The greener route to produce ethanal commercially is the oxidation of ethene with an ionic catalyst.

Explanation:

1. Catalytic cracking of ethanol:
- Catalytic cracking of ethanol involves the breaking down of ethanol molecules into smaller hydrocarbon molecules.
- This process requires high temperatures and produces a mixture of hydrocarbon gases, including ethene.
- The catalytic cracking process is energy-intensive and requires the use of fossil fuels as a heat source, contributing to greenhouse gas emissions.
- Additionally, the cracking process can generate a significant amount of waste and byproducts, further impacting the environment.

2. Oxidation of ethene with an ionic catalyst:
- The oxidation of ethene with an ionic catalyst is a more environmentally friendly route to produce ethanal commercially.
- This process involves the reaction of ethene (C2H4) with oxygen (O2) in the presence of an ionic catalyst, such as silver nitrate (AgNO3).
- The reaction proceeds under mild conditions and does not require high temperatures or the use of fossil fuels as a heat source.
- The ionic catalyst promotes the selective oxidation of ethene to ethanal, minimizing the formation of unwanted byproducts.
- The process has a high atom efficiency, meaning that a large percentage of the starting materials is converted into the desired product.
- The oxidation of ethene with an ionic catalyst is a more sustainable and efficient method compared to catalytic cracking of ethanol.

3. Steam reforming of methanol:
- Steam reforming of methanol involves the reaction of methanol with steam to produce hydrogen (H2) and carbon monoxide (CO).
- While this process is commonly used for hydrogen production, it is not a direct route to produce ethanal.
- The production of methanol, the precursor for this process, often involves the use of fossil fuels and releases greenhouse gases.
- Additionally, the reforming process requires high temperatures and can produce carbon dioxide as a byproduct.

4. Dehydrogenation of ethylene:
- The dehydrogenation of ethylene involves the removal of hydrogen atoms from ethylene (C2H4) to produce ethane (C2H4).
- This process requires high temperatures and often uses fossil fuels as a heat source.
- The dehydrogenation process is energy-intensive and can generate greenhouse gas emissions.
- It is not a direct route to produce ethanal and may require further reactions to convert ethane into ethanal.

In conclusion, the oxidation of ethene with an ionic catalyst is the greener route to produce ethanal commercially. It offers a more sustainable and efficient process compared to the other options mentioned.