Impregnation adsorption from solution

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. 

The support, zirconia (ISA), was supplied by the Norton Company. The oxide was grounded and sieved to a particle size ranged from 0.16 to 0.25 mm, and calcined at 773 K. Its surface properties, 63.3 m g of specific surface and average pore diameter of 8.60 nm, were determined from the nitrogen adsorption isotherms. The catalysts were prepared by adsorption from solution and/or impregnation of precursor(s), ruthenium nitrosyl nitrate (Alfa) and hexachloroplatinic acid (Aldrich), onto the support. Being zirconia isoelectric point 6.5 (determined by electrophoresis [17] using a Malvern Instrument Zetasizer 4) the precursors solution pH value was kept sufficiently low to enable the desired adsorption of complex metal anions. 

The interactions between the sohd support and the IL have a strong influence on the resulting properties of the system (e.g., on ionic mobility) these properties can be also affected by several factors including the way the sample is prepared (adsorption from solution [76, 77], incipient wetness impregnation (IWI) method. 

Figure 19.10 Influence of the loading procedure on the release of [P Jflbu] at 20% loading in PBS (pH 7.4) adsorption from solution (blue) and incipient wetness impregnation (red).

In industrial applications activated carbons are used as supports for precious metal and metal oxide catalysts. These catalysts can be prepared by adsorption from solution, impregnation, precipitation and other techniques as gas phase deposition [4]. The most common way of preparation is adsorption and impregnation by bringing the activated carbon in contact with a solution of the desired metal compound or with a solution of a metal precursor, in most times a complex salt. Then the impregnated activated carbon is dried. Reduction is carried out when the metal precursor has to be transformed in the metal. Important quality criteria are ... 

When a carrier is impregnated with a solution, where the catalyst deposits will depend on the rate of diffusion and the rate of adsorption on the carrier. Many studies have been made of Pt deposition from chloroplatinic acid (HgPtClg) with a variety of acids and salts as coim-pregnants. HCl results in uniform deposition of Pt. Citric or oxalic acid drive the Pt to the interior. HF coimpregnant produces an egg white profile. Photographs show such varied distributions in a single pellet. 

It is of special interest for many applications to consider adsorption of fiuids in matrices in the framework of models which include electrostatic forces. These systems are relevant, for example, to colloidal chemistry. On the other hand, electrodes made of specially treated carbon particles and impregnated by electrolyte solutions are very promising devices for practical applications. Only a few attempts have been undertaken to solve models with electrostatic forces, those have been restricted, moreover, to ionic fiuids with Coulomb interactions. We would hke to mention in advance that it is clear, at present, how to obtain the structural properties of ionic fiuids adsorbed in disordered charged matrices. Other systems with higher-order multipole interactions have not been studied so far. Thermodynamics of these systems, and, in particular, peculiarities of phase transitions, is the issue which is practically unsolved, in spite of its great importance. This part of our chapter is based on recent works from our laboratory [37,38]. 

In this paper we report (i) the catalytic activity for SCR of VOx/Zr02 samples prepared by various methods (adsorption from aqueous metavanadate solutions at different pH values, dry impregnation, and adsorption from VO(acetylacetonate)2 in toluene), (ii) sample characterization (nuclearity, dispersion and oxidation state) by means of XPS, ESR and FTIR and (iii) the nature and reactivity of the surface species observed in the presence of the reactant mixture. Catalytic results are here reported in full. Characterization data relevant to the discussion of the catalytic activity will be given, whereas details on the catalysts preparation and... 

VOx/ZrOz samples were prepared by three methods (i) adsorption from a solution of ammonium metavanadate (AV) at pH values from 1 to 4, adjusted by nitric acid, (ii) dry impregnation with AV solutions and (iii) adsorption from a solution of VO(acetylacetonate)2 in toluene. 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

Comparing n-hexane adsorption on US-69 and modified zeolites is possible to mark, that internal adsorption volume of a sample prepared by impregnation by a solution of acids (BP-US-69 (2)) has decreased insignificantly, and its share has made 0.91-0.95 in relation to starting zeolite. On data of n-hexane adsorption available volume for molecules has made 0.8 from the value for US-69 for BP-US-69 (1) modified by reagent vapors. 

Different synthetic approaches have been described for the formation of zeolite inclusion compounds, including direct adsorption, impregnation, ion-exchange from solutions or solid-state ion-exchange, ship-in-the-bottle synthesis, formation of large molecules (e.g., by polymerization reactions), and zeolite synthesis around the metal complex. Some examples of these approaches are given in the next sections. 

The spectrum of a non-calcined solid impregnated with AHM and PA solution (P/Mo=0.4) is similar to that of AHM which indicates that, during adsorption, the PjMojOjs species depolymerizes. With respect to the non-calcined solids impregnated with FK solutions in different solvents, the spectra show that, for the adsorption from E-W and DMF, the FK species are present. However, in samples obtained from aqueous solutions, this phase appears to be degraded. It has to be point out that conclusions arrived at coincide with those obtained from both NMR and adsorption isotherm smdies. 

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