Ostwald process performance:\nDuring nitric acid manufacture, catalytic oxidation of ammonia over platinum at about 800 °C converts NH3 to NO with approximately what percent conversion?

Introduction / Context:
The Ostwald process converts ammonia to nitric oxide (NO) over platinum–rhodium gauze at high temperature, followed by oxidation to NO2 and absorption to form HNO3. The initial converter performance is a key plant KPI, typically measured as the single-pass conversion of NH3 to NO under steady state. Knowing the characteristic conversion helps diagnose catalyst health and operating conditions.

Given Data / Assumptions:

• Operating temperature near 800–900 °C.
• Platinum-group metal gauze catalyst.
• Well-mixed feed with the proper NH3/O2 ratio and minimal poisons.

Concept / Approach:
Under optimized conditions, the oxidation of NH3 is highly selective and near-quantitative to NO at the reactor outlet. Practical plants achieve about 96–99% conversion of NH3 to NO in the first stage. The canonical exam value often cited is approximately 98% conversion, acknowledging minor side reactions (to N2 and N2O) and losses due to catalyst wear or maldistribution.

Step-by-Step Solution:
Recognize that NH3 oxidation is fast and exothermic over Pt–Rh gauze.Industrial converters are designed to achieve conversion in the high 90s.Select the closest standard figure from the options: 98%.

Verification / Alternative check:
Plant heat balances and downstream absorber loading imply high NO production; emissions controls target minor by-products (N2O). Operating manuals quote conversions approaching 98–99% on fresh, clean gauze.

Why Other Options Are Wrong:
38%, 68%, and 82% are too low for modern converters and would cause severe efficiency losses. 92% is closer but still below the widely referenced benchmark in well-operated units.

Common Pitfalls:
Confusing conversion with selectivity; although conversion is very high, selectivity to NO vs. N2O/N2 can vary with temperature, gauze condition, and mixing.

Final Answer:
98