Dehydroaromatisaation

Dehydroaromatization is a class of catalytic reactions in which aliphatic hydrocarbons are converted into aromatic hydrocarbons through net removal of hydrogen. The process combines dehydrogenation, cyclization, and aromatization steps, often with the concurrent elimination of hydrogen gas. It is distinct from simple dehydrogenation and from conventional aromatization, as it emphasizes formation of an aromatic ring from saturated or partially unsaturated precursors, typically under gas-phase conditions and at elevated temperatures.

Typical substrates include cycloalkanes such as cyclohexane, which can be dehydroaromatized to benzene, releasing hydrogen: C6H12 → C6H6 + 3 H2. Propane and other light alkanes can also be converted to aromatics, notably benzene, under suitable catalysts and high temperatures. The scope and selectivity of products depend on the substrate, catalyst, and reaction conditions.

Catalysts employed for dehydroaromatization include metal-loaded zeolites and related solid catalysts. Common systems use gallium, indium, or zinc anchored on zeolites (for example Ga-ZSM-5) or platinum-group metals on alumina or silica supports. Reaction conditions typically involve high temperatures (approximately 500–700°C) and the presence of the hydrocarbon feed, with hydrogen partial pressure influencing selectivity. The reaction mechanisms are debated but involve initial dehydrogenation to produce olefins or cyclized intermediates, followed by cyclization to aromatic rings and final dehydrogenation.

Applications and challenges: DHA offers a route to aromatics from abundant alkanes, which is attractive for petrochemical feedstock diversification but faces issues of catalyst deactivation by coke, limited selectivity to single aromatic products, and high energy requirements. Ongoing research aims at improving catalyst design, lifespan, and selectivity, and at integrating dehydroaromatization with other refinery processes.