Secondary reactions of methyl radicals with lanthanide oxides: their role in the selective oxidation of methane

• Published in: Journal of physical chemistry (1952) 1989-04, Vol.93 (8), p.2896-2898
• Main Authors: Tong, Youdong, Rosynek, Michael P, Lunsford, Jack H
• Format: Article
• Language: English
• Subjects: 400500 - Photochemistry; ACTIVATION ENERGY; ALKANES; ALKYL RADICALS; CERIUM COMPOUNDS; CERIUM OXIDES; CHALCOGENIDES; CHEMICAL REACTION KINETICS; CHEMICAL REACTIONS; Chemistry; DATA; EFFICIENCY; ELECTRON SPIN RESONANCE; ENERGY; EUROPIUM COMPOUNDS; EUROPIUM OXIDES; Exact sciences and technology; EXPERIMENTAL DATA; Free radicals chemistry; HYDROCARBONS; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; LANTHANUM COMPOUNDS; LANTHANUM OXIDES; MAGNETIC RESONANCE; MATRIX ISOLATION; METHANE; METHYL RADICALS; NEODYMIUM COMPOUNDS; NEODYMIUM OXIDES; NUMERICAL DATA; Organic chemistry; ORGANIC COMPOUNDS; OXIDATION; OXIDES; OXYGEN COMPOUNDS; PRASEODYMIUM COMPOUNDS; PRASEODYMIUM OXIDES; RADICALS; RARE EARTH COMPOUNDS; REACTION KINETICS; Reactivity and mechanisms; RESONANCE; SAMARIUM COMPOUNDS; SAMARIUM OXIDES; TERBIUM COMPOUNDS; TERBIUM OXIDES; YTTERBIUM COMPOUNDS; YTTERBIUM OXIDES
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100345a012

Reactions between methyl radicals and certain members of the lanthanide oxide series have been studied by using a matrix isolation electron spin resonance technique. Methyl radicals react extensively with the lanthanide-metal oxides CeO{sub 2}, Pr{sub 6}O{sub 11}, and Tb{sub 4}O{sub 7}, all of which have multiple cationic oxidation states. By contrast, the oxides La{sub 2}O{sub 3}, Nd{sub 2}O{sub 3}, Sm{sub 2}O{sub 3}, Eu{sub 2}O{sub 3}, and Yb{sub 2}O{sub 3} react with CH{sub 3}{sup {sm bullet}} radicals to only a small extent. Consistent with this observation, the former group of oxides is ineffective in the generation of CH{sub 3}{sup {sm bullet}} radicals which emanate into the gas phase. The reaction of CeO{sub 2} with CH{sub 3}{sup {sm bullet}} radicals is strongly inhibited by the addition of Na{sub 2}CO{sub 3}, and consequently radical production is enhanced. This effect is manifested in the catalytic properties of CeO{sub 2}, which is a complete oxidation catalyst in its pure form but becomes a good catalyst for the oxidative coupling of methane following the addition of Na{sub 2}CO{sub 3}.