Nanocrystalline preparation

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

Kanatzidis MG, Pottgen R, Jeitschko W (2005) The metal flux a preparative tool for the exploration of intermetallic compounds. Angew Chem Int Ed 44 6996-7023 Trindade T, O Brien P, Pickett NL (2001) Nanocrystalline semiconductors Synthesis, properties, and perspectives. Chem Mater 13 3843-3858... 

According to the characterizations by TEM and XRD, the sample prepared from a CH4/H2 plasma was composed of nanocrystalline diamond and disordered microcrystalline graphite. Then nondiamond carbon was effectively removed with an increase in [CO]. It is therefore concluded that the VDOS of the nanocrystalline diamond and DEC films extracted from the HREELS data is in qualitative agreement with the characterizations of TEM and XRD. Although the HREELS probes only the region near the surface, the agreement suggests that the surface dynamics do not differ dramatically from those of the bulk. 

The preparation of ZnSe materials is an area of interest and study. The coordinating ability of the solvent used in the solvothermal synthesis of zinc selenide was demonstrated to play an important role in the nucleation and growth of nanocrystalline ZnSe.604 Thermolysis of bis [methyl( -hexyl)di-seleno]carbamato]zinc gave highly monodispersed particles characterized by electronic spectroscopy, photoluminescence, X-ray diffraction, and electron microscopy.605... 

Elbaum R, Vega S, Hodes G (2001) Preparation and surface structure of nanocrystalline cadmium sulfide (sulfoselenide) precipitated from dimethyl sulfoxide solutions. Chem Mater 13(7) 2272-2280... 

Vijay Kumar R, Elgamiel R, Diamant Y, Gedanken A (2001) Sonochemical preparation and characterization of nanocrystalline copper oxide embedded in poly(vinyl alcohol) and Its effect on crystal growth of copper oxide. Langmuir 17(5) 1406-1410... 

Juengsuwattananon K, Jaroenworaluck A, Panyathanmapom T, Jinawath S, Supothina S (2007) Effect of water and hydrolysis catalyst on the crystal structure of nanocrystalline Ti02 powders prepared by sol-gel method. Physica status solidi a 204(6) 1751-1756... 

Taghvaei, V., Habibi-Yangjeh, A., and Behboudnia, M. (2010) Hydrothermal and template-free preparation and characterization of nanocrystalline ZnS in presence of a low-cost ionic liquid and photocatalytic activity. Physica E, 42 (7), 1973-1978. 

There has been substantial interest in the preparation and characterization of materials consisting of particles with dimensions in the order of 2-100 nm, so-called nanocrystalline materials. 336-343 One factor driving interest in nanoparticle research is the perceived need for the further miniaturization of... 

XRD patterns of the prepared samples V-Mo-Zeolite are similar to that of zeolites which suggests that the metal species (i.e. oxide, cations,...) are well dispersed through the zeolites structure and the absence of bulk phases in the XRD patterns implies that for these samples the molybdenum and vanadium oxides are present in either a nanocrystalline state or as a small crystallites which measured less than 4 nm in diameter. Furthermore, XRD and FTIR (1500-400 cm 1) showed no significant damage of the zeolite host structure after exchange and thermal treatment except for the sample V2MoMor. 

Outside of catalyst preparation, reaction of sucrose with metal nitrates has been used to prepare nanocomposite mixed oxide materials. Wu et al. [46] reported the synthesis of Mg0-Al203 and Y203-Zr02 mixed oxides by reaction of nitrate precursors with sucrose. The resulting powders had smaller particles than those prepared without sucrose. Das [47] used a similar method in the presence of poly vinylalcohol to produce nanocrystalline lead zirconium titanate and metal ferrierites (MFe204, M = Co, Ni, or Zn). The materials prepared using sucrose had smaller crystallites than those made without. Both authors observed an exothermic decomposition of the precursors during calcination. 

Pathan, H. M. Sankapal, B. R. Desai, J. D. Lokhande, C. D. 2003. Preparation and characterization of nanocrystalline CdSe thin films deposited by SILAR method. Mater. Chem. Phys. 78 11-14. 

Grosso, D. Boissiere, C. Nicole, L. Sanchez, C. 2006. Preparation, treatment and characterisation of nanocrystalline mesoporous ordered layers. /. Sol-Gel Sci. Technol. 40 141-154. 

Menzies, D. B. Dai, Q. Bourgeois, L. Caruso, R. A. Cheng, Y. B. Simon, G. P. Spiccia, L. 2007. Modification of mesoporous Ti02 electrodes by surface treatment with titanium(IV), indium(III) and zirconium(IV) oxide precursors Preparation, characterization and photovoltaic performance in dye-sensitized nanocrystalline solar cells. Nanotechnology 18 125608. 

Due to recent developments in synthesis, the preparation of nanocrystalline polymorphs, which are usually unstable as bulk phases, has been achieved for several materials such as ZrC>2, Ti02 and various perovskites. The appearance of these exotic materials does not necessarily mean that they are thermodynamically stable, since the kinetics (templates and surfactants) are probably more important for the processes than the thermodynamics. Adsorption of water may also play an important role as in the case of alumina, but in the data given in Figure 6.19 the effect of water has been accounted for [25]. 

Oxidative catalysis over metal oxides yields mainly HC1 and C02. Catalysts such as V203 and Cr203 have been used with some success.49 50 In recent years, nanoscale MgO and CaO prepared by a modified aerogel/hypercritical drying procedure (abbreviated as AP-CaO) and AP-MgO, were found to be superior to conventionally prepared (henceforth denoted as CP) CP-CaO, CP-MgO, and commercial CaO/MgO catalysts for the dehydrochlorination of several toxic chlorinated substances.51 52 The interaction of 1-chlorobutane with nanocrystalline MgO at 200 to 350°C results in both stoichiometric and catalytic dehydrochlorination of 1-chlorobutane to isomers of butene and simultaneous topochemical conversion of MgO to MgCl2.53-55 The crystallite sizes in these nanoscale materials are of the order of nanometers ( 4 nm). These oxides are efficient due to the presence of high concentration of low coordinated sites, structural defects on their surface, and high-specific-surface area. 

Instead of using high-temperature melting to make the precursor alloys, an alternative wet chemistry technique has been proposed where nickel(O) and aluminum coordination compounds are blended together and treated to give nanocrystalline NiAlx alloys with 1 < x < 3 [48], The alloys are leached in the same way as standard skeletal catalysts. Catalysts with higher activity than commercially available Raney nickel have been prepared by this technique, with the activity attributed to the finer structure and homogeneity of the alloys [48,49],... 

---