Low-temperature chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) was achieved on two different types of Co xMg1-xO catalysts prepared by different techniques: atomic layer deposition (ALD) and impregnation. The chirality distribution of SWNTs grown on the ALD-prepared CoxMg1-xO catalyst is wider than that of SWNTs grown on the impregnation-prepared CoxMg 1-xO catalyst. The different chirality distributions of SWNTs are related to their different growth modes. The ALD-prepared CoxMg 1-xO catalyzes the growth of SWNTs by "tip growth" mode, as revealed by in situ environmental transmission electron microscopy studies. In contrast, SWNTs grow on the impregnation-prepared CoxMg 1-xO by "base growth" mode. "Base growth" is attributed to strong metal-support interactions between the epitaxially formed Co nanoparticles and the underlying MgO support, accounting for the synthesis of SWNTs with high chiral-selectivity. In addition, impregnation-prepared Co xMg1-xO catalysts calcinated at different temperatures were systematically studied and their catalytic performances in synthesizing carbon nanotubes were elucidated. This work illustrates the influence of metal-support interactions and catalyst reducibility on the chirality- distribution of the synthesized SWNTs. © the Partner Organisations 2014.