Kinetics and mechanism of the oxidative coupling of methane over 1% Sr/La[sub 2]O[sub 3]

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7178904

Feng, Yan

The kinetics and mechanism of the oxidative coupling of methane on 1% Sr/La[sub 2]O[sub 3] were investigated in a flow reactor coupled with photoionization mass spectrometer. Methyl radicals (CH[sub 3] (g)) were quantitatively measured along the catalyst bed using photoionization mass spectrometry (PIMS) and laser photolysis technique. The determination of CH[sub 3] (g) production rate law, stoichiometric conversion of CH[sub 3] (g) to C[sub 2]H[sub 6] (g) and of C[sub 2]H[sub 6] (g) to C[sub 2]H[sub 4] (g), and conversion efficiency of CH[sub 4] (g) to CH[sub 3] (g) on this metal oxide catalyst advances knowledge on mechanism of the catalytic conversion of methane to higher hydrocarbons, a potential process to provide an alternative for the future fuels. Photoionization mass spectrometry technique was developed to study gas-phase kinetic studies of polyatomic free radicals. This technique has high selectivity for the detection of gas phase polyatomic radicals, which normally has low ionization energy, via selecting appropriate ionizing energy. CH[sub 3] production rates depend first order on [CH[sub 4]] and shows, (1) zero dependence of [O[sub 2]] when [O[sub 2]] is large (e.g. >10% of total carrier gas density), and (2) half order dependence of [O[sub 2]] when [O[sub 2]] is small. A mechanism, which assumes gas phase methane reacts with active surface sites generated by dissociatively adsorption of gas phase oxygen on catalyst surface, can best describe the observed CH3 production. Gas phase recombination of CH[sub 3] (g) can account for observed ethane production. At temperature less than 1100 K, gas phase pyrolysis of ethane cannot account for by heterogeneous reaction of ethane. The increase of catalyst activity will decrease the conversion efficiency of CH[sub 4] to CH[sub 3](g). Consequently, high selectivity of C[sub 2] production can only be achieved at low activity of catalyst surface.

• Research Organization: Catholic Univ. of America, Washington, DC (United States)
• OSTI ID: 7178904
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKALINE EARTH METAL COMPOUNDS
ALKANES
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COUPLING
HYDROCARBONS
KINETICS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
METHANE
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
REACTION KINETICS
STRONTIUM COMPOUNDS
SURFACE PROPERTIES