An experimental and numerical investigation is reported of NO{sub x} emissions from both catalytically stabilized and noncatalytic, lean premixed, atmospheric combustion of methane. Experiments were in a tubular, adiabatic flow reactor with catalytically active or inactive honeycomb structures and with adiabatic flame temperatures from 1,300 to 1,500 C. In order to study the effect of catalytic conversion on NO{sub x} formation, the fraction of fuel converted within the catalyst was varied within the range of 0% (corresponding to noncatalytic combustion) to 100%. In all cases, complete burnout is accomplished in a subsequent, homogeneous combustion zone. NO{sub x} emissions were computed with combinations of ideal reactor models such as one-dimensional flames, perfectly stirred and plug flow reactors, and catalytic oxidation reactors (Cat). In the Cat model, it is assumed that no intermediates and no NO{sub x} are formed, whereas for the homogeneous combustion models a detailed chemical reaction mechanism including NO{sub x} formation is employed. The NO{sub x} emissions of catalytically stabilized, premixed combustion are remarkably lower than those of noncatalytic, premixed combustion and depend on the fraction of catalytically converted fuel. The higher this fraction, the lower are the NO{sub x} emissions. The calculated results compare well with the experimentalmore » data, hence validating the modeling assumptions.« less