Carbonylation of Dimethyl Ether with CO on Solid 12-Tungstophosphoric Acid: In Situ Magic Angle Spinning NMR Monitoring of the Reaction Kinetics
The Journal of Physical Chemistry C
, E-ISSN: 1932-7455
Kazantsev Maxim S.
Luzgin Mikhail V.
Stepanov Alexander G.
Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia
Knowledge of the elementary steps of the reaction on the surface of a heterogeneous catalyst is crucial for understanding the reaction mechanism. This valuable information could be provided by in situ monitoring of the reaction with solid-state NMR spectroscopy. In this paper, the kinetics of the dimethyl ether (DME) carbonylation on 12-tungstophosphoric acid has been followed with high temperature H-1 magic angle spinning (MAS) NMR. The equilibrium of the initial ether activation toward the intermediate surface methoxy species has been examined with C-13 MAS NMR as well. The energy profile of DME carbonylation with CO to the Keggin acetate on H3PW12O40 has been established. The apparent activation energy of the carbonylation, 95 +/- 10 kJ mol(-1), represents a sum (within experimental error) of the standard enthalpy of the methoxy group formation, 57 +/- 4 kJ mol(-1), and the activation barrier of the rate-determining step of the process, the interaction between methoxy group and carbon monoxide, 50 +/- 4 kJ mol(-1).