Thank you! Presumably if you had some way of rapidly removing the ammonia produced from the reaction, like maybe a high-temperature highly polar solvent that r

Thank you! Presumably if you had some way of rapidly removing the ammonia produced from the reaction, like maybe a high-temperature highly polar solvent that reacted reversibly with the ammonia, but didn't dissolve much hydrogen or nitrogen, you could get by with a lower equilibrium amount of ammonia and thus much lower pressure. Anhydrous phosphoric acid seems like a potential candidate? But that's obvious enough that people probably tried it a century ago.