Synthesis method, surface oxide-support

Among various methods to synthesize nanometer-sized particles [1-3], the liquid-phase reduction method as the novel synthesis method of metallic nanoparticles is one of the easiest procedures, since nanoparticles can be directly obtained from various precursor compounds soluble in a solvent [4], It has been reported that the synthesis of Ni nanoparticles with a diameter from 5 to lOnm and an amorphous-like structure by using this method and the promotion effect of Zn addition to Ni nanoparticles on the catalytic activity for 1-octene hydrogenation [4]. However, unsupported particles were found rather unstable because of its high surface activity to cause tremendous aggregation [5]. In order to solve this problem, their selective deposition onto support particles, such as metal oxides, has been investigated, and also their catalytic activities have been studied. 

Niobium Products Co., 50 m /g). Many different synthesis methods have been used to prepare supported metal oxide catalysts. In the case of supported vanadium oxide catalysts, the catalysts were prepared by vapor phase grafting with VOCI3, nonaqueous impregnation (vanadium alkoxides), aqueous impregnation (vanadium oxalate), as well as spontaneous dispersion with crystalline V2O5 [4]. No drastic reduction of surface area of the catalysts was observed. 

To investigate the effect of the synthesis method on the structure-reactivity relationship of the supported metal oxide catalysts, a series of V205/Ti02 catalysts were synthesized by equilibrium adsorption, vanadium oxalate, vanadium alkoxides and vanadium oxychloride grafting [14]. The dehydrated Raman spectra of all these catalysts exhibit a sharp band at 1030 cm characteristic of the isolated surface vanadium oxide species described previously. Reactivity studies with... 

This unique micro structure can be described as an intermediate stage between a supported catalyst and a bulk metallic sponge or skeletal Raney-type catalyst. It enables a reasonably high dispersion of Cu and exposure of many Cu-ZnO interfaces at a high total Cu content. The specific Cu surface area (SACu) of methanol catalysts can be determined by reactive N20 titration [59, 60], which causes surface oxidation of the Cu particles and allows calculation of SAcu from the amount of evolved N2. The SACu of state-of-the-art methanol synthesis catalysts measured by this method... 

On the preparation side, the development of more economical synthesis methods apt for the commercial-scale production of high-surface-area solids is required. Methods such as atomic layer epitaxy offer a good route to obtain supported mixed oxides. However, this method in its present version is expensive and restricts the potential applications of these materials. The key factor in these methods is to achieve a good spreading of the active material on the support surface. New characterization procedures are needed to ascertain whether or not the supported nanoparticles of the desired compound are indeed formed. 

The nature of the supported metal oxide species depends upon a number of factors the preparation method (wet chemical synthesis plus calcination), chemical interactions between the support and surface layers, and surface density (surface oxide weight loading and specific surface area of the support oxide) [5]. Figure 11.1 schematically demonstrates the various dehydrated surface structures commonly observed for a mono-oxo metal oxide isolated, oligomeric, polymeric, and crystalline species. Several reviews comprehensively catalog the expected surface structures for transition metal mono- and polyoxoanions in four-, five-, and sixfold coordination under nonreaction conditions [3, 23-25],... 

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]. 

Therefore, the loaded metals virtually interacted with an oxidized surface rather than the native carbide surface. Schweitzer et al. developed a synthesis method that could allow a direct contact of Pt with the genuine Mo C surface [65]. In the WGS reaction, the resulting Pt/MOjC catalysts exhibited a higher activity than the most active oxide-supported Pt catalysts and a commercial Cu-Zn-Al catalyst. Moreover, the experimental rates were more consistent with those predicted by the perimeter model than by the particle surface model, suggesting that the rate-determining step for WGS on Pt/Mo C catalysts occurred at the perimeters of the Pt particles. 

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