Impregnation, metal deposition

Fig. 6.5 Syntheses of metal loaded nanoparticles (Au) on metal oxide supports using impregnation, coprecipitation, deposition-precipitation, and photo-deposition methods. For Pt loaded nanoparticles H2PtCl6 (aq) is used.

Che et al. also prepared Pt/Ru nanoparticle-filled carbon tubes with a diameter of 200 nm (40). They impregnated carbon-deposited film with a mixture of aqueous solutions of HiPtClf, and RuCI3. After drying in air, the metal compounds in the pores were reduced by H2 flowing at 580°C for 3 h. Then the underlying alumina was dissolved away in HF solution. TEM observation of this sample revealed the presence of Pt/Ru nanoparticles (about 1.6 nm) dispersed on the inner wall of the tubes. 

Preparation and characterization of the metal deposits. Pt deposit was made by impregnation with PtClg and reduction in H2at 753 K. The Pt particle size distribution was determined by transmission electron microscopy (TEM) (8, 9 ) (Figure 3) and H2, O2 chemisorptions and titrations (43). The Pt particle size distribution was narrow with a surface weighted mean diameter of ca. 2 mn, almost independent of the Pt content between 0.5 and 10 wt (9 ), provided the preparation method, which includes a treatment in O2 before the reduction, was thoroughly followed. 

The use of various methods (coprecipitation, impregnation and deposition-precipitation) confirmed the superiority of the transition metal oxides as supports,69 these being more easily reducible than the ceramic oxides that gave low activities (Table 6.6). With mixed Fe2C>3-MgO supports activity increased with iron content, not withstanding a growth in gold particles size.69... 

Known amounts of salt(s) of catalytic metals are dissolved in aqueous solutions and impregnated into carrier materials. The wet mass is dried at 110°C and calcined in air at 300-500°C, releasing the decomposable salt components and depositing the metal oxide on the surface within the depths of the porous carrier. For many oxidation reactions the catalyst is now ready for use but for hydrogenation it is necessary to reduce the impregnated metal oxide or salt chemically. Usually this is accomplished by flowing H2, under conditions consistent with the maximum temperature of use for the reaction of interest. 

Palladium can be deposited at low reduction temperatures on alumina or silica supports, either from the gas phase by ALE or from a solution by impregnation methods, using Pd(thd)2 as precursor , as was described for ruthenium in Section lV.B.2.b. During ALE the precursor reacted to yield mainly metallic Pd, whereas on alumina only a small part of the impregnated metal source probably was dissociatively adsorbed yielding Pd(0). Associate adsorption describes the interaction of Pd(thd)2 with the alumina and... 

Usually improvement combustion processing or after combustion treatment are used nowadays for NO reduction. However, they are some problems as like a complex, expensive setup, harmness gas emission, and corrosion metal. In recent years, to overcome these problems, some researchers have reported that NO is reduced more effectively use of the adsorption characteristics of activated carbons (ACs) and activated carbon fibers (ACFs) [6-8]. Also, some researchers are studying for NO reduction using metal supported ACs and ACFs by impregnation, metal plating, deposition, and so on [9-13]. However, metal supporting methods on ACs and ACFs in a second and their NO removal efficiency are not studied yet systematically. 

In the case of vapour-phase processes for metal deposition on the support, only limited control of dispersion and distribution of the metal crystallites is possible. In the case of liquid-phase systems, they do not provide as wide a range of catalysts as is possible with techniques based on adsorption from solution. However, the technique does provide a means of preparing well characterized surface-impregnated supports. 

Two procedures for metal introduction in chitosan base were used impregnation and coprecipitation. According to the first procedure the metal deposition on chitosan micro beads was carried out from aqueous and alcohol solutions of NazPdCU, HzPdCU, RhCb, Rh2(CH3COO)4, ZnS04 and Pb(CH3COO)2. Pd and Pb/Zn in bimetallic catalysts was deposited by subsequent precipitation. Pd-Pb (Zn) atomic ratios were 1/1. Metal contents in the resulting samples were 0.5 - 4%. 

In general, activities of chitosan based catalysts prepared by impregnation method in hydrogenation of unsaturated organic compounds were comparable with those of traditional heterogeneous catalyst (as calculated per 1 mole of metal). It should be noted that the chitosan pretreatment influenced very much the catalyst activity. For instance, immediate Pd deposition from alcohol solution on dry chitosan fibers or micro beads led to almost completely inactive catalytic systems, regardless of the metal content. On the other hand, metal deposition on chitosan micro beads or fibers preliminary swollen in water dramatically improved the catalytic activity. 

When a modification either during the synthesis or by post synthesis procedure has been performed the first question which everyone is asking himself is to determine if the modifier element has been incorporated in the lattice framework at the lattice position or at cationic sites location (exchangeable sites for instance) or at last entrapped in the cavities or pores as tiny clusters or metallic oxide particles or even metallic oxide crystallites as impregnated or deposited near the zeolitic crystallites. 

Thus, if impregnation leaves metal deposited over the same fraction of external and internal surfaces of the support, a 0.1-cm particle with Sg = 300m /g would have 99.999% of the metal on internal surfaces. 

It is also possible to prepare catalysts by contacting the support with a suspension in which the precursor is not totally dissolved ( slurry or solvent-assisted spreading ) [54, 55). The equihbrium of dissolution is shifted by the adsorption of the precursor on the support surface, which depletes progressively the Kquid phase from the dissolved ions. Molybdenum-containing catalysts have been prepared from M0O3 by this method, with high yields in metal deposition [55]. Thanks to their viscosity, slurries are also convenient to impregnate foams [56]. 

In this work the formation of nickel, cobalt or zinc aluminum hydrotalcite-type coprecipitates upon impregnation of y-alumina at near neutral pH and ambient temperature was confirmed by EXAFS and X-ray dif action. The role of the metal ion concentration in solution on the composition of the supported coprecipitate was studied as well as the influence of the specific surface area of the Y-alumina. The deposition of Co(II), Ni(II) and Zn(II) ions onto a commercial almnina was first investigated. Since the coprecipitation mechanism is likely to be affected both by the impurity level and the thermal pretreatment of the carriers before impregnation, supports of high purity were prepared by hydrolysis of aluminum alkoxides and were submitted to identical pretratments immediately before impregnation. The deposition of Ni(ll) onto these supports was then examined. 

Impregnation. The polymer or solid electrolyte membrane is inunersed in a solution of a suitable compound of the metal to be deposited and is saturated with the solution the saturation can be accelerated for Nation by adding methanol to the solution. The membrane is then immmed, one or both sides, in a solution of a strong reductant so the metal deposits where the reductant is placed. The procedure can be repeated to obtain a thicker metal film. 

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