Ammonia synthesis catalyst (Haber–Bosch): Which catalyst material is used in finely divided, promoted form for the industrial manufacture of ammonia from nitrogen and hydrogen?

Introduction:The Haber–Bosch process synthesizes ammonia (NH3) by reacting nitrogen with hydrogen over a heterogeneous catalyst at elevated temperatures and pressures. Catalyst choice dictates activity, selectivity, and operating conditions.

Given Data / Assumptions:

• Reaction: N2 + 3 H2 ⇌ 2 NH3.
• Typical conditions: 350–550°C, 100–250 bar.
• Need a robust, economical, and active catalyst.

Concept / Approach:Promoted iron (wustite-derived) catalysts, often containing potassium, alumina, calcium, and other promoters, are standard in ammonia plants due to cost-effectiveness and proven longevity. While ruthenium-based catalysts are more active per site, they are used in specialized low-pressure designs. Alternatives listed serve other processes: nickel for methanation/hydrogenation, vanadium pentoxide for SO2 oxidation, alumina as a support, copper chromite for hydrogenations.

Step-by-Step Solution:Match process to catalyst: Haber–Bosch → promoted iron.Eliminate catalysts associated with other reactions.Select “iron” as the correct answer.

Verification / Alternative check:Ammonia plant licensors and textbooks consistently specify magnetite/wustite-derived iron catalysts with promoters as the workhorse for NH3 synthesis loops.

Why Other Options Are Wrong:

• Nickel: Methanation/hydrogenation, not primary NH3 synthesis catalyst.
• V2O5: Catalyzes SO2 → SO3 in sulfuric acid plants.
• Alumina: Common support/promoter, not the active metal.
• Copper chromite: Hydrogenation and dehydrogenation, not NH3 synthesis.

Common Pitfalls:Confusing supports/promoters with the active catalytic phase; in ammonia synthesis, elemental iron provides the active sites for N2 dissociation.

Final Answer:iron