Elucidating the structure of the W and Mn sites on the Mn-Na2WO4/SiO2 catalyst for the oxidative coupling of methane (OCM) at real reaction temperatures
نویسندگان
چکیده
The performance of the Mn-Na2WO4/SiO2 catalyst for oxidative coupling methane (OCM) has been ascribed to crystalline phases that are not present at reaction temperatures (>700 °C). evolution W and Mn sites structure was monitored via in situ TPO-XRD, -Raman, -XANES spectroscopies. TPO-XRD shows identified on Mn-Na2WO4/SiO2, Na2WO4/SiO2, WO3/SiO2 catalysts room temperature do exist relevant OCM temperatures. ? ? ? ?-WO3, ? ?-cristobalite, cubic orthorhombic molten-Na2WO4 phase transitions occur upon heating. TPO-Raman spectra show bond order with octahedral (Oh) tetrahedral (Td) symmetry changes during ? ?-WO3 transitions, respectively. TPO-XANES due distortion degree variations because all samples preserve essentially W6+ valence Oh-Mn3+ always catalyst. Steady-state tests Oh-W6+ inactive Td-W6+ less distorted more active towards activation presence sites.
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ژورنال
عنوان ژورنال: Journal of Catalysis
سال: 2022
ISSN: ['0021-9517', '1090-2694']
DOI: https://doi.org/10.1016/j.jcat.2021.06.021