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Multi-walled carbon nanotubes (MWCNTs) have been successfully synthesized with titanate-modified palygorskite as catalyst and acetylene as carbon source by chemical vapor deposition (CVD) at high temperature. Transmission electron microscopy (TEM) studies showed that there were a lot of carbon nanotubes partially filled with elongated foreign material in their inner cavities. X-ray energy dispersive spectrum (EDS) analyses and selected area electron diffraction (SAED) investigations on the encapsulated material revealed that it was single crystalline iron carbide (Fe3C) derived from ferric precursors in the mineral. The yield of carbon nanotubes was influenced by preparation temperature based on thermal gravimetric analyses (TGA). The relative quantity of Fe3C nanowires was influenced by the temperature and the local structure of nanotubes upon TEM observations. A growth mechanism is also proposed in the paper. [Copyright &y& Elsevier]