Deposition-Reduction DR

The deposition-reduction (DR) method is based on the weak electrostatic interactions of polymer surfaces with the oppositely charged Au(III) complex ions, leading to the reduction of Au(III) exclusively on the polymer surfaces. Appropriate anionic or cationic Au(III) precursors are chosen based on the zeta potentials of polymer supports (Figure 3.6) [43]. 

Figure 3.6 Schematic representation of deposition-reduction (DR) method (a) positiveiy charged supports and (b) negativeiy charged supports.

Highly active Au catalysts can be prepared by an appropriate selection of preparation methods such as co-precipitation (CP), deposition-precipitation (DP), deposition-reduction (DR) and solid grinding (SG) with dimethyl Au(III) acetylacetonate, depending on the kind of support materials and reactions targeted. 

The deposition reduction (DR) method was used in an initial attempt to deposit nanogold on the surfaces of BP a solution of HAUCI4 in methanol was added to a turbid solution of BP in methanol, followed by filtration, dispersion in methanol, and reduction with NaBH4. However, nanogold was not deposited on the surface. The zeta potential of the support is negative (-33.24 mV), so AuCl4 hardly binds to the surface. To overcome this difficulty, we used polyethyleneimine (PEI) as a binder for nanogold deposition. ... 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Thermal analysis of CA-containing catalysts (not shown) revealed that CA decomposition occnrs at about 200°C. Powder XRD patterns of NiMo and NiMoCA catalysts did not show the presence of any crystalline phase, pointing out a good dispersion of the deposited metal oxide species in all samples. However, DRS and TPR characterization resnlts (Figs. 3 and 4) indicate that, as expected, citric add addition increased the dispersion of oxidic Mo species on SBA-15 surface and made their reduction much easier and more complete. The dispersion of sulfided M0S2 particles was also improved by CA addition (Table 2). 

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