Carbon nanotube -based catalysts investigation

The type of carbon formed depends on the reaction conditions, whereby higher reaction temperatures favour the formation of the more inert-graphitic carbon nanotubes. Based on kinetic and isotopic investigations on the mechanism of DRM reaction over Ni/MgO catalysts, Wei and Iglesia [189] observed a similarity in turnover rates and first-order rate constants with methane decomposition. Hence, they concluded that the dissociation is the kinetically relevant step for the DRM reaction and that the Ni behavior resembles that of supported noble metal catalysts (Rh, Pt, Ir, Ru). 

A crucial problem connected to carbon nanotube synthesis on supported catalysts on an industrial scale is the purification step required to remove the support and possibly the catalyst from the final material. To avoid this costly operation, the use of CNT- or CNF-supported catalysts to produce CNTs or CNFs has been investigated. Although most catalytic systems are based on nickel supported on CNFs (see Table 9.4), the use of MWCNTs [305,306] or SWCNTs [307] as supports has also been reported. Nickel, iron [304,308-310], and bimetallic Fe-Mo [305] and Ni-Pd [295] catalysts have been used. Compared to the starting CNTs or CNFs, the hybrid materials produced present higher specific surface area [297,308] or improved field emission characteristics [309]. 

In the first DSSC prototypes the catalyst for the process of 13 reduction was a thin platinum layer. In these prototypes dyes based on organic ruthenium complexes were used. Ruthenium compounds are not only expensive but also the world resources of ruthenium are very limited. The problem of replacing the platinum catalyst was not easy to solve. As a result of many investigations it was shown that combined catalysts containing some carbonaceous materials (e.g., carbon nanotubes) had an activity and stability comparable to those of platinum catalysts. Gradually, new dyes with acceptable properties were also found. 

Smaller catalyst libraries have been investigated by several other research groups. For example, Chen et al. electrodeposited a small library of noble metals (Pt, Ru, Rh, and Au) by means of a capillary-based droplet cell onto carbon nanotubes predeposited on glassy carbon by electrophoretic accumulation, and screened their ORR activity in a 0.1 M phosphate solution using the oxygen competition mode (pH = 6.7) [68, 82]. Our group employed RC-SECM to map the ORR activity of Pt, and Pt-based alloy nanoparticles, including core-shell structures... 

Nano-confinement of metal and semi-conductor materials can lead to marked changes in their electronic behaviour. Their unique properties resulted in an increased interest in using these nanoparticles (NPs) in materials science. Furthermore, with the discovery of the symbiotic nature of metal/semi-conductor heterostructures, the use of NPs in applications such as photocatalysis and opto-electric devices, like photovoltaic cells, has increased. The exceptional properties of carbon nanotubes (CNTs), as well as their unique structure, have led to increased investigation into their behavior in such hetero-structured complexes. Large surface-to-volume ratios, chemical inertness, and lack of porosity make CNTs prime candidates as catalyst supports. In more complex systems, the electrical properties of the CNTs increase the yield of catalyzed reactions due to the electronic interactions of certain NPs and CNTs. Based on the fact that charge transfer between quantum dots and CNTs has been reported, certain semi-conducting NPs have been covalently linked to CNTs to make hetero-junction electronic devices. ... 

In the present work, the catalytic activity of palladium catalysts either on activated carbon or carbon nanotubes was studied in the one-pot synthesis of f -l-phenylethyl acetate. The influence of the acid-base properties of the support on the catalytic activity has been investigated by treating oxidized CNTs with NH3 at different temperatures in order to introduce various amorrrrts of basic N-corrtairring groups on the srrrface [12]. 

Carbon nanotubes were synthesized on the surface of carbon fiber using CVD technique. Ni was used as a catalyst and coated on the surface of carbon fiber through electroless dip coating technique. The as-received and CNT coated carbon fiber samples were characterized using SEM, TEM, DT/ TGA etc. Following conclusions were made based on the above experimental investigation. 

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