Titania activity enhancement

In our experiment, photocatalytic decomposition of ethylene was utilized to probe the surface defect. Photocatalytic properties of all titania samples are shown in table 2. From these results, conversions of ethylene at 5 min and 3 hr were apparently constant (not different in order) due to the equilibrium between the adsorption of gaseous (i.e. ethylene and/or O2) on the titania surface and the consumption of surface species. Moreover it can be concluded that photoactivity of titania increased with increasing of Ti site present in titania surface. It was found that surface area of titania did not control photoactivity of TiOa, but it was the surface defect in titania surface. Although, the lattice oxygen ions are active site of this photocatalytic reaction since it is the site for trapping holes [4], this work showed that the presence of oxygen vacancy site (Ti site) on surface titania can enhance activity of photocatdyst, too. It revealed that oxygen vacancy can increase the life time of separated electron-hole pairs. 

Ao, Y., Xu, J., Fu, D., and Yuan, C. (2009) Synthesis of C,N, S-tridoped mesoporous titania with enhanced visible light-induced photocatalytic activity. Microporous and Mesoporous Materials, 122 (1—3), 1-6. 

Li, Y., Ma, G., Peng, S., Lu, G., and Li, S. (2008) Boron and nitrogen co-doped titania with enhanced visible-light photocatalytic activity for hydrogen evolution. Applied Surface Science,... 

Although this review has dealt with the interactions of metals with reduced oxide surfaces, metal-support interactions are certainly not limited to these. Evidence for metal-support interaction involving non-reduced surfaces exists even in the metal/ titania system. Enhanced hydrogenolysis activities have been found for low-temperature-reduced Rh/titania (7) and Ru/titania (49). These effects presumably involve interaction with Ti4+ ions. 

Sub-nanometer Ti clusters have been homogeneously dispersed within DWCNTs presenting an inner diameter ranging from 1.0 to 1.5 nm. The confined titania exhibits a much higher activity than the titania particles attached on the outside walls of the DWNTs in the epoxidation of propylene by H2O2 [207]. XPS, XANES, and Raman spectroscopy data suggest electron transfer from titanium to the inner surfaces of the DWCNTs. In contrast, no electron transfer has been observed for the outside titania. The enhanced activity of the confined titania clusters is likely attributed to their small size and interaction with the DWCNT surface. 

Hayden BE, Pletcher D, Suchsland J-P. 2007. Enhanced activity for electrocatal)4ic oxidation of carbon monoxide on titania-supported gold nanoparticles. Angew Chem Int Ed 46 3530-3532. 

N-doped titania demonstrated promising activity under visible light for the degradation of Rhodamine B in aqueous solutions [85], In thin-films of N-doped Ti02, the formation of nitride phases enhanced the catalytic properties of the film [86]. 

Whereas the effect of water on deactivation and on the overall activity of the FTS varies with the support, similar effects of water on the selectivity is reported for all catalysts, to a certain degree independent of the support, promoter and conditions. The effect can be summarized as an increase in C5 + selectivity, a decrease in methane selectivity, and in some instances a weak enhancement of the C02 selectivity is observed. Fig. 4 illustrates the effect on the C5 + and methane selectivity of adding water to cobalt catalysts supported on alumina, silica and titania, and both unpromoted and Re-promoted catalysts are shown. At the outset these selectivities are strong functions of the conversion, the C5 + selectivity increasing and the methane decreasing with increasing conversion, as illustrated by the trendlines in the figures. The points for methane are below, and C5 + -selectivity is above the line when water is added. Similar results were reported by many authors for alumina-supported catalysts,16-19 23 30 silica-supported catalysts,30 37 46-48 and titania-supported catalysts.19 30... 

The main difference between titania nanotube and the ID nanostructures discussed before is the presence of an hollow structure, but which has significant consequences for their use as catalytic materials (i) in the hollow fiber nanoconfinement effects are possible, which can be relevant for enhancing the catalytic performance (ii) due to the curvature, similarly to multi-wall carbon nanotubes, the inner surface in the nanotube is different from that present on the external surface this effect could be also used to develop new catalysts and (iii) different active components can be localized on the external and internal walls to realize spatially separated (on a nanoscale level) multifunctional catalysts. 

Titania-silica aerogels possess very high surface areas (600 to 1000 m2/g) and large pore volumes (1 to 4 cm3/g), and thereby have attracted considerable interest for photocatalysis. A number of studies have shown that titania-silica intimate mixtures exhibit enhanced UV photocatalytic activity compared with pure titania [180-183],... 

Chen, Q. Shi, H. Shi, W. Xu, Y. Wu, D., Enhanced visible photocatalytic activity of titania-silica photocatalysts effect of carbon and silver doping. CataLScience Techn. 2012,2 1213-1220. 

Crystallinity. It seems that the degree of crystallinity of Ti02 is an important factor in obtaining active Ti02 (46). Indeed, amorphous titania is poorly active. An optimum calcination temperature of amorphous samples presumably corresponds to a compromise between an enhanced crystallinity, together with a decreased density of lattice defects, and limited decreases in surface area and coverage by OH groups. 

Preparation of Pt-TiOx/Pd membranes. It was also desirable to prepare metalloceramic membranes in which the catalytic activity of the ceramic phase was enhanced through the addition of a noble metal. The very low surface area of the titania films prepared as described above made them difficult to impregnate with adequate dispersion by traditional incipient wetness techniques. Instead, finely ground titania (>200 mesh) was impregnated with platinum via the incipient wetness method with a chloroplatinic acid solution. This powder was then sprinkled onto the surface of a freshly dipped membrane, which was dried and heat treated as described. These materials were activated before use at 350°C in hydrogen for three hours. 

Fig. 3 shows the activity of a titania-supported catalyst in the oxidation of 1-butene. The application of titania as a support not only results in an improvement of the stability of the catalyst but also enhances its activity. Although the decrease in activity for the titania-supported catalyst is smaller than for the 7-alumina-supported one, the two stages of... 

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