Hydrogenation CNTs support

A typical probe reaction for estimating catalytic properties in selective hydrogenations is the hydrogenation of cinnamaldehyde. This molecule contains both a C=C and a C=0 double bond, thus the formation of hydrocinnamaldehyde and/or cinnamyl alcohol by reduction of the one or the other, or the formation of phenyl propanol in the case of complete reduction may indicate the potential of the catalyst for other fine chemical transformations. Indeed, this reaction was one of the first to be tested by CNT-supported catalysts [120]. Noble metals show a high activity in this reaction and... 

The hydrogenation of a,P-unsaturated substrates on CNF- or CNT-supported catalysts has been the subject of several studies. Although the C=C bond is... 

The liquid-phase selective hydrogenation of the C=C bond in a, 3-unsaturated cinnamaldehyde was studied to show the benefit of the use of the CNTs support versus the traditional powder activated charcoal-based catalyst [75, 76]. The catalyst consisted of homogeneous palladium nanoparticles dispersed inside the carbon nanotubes. The characteristics of the Pd-based catalyst have already been detailed above. 

PGMs such as Pt and Pd (Figs 11.5 and 11.6). The membranes developed have been tested with various reactions, such as in proton exchange membrane (PEM) fuel cells and in hydrocarbon hydrogenation (e.g., Halonen et al, 2010 Job et al., 2009 Stair et al., 2006). The nanostructured membrane AAO framework studied by Stair et al. (2006) is presented in Fig. 11.6. A similar type of a framework has been used also with the CNT support framework (Kordas et al, 2006). This kind of a structure provides more uniform contact time and controlled reagent flow, as well as decreased sintering phenomena (Stair et al, 2006). By designing new catalyst systems by... 

Such a difference in terms of product selectivity was attributed to the complete absence of any acidic sites on the carbon nanotubes sur ce and also to the absence of micropores which could induce re-adsorption and consecutive reaction [16]. The presence of micropores could artificially increase the contact time and as a consequence, modify the hydrogenation pathway. The influence of the support nature on the electronic properties of the metallic phase eould also be put forward to explain these results. Depending on the metal-support interaction, the metal particles could exhibit different exposed faces and as a consequence, significantly modify the chemisorption of the reactant on their surface. According to the interaction between the C=C bond and the laces exposed by the palladium particles, the residence time and the desorption of the intermediate could be different and thus, lead to a different selectivity. The presence of palladium aggregates on the activated charcoal as compared to the individual palladium dispersion on the CNTs could be the illustration of this difference in exposed crystalline feces. 

A rhodium complex grafted onto MWCNTs was also reported to be very active in cyclohexene hydrogenation [218,242], Such a catalyst is more active than that supported on activated carbon, and interestingly, the turnover frequency (TOF) increases dramatically after recycling. Pd/CNT catalysts were found to be active in cyclooctene [243] and benzene [244] hydrogenation, and for the latter... 

More than a hundred articles have been published on the use of CNTs or CNFs as catalyst supports for DMFC and PEMFC. The most studied reaction is methanol oxidation (anode catalyst), followed by oxygen reduction (cathode catalyst) and to a lesser extent, hydrogen oxidation (anode catalyst). Platinum is... 

Other procedures for the synthesis of CNTs use a gas phase for introducing the catalyst, in which both the catalyst and the hydrocarbon gas are fed into a furnace, followed by a catalytic reaction in the gas phase. The method is suitable for large-scale synthesis, because nanotubes are free from catalytic supports and the reaction can be operated continuously. A high-pressure carbon monoxide reaction method, in which the CO gas reacts with iron pentacarbonyl to form SWNTs, has been developed [38]. SWNTs have been synthesized from a mixture of benzene and ferrocene in a hydrogen gas flow [55]. In both methods, catalyst nanoparticles are formed through thermal decomposition of organometallic compounds, such as iron pentacarbonyl and ferrocene. 

---