The effect of powder sintering on the palladium-catalyzed formation of carbon nanofibers from ethylene-oxygen mixtures

Carbon nanofiber growth on palladium particles from ethylene-oxygen mixtures was investigated with respect to thermal history. Electron microscopy, combined with focused ion beam cross-sectioning show particles sinter quickly, but can be stabilized by the addition of a short carbon deposition step at a temperature below the general reaction temperature. This step generates a thin layer of carbon on the catalyst which reduces sintering once the temperature is raised to the optimal reaction temperature. For example, high temperature (e.g. 500 °C) catalyst pre-treatment leads to catalyst particle sintering, and subsequent fiber growth produces large diameter fibers. In contrast, small diameter fibers form on catalyst particles pretreated at low temperature (ca. 350 °C), even if the fibers are grown at a temperature at which deposition rates are faster (e.g. 550 °C). These results led to the development of unique multiple temperature fiber growth protocols that produce smaller diameter fibers while improving the deposition rate.