We have examined HCN synthesis by the ammoxidation of CH4, C2H6, and CH4/C2H6 mixtures in air or Oz at atmospheric pressure on alpha-Al2O3 foam monoliths coated with 1-10 wt % Pt and on Pt-10% Ph gauzes. The HCN reaction system was found to be highly sensitive to the catalyst microstructure because we observed activation and differences in performance on catalysts with different support materials. For CH4 ammoxidation on Pt monoliths we observe HCN yields > 63% based on CH4 and NH3 fed which is comparable to yields obtained on commercially used Pt-10% Ph gauzes (similar to 65%). With C2H6 rather than CH4, we achieve HCN yields of similar to 42% (carbon and nitrogen basis). We also examined CH4/C2H6; mixtures (at fixed C/N and (C + N)/O-2) for HCN synthesis. HCN yields were found to decrease by 5-7% with increasing C2H6 in the feed hydrocarbon mixture (up to 14%). Results for experiments with Pt-10%Rh gauzes used commercially are shown in all cases to allow comparisons with Pt monoliths. C2H6 ammoxidation on Pt monoliths and gauzes at acetonitrile synthesis stoichiometries yields negligible amounts of higher nitriles (< 0.01%), although HCN is produced on both. C2H4 is the dominant product on the monoliths while CO is the dominant product on the gauze.