Due to a lack of evidence-based molecular level understanding of OCM surface reaction mechanism over the Mn2O3-Na2WO4/SiO2 catalyst, most historically accepted OCM mechanisms like the Lunsford mechanism and the Li mechanism speculate Mn-O bonds to be critically involved in either CH4 or O2 activation during OCM reaction, respectively. The Lunsford mechanism postulates that WOx serves only as the stabilizing agent while all catalytic steps occur over Mn-O-Na sites. On the other hand, the Li mechanism posits a two-site mechanism where adjacent WO4 and Mn2O3 sites are involved in a redox cycle switching between W5-6+ and Mn2-3+ states. This presentation will focus on elucidating the nature and role of surface MnaOb and Na-WOx catalytic sites based on in-situ characterization (UV-vis DRS, Raman), temperature-programmed surface reaction (TPSR), steady-state catalytic tests, and DFT modelling. Specifically, the validity of both Lunsford mechanism (site: Mn-O-Na) and Li mechanism (site: adjacent WO4, Mn2O3) will be tested based on advanced experimental characterization of a series of model catalysts and ab initio computational insights.

Nature and role of MnaOb surface sites in SiO2-supported, Mn- & Na-promoted Tungsten oxide catalysts (Mn-Na-WOx/SiO2) for oxidative coupling of methane (OCM)

ACS Spring Meeting 2021

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