Oxidative coupling of methane over Na{sub 2}WO{sub 4}/CeO{sub 2} and related catalysts
- Texas A & M Univ., College Station, TX (United States)
Na{sub 2}WO{sub 4}/CeO{sub 2} is an active and selective catalyst for the oxidative coupling of methane (OCM). At 780{degrees}C and using a reactant feed of CH{sub 4}:O{sub 2}He=4.8:1.0:5.6, a C{sub 2} selectivity in excess of 70% can be achieved over a 9.4 mol% Na{sub 2}WO{sub 4}/CeO{sub 2} catalyst at a CH{sub 4} conversion of 22%. By contrast, the C{sub 2} selectivity exhibited by pure CeO{sub 2} under the same reaction conditions, in the absence of Na{sub 2}WO{sub 4} promoter, is <10%. The promoted catalyst is relatively insensitive to deactivation by formation of surface carbonate species. A comparable effect occurs for Na{sub 2}WO{sub 4} and CeO{sub 2} remain as discrete phases, and that no new bulk compounds or solid solutions are formed. X-ray photoelectron spectra demonstrate that all surface oxygen exists as lattice O{sup 2-} on the calcined catalysts and reveal no evidence for additional surface oxygen species, such as O{sub 2}{sup 2-} or O{sup -}, that might serve as sites CH{sub 4} activation. Pulse reaction experiments show that bulk lattice oxygen species do not participate directly in the activation of methane exist only in the presence of gas phase oxygen. Ion scattering spectroscopy and in situ Raman spectroscopy indicate that the initial CeO{sub 2} surface of the calcined catalyst is completely covered by one or more layers of Na{sub 2}WO{sub 4}, which exists in the molten state under reaction conditions. 20 refs., 14 figs., 5 tabs.
- OSTI ID:
- 98973
- Journal Information:
- Journal of Catalysis, Vol. 154, Issue 1; Other Information: PBD: Jun 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Deciphering the Mechanistic Role of Individual Oxide Phases and Their Combinations in Supported Mn–Na2WO4 Catalysts for Oxidative Coupling of Methane
Elementary reactions in the oxidative coupling of methane over Mn/Na{sub 2}WO{sub 4}/SiO{sub 2} and Mn/Na{sub 2}WO{sub 4}/MgO catalysts