Oxidation Stability of Multiwalled Carbon Nanotubes for Catalytic Applications

The oxidation of multiwalled carbon nanotubes (CNTs) was investigated with regard to a detailed prediction of the lifetime of this material as a catalyst for oxidative dehydrogenations. A power-law kinetics is found to be adequate for the description of CO2 formation in the temperature range of 623-823 K and under O-2 partial pressures of 0.025-0.6 bar. The stability against oxidation can be enhanced by passivation with B2O3 or P2O5 and by high temperature treatment. The progress of oxidative degradation was monitored by TEM and Raman spectroscopy. A mechanistic study supported by high pressure XPS and SSITKA reveals full agreement with the established model of the oxidation of conventional carbon materials; however, the theory of sequential layer degradation as observed for single crystal graphite is not transferable to a technical grade CNT material, and instead, various modes of propagation of combustion sites are identified.