The flow, mixing and mass transfer in a catalytic stirrer containing catalyst coated porous micro-fiber elements, based on a concept introduced by Moulijn, were studied in a lab-scale reactor with 13 samples of materials with fiber diameters from 8 to 35 pm and porosity values between 0.60 and 0.90. Pressure drop in these sintered metallic fiber materials was shown to follow a modified Kozeny-Carman equation: Delta P/L = [2 + 0.053 (epsilon/1-epsilon)(3)] mu 16/d2(f)(2) (1-epsilon)(2)/epsilon(0)(3 mu) When rotating in the reactor, the flow through the fiber mats can be estimated from mu(-1) = tau/L =32 mu L/alpha D rho d(f)(2) [2(1-epsilon)(2)/epsilon(3) + 0.053/(1-epsilon)] mu(T)(-2) where alpha(D) is a drag coefficient of around 2.5. Flow through the catalyst in an operational stirrer can be adjusted over several orders of magnitude by manipulating parameters, such as rotational speed, dimension of the fiber stack and its material characteristics. Mass transport between fibers and the liquid flow through fiber stacks follows: epsilon Sh = 0.47Re(1)/(SC1/3)-S-2 (c) 2005 Elsevier B.V. All rights reserved.