1. Ru and Os are more active catalysts for ammonia synthesis, but why usually use Fe-based catalysts rather than Ru or Os for ammonia synthesis?

Is there any other reasons except the iron is a cheap and abundant resource?

2. According to Le Chatelier's principle, the higher the pressure and the lower the temperature, the better the ammonia yield.

So question is that ammonia synthesis is a exothermic reaction but why need high temperature?

3. Why the ammonia synthesis from N2 and H2 over Fe-based catalyst is very sensitive to the presence of CO gas in the feed?