Diamond-supported

Fig. 2. Basic principle of the diamond cell. Pressure is generated in the gasket hole when the diamonds are pushed against one another. The sample and a small chip of ruby for pressure calibration are placed in the hole and the latter is filled with a pressure-transmitting medium. The purpose of the gasket is to provide containment for the pressure medium as well as support the diamond Dais. Suitable apertures in the diamond support Mocks provide access to optical, x-ray. and other radiation...

Fig. 2. Intersection of a miniature diamond anvil cell (from Michael (2000)). The pressure range extends up to 35 GPa at room as well as at low temperatures. 1 -Screws for pressure generation, 2 - cell body, 3 - piston, 4 - adjustment screws, 5 - diamond support, 6 - diamond, 7 - tilting diamond mount hemisphere.

Part VI discusses novel advanced electrocatalytic materials, including polymer-embedded nanoparticle electrodes for PEM fuel cells and synthetic diamond-supported electrocatalyst nanoparticles for toxic organic compound treatment. 

This paper deals with the detailed studies on oxidized diamond-supported catalyst in the... 

Catalytic reactions were carried out using a micro fixed bed flow type reactor. 60 to 400 mg of oxidized diamond-supported catalyst was used. The effluent was analyzed by an on-line micro gas chromatograph. 

Dehydrogenation of alkanes with oxidized diamond supported Cr203 and V2O5 catalysts. 

Several reactions were tested with oxidized diamond-supported metal oxide catalysts. Dehydrogenation of ethane was carried out in both ethane and CO2 mixed gas and ethane and Ar flow. The results are shown in Fig. 2. 

Fig. 3 shows the temperature dependence of ethane dehydrogenation in the presence or absence of CO2. Ethylene yield in uncatalyzed runs did not depend on the atmosphere. Over oxidized diamond-supported Cr203 catalyst, in the presence of CO2, the ethylene yield increased linearly with an increase of the reaction temperature, and reached 40% at 700 °C. 

The effect of the partial pressure of carbon dioxide on the ethane dehydrogenation over oxidized diamond-supported Cr203 catalyst was examined. The results are shown in Fig. 4. Ethane conversion and ethylene yield markedly increased at a low partial pressure of CO2, and increased with increasing partial pressure. However, the ethylene selectivity slightly decreased with increasing partial pressure. The following reaction with CO2, in the dehydrogenation of ethane, would be possible ... 

To investigate amount and type of deposited carbon, catalysts after the reaction were examined with Raman spectroscopy. The Raman spectra of used oxidized diamond-supported Cr203 catalysts in the presence and absence of CO2 were recorded. Two bands were observed in the spectra of carbon deposited both in the presence and absence of CO2. One appeared at around 1350 cm and the other at 1600 cm. The intensities of these absorptions in the spectra of the catalyst tested in the absence of CO2 were much stronger than those of the catalysts tested in the presence of CO2. This indicates that the amount of carbon deposited in the absence of CO2 was larger than that in the presence of CO2. 

Dehydrogenation of propane and butane using oxidized diamond supported catalysts... 

As shown above, oxidized diamond exhibited considerable activity in the oxidative dehydrogenation of alkanes, hence further studies on the oxidized diamond supported catalysts were exploited. Nickel-loaded alumina is generally used for the partial oxidation of methane (reaction 5). However, carbon deposition onto the nickel is the major problem in the commercialization of this process. 

We have previously shown that Ir-loaded TiOz exhibited excellent catalytic activity without carbon deposition in a prolonged run [3]. The reaction was proposed to proceed through a two-step process, that is complete oxidation of methane to give CO2 and HzO, followed by reforming reactions. At a lower temperature of 600 C, Ni-AlzOz catalyst is not active. The use of oxidized diamond-supported catalyst was examined under oxidative conditions. Diamond is believed to be inert to chemical reactions. However, in the presence of oxygen diamond can be oxidized to carbon dioxide. If the oxidized diamond support could be utilized under oxidative conditions, application of diamond support could be expanded to many catalytic reactions. 

Fig. 5 shows the effect of various supports of nickel-loaded catalysts and reaction temperature on the methane conversion, in the partial oxidation of methane. At methane to oxygen ratio of 5 1, the maximum conversion of methane is 40 %, when reaction (5) proceeded, and 10% when complete oxidation proceeded. Only the oxidized diamond-supported Ni catalyst exceeded 10% conversion above 550 C, indicating that the synthesis gas formation proceeded. Ni-loaded LazOz catalyst afforded considerable methane conversion above 450 °C, but the product is mainly COz. Other supports to nickel showed no or only slight catalytic activity in the partial oxidation of methane. These results clearly show that oxidized diamond has excellent properties in the partial oxidation of methane at a low temperature, giving synthesis gas. Fig. 6 shows the effect of temperature on the product distribution, in the partial oxidation of methane. Above 550 °C, Hz and CO were produced, and below 500 °C, only complete oxidation occurred. The Hz to CO ratio should be 2 according to the stoichiometry. However, 3.2 and 2.8 were obtained at 550 and 600 °C, respectively. 

These results show that on oxidized diamond, the interaction of nickel oxide and the support is weak, compared to other support such as alumina or titania. Such a weak interaction between support and loaded metal or metal oxide is one of the most characteristic feature of oxidized diamond support. 

In 2001, Tarasevich and his collaborators reported a comparison between electrocatalysts for oxygen reduction prepared using a disperse synthetic diamond powder promoted with CoTMPP and its pyropolymers . Two types of diamond powders with specific area of 5.8 and 170 m /g were used as catalyst supports and the activity of the catalysts obtained with the diamond supports was compared to that obtained with the same CoTMPP precursor loaded on acetylene black. In all cases, the loading was one monolayer of CoTMPP. These authors found a much lower activity for the electrocatalysts prepared on synthetic diamonds than for that catalyst prepared on acetylene black. The kinetic mechanisms of ORR was, however, the same for both supports. 

Fig. 2.2 Variation in power density for H2/O2 AMFCs as a function of fully hydrated RG-AEM thickness. The cells contained ETFE-derived RG-AEMs. All electrodes were treated with SIONl ionrancu-and utilized E-TekPl/C (20% mass) catalyst-loaded carbon cloth (squares) or carbon paper (diamonds) supports...

Figure 39.11 A core of synthetic diamond supported by a ring of cemented carbide.

To increase the surface area of conductive diamond supports, a technique called vacuum annealing is utilized in place of doping that anneals un-doped nanocrystalline diamonds to make a conductive diamond. These diamonds, also termed nanodiamonds, are advantageous as catalyst supports because they have high surface areas created by the crevices and surface boundaries between the nanocrystallites. These surface defects acting in favor of platinum deposition however cripple the stability of the material compared to pure diamond. 

Nakagawa K, Kajita C, Ikenaga NO, Gamo MN, Ando T, Suzuki T (2003) Dehydrogenation of light alkanes over oxidized diamond-supported catalysts in the presence of carbon dioxide. Catal Today 84 149-157... 

The very high stability of conductive boron-doped diamond makes it attractive as a diu-able catalyst support for PEM fuel cells. The boron-doped diamond-supported catalysts have shown excellent stability toward ORR [21] and the electrochemical oxidation of methanol [22]. However, there are still some problems with doped diamonds as electrocatalyst supports the low conductivity, the low surface area, and the poor dispersion of the metal particles. In addition, it is still difficult to realize a homogeneous and controllable boron doping level in diamond powders [23]. 

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