Oxidation supported nanocrystalline

In the catalysis community, there is considerable interest in the catalytic properties of oxide-supported nanocrystalline gold, which has been found to be remarkably active for the oxidation of CO [Hamta, 1997]. In electrochemistry, the ability of gold to oxidize CO, in the absence of an oxide support, has been known for many years [Roberts and Sawyer, 1964],... 

Table 11.2 and assume A=100, which is rather conservative value, to compute J via Eq. (11.32) and O via Eq. (11.22). The results show t p 0.91 which implies that the O2 backspillover mechanism is fully operative under oxidation reaction conditions on nanoparticle metal crystallites supported on ionic or mixed ionic-electronic supports, such as YSZ, Ti02 and Ce02. This is quite reasonable in view of the fact that, as already mentioned an adsorbed O atom can migrate 1 pm per s on Pt at 400°C. So unless the oxidation reaction turnover frequency is higher than 103 s 1, which is practically never the case, the O8 backspillover double layer is present on the supported nanocrystalline catalyst particles. 

Recently, an IR spectroscopic characterization of CO adsorption on Au supported on nanocrystalline Ce02 was performed by Corma et al. [67, 86]. The presence of Au3 +, Au + and Au° species was indicated by their characteristic Aux-CO frequency. Furthermore, it was proposed that there was a direct correlation between the concentration of Au3 + species and catalytic activity for CO oxidation over nanocrystalline Ce02 supported Au. No correlation was found between catalytic activity and the concentration of Au + or Au°. These results can also be interpreted as showing that the junction perimeter interface between Au NPs and the Ce02 support is composed of Au3 + and acts as the reaction site, the length of which defines the catalytic activity. 

Summarizing, Raman spectra can be recorded of single crystals, powders, glasses, nanocrystalline, and amorphous materials, and of surface species such as transition metal compounds on high-surface-area oxide supports or surface adsorbates on some metals. Thus, Raman spectroscopy is a potentially valuable tool for the characterization of a broad range of catalytic materials and surfaces. 

The aerogel-prepared metal oxide nanoparticles constitute a new class of porous inorganic materials because of their unique morphological features such as crystal shape, pore structure, high pore volume, and surface areas. Also, it is possible to load catalytic metals such as Fe or Cu at very high dispersions on these oxide supports and hence the nanocrystalline oxide materials can also function as unusual catalyst supports. Furthermore, these oxides can be tailored for desired Lewis base/Lewis acid strengths by incorporation of thin layers of other oxide materials or by preparation of mixed metal oxides. 

Cyclic Voltammetry as a Potential Predictive Method for Supported Nanocrystalline Gold Catalysts for Oxidation in Aqueous Media... 

Recent studies of ceria systems have focused on the development of synthetic approaches to make size-controlled and shape-controlled nanostructures. The thermolysis of an acidified Ce(N03)4 solution was reported as a method for the preparation of nanocrystalline CeOg ( 4 nm, surface area 180 m -g ). The deposition of gold on these nanocrystalline particles provides experimental evidence for the size effect of supports. It was shown that the activity of the resulting gold catalyst in CO oxidation was two orders of magnitude higher than that of catalysts prepared by co-precipitation or by Au deposition on a regular cerium oxide support (surface area 70 m -g ). 

Xie, X. Otremba, T. Littlewood, R Schomaacker, R. Thomas, A. One-Pot Synthesis of Supported, Nanocrystalline Nickel Manganese Oxide for Dry Reforming of... 

Nanoparticlulated gold supported by nanocrystalline or mesostruc-tured nanocrystalline ceria catalysts represents an alternative to catalysts for selective aerobic oxidation of aliphatic and aromatic aldehydes which is much better than the gold supported by the precipitated ceria (Corma and Domine, 2005). The ceria or yttria supported Au are also active and extremely selective for the homocoupling of arylboronic acids, and the activity is directly correlated with Au(lll) (Carrettin et al., 2005). 

Catalytic properties Phosphorus is known to have deactivation effects for some automotive catalysts and the formation of CeP04 has been identified in phosphorus contaminated catalysts (Uy et al., 2003). Nanocrystalline LaP04 would act as Lewis acid in a catalytic process, which could be determined by a temperature-programmed ammonia adsorption/desorption process (Onoda et al., 2002 Rajesh et al., 2004, 2007). In addition, the rare earth phosphate NCs could act as supports for example, Pd, Pt, or Rh supported on RPO4 show excellent catalytic reduction of NO into N2 and O2 (Tamai et al., 2000), and gold supported on RPO4 shows catalytic activity and stability for CO oxidation. 

Kugai, J., Subramani, V., Song, C., Engelhard, M.H., and Chin, Y.-H. Effects of nanocrystalline Ce02 supports on the properties and performance of Ni-Rh bimetallic catalyst for oxidative steam reforming of ethanol. Journal of Catalysis, 2006, 238 (2), 430. 

Zhu and co-workers [102] have combined sol-gel processing with a liquid crystalline templating approach in order to synthesise meso-structured silica-titania mixed oxide monoliths, in which the nanocrystalline titania was well dispersed inside the silicate framework. It was shown that the mixed oxide monoliths were excellent support materials for Au catalysts. 

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