High impact polypropylene was produced in a two-reactor polymerization process operating in series using two different Ziegler-Natta catalysts (referred to as catalysts A and B) that had been prepared by Sirius emulsion technology in the absence and presence of SiO2 nanoparticles, respectively. The homo polypropylene matrix was produced in liquid bulk and the ethylene/propylene rubber in gas phase under industrial conditions. Catalyst B was prepared with the same emulsion technology as catalyst A, except that SiO2 nanoparticles (average particles size 80 nm) were added during catalyst preparation. Scanning electron microscopy studies showed that the nanoparticles were fairly evenly distributed within catalyst B particles, although there was some agglomeration. It was shown that the nanoparticles in catalyst B increased the internal porosity in the homo polypropylene matrix particles and this enabled a significant increase in the rubber content. Maximum rubber content, before running into stickiness problems, was approximately 25 wt % for catalyst A without nanoparticles, whereas the maximum rubber content for catalyst B was almost doubled to 45 wt % due to the beneficial transformation of the internal catalyst morphology by the nanoparticles. In addition, it was also found that the reaction was not mass transfer limited during the ethylene/propylene rubber polymerization stage, even at very high rubber contents where all pores and cavities were filled with rubber. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2040-2048