Carbonylation of Dimethyl Ether on Rh/Cs2HPW12O40: Solid-State NMR Study of the Mechanism of Reaction in the Presence of a Methyl Iodide Promoter
Journal of Catalysis
, E-ISSN: 1090-2694
||12-Tungstophosphoric acid, 13C solid-state NMR, Carbon monoxide, Carbonylation, Dimethyl ether, Mechanism, Methyl iodide promoter, Rh methyl, Rhodium carbonyls
Kazantsev Maxim S.
Luzgin Mikhail V.
Volkova Galina G.
Stepanov Alexander G.
Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia
Using C-13 solid-state nuclear magnetic resonance, the carbonylation of dimethyl ether (DME) with carbon monoxide has been studied on solid Rh/Cs2HPW12O40 in the presence of a methyl iodide promoter. The observed decrease in the reaction temperature in comparison with halide-free systems is caused by a change of the reaction mechanism. At first, the activation of the promoter and CO on Rh/Cs2HPW12O40 produces methyl rhodium carbonyl species. Carbon monoxide is then embedded into the Rh-CH3 bond to afford Rh acetyl. Rapid migration of the acetyl group from the Rh center to a Bronsted acid site of Rh/Cs2HPW12O40 gives rise to an acetate group attached to the Keggin unit (Keggin acetate). Bronsted acid sites provide dimethyl ether activation with the formation of a surface methoxy group. The latter, through reaction with hydrogen iodide, which is produced at the stage of Rh acetyl-to-Keggin acetate transformation, restores methyl iodide for subsequent carbonylation stages. Methyl acetate formation from a Keggin acetate and DME closes a catalytic cycle.