Mechanistic aspects of the oxidative coupling of methane over a NaOH/CaO catalyst

Comprehensive Kinetics of Oxidative Coupling of Methane over the La2O3/CaO Catalyst

“…For the La 2 O 3 /CaO catalyst this effect was explained by competitive adsorption of oxygen, methane, and carbon dioxide. A similar explanation was proposed by Lehmann and Baerns (1992) for the NaOH/CaO catalyst. In the equation used for calculation of the rate of ethane formation (eq 12) an absorption term for methane was neglected.…”

“…Rate Equations. The maximum in the rate of hydrocarbon formation with respect to oxygen partial pressure measured over the La 2 O 3 /CaO catalyst was also re-ported for Sm 2 O 3 (Otsuka et al, 1986) and NaOH/CaO (Lehmann and Baerns, 1992). For the La 2 O 3 /CaO catalyst this effect was explained by competitive adsorption of oxygen, methane, and carbon dioxide.…”

“…The water gas shift reaction (steps 9 and 10), which can influence the CO-to-CO 2 ratio, was mostly neglected in published kinetics. However, this reaction was experimentally confirmed for many catalysts in the temperature range between 700 and 800 °C, e.g., for Sr/La 2 O 3 (Deboy and Hicks, 1988) Li/ZnO (Zhang et al, 1988), Li/MgO (Roos et al, 1987), NaOH/CaO (Lehmann and Baerns, 1992), PbO/SiO 2 (Lugo et al, 1993), Sm 2 O 3 (Ekstrom, 1992), and CaO/CeO 2 (Zhang and Baerns, 1991).…”

“…Carbon oxides are often lumped to a pseudocomponent CO x which is generated parallel to ethane. The latter approach was previously applied in the kinetics developed for catalysts consisting of NaOH/CaO (Lehmann and Baerns, 1992), Sm 2 O 3 (Otsuka et al, 1986), PbO/MgO (Asami et al, 1987), Li/MgO (Mirodatos and Martin, 1988), PbO/Al 2 O 3 (Mleczko et al, 1994), and NaNiTiO 3 (Santamaria et al, 1991). Alternatively, formation of CO 2 as the only nonselective, primary product of methane oxidation was proposed, e.g.…”

Strategies To Improve the Activity While Maintaining the Selectivity of Oxidative Coupling of Methane at La2O3: A Density Functional Theory Study

“…Recently, the oxidative coupling of methane (OCM) has been proposed to be a promising approach to tackle this challenge. , In the OCM reactions, CH 4 can be directly converted to C 2 H 6 and C 2 H 4 with H 2 O as the byproduct in the presence of O 2 and efficient catalysts . It was commonly conceived that the first step of the OCM reactions involves the dehydrogenation of CH 4 and the formation of gas-phase methyl radicals (CH 3 · ), − which was supported by experimental evidence of the identification of this species. , Subsequently, the coupling of two CH 3 · gives rise to the C 2 H 6 product, and the C 2 H 4 can occur via further dehydrogenation of C 2 H 6 . At the same time, excessive oxidation of methyl groups on the surface or in the gas phase leads to the formation of CO and CO 2 as the unwanted byproducts .…”