A mixture of catalysts Cr₂O₃ + Al₂O₃ + SiO₂ at 500°C is used when benzene is prepared from which compound?

Benzene can be prepared from n-hexane (C₆H₁₄) through a process known as catalytic dehydrocyclization. This method uses a mixture of catalysts — Cr₂O₃ (chromium oxide), Al₂O₃ (aluminum oxide), and SiO₂ (silicon dioxide) — at a high temperature of about 500°C. These catalysts help convert the straight-chain hydrocarbon (n-hexane) into a cyclic aromatic compound (benzene) by removing hydrogen atoms and rearranging the carbon skeleton.

During the reaction, n-hexane undergoes simultaneous dehydrogenation (loss of hydrogen) and cyclization (ring formation). The chemical reaction can be summarized as:
C₆H₁₄ → C₆H₆ + 4H₂.

The catalyst mixture provides the ideal surface for this transformation. Chromium oxide acts as the main active catalyst promoting dehydrogenation, while alumina and silica increase the surface area and stabilize the reaction medium. This combination ensures high efficiency and thermal stability at elevated temperatures.

The resulting product, benzene (C₆H₆), is a stable aromatic compound with a delocalized π-electron system. The hydrogen gas released is often collected as a useful by-product. This industrial process is part of petroleum reforming, which increases the aromatic content of fuels and provides raw materials for the chemical industry.

Benzene produced through this route is widely used in manufacturing plastics, detergents, synthetic fibers, dyes, and pharmaceuticals. Understanding this catalytic conversion is essential in organic chemistry as it demonstrates how hydrocarbons are transformed into aromatic compounds through controlled industrial reactions.