Platinum/titania catalysts

Tanaka et al. [73] developed another MEMS system for the catalytic combustion of butane. It is composed of a combustion chamber 8 mm wide, 14 mm long and 150 pm deep which was prepared by anisotropic wet etching of a silicon substrate. The substrate was then covered with Pyrex glass applying anodic bonding. Combustion was performed on a platinum/titania catalyst... 

Platinum-titania-sepiolite monolithic catalysts for the reduction of nitric oxide with propene in lean-burn conditions... 

K. Matsuo and K. Nakano. Performances of Platinum Metal Catalysts Supported on Titania Coated Silica Prepared from Metal Organics. Appl. Surf. Sci. 33/34 269 (1988). 

Figure 4 shows the total conversion of ethanol as a function of temperature as measured by gas chromatography. Except for the silica catalysts, the platinum catalysts exhibit equal or lower light-ofif temperatures than the supported catalysts with palladium as active material (compare with Figure 7). The platinum on alumina and platinum on titania catalysts are more active than the other catalyst combinations. The conversion curves for the Pd and Pt on ceria catalysts practically coincide, which implies that ceria would be a more suitable support material for a palladium catalyst than for a platinum catalyst. The activities of the silica catalysts are low. This observation is consistent with recent results in another research project using the same type of silica sol (Zwinkels et al, 1994). According to these experiments, it is crucial to reduce the alkali content to a very low level in the support, since sodium increases the mobility of silica, which poisons the active platinum and palladium sites. Platinum is apparently more sensitive to this phenomenon than palladium.

The BET surface area measurements and pore volimie measurements were performed on a Micromeritics ASAP 2000 by nitrogen adsorption using a volumetric method. The BET siuface areas for the fresh alumina, ceria, silica and titania catalysts were 124, 91, 64 and 87 m /g washcoat, respectively. Spent catalysts from the ethanol oxidation experiments have been characterized. The results from these measurements show that the platinum on ceria catalyst has lost more than half of its original surface area, while Pd/Ce02 exhibits stability towards sintering (see Table 1). The titania catalysts have lost ca 30% of their surface areas, while the surface areas of the alumina and silica catalysts have remained practically unchanged. 

Novel procedure for the preparation of highly active platinum-titania and pjdladium-titania aerogel catalysts with favourable textural properties... 

The ceria/titania based catalyst was also more stable. The catalyst showed 60-h durability under the conditions provided in Figure 4.24. However, the weight hourly space velocity of21.2 L (hgcat) was relatively low. About ten-times higher yields can be achieved with platinum/ceria systems. The activity of the platinum/ceria catalyst is approximately 15-times higher compared with a platinum/alumina catalyst for the... 

Takenaka ct al. studied the activity of various catalysts for carbon monoxide methanation in the absence of carbon dioxide [342]. From the different active species on a silica carrier, 5 wt.% ruthenium, 10wt% nickel and 10 wt.% cobalt were significantly more active than iron, palladium or platinum, each prepared with an active species content of 10 wt.%. Then Takenaka tested nickel, ruthenium and cobalt catalysts on different carrier materials, namely, alumina, silica, titania and zirconia. The formulations most active were nickel/zirconia and mthenium/ titania catalysts. The best performing catalyst was the 5 wt.% mthenium/titania, which converted the carbon monoxide apart from less than 20 ppm from a feed mixture containing 60 vol.% hydrogen, 15 vol.% carbon dioxide, 0.9 vol.% steam, 0.5 vol.% carbon monoxide, with a balance of helium at 220 °C. The space velocity was rather high at 300 L (hgcat) -... 

Rosa et al. [251] set up a complete 5-kW diesel fuel processor based on autothermal reforming and catalytic carbon monoxide clean-up, which was dedicated to a low temperature PEM fuel cell. The breadboard system was composed of the autothermal reformer operated between 800 and 850 °C with a ruthenium/perovskite catalyst (see Section 4.2.8), a single water-gas shift reactor containing platinum/titania/ceria catalyst operated between 270 and 300 °C (see Section 4.5.1), and a preferential oxidation reactor containing platinum/alumina catalyst operated between 165 and 180 °C. Figure 9.54 shows the gas composition and reactor temperatures achieved. The hydrogen content of the reformate was in the range from 40 to 44 vol.% on a dry basis. The carbon monoxide content of the reformate was 7.4 vol.% and could be reduced to values of between 0.3 and 1 vol.% after the water-gas shift reactor and to below 100 ppm after the preferential oxidation reactor. 

Effect of platinum content. Since a beneficial role of platinum deposited on titania had been reported for the photocatalytic oxidation of some organic compounds (refs 6, 7), several catalysts, from 0.5 to 10 wt % Pt with a constant particle size, were prepared and studied. The variations of the initial rate of formation of cyclohexanone as a function of Pt contents are shown in Fig. 2. There is not only no beneficial effect of Pt as mentioned in refs.(6, 7) but a... 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Although the decomposition of ozone to dioxygen is a thermodynamically favoured process,126 it is thermally stable up to 523 K and catalysts are needed to decompose it at ambient temperature in ventilation systems, in the presence of water vapour and at high space velocity. A limited number of catalysts have been evaluated and active components are mainly metals such as platinum, palladium and rhodium, and metal oxides including those of manganese, cobalt, copper, iron, nickel and silver. Supports that have been used include 7-alumina, silica, zirconia, titania and activated carbon.125,170... 

Zhao, W., C.C. Chen, X.Z. Li, J.C. Zhao, H. Hidaka and N. Serpone (2002). Photodegradation of sulforhodamine-b dye in platinized titania dispersions under visible light irradiation Influence of platinum as a functional co-catalyst. Journal of Physical Chemistry B, 106(19), 5022-5028. 

Shown in Table 9.7 are some examples of incorporating catalysts into porous ceramic membranes. Both metal and oxide catalysts have been introduced to a variety of ceramic membranes (e.g., alumina, silica, Vycor glass and titania) to make them catalytically active. The impregnation/heat U eatment procedures do not appear to show a consistent cause-and-effeci relationship with the resulting membrane permeability. For example, no noticeable change is observed when platinum is impregnated into porous Vycor glass... 

Commercial SCR catalyst used in connection with coal-based power stations are generally composed of base metals, since platinum-group metal catalysts are too readily poisoned and have too narrow an operating temperature window for this application. Favored compositions are titania-based together with active components, normally oxides of vanadium, tungsten, or molybdenum. For these systems the optimum reaction temperature is usually in the range 3(XM00°C. 

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