ANS:A - dehydrogenation of naphthenes.

The main reaction in catalytic reforming of naphtha is the dehydrogenation of naphthenes. Here’s why: Catalytic reforming is a process aimed at increasing the octane number of naphtha, which is a gasoline blending component. The primary reactions involved include:

• Dehydrogenation of Naphthenes: This reaction involves removing hydrogen atoms from naphthenic hydrocarbons (also known as cycloalkanes) to form aromatic hydrocarbons. This process increases the octane rating of the gasoline fraction.
• Isomerization: Isomerization reactions convert straight-chain or normal paraffins into branched-chain isoparaffins, which also contribute to higher octane ratings.
• Dehydrocyclization: This reaction converts paraffins and naphthenes into aromatic hydrocarbons, further enhancing the octane number of the gasoline product.

• Hydrogenation of Naphthenes: This would reduce the octane rating as it adds hydrogen atoms to naphthenes, making them more saturated.
• Hydrocracking of Paraffins: Hydrocracking breaks down heavier hydrocarbons into lighter ones, which is not the primary focus of catalytic reforming.
• Saturation of Olefins: Saturation involves adding hydrogen to olefins (alkenes), which would not increase the octane rating but rather decrease it by reducing the number of double bonds.