Supports anatase

Still another model for the spreading of an active oxide (V2O5) under oxidizing conditions onto the surface of a support (anatase) was proposed by Haber et al. [40]. In this model, the active phase crystallite spreads spontaneously at the beginning of the thermal treatment (hot plate effect) which leads to amorphiza-tion of the active phase. Thereafter the spreading is... 

A large variety of organic oxidations, reductions, and rearrangements show photocatalysis at interfaces, usually of a semiconductor. The subject has been reviewed [326,327] some specific examples are the photo-Kolbe reaction (decarboxylation of acetic acid) using Pt supported on anatase [328], the pho-... 

Figure C2.17.1. Transmission electron micrograph of a Ti02 (anatase) nanocrystal. The mottled and unstmctured background is an amorjihous carbon support film. The nanocrystal is centred in die middle of die image. This microscopy allows for die direct imaging of die crystal stmcture, as well as the overall nanocrystal shape. This titania nanocrystal was syndiesized using die nonhydrolytic niediod outlined in [79].

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

The various ratios of rutileranatase in titania support were obtained by calcination of pure anatase titania (obtained fi om Ishihara Sangyo, Japan) in air at temperatures between 800-1000°C for 4 h. The high space velocity of air flow (16,000 h" ) insured the gradual phase transformation to avoid rapid sintering of samples. The ratios of rutile anatase were determined by XRD according to the method described by Jung et al. [5] as follows ... 

In this present study, we basically showed dependence of the number of reduced cobalt metal surface atoms on dispersion of cobalt oxides along with the presence of rutile phase in titania. Both XRD and SEM/EDX results (not shown) revealed good distribution of cobalt oxides over the titania support. However, it can not differentiate all samples containing various ratios of rutile/anatase phase. Thus, in order to determine the dispersion of cobalt oxide species on titania, a more powerful technique such as TEM was applied with all samples. The TEM micrographs for all samples are shown in Figure 1. The dark spots represented cobalt oxides species present after calcination of samples dispersing on titania consisting various... 

The present research showed a dependence of various ratios of rutile anatase in titania as a catalyst support for Co/Ti02 on characteristics, especially the reduction behaviors of this catalyst. The study revealed that the presence of 19% rutile phase in titania for CoATi02 (C0/RI9) exhibited the highest number of reduced Co metal surface atoms which is related the number of active sites present. It appeared that the increase in the number of active sites was due to two reasons i) the presence of ratile phase in titania can fadlitrate the reduction process of cobalt oxide species into reduced cobalt metal, and ii) the presence of rutile phase resulted in a larger number of reduced cobalt metal surface atoms. No phase transformation of the supports further occurred during calcination of catalyst samples. However, if the ratios of rutile anatase were over 19%, the number of active sites dramatically decreased. 

The commonly used catalyst today is a vanadia on a titania support, which is resistant to the high SO2 content. Usually the titania is in the anatase form since it is easier to produce with large surface areas than the rutile form. Several poisons for the catalyst exist, e.g. arsenic and potassium. The latter is a major problem with biomass fuel. In particular, straw, a byproduct from grain production, seems to be an attractive biomass but contains potassium, which is very mobile at reaction tern-... 

Figure 6 shows transmission electron micrographs of Au particles supported by (a) monocrystalline ellipsoidal (B), (b) monocrystalline pseudocubic, and (c) monocrystalline platelet-type hematite particles (see also Figure 5 for Au particles on polycrystalline ellipsoidal (A) particles). Figure 7 shows Au particles deposited on (a) a-FeOOH, (b) P-FeOOH, (c) ZrOj (A), (d) ZrOj (B), and (e) Ti02 (anatase). 

The process has been commercially implemented in Japan since 1977 [1] and a decade later in the U.S., Germany and Austria. The catalysts are based on a support material (titanium oxide in the anatase form), the active components (oxides of vanadium, tungsten and, in some cases, of molybdenum) and modifiers, dopants and additives to improve the performance, especially stability. The catalyst is then deposited over a structured support based on a ceramic or metallic honeycomb and plate-type structure on which a washcoat is then deposited. The honeycomb form usually is an extruded ceramic with the catalyst either incorporated throughout the stmcture (homogeneous) or coated on the substrate. In the plate geometry, the support material is generally coated with the catalyst. 

Liu, B. Zeng, H. C., Carbon Nanotubes Supported Mesoporous Mesocrystals of Anatase Ti02. Chem. Mater. 2008,20 2711-2718. 

Preparation of Gold Nanocatalysts Supported on Anatase and Brookite... 

Curves (a) and (b) in Fig. 5.3 compare the light-off curves for the gold catalysts supported on anatase and brookite after being treated with O2 at 300°C. Interestingly, the catalytic activity of the brookite-supported gold catalyst remained highly active, with the onset for 100% CO conversion occurring around —20°C. In contrast, the onset... 

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