A 1.0% Pd/SiO2 catalyst for SO2 oxidation is being studied using a stoichiometric O2/SO2 feed ratio at a total pressure of 2 atm. At a temperature of 673 K, a rate of 2:0 mole SO2 s-1 L cat-1 occurs. The average velocity for SO2 molecules is 3 x 104 cm s-1, and the average pore diameter in the alumina is 120 A ˚ (10 A = 1 nm). Assume the Pd is uniformly distributed throughout the catalyst particles. What is the largest particle size (diameter in cm) one can use in the reactor and still be assured that you have no significant diffusion effects?