A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air–fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel-lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich-lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H2.