Simultaneous heat, mass and momentum transport phenomena accompanying phase transition and exothermic chemical reaction in unsaturated capillary porous media are investigated in this study with respect to a partially externally wetted nonisothermal catalyst pellet. The internal wetting efficiency, on which the effectiveness factor is strongly dependent, is determined by the internal and external transport processes, and is sensitive to the extent of external wetting as well as the degree of saturation of the surrounding gas. Adsorbate and capillary condensate transport, generally ignored for catalytic reactions, can have a dominating influence on the rate of reaction in the vapor-filled region.