Mesoporous aluminas with average pore sizes of 4.3-7.8 nm were prepared by anodization of an aluminum film (AAO), and by a sol-gel templating method (TPL). In addition to a commercial alumina and sulfated TPL, the aluminas were used as supports for cyclopentadienyl zirconocene dichloride (CP2ZrCI2) and trimethyl(eta 5-pentamethylcyclopentadienyl)zirconium (Cp*ZrMe3) and tested in the polymerization of ethylene. The metallocenes supported on the alumina prepared with the templating method and its sulfated modification exhibited polymerization activities of 440 and 350 kg(PE)/(MOl(Zr) X h X bar), respectively, comparable to that obtained with silica-supported metallocenes (390 kg(PE)/moI(zr), X h X bar)). The acid site distribution of the aluminas was studied with FTIR and temperature programmed desorption (TPD) of pyridine, and also the amount of medium and strong acid sites was determined gravimetrically from the adsorption of pyridine. Relative to the surface area, AAO with the highest amount of acid sites (2.10 Pmolpy M. AQ) adsorbed CP2ZrCl2 and Cp*ZrMe3 the most. Study of the polymers' morphology with a scanning electron microscope revealed polyethylene nanofibers in all the polymer samples, also in those obtained from the reference polymerizations with homogeneous CP2ZrCl2 and Cp*ZrMe3. This finding suggests that a catalyst support with a tubular pore structure is not a prerequisite for the formation of polymer nanofibers. (C) 2007 Wiley Periodicals, Inc. J