The temperature chosen is a compromise between yield and rate. Using a catalyst in the Haber process means that a lower temperature can be used whilst keeping the rate of reaction high.

However, the rate of reaction is low at low temperatures. So, as in the Haber process, a compromise temperature of 450 °C is chosen. If the pressure is increased, the equilibrium position moves ...

Haber on the A award of the Nobel Prize at Stockholm ... soon made it clear that the basis of an important technical process could be found in ammonia synthesis, and further work was undertaken ...