A supported metallocene catalyst was synthesized by sequentially loading methylaluminoxane (MAO) (30 wt % in toluene) and ((BuCp)-Bu-n)(2)ZrCl2 on partially dehydroxylated silica ES 70 modified by (BuSnCl3)-Bu-n. Its shock load hydrogen responsiveness was evaluated by polymerizing ethylene for I h at 8.5 bar (g) and 75 degrees C without separately feeding the MAO cocatalyst. The shock load hydrogen feeding increased the ethylene consumption (at a fairly constant rate), catalyst productivity, as well as the resin bulk density and average particle size at Delta P (of hydrogen) >=similar to 3.0 psi. The bulk density increased from 0.25 to 0.31 g/cm(3). This shows a procedure for overcoming the inherent drop in catalyst productivity caused by heterogenization. of metallocenes (that is a method for catalyst activation) and improving the resulting resin bulk density. The volume-weighted