Liquid-phase reductive deposition

Liquid-Phase Reductive Deposition of Metal Nanoclusters Selective onto Oxide Surfaces... 

Recently, Soria et al. [109] also investigated the effect of synthesis method on the WGS activity of Au/Fc203 catalysts. They prepared catalysts by deposition-precipitation method, liquid phase reductive depositions and double impregnation method. Among the various catalysts, the catalyst synthesized by deposition-precipitation method exhibits higher CO conversion. 

Liquid-phase reductive deposition as a novel nanoparticle synthesis method and its application to supported noble metal catalyst preparation, Y. Sunagawa, K. Yamamoto, H. Takahashi, and A. Muramatsu, Catal Today, 2008,132, 81. 

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

The liquid-phase reduction method was applied to the preparation of the supported catalyst [27]. Virtually, Muramatsu et al. reported the controlled formation of ultrafine Ni particles on hematite particles with different shapes. The Ni particles were selectively deposited on these hematite particles by the liquid-phase reduction with NaBFl4. For the concrete manner, see the following process. Nickel acetylacetonate (Ni(AA)2) and zinc acetylacetonate (Zn(AA)2) were codissolved in 40 ml of 2-propanol with a Zn/Ni ratio of 0-1.0, where the concentration of Ni was 5.0 X lO mol/dm. 0.125 g of Ti02... 

Precipitation or coprecipitation methods are also often used. Suh et al. [40] analyzed the effect of the oxygen surface functionalities of carbon supports on the properties of Pd/C catalysts prepared by the alkali-assisted precipitation of palladium chloride on carbon supports, followed by liquid-phase reduction of the hydrolyzed salt with a saturated solution of formaldehyde. They observed that the metal dispersion increased with increasing amount of oxygen surface groups. Nitta et al. [41] also used a deposition-precipitation method, with sodium carbonate and cobalt chloride or nitrate, to prepare carbon-supported Co catalysts for the selective hydrogenation of acrolein. 

The second processing step consisted of salt decomposition with the subsequent reduction to pure metal. The method of chemical deposition of metal salts from the water salt solution with the subsequent reduction to pure metal by liquid phase reducer has been applied to prepare graphite-tin CMs. In this case tin chloride was used for impregnation and potassium tetrahydroborate was used as liquid phase reducer. 

The liquid-phase hydrogenation of various terminal and internal alkynes under mild conditions was largely described with metal nanoparticles deposited/in-corporated in inorganic materials [83, 84], although several examples of selective reduction achieved by stabilized palladium, platinum or rhodium colloids have been reported in the literature. 

A photoinduced electron relay system at solid-liquid interface is constructed also by utilizing polymer pendant Ru(bpy)2 +. The irradiation of a mixture of EDTA and water-insoluble polymer complex (Ru(PSt-bpy)(bpy) +, prepared by Eq. (15)) deposited as solid phase in methanol containing MV2+ induced MV 7 formation in the liquid phase 9). The rate of MV formation was 4 pM min-1. As shown in Fig. 14, photoinduced electron transfer occurs from EDTA in the solid to MV2+ in the liquid via Ru(bpy)2 +. The protons and Pt catalyst in the liquid phase brought about H2 evolution. One hour s irradiation of the system gave 9.32 pi H2 after standing 12 h and the turnover number of the Ru complex was 7.6 under this condition. The apparent rate constant of the electron transfer from Ru(bpy)2+ in the solid phase to MV2 + in the liquid was estimated to be higher than that of the entire solution system. The photochemical reduction and oxidation products, i.e., H2 and EDTAox were thus formed separately in different phases. Photoinduced electron relay did not occur in the system where a film of polymer pendant Ru complex separates two aqueous phases of EDTA and MV2 9) (see Fig. 15c). 

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