exhibited promising catalytic properties for a hydrogenation of the glucose reactions.