Ziegler-Natta catalysts based on TiCl(4) supported on clay/MgCl(2) were obtained and tested in propylene polymerization. Two types of clay: the sodium clay Gelmax 400 and the organophylic one Cloisite 30B were employed. The catalysts preparation involved the treatment of the clays with an alcohol adduct of MgCl(2) followed by treatments with TiCl(4) and triethylaluminium (dealcoholation), optionally using ethyl benzoate as internal electron donor. The catalyst performance showed to be markedly influenced by the clay type and synthesis conditions. Dealcoholation was the main factor that affected the catalyst activity. Impregnation of clay/MgCl(2) supports with Ti generated catalysts with about 5 wt.% of titanium and crystalline structure with different families of lamellar structures, evidenced by low intensity peaks at different (0 0 1) plane 2 theta position in the X-ray diffraction curves of the clay-supported catalysts. The catalysts were used in the polymerization of propylene producing polypropylenes with significant isotacticity and crystallinity. Among the catalysts, that prepared using the sodium clay as support without internal donor showed the higher catalytic activity (6433 g PP/gTi). Due to different catalyst activity, polypropylenes with different contents of clay were obtained. The residual clay acts as filler, PP nanocomposites, were obtained by this in situ method, some of them highly filled. The degradation behavior of these highly filled nanocomposites was highly improved with increasing of the on set and maximum degradation temperatures in the range of 200 degrees C. The shape of the polymer particles was very similar to those of catalyst particles due to the replica phenomenon, also observed for these catalyst systems. (C) 2011 Elsevier B.V. All rights reserved.