The highest industrial consumption of molecular hydrogen is to produce compounds of element :

Hydrogen combines with nitrogen to produce Ammonia in Haber's process. <br/><br/> $\mathrm{N}_{2}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{g})$ <br/><br/> In this process, iron oxide is used with small amounts of $\mathrm{K}_{2} \mathrm{O}$ and $\mathrm{Al}_{2} \mathrm{O}_{3}$ to increase the rate of attainment of equilibrium. <br/><br/> Optimum conditions for the production of ammonia are a pressure of $200 \mathrm{~atm}$ and a temperature of $700 \mathrm{~K}$. <br/><br/> Earlier, iron was used as a catalyst with molybdenum as a promoter in this reaction.