LaFexMoyMnzO3 perovskite as catalyst precursors for the CVD synthesis of carbon nanotubes

Perovskites LaFexMoyMnzO3 (x = 0.27–0.90, y = 0.00–0.09 and z = 0.01–0.10) were prepared, characterized and investigated as catalyst precursors for the CVD synthesis of carbon nanotubes (NT) from CH4 between 900 and 1100 °C. XRD, TPR and Mössbauer data showed the formation of single-phase perovskites that incorporate all of the metals. Raman and SEM data taken after CVD growth with unsupported perovskite precursors indicate that large diameter multi-walled NT (MWNT) are produced, even under a variety of pre-reduction and CVD conditions. The 25, 33 and 50 wt% perovskites dispersed on Al2O3 show a quite different CVD growth activity: (i) single- and double-walled NT are formed at high yields, (ii) the presence of Mo in the precursor catalyst has an important effect on the formation of SWNT, (iii) a control on the pre-reduction conditions changes the characteristics of the NT produced and (iv) the catalyst shows an improved thermal stability. This selectivity for smaller diameter NT growth is rationalized by the influence of the Al2O3 matrix on the sintering of the metals at high temperature. Our results demonstrate that isolated perovskite particles are formed on the support matrixes and yield smaller catalytic aggregates.