Oxygen pathways in oxidative coupling of methane and related processes. Case study: NaWMn/SiO2 catalyst

In situ X-ray diffraction computed tomography studies examining the thermal and chemical stabilities of working Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes during oxidative coupling of methane

“…However, it temporarily reappeared after the introduction of the reaction mixture containing pure CO 2 (possibly due to the CO 2 reduction by Mn 2+ /Mn 3+ ). This observation is in good agreement with previous work on a Na-Mn-W/SiO 2 catalyst-membrane system; 51,53 the active catalyst does not need to contain the crystalline Mn 2 O 3 phase. It is also clear that in the presence of CH 4 , the crystalline Mn 2 O 3 loses its long-range order, most likely due to bulk reduction to Mn 2+ .…”

Effect of thermal treatment on the stability of Na–Mn–W/SiO2 catalyst for the oxidative coupling of methane

“…It should be noted that the presence of Na could not be determined with these measurements. can occur between these components that are bound to have an effect on the catalyst activity and stability 52 . The catalyst performance during the OCM reaction was monitored with mass spectrometry analysis and the results are presented in Figure 8.…”

Fluctuating Storage of the Active Phase in a Mn‐Na2WO4/SiO2 Catalyst for the Oxidative Coupling of Methane

“…This is in agreement with O 2 ‐TPD experiments performed by Gordienko et al., who identified two forms of lattice oxygen that may potentially contribute to catalysis upon desorption at relevant temperatures. The source of oxygen has been attributed to manganese oxide, or any unspecified lattice oxygen . Potentially more decisive is the release of an active form of sodium oxide species that has been proposed to catalyse the oxidative coupling of methane by generation of OH radicals at high temperatures, presumably under involvement of homogeneous gas‐phase reactions due to the high volatility of sodium compounds under operation conditions …”

“…Furthermore, the supported Mn 7 SiO 12 phase was observed to function as oxygen‐donor at working temperatures, which further enhances sodium oxide formation and, thus, has implications for the reactivity. However, the availability of adsorbed or lattice oxygen due to the presence of redox‐active elements alone cannot be responsible for the outstanding performance of the Mn‐Na 2 WO 4 /SiO 2 catalyst and does not explain the mechanistic role and importance of Na in this system. On the other hand, a pure silica‐supported sodium oxide would rapidly deactivate under the severe reaction conditions applied in the oxidative coupling of methane .…”

“…Despite extensive investigations, both the active site and working mechanism of the catalyst remain much debated . In general, most research has been directed towards the structural characterization of the catalyst before and after the reaction or in a quenched state . Only limited efforts have, however, been made to elucidate the nature of the catalyst under working conditions.…”