Catalysts are usually made of a dense but porous material such as activated carbon, zeolites, etc. that provide a large surface area. Liquids that are produced as a by-product of a gas reaction at the catalyst site transport to the surface of the porous material, slowing down transport of the gaseous reactants to the catalyst active site. Understanding the dynamics of the liquid films in the gas channel is critical to maintain performance and durability of the catalyst assembly. We develop a mathematical model for liquid films dynamics and study different regimes.