Oxidative dimerization of methane over sodium-promoted calcium oxide

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/0021-9517(88)90089-9· OSTI ID:6961309

Lin, C; Wang, J; Lunsford, J H

Sodium-promoted calcium oxides are active and selective catalysts for the partial oxidation of methane to ethane and ethylene using molecular oxygen as an oxidant. In a conventional fixed-bed flow reactor, operating at atmospheric pressure, a 45% C/sub 2/ (sum of ethane and ethylene) selectivity was achieved at a 33% methane conversion over 2.0 g of 15 wt% Na/CaO catalyst at 725/sup 0/C with a gas mixture of CH/sub 4//O/sub 2/ = 2. The other products were CO, CO/sub 2/, and H/sub 2/. EPR results indicated that (Na/sup +/O/sup -/) centers in Na/CaO are responsible for the catalytic production of CH/sub 3//sup ./ from methane via hydrogen atom abstraction. These CH/sub 3//sup ./ radicals dimerize, primarily in the gas phase, to form C/sub 2/H/sub 6/, which further oxidizes to C/sub 2/H/sub 4/. Increasing temperatures reverse the gas-phase equilibrium CH/sub 3//sup ./ + O/sub 2/ in equilibrium CH/sub 3/O/sub 2//sup ./ to produce more CH/sub 3//sup ./ and increase the C/sub 2/ selectivity. The CH/sub 3/O/sub 2//sup ./ eventually is converted to carbon oxides under the reaction conditions employed; therefore, increasing O/sub 2/ pressures decrease the C/sub 2/ selectivity. There is evidence that CH/sub 3/O/sub 2//sup ./ in the presence of C/sub 2/H/sub 6/ initiates a chain reaction that enhances the methane conversion. The addition of Na/sup +/ to CaO also reduces the surface area of the catalysts, thus minimizing a nonselective oxidation pathway via surface methoxide intermediates.

• Research Organization: Texas A and M Univ., College Station (USA)
• OSTI ID: 6961309
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 111:2; ISSN JCTLA
• Country of Publication: United States
• Language: English

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CALCIUM OXIDES
CATALYTIC EFFECTS
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