Dendrimer thermolysis

A working model for dendrimer thermolysis during calcination involves the PA-MAM dendrimer backbone initially reacting with oxygen (which may or may not be activated by a nanoparticle) in a relatively facile process to generate carboxylates and other surface species. Removal of carbonaceous species closely associated with the nanoparticle is required for complete activation of the catalyst. For Pt DENs, the surface carboxylates may be strongly adsorbed to the nanoparticle surface and extended O2 treatments are required for deep oxidation of the hydrocarbon to reach reasonably volatile species. Once formed, however, it appears that they can be removed more readily with a hydrogen treatment than with further oxidation. 

Dendrimer thermolysis, i.e., the removal of the dendrimer component via exposure to high temperatures in oxidative, reducing, or neutral gas-phase environments, is the technique that has been so far exclusively employed for this task. Other potential low-temperature removal methods, such as chemical leaching of the dendrimCT or treatment under plasma conditions, have been suggested but not demonstrated experimentally. 

Dendrimer thermolysis experiments conducted on Pt/AljOj catalysts show that 400°C is the lowest temperature that will result in the removal of adsorbed carbox-ylates. It is not until these carboxylates are removed from the surface that the platinum nanoparticles exhibit significant CO uptake, indicating that the dendrimer decomposition products, possibly including undetectable nitrogen moieties, interfere with the metal active sites (Figure 9.8). ... 

A. Singh and B. D. Chandler, Mild thermolysis conditions for the activation of dendrimer encapsulated R nanoparticles, Langmuir, 21, 10776-10782 (2005). 

Evaluating dendrimer templated nanoparticles in the absence of the dendrimer provides opportunities for insights into these new materials. In order to pursue these investigations, it is first necessary to immobilize DENs onto an appropriate substrate and to gently remove the dendrimer shell see Scheme 5. Opportunities for controlling nanoparticle size and composition make DENs potentially important precursors for heterogeneous catalysts and electrocatalysts, and DEN deposition and thermolysis are similarly critically important steps in pursuing these applications [45]. 

Thermogravimetric analysis measurements have also provided information regarding dendrimer decomposition. Thermolysis of G40H dendrimers on a gold surface in both air and argon environments has shown that the greatest weight loss... 

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