Dingjun Wang

Catalytic conversion of methane to benzene over Mo/ZSM-5

Dehydroaromatization of methane to benzene occurs over a 2 wt% Mo/ZSM-5 catalyst at 700‡C under non-oxidizing conditions. Following an initial induction period, during which CH4 reactant reduces the original Mo6+ ions in the zeolite to Mo2C and deposition of coke occurs, a benzene selectivity of ∼ 70% at a CH4 conversion of 8–10% could be sustained for more than 16 h. X-ray photoelectron spectroscopy and X-ray powder diffraction measurements indicate that the reduced Mo is highly dispersed in the channels of the zeolite. Initial activation of CH4 reactant occurs on Mo2C sites, leading to the formation of C2H4 as the primary product. The latter then undergoes subsequent oligomerization reactions on acidic sites of the zeolite to form aromatic products.

Effect of carbon dioxide on the selectivities obtained during the partial oxidation of methane and ethane over Li+/MgO catalysts

AtT ⩽ 650 °C carbon dioxide either formed during reaction or added to the system increases the selectivity for the desired hydrocarbon products during the oxidative coupling of methane and the oxidative dehydrogenation of ethane reaction over Li+/MgO catalysts. Similarly, CO2 inhibits secondary reactions of CH3-radicals with the surface of the Li+/MgO. The improved selectivities are attributed to the poisoning effect that CO2 has on the secondary reactions of alkyl radicals with the surface.

The conversion of methane to benzene over Mo/ZSM-5 zeolites in the absence of an oxidant

Methane may be converted to benzene over a Mo/ZSM-5 zeolite that is in the acidic form. Benzene selectivities of 65% have been achieved at methane conversion levels of ca. 10%. Mo2C is believed to activate CH4. Ethylene which is formed as an intermediate is converted to benzene over the acidic centers in the zeolite. The development of C6H6 selectivity during the first 1 h on stream is attributed to coke-induced constraints in the zeolite which inhibit the formation of polycyclic aromatics, including naphthalene.