Catalytic combustion is generally accepted as an environmentally preferred alternative for generation of heat and power from fossil fuels, as it has stable combustion under very lean conditions with such low emissions as NOx, CO and UHC typically at temperatures lower than in the conventional flame combustion. Yet, the commercial application of catalytic combustion has been delayed due to the difficulty in handling complicated reaction processes occurring over the catalysts. In this work, numerical studies on the catalytic combustion behavior over Pd-based catalysts for the BOP (balance of plant) of MCFC power generation systems have been conducted. After introducing the governing equations, numerical investigations on the catalyst performance with the gaseous $CH_4$ and $C_3H_8$ fuels are conducted by changing such parameters as excess air ratio, space velocity, inlet temperature, and $H_2$ addition over the catalytic combustion systems adopted in the BOP of 5 kW MCFC power generation systems. Catalytic combustion is fond to be more active in case of lower excess air ratio, lower space velocity, higher inlet temperature, and higher supply rates of additional $H_2$ fuel. Also, it can be found that the reaction rate is faster and the outlet temperature is higher when $C_3H_8$ is used rather than $CH_4$.