Influence of Al2O3 on the performance of CeO2 used as catalyst in the direct carboxylation of methanol to dimethylcarbonate and the elucidation of the reaction mechanism

The reaction mechanism for the carboxylation of methanol to dimethylcarbonate has been elucidated by using DRIFT and solid state and solution multinuclear NMR spectroscopy. Modified ceria catalysts perform better than ceria. In this paper we show that modification of ceria by loading alumina strongly reduces the oxidation of methanol and the consequent reduction of Ce(IV) to Ce(III) with increase of both the life of the catalysts and their selectivity. The combination of surface techniques (XPS and BET) with structural techniques (XRD) has allowed a good characterisation of the working catalysts. Spectroscopic analyses (DRIFT and multinuclear solid state and solution NMR) have permitted the monitoring of the species formed on the surface of the catalyst and released from it. The formation of DMC takes place in successive steps such as (i) interaction of methanol with the catalyst surface with the formation of the surface-bound [single bond]OCH3 ; (ii) building on the catalyst surface of the hemicarbonate moiety [-OCH3 [arrow right]-OC(O)OCH3 ]; and (iii) reaction of the latter with the gas-phase methanol to afford the organic carbonate. [PUBLICATION ABSTRACT]