Supports rutile

The reaction of photo-induced sulphur desorption from the surfaces of the metal oxide-supported (rutile and anatase Ti02, SrTiOs, ZnO, Fe203 and Sn02) Au nanoparticles in water at room temperature has also been studied [209]. It was found to be driven by an upward shift of the Fermi energy of the metal oxide-loaded Au nanoparticles with irradiation. It has also been demonstrated that this phenomenon is applicable to the low-temperature cleaning of sulphur-poisoned metal catalysts. 

In Fig. 5.21, from Dawson s paper, the uptake at X for the 250°C-outgassed sample is dose to the calculated value for a monolayer of water with a (H20) = 101 A. Point X has therefore been ascribed to a close-packed monolayer of water on a hydroxylated surface of rutile. The fact that the differential entropy of adsorption relative to the liquid state (calculated from the isosteric heat of adsorption) changes sharply from negative to positive values in this region with A s 0 at X was regarded as supporting evidence. ... 

Observing NEMCA, and actually very pronounced one, with Ti0224 and Ce0271 supports was at first surprising since Ti02 (rutile) and Ce02 are n-type semiconductors and their ionic (O2 ) conductivity is rather low so at best they can be considered as mixed electronic-ionic conductors.77... 

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 ... 

Co/Rn titania support containing n% of rutile phase (R)-supported cobalt... 

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-... 

Kim43,49 utilized the effect of water on the activity in FTS patents using un-promoted and promoted cobalt deposited on Ti02 (rutile). For a wide range of external H20 addition levels, beneficial effects of increased productivity could be realised. However, when more than 28% water was added to the feed of the rhenium based version, the CO conversion was affected negatively. More recent experimental investigations of the effect of added water on the rate of the FTS over titania-supported Co are summarized in Table 4. 

Aqueous solutions of 3-hydroxypropanal were reduced using Ti02 supported ruthenium catalysts at 40-60 °C using 40 bar of hydrogen. The most stable catalysts were found to be ruthenium catalysts supported on low surface area macroporous rutile. 

Rutile and anatase are used in photocatalysis and as catalyst supports and we describe some important structural features later. The titanium-oxygen system plays a key role in understanding stoichiometric variations. The highest oxide, Ti02, is polymorphic and the four known crystal structures are rutile, anatase, brookite and a high-pressure form similar to a-Pb02. 

The Anderson—Hyde dislocation model differs from the earher model based on the cooperative diffusion mechanism described by Andersson and Wadsley (1966), in which CS planes, e.g. in rutile, were diought to be produced by cation migration during reduction.The reduced oxygen potential at die surface means an enhanced Ti-potential and dierefore die Ti ions diffuse cooperatively into the crystal down diis Ti-potential gradient. However, diere is no experimental evidence to support this hypodiesis. This mechanism is also less hkely since diis would involve a large number of cations. 

The influence of the specific oxide support phase upon the structure and reactivity of the surface vanadia species was also recently investigated.54 A series of titania-supported vanadia catalysts were synthesized over a series of Ti02 supports possessing different phases (anatase, rutile, brookite and B). Raman and solid state vanadium-51 characterization studies revealed that the same surface vanadia species were present in all the different V20/ri02 catalysts54. The reactivity of the surface vanadia species on the different oxide supports was probed by methanol oxidation and the TOFs are shown in Figure 6 (all the catalysts contained 1% V205)... 

Essentially the same methanol oxidation TOFs were obtained on the different oxide supports. The Degussa P-25 titania support (90% anatase 10% rutile) was also examined, as shown in Figure 6, because it possesses very low levels of surface impurities and represents a good reference sample. The invariance of the methanol oxidation TOF with the specific phase of the titania support reveals that the oxidation reaction is controlled by a local phenomenon, the bridging V-O-Support bond, rather than long range effects, the structure of the 2 support. Thus, the phase of the oxide support does not appear to influence the molecular structure or reactivity of the surface vanadia species. 

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