Detailed kinetic modeling of catalytic oxidative coupling of methane

Autothermal Oxidative Coupling of Methane over Pt/Al2O3 Catalysts Doped with Rare Earth Oxides

“…2C). Since sufficiently high temperatures were reported as prerequisite for methyl radical formation, subsequent gas phase recombination to form C 2 H 6 , and subsequent dehydrogenation [27,[29][30][31], this more pronounced heat evolution is, in addition to methyl radical production from heterogeneous reaction pathways, an important factor that enables the higher C 2 selectivities observed over the REO-doped catalyst samples (Fig. 1A).…”

“…The correlation between the temperature, the conversion of oxygen, and the product composition became particularly clear in recent mechanistic studies by Chawla et al [30,31]. On the one hand, oxidation reactions typically consume the majority of O 2 , which results in pronounced heat evolution.…”

“…OH or O radicals, which form under these harsh conditions, attack CH 4 and result in methyl radical formation. However, despite the high oxygen content in the feed gas stream, also pyrolytic reaction pathways become relevant, during which H radicals attack CH 4 molecules to form species [31]. Herewith, the OCM reaction mechanism exhibits parallels to reactions taking place during non-oxidative coupling of methane (NOCM) [18,41,42].…”

“…Please note that the temperature shown in Fig. 2C is the downstream temperature monitored with a distance of about 5 mm from the catalyst and is therefore not representing the temperature inside the catalyst itself, which is likely even higher [29][30][31]. La 2 O 3 is known to stabilize Al 2 O 3 by either inhibiting a phase transition or by forming mixed oxides [44][45][46].…”

“…Due to high temperatures resulting from the simultaneously ongoing CPOX at very short contact times, the reaction runs autothermally and consequently an additional energy input becomes obsolete. Recent studies by Chawla et al [30,31] combining experiments and simulations underscore that methyl radicals play a key role during Pt-catalyzed OCM (Pt-OCM). These CH 3 • species mainly originate from homogeneous gas phase chemistry that is enabled by the high reaction temperatures, and their formation typically involves the attack of an H radical, an OH radical, or an O radical on the CH 4 molecule.…”