Partial wetting in porous catalysts: wettability and wetting efficiency

Qualitative changes in the local (pore level) wetting efficiency of a porous catalyst as a function of catalyst wettability are proposed based on monitoring the 1-D motion of the solid-liquid-gas contact line. As catalyst wettability is increased, the resulting wetting efficiency is likely to show two distinct transitions viz., (1) a sudden decrease that is inspired by coalescence of neighboring rivulets and, (2) a sudden increase that is inspired by porous nature of the catalyst. As catalyst wettability decreases, the wetting efficiency is likely to decrease in the beginning but can then be held constant due to pinning or holding of the retracting contact line by liquid-filled pores. This will result in comparatively much higher wetting efficiencies. It is further proposed that under favorable circumstances this pinning can disappear and will, thus, allow the contact line to retract and wetting efficiency to decrease. In the end, the effect of catalyst geometry on the relation between wetting efficiency and wettability is presented. (C) 2002 Elsevier Science Ltd. All rights reserved.