Ammonia synthesis converter operating window: choose the most appropriate combination of pressure and temperature used in modern Haber–Bosch converters for high conversion with viable kinetics.

Introduction / Context:
Ammonia synthesis (N2 + 3 H2 ⇌ 2 NH3) is exothermic and involves a reduction in total moles. Process conditions must balance equilibrium (favours low temperature and high pressure) with kinetics (favours higher temperature). Modern converters use promoted iron or ruthenium catalysts in a defined pressure–temperature window to achieve practical rates and yields.

Given Data / Assumptions:

• Catalysts require elevated temperature for acceptable rates.
• Equilibrium favours higher pressure and moderate temperature.
• Industrial design optimises between 150–300 atm and roughly 400–500 °C.

Concept / Approach:
High pressure pushes equilibrium toward ammonia (fewer moles), while very high temperature would harm equilibrium conversion despite faster kinetics. Conversely, too low a temperature slows the reaction excessively. Thus, the standard operating window sits around a few hundred atmospheres and mid-range temperatures of 400–500 °C.

Step-by-Step Solution:

Verification / Alternative check:
Published plant data and licensor information commonly report loop pressures on the order of 100–200 bar and converter inlets around 400–450 °C, with multi-bed quench or interbed cooling.

Why Other Options Are Wrong:

• 200 atm & 1000 °C: temperature far too high; equilibrium would collapse.
• 450 atm & 200 °C: kinetics too slow at 200 °C.
• 450 atm & 550 °C: excessive temperature; equilibrium penalty.
• Near 1 atm & below 200 °C: impractically slow and unfavourable equilibrium.

Common Pitfalls:
Assuming “higher temperature is always better”; for exothermic equilibria, too much heat reduces conversion.

Final Answer:
about 150–300 atm and 400–500 °C