Sm[sub 2]O[sub 3]/Al[sub 2]O[sub 3] catalysts for methane coupling. Influence of the structure of surface Sm-Al-O phases on the reactivity

• Published in: Journal of physical chemistry (1952) Vol. 97:36
• Main Authors: Capitan, M.J., Malet, P., Centeno, M.A., Munoz-Paez, A., Carrizosa, I., Odriozola, J.A.
• Format: Journal Article
• Language: English
• Published: United States 09.09.1993
• Subjects: 661300 > Other Aspects of Physical Science > (1992-); ALKANES; ALUMINIUM COMPOUNDS; ALUMINIUM OXIDES; CATALYSTS; CHALCOGENIDES; CHEMICAL REACTIONS; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CRYSTAL STRUCTURE; DIMERIZATION; HYDROCARBONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METHANE; ORGANIC COMPOUNDS; OXIDATION; OXIDES; OXYGEN COMPOUNDS; POLYMERIZATION; RARE EARTH COMPOUNDS; SAMARIUM COMPOUNDS 400201 > Chemical & Physicochemical Properties; SAMARIUM OXIDES; SURFACE PROPERTIES
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100138a027

The oxidative dimerization of methane has been studied over samarium oxide supported on alumina as a function of the samarium loading and the calcination temperature. The structure of the supported phase has been determined by EXAFS. The EXAFS results state that all the samarium ions are present at the catalyst surface for Sm[sub 2]O[sub 3] contents lower than 20% w/w. At the higher loadings tried, crystalline phases containing Sm appear, their structure depending upon the calcination temperature. The activity/selectivity toward C[sub 2] per exposed samarium ion is higher for samples containing less than a monolayer of samarium. In this case, the coordination polyhedron around samarium ions points to a nonordered structure that blocks highly reactive sites on the alumina surface. On increasing the samarium loading, two phases develop depending upon the calcination temperature; at low temperatures an oxide-like structure grows over the alumina support while at higher temperatures a perovskite-like phase evolves. For the same samarium loading, the oxide-like structure shows better selectivity toward C[sub 2] than the SmAlO[sub 3] phase. 43 refs., 10 figs., 8 tabs.