An increased utilization of biomass for heat and power production contributes to reduced emission of the greenhouse gas CO2. However, when combusted in small-scale units, such as domestic stoves and boilers, the emissions of unburned gases, i.e. CO and light and heavy hydrocarbons, tend to be high. An attractive solution to reduce these emissions is the integration of oxidation catalysts. In this paper the development of a multidimensional heterogeneous mathematical model for the simulation of one channel in a monolithic catalyst is presented. The results of the simulation are compared with experimental data from a wood fired domestic boiler in which a monolithic catalyst has been integrated. The results show that the mass transfer inside the channels limits the conversion and that segmentation of the monolithic catalyst may therefore significantly increase the conversion. A good agreement between the simulation and the experimental data was achieved, for both the segmented and the unsegmented catalyst, and the model was proven to be a valuable tool for the optimization of the catalyst design.