Which of the following is the role of $\mathit{Mo}$ in the given equation?

${N_2}_{\left(g\right)}+3{H_2}_{\left(g\right)}\mathit{ }\overleftrightarrow{Fe/Mo}\mathit{ } 2N{H_3}_{\left(g\right)}$

$\mathit{Mo}$ is a catalyst promoter in the given equation.
Haber’s process manufactures ammonia ($N{H}_3$). In this process, pure nitrogen and hydrogen gas are reacted by a ratio of $1:3$ by the volume, and the temperature throughout the reaction is $400°\mathit{C }- 500°C$, and the pressure is $200\mathit{ – }900\mathit{ atm}$ pressure—the reaction forwards in the presence of iron as catalyst and $\mathit{Mo}$ as a promoter.
${N_2}_{\left(g\right)}+3{H_2}_{\left(g\right)}\mathit{ }\overleftrightarrow{\mathit{F}\mathit{e}\mathit{/}\mathit{M}\mathit{o}}\mathit{ } 2N{H_3}_{\left(g\right)}$