This work elucidates the contributions of different decomposition reactions, namely, steam reforming, hydro-cracking, dry reforming, and (thermal) cracking reactions, to the conversion of tar and light hydrocarbons during the catalytic cleaning of a biomass derived raw gas. A raw gas that contained a high content of steam and that was produced in the Chalmers indirect biomass gasifier was taken as the reference. The representative reactions associated with the upgrading of the given raw gas were identified to investigate the individual effects and thereafter reassembled to investigate the synergistic effects. Ilmenite was used as the catalyst, and the temperature range of 750 degrees-900 degrees C was the focus. For this process, it was discovered that the complete steam reforming, steam dealkylation, and hydro-cracking reactions are important, whereas the dry reforming reaction is not relevant. In addition, the water gas shift reaction occurs significantly and can promote the hydron-cracking reaction. These results provide insights into the most important reactions for inclusion in kinetic models of catalytic gas cleaning.