Ammonia synthesis catalyst and promoter functions: In the Haber–Bosch process, a catalyst is essential because the reaction is reversible and nitrogen dissociation is difficult. What is the principal role of adding a promoter along with the catalyst?

Introduction / Context:
Industrial ammonia synthesis uses an iron-based catalyst operating at elevated temperatures and pressures. Promoters—minor additives such as K2O, Al2O3, CaO, and others—are widely employed to enhance performance and durability of the catalyst.

Given Data / Assumptions:

• Standard iron (magnetite-derived) catalyst system.
• Operation under typical Haber–Bosch conditions.
• Promoters used in conventional proportions.

Concept / Approach:
Promoters serve multiple roles: electronic/structural modification that boosts intrinsic activity (e.g., potassium as an electronic promoter), stabilization against sintering and poisoning, and improvement of mechanical strength and thermal robustness via structural promoters (e.g., alumina). Because all these functions are beneficial and commonly cited, the inclusive statement is correct.

Step-by-Step Solution:
Electronic promoters raise activity/selectivity by modifying adsorption energetics.Structural promoters enhance strength and thermal stability, resisting sintering.Collectively, promoters stabilize, strengthen, and improve effectiveness → choose 'All of the above'.

Verification / Alternative check:
Plant experience shows promoted catalysts maintain activity longer and tolerate thermal cycling better than unpromoted iron, confirming the multiple roles.

Why Other Options Are Wrong:
Each single-role option is incomplete; promoters typically deliver several benefits simultaneously.

Common Pitfalls:

• Confusing promoters with poisons; small amounts of certain species (e.g., sulfur) are harmful, not promotional.
• Overlooking that overpromotion can alter pellet strength or diffusion properties.

Final Answer:
All of the above (a, b, and c)