Nanotubes Containing Nanoparticle Catalysts

Carbon nanotubes supporting catalysts have been employed in several catalytic reaction processes and some examples are presented below to illustrate the pecu-Uar catalytic properties of these catalysts. The catalytic performance is compared with that obtained on state-of-the-art traditional catalysts. 

The preferential location of the metal particles inside the tubes could be explained by the fact that during the impregnation process, the liquid completely filled the 

However, it is noteworthy that because the classical TEM image is only a 2D projection of the entire sample, one cannot attribute with certitude the exact loca-hon of the palladium parhcles with respect to the carbon nanotube surface. The resolution of the individual metal particles was also difficult to solve due to the projection of a relatively thick 3D sample on a planar surface. 

The precise locahon of the palladium nanoparticles was further evaluated by a TEM 3D technique (tomogram) which is a promising technique due to its high resolution level which is not accessible by other 3D methods, such as X-ray/ XANES tomography, SIMS or microtome/AEM sechoning methods. It is 

3D TEM slices along the tube thickness are presented in Eig. 7.13 which allows one to accurately observe the location of the palladium particles with respect to the tube morphology. The presence of some amorphous-like phase inside the channel was attributed to the ethanol used for the preparation of the sample. 

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S. Santra, P. Ranjan, P. Bera, P. Ghoshc, S.K. Mandal, Anchored palladium nanoparticles onto single walled carbon nanotubes efficient recyclable catalyst for N-containing heterocycles, RSC Adv. 2 (2012) 7523-7533. 

Pumera, M. 2007. Carbon nanotubes contain residual metal catalyst nanoparticles even after washing with nitric acid at elevated temperature because these metal nanoparticles are sheathed by several graphene sheets. Langmuir 23 6453-6458. 

At present the most efficient solid photocatalyst for CO2 reduction by H2 is based on Ti02, a semiconductor that is suitably modified to increase the efficiency under solar light irradiation and contain co-catalysts to increase production rate and selectivity of the process. One of the most efficient photocatalysts has been reported by Grimes and coworkers who have used anodized titania nanotubes in the anatase phase doped with nitrogen and platinum and copper nanoparticles as photocatalyst for the gas phase CO2 reduction by H2O production rates to methane as high as 75 ppm cm h have been achieved for this type of titania photocatalyst under solar light illumination [23, 25]. 

CN s of exceptionally high purity are required for optimum performance in applications but the synthetic products usually contain impurities such as amorphous carbon, carbon nanoparticles, and some metal catalyst. Different methods have been described for the purification of nanotubes [77] most involve oxidation by use of mineral acids and/or gas phase oxidation to remove catalytic metal particles... 

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