Which of the following is not an example of heterogeneous catalytic reaction ?

Answer

To determine which of the following is not an example of a heterogeneous catalytic reaction, we need to analyze each option provided:

1. **Ostwald's Process**:
- In this process, ammonia (NH3) reacts with oxygen in the presence of a catalyst (platinum or rhodium) at high temperature and pressure to produce nitrogen oxides (NO) and water.
- Here, the catalyst is in a different phase (solid) than the reactants (gases), which qualifies it as a heterogeneous catalytic reaction.

2. **Combustion of Coal**:
- In this reaction, carbon (from coal) reacts with oxygen to produce carbon dioxide (CO2).
- Notably, there is no catalyst involved in this reaction; it is a direct combustion reaction. Therefore, this is not a heterogeneous catalytic reaction.

3. **Hydrogenation of Vegetable Oils**:
- In this reaction, unsaturated vegetable oils (with double bonds) react with hydrogen (H2) in the presence of a nickel catalyst.
- The catalyst (nickel) is in a different phase (solid) than the reactants (liquid), making this a heterogeneous catalytic reaction.

Based on the analysis above, the option that is not an example of a heterogeneous catalytic reaction is:

**Combustion of Coal.**

### Step-by-Step Solution:
1. **Identify the reactions**: List the processes given in the options.
2. **Analyze each reaction**:
- **Ostwald's Process**: Involves a catalyst (heterogeneous).
- **Combustion of Coal**: No catalyst present (not heterogeneous).
- **Hydrogenation of Vegetable Oils**: Involves a catalyst (heterogeneous).
3. **Determine the correct answer**: Identify which reaction does not involve a catalyst.