(337b) Growth of Single-Walled Carbon Nanotube Carpets From Alumina-Supported Fe Catalysts: Role of Alumina Type

The important role alumina plays as a catalyst support in single-walled carbon nanotube (SWNT) carpet growth is unsurprising as it is a well known structural modifier or catalyst promoter in hydrocarbon reforming and ammonia synthesis reactions. Although a lot of studies have been carried out so far to explain the role of alumina and the Fe-alumina interaction in the these reactions, an important area of SWNT growth that has not yet been studied explicitly is how the type of alumina affects the activity and lifetime of the catalyst, and the growth termination process. Here, we explore the Ostwald ripening behavior, catalyst lifetime, and mass loss (or sub-surface diffusion) of Fe catalysts deposited on different alumina supports: (a) sapphire; 10 nm thick alumina film deposited by (b) atomic layer deposition (ALD), (c) e-beam, (d) annealed e-beam, and (e) magnetron sputtering. The study reveals a strong dependence of the Ostwald ripening behavior, SWNT carpet height or the catalyst lifetime on the type of alumina used as catalyst support. TEM, ellipsometry, and XPS have been used to account for the marked differences observed.