A first-order heterogenous reaction A → B is carried out using a porous spherical catalyst. Assume isothermal conditions, and that intraphase diffusion controls the reaction rate. At a bulk A concentration of 0.3 mol L⁻¹, the observed reaction rate in a 3 mm diameter catalyst particle is 0.2 mol s⁻¹ L⁻¹ catalyst volume. At a bulk A concentration of 0.1 mol L⁻¹, the observed reaction rate, in mol s⁻¹ L⁻¹ catalyst volume, in a 6 mm diameter catalyst particle, is ______