Preparation of the Supported Catalyst

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... 

Figure 2 schematically presents a synthetic strategy for the preparation of the structured catalyst with ME-derived palladium nanoparticles. After the particles formation in a reverse ME [23], the hydrocarbon is evaporated and methanol is added to dissolve a surfactant and flocculate nanoparticles, which are subsequently isolated by centrifugation. Flocculated nanoparticles are redispersed in water by ultrasound giving macroscopically homogeneous solution. This can be used for the incipient wetness impregnation of the support. By varying a water-to-surfactant ratio in the initial ME, catalysts with size-controlled monodispersed nanoparticles may be obtained. 

Figure 3.6 Schematic representation of the supported catalyst preparation from its precursor using precursor concept and conditioning. (Adapted from Bonnemann H. et at, Fuel Cells, 4, 1,2004. With permission from Wiley VCH.)...

Representative results of TA-modified Ni black and supported Ni catalysts are compiled by Tai and Sugimura [26], Summarizing the hydrogenation activity, and the e.d. ability widely varies with the precursor preparation method. The supported catalysts display the highest activity, while Raney-modified catalysts give the best e.d. abilities. 

The catalytic performances of the supported catalysts clearly demonstrated the improvement in terms of activity or selectivity by such optimized catalytic systems. This improvement is related to a nanometer control of the critical characteristics of the active sites. Enhancement of the catalytic performances and the understanding of structure-reactivity relationships can only be achieved by advancing the understanding of different preparation methods, eventually leading to better control over the characteristics of the active sites at a nanometer scale. Moreover, new properties of these solids may be found, which could have a great impact on catalytic reactions. 

Reasons for the Use of Metal Binary Carbonyl Compounds as Precursors in the Preparation of Tailored Supported Catalysts... 

Several reasons can be considered for using metal binary carbonyl precursors in the preparation of metal supported catalysts ... 

In this chapter we report on the gas-phase preparation of metal-supported catalysts, that is on the deposition of dispersed metallic nanoparhcles onto a surface. Taking most of the examples from the thoroughly studied chemistry of the [Mo(CO)is]/oxide support system, we successively consider (i) surface organometallic chemistry issues, (ii) the methods used to avoid chemical contaminahon of the deposit and (iii) the competition between nucleation and growth. 

When we are interested in the reproducible preparation of metal-supported catalysts it is also necessary to integrate the mesoscopic scale. Indeed, the deposit needs to be homogeneous, with particles anchored not only on all the support grains but also in their porosity. The use of CVD-fluidized bed reactors, for which we have gained some experience [85, 86], is one of the most elegant ways to master a process that fulfils these requirements under relatively mild conditions. 

The preparation of real supported catalysts will involve the deposition of a precursor salt followed by decomposition and/or reduction to the final metallic state. We shall consider the influence of the precursors and the effect of oxidative pretreatments later. First, we consider how the shapes of supported metal particles will vary with time under reducing conditions, since this represents the working condition for most metal catalysts. A comprehensive review of sintering and redispersion in supported metals has been presented by Ruckenstein and Dadyburjor.232... 

Pt superfine clusters on conductive supports are effective catalysts of redox reactions proceeding in fuel cells. High specific surface, support conductivity, high dispersity (nanosizes of Pt clusters) and their strong fixation on a surface are necessary criterions of preparation of the effective catalyst. From these points of view CNM for example single- (SWNT) and multi-walled (MWNT) nanotubes, nanofibers (CNF) and x-ray amorphous carbon (AC) can be a successful supports of Pt clusters. 

In heterogeneous catalysis, the first tests on UPD were performed on bulk catalysts which allows, for the preparation of the bimetallic catalyst, easy control of the electrochemical potential by an external device (potentiostat). In the same way all electrochemical techniques, particularly the control of catalyst potential required for submonolayer deposition, can be extrapolated to metallic catalysts supported on conductive materials such as carbon or carbides [8]. 

Metal-supported catalysts are among the important classes of synthetic materials developed in the past 50 years. The importance of these materials can be gauged from the fact that about 20% of the U.S. national gross product is dependent on such catalysts. Thus, the preparation of zero valent metal particles supported catalysts is very vital to the economy of any nation. Before discussing the advantages of the SMAD method, it is worthwhile to briefly review the traditional methods of preparation of metal-supported catalysts. 

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