Measurements of kinetic isotope effects and hydrogen/deuterium distributions over methane oxidative coupling catalysts

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90262-5· OSTI ID:6777113

Nelson, P F; Lukey, C A ^[1]; Cant, N W ^[2]

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1. CSIRO Division of Coal Technology, New South Wales (Australia)
2. Macquarie Univ., New South Wales (Australia)

The kinetic isotope effect for CH{sub 4} compared to that for CD{sub 4} has been measured for the oxidative coupling reaction of methane over Li/MgO, SrCO{sub 3}, and Sm{sub 2}O{sub 3} catalysts in a flow reactor. Each catalyst gave results consistent with C-H bond breaking being the slow step. For temperatures between 680-780 C over Li/MgO, k{sub H}/k{sub D} decreased slightly with temperature. The isotope effect for ethane production was more sensitive to the level of conversion and declined from 1.8 at low conversion to near unity under conditions where the ethylene to ethane ratio was high ({approximately}1). Selectivities to hydrocarbons were lower with CD{sub 4} and did not change with decreased flow rates, implying that either CO{sub x} and C{sub 2} products arise by totally separate slow steps or, if a common step with CH{sub 3} radicals is involved, then CO{sub x} formation occurs on the catalyst. Experiments with CH{sub 4}/CD{sub 4} mixtures showed that CH{sub 3}CD{sub 3} and CH{sub 2}CD{sub 2} were the dominant mixed products. The distribution of the ethanes always reflected the relative concentrations of CH{sub 3} and CD{sub 3} determined by the kinetic isotope effect. At low ethylene to total C{sub 2} ratios ({approximately}0.2) this was also true for ethylene; but at higher ratios substantial exchange to produce ethylenes other than C{sub 2}H{sub 4}, CH{sub 2}CD{sub 2}, and C{sub 2}D{sub 4} occurred. The concentration of the exchanged methanes correlated with total methane conversion but was dependent on the surface. Exchange in the ethylenes also correlated with exchange in the methanes and purely gas phase processes appear at least partially responsible. H{sub 2}:HD:D{sub 2} ratios are always at equilibrium and exchange also occurs between CD{sub 4} and H{sub 2}.

• OSTI ID: 6777113
• Journal Information: Journal of Catalysis; (USA), Vol. 120:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
LITHIUM
CATALYTIC EFFECTS
MAGNESIUM OXIDES
METHANE
CATALYTIC REFORMING
OXIDATION
SAMARIUM OXIDES
STRONTIUM CARBONATES
CARBON OXIDES
CHEMICAL REACTION KINETICS
DEUTERIUM
ETHANE
ETHYLENE
ISOTOPE RATIO
MIXTURES
SYNTHESIS
TEMPERATURE DEPENDENCE
ALKALI METALS
ALKALINE EARTH METAL COMPOUNDS
ALKANES
ALKENES
CARBON COMPOUNDS
CARBONATES
CHALCOGENIDES
CHEMICAL REACTIONS
DISPERSIONS
ELEMENTS
HYDROCARBONS
HYDROGEN ISOTOPES
ISOTOPES
KINETICS
LIGHT NUCLEI
MAGNESIUM COMPOUNDS
METALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
REACTION KINETICS
REFORMER PROCESSES
SAMARIUM COMPOUNDS
STABLE ISOTOPES
STRONTIUM COMPOUNDS
030300* - Natural Gas- Drilling
Production
& Processing