Deposition methods impregnation

Many examples can be found in the literature on this point. The reducibility of vanadia catalysts has catalytic implications for selective oxidation reactions where they found real use. The support nature and the preparation method affect the reducibility of the vanadia phase. In Ref. [19] pure titania or bilayered titania/silica supports were chosen and concerning the vanadia deposition method, impregnation and atomic layer deposition procedures were performed. The reducibility of vanadia improved with increasing titania loading as shown by the calculated AOS. The lowest AOS were associated to vanadia on pure titania supports (Uox.av = 3.5) while vanadia on titania-silica supports achieved at maximum nox.av of 3.7-3.S. AOS of vanadium after reduction was independent of the preparation method. 

VOx supported on TiOi showed good catalytic activity in the selective oxidation of H2S to ammonium thiosulfate and elemental sulfur. V0x/Ti02 catalysts prepared by the precipitation-deposition method can achieve higher vanadium dispersions, and higher H2S conversions compared to those prepared by the impregnation method. 

In order to combine the catalytic activity of highly dispersed metal species and that of zeolites, metals can be deposited in the pores and on the external surface of zeolite particles. In this way, a catalyst is formed with both a metal functionality, e.g., redox or hydrogenation activity, and an acidic function. The metals can be deposited by different methods. Impregnation of a zeolite with a metal... 

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.

It is known that washing has to be avoided after the component precursor has been deposited by impregnation. When other deposition methods are involved, the washing step has been reported to have various effects. 

Nickel was deposited by impregnation of zeolite powders using the incipient wetness method with a 3% wt solution of Ni(NOj)2 bH O (Baker Analyzed). The solids were dried at 100°C in air for 24 hours and calcined in flowing air (2.4 1 ) at 500°C for 2 hours the nickel content of all samples was 2.5% wt. Before reaction the catalysts were prereduced in flowing hydrogen (2.01/h) at 500°C for 2 hours. 

With a view to optimizing the activity and selectivity of the Au/C catalyst, a short screening on deposition and activation methods was carried out. Comparing, in Table 3, three different deposition methods, namely alkaline precipitation (entry 1), absorption from diluted solution of HAUCI4 (entry 2) and incipient wetness impregnation (entry 3), followed by reduction of gold to metal, we observed that the first method performed the best. Although all the methods show... 

Erkey and co-workers [59-61] prepared Pt- and Ru-doped carbon aerogels using a supercritical deposition method. This involved dissolution of an organometallic precursor in a supercritical fluid and the exposure of a solid substrate to this solution. After impregnation of the support with the metal precursor, it was converted to the metal form by different methods. Dimethyl(l,5-cyclooctadiene) platinum(ll) was used as a precursor for Pt [59,60], and two different Ru complexes, trisacetylacetonate Ru(lll) and Ru(cod)(tmhd)2, were used for Ru [61], Monolithic organic and carbon aerogels... 

For industrial application usually such metals as palladium, platinum, iron, ruthenium, cobalt, molybdemun, nickel, either alone or as bimetallic catalyst are used. They are introduced using ion exchange, excess solution impregnation, incipient-wetness impregnation or physical vapor deposition methods. 

The above analysis of coating deposition methods visualizes that Cl impregnated in coating compositions requires specific technological operations. These technologies, equipment and methodology have rightfully occupied a place in rust protection means of metal ware. 

If complete deposition onto a preformed support is important, different deposition methods like impregnation or deposition-precipitation should be considered (Chapters 4 and 6). 

For the successful deposition of platinum nanoparticles on CNT, most deposition methods known previously from the impregnation of carbon supports can be applied [63]. However, in order to achieve a homogeneous distribution of the metallic nanoparticles on all nanotubes, these have to be activated before deposition. Moreover, since they are often entangled, such that the reduction agent... 

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

Beckel et al. [8] summarized thin-film deposition techniques in a slightly different grouping clustering the techniques mainly under vacuum deposition and liquid precursor-based thin-film deposition, and mentioned some interesting methods that were not included by Menzler et al. [7], such as polymeric precursors and impregnation. Table 10.3 gives their deposition method groupings. 

Physical vapor deposition methods (PVD) offer the possibility of preparing catalysts in which no foreign ions or molecules are introduced as is the case in the conventional "wet" impregnation methods. In evaporation methods however, the contact between metal and substrate produced by the deposition of metallic vapors is too weak to favor strong interactions and to enhance the catalytic activity and stability. By contrast, when a high-energy method like ion implantation is used, the metal is buried too deeply in the substrate and only a limited number of sites are available for the catalytic reactions. So far, direct-current sputtering has been the only PVD method whereby reasonable amounts of active catalysts could be prepared [1]. 

Figure 14.6. For example, in the impregnation method, the size of the Pt nanoparticles is controlled by the structure of the support material which acts as the confining medium to restrict reaction, diffusion, and aggregation processes. In the colloidal method, the Pt size is controlled either by electrostatic hindrance or the addition of a protecting agent, which will adhere onto the surface of Pt nanoparticles. For the ion-exchange mefliod, the surface groups of flie support material provide the anchorage sites for the Pt particles and control the dispersion and distribution of the Pt nanoparticles. In this section, some examples of Pt deposition methods will be discussed.

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