Plasma-catalytic ammonia synthesis is known since early 1900s but the possible reaction pathways are currently under investigation. In this article, we present the use of various transition metals and gallium-rich alloys for plasma-catalytic ammonia synthesis. The best three metallic catalysts were identified to be Ni, Sn and Au with the highest ammonia yield of 34%. Furthermore, as compared to its constituent metals some alloys presented about 25-50% better yields. The metals employed were classified in two different categories according to their behavior during ammonia plasma-catalysis. Category I metals are nitrophobic and the measured concentration of Hα in the gas phase inversely correlates with ammonia yield and directly correlates with the binding strength of H on the catalyst surface. Whereas for metals in Category II, the concentration of Hα tend to be lower than for category I metals, consistent with their theoretical predicted behavior as hydrogen sinks. For these metals, the concentration of Hα correlates with ammonia yield.