Fig. reports the plasma-only, non-catalytic NO yields, plotted as NO partial pressure for ready comparison to experiment, as a function of assumed vibrational temperature and inlet atomic N density as descriptors because of their relevance in plasma N 2 oxidation. The partial pressures of other species are reported in Supplementary are of similar orders of magnitude overall but less sensitive to vibrational temperature and more sensitive to N radical density. These differences become more evident when plotted as a ratio of yields, as shown in Fig. . The plasma-catalyst combination is expected to have a negligible to deleterious effect on NO yields across a large swath of N radical densities and vibrational temperatures. In contrast, the combination has dramatically greater yields than the plasma-only reactor at relatively high N radical densities and especially at the lower limit of vibrational temperatures, conditions typical of low-P radio frequency and microwave plasmas. The origins of this catalytic influence are revealed by an analysis of relative steady-state reaction fluxes normalized to the overall NO production rate. and upper right corner of Fig. ), the absolute catalyzed TOF reaches its maximimum of 0.22 s -1 . Catalyzed rates are dominated by the large fluxes of N radicals to the catalyst and their subsequent reactions to NO or recombination to N 2 . These surface reactions become more effective at directing N into channels that produce NO than is the homogeneous phase, where the reverse Zeldovich reaction depletes NO. As a result, this regime is yellow in Fig. . At high N radical density but lower vibrational temperature (Fig. and upper left corner of Fig. ), surface reactions remain dominated by N adsorption and reaction to NO or N 2 .