Nanocrystalline catalysts

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. 

Ying, X Y., and Tschope, A., Gas phase synthesis of nonstoichiometric nanocrystalline catalysts, in Advanced Catalysts and Nanostructured Materials Modern Synthetic Methods (W. R. Moser, Ed.), p. 231, Academic Press, San Diego (1996). 

However, little has been reported about the acidic and catalytic properties of S04 /Zr02-Si02. In this paper, S04 /Zr02-Si02 nanocrystalline catalysts were prepared by a chemical method. The structure, acidic properties and catalytic activity of the catalysts were investigated by using X-ray diffraction (XRD), IR, DTA, Hammett indicators and catalytic esterification reaction of acetic acid with glycerin. 

The precursors were placed in a stirred solution of IM H2SO4 solution for 2h. The solids, S04 /Zr02-Si02, were then filtered and dried at 100°C for 12h. The sulfated precursors were powdered and calcined at different temperatures for 2-6h to prepare the S04 /Zr02-Si02 nanocrystalline catalysts. 

The S04 VZr02-Si02 nanocrystalline catalysts were prepared by a chemical method in three steps. First, Zr(OH)4 sols were prepared from the ZrOCU solution reaction with... 

Figure 10.24. Rates of hydrogen absorption by LaNis at 298 K for (a) polycrystalline LaNis, (b) nano-crystaiiine LaNis, and (c) nanocrystaiiine LaNis with Pd nanocrystalline catalyst attached (Zaiuska et ai., 2001, with permission).

Yi J, Miller JT, Zemlyanov DY. A reusable imsupported rhenium nanocrystalline catalyst for acceptorless dehydrogenation of alcohols through y-C-H activation. Angew Chem Int Ed Engl. 2014 53 833-836. 

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]. 

The XRD pattern of the catalyst. Fig. 3. can be understood as thermal treatment lead to the crystallization of the catalyst and mixture of a majority of nanocrystalline MosOu-type oxide with minor amounts of nanocrystalline M0O3 and Mo02-type material [5]. The crystallization of the catalyst takes place only in a small temperature range and above which decomposes. The FTIR pattern. Fig. 4. shows the peak at 711 cm suggests that there exits a multi phase component like Mo (or V or W)-0- Mo bond [6]. 

The present work demonstrates that the mixed oxide catalyst with inhomogeneous nanocrystalline MosOu-type oxide with minor amount of M0O3- and Mo02-type material. Thermal treatment of the catalyst shows a better performance in the formation of the crystals and the catalytic activity. The structural analysis suggests that the catalytic performance of the MoVW- mixed oxide catalyst in the partial oxidation of methanol is related to the formation of the M05O14 t3 e mixed oxide. 

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... 

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. 

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. 

Figure 2.6 Claisen-Schmidt condensation-asymmetric epoxidation reactions over nanocrystalline aerogelpre pared AP-MgO catalysts.

Figure 2.7 Illustration of Fe203 catalyst on nanocrystalline CaO for the destructive adsorption of CCI4.

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],... 

Figure 5 shows the absorption and desorption kinetics of nanocrystalline MgH2 with ceramic catalysts at 300°C. The BCN catalyst addition was very effective to enhance the desorption kinetics in comparison to pure MgH2 and SDC added composite. 

S. Carrettin, P. Concepcion, A. Corma, J. Lopez-Nieto, and V. F. Puntes, Gold catalysts Nanocrystalline Ce02 increases the activity of Au for CO oxidation by two orders of magnitude, Angew. Chem. Int. Ed. 43(19), 2538-2540 (2004). 

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