Steam reforming of naphtha for ammonia synthesis gas: Thermochemical nature of the primary reforming step (with nickel catalyst and steam) is best described as

Introduction / Context:
Ammonia plants generate hydrogen by reforming hydrocarbons. When naphtha is the feed, it is vaporized, mixed with steam, and passed over a nickel-based catalyst in heated tubes. Recognizing that this stage consumes heat is critical for furnace design, energy integration, and catalyst life management.

Given Data / Assumptions:

• Feed: light naphtha hydrocarbons (approximate paraffinic mix).
• Reactor: tubular, fired primary reformer with Ni/Al2O3 catalyst.
• Process: hydrocarbons + H2O → CO + H2 (with shift downstream).

Concept / Approach:
Steam reforming breaks C–C and C–H bonds using steam, forming H2 and CO/CO2. The net chemistry is strongly endothermic, requiring continuous high-temperature heat input from a dedicated furnace. Catalysis is essential to achieve practical rates and selectivity; without Ni catalysts, the process would be too slow and would coke rapidly. Subsequent secondary reforming/shift steps have different heat effects, but the primary reforming step remains endothermic and catalytic.

Step-by-Step Solution:

Verification / Alternative check:
Energy balances show large radiant duty to sustain reformer outlet temperatures; flue gas heat recovery confirms substantial heat input.

Why Other Options Are Wrong:

• Autocatalytic/non-catalytic: contradicts established Ni-catalyzed practice.
• Exothermic: opposite of observed heat requirement.
• Athermal/self-sustaining: not physically accurate for steam reforming.

Common Pitfalls:
Confusing steam reforming with partial oxidation (exothermic); many modern plants use autothermal reforming combining both, but the pure steam reformer is endothermic.

Final Answer:
Endothermic (heat absorbed) and catalytic.