A CHA zeolite supported Ga-oxo cluster for partial oxidation of CH4 at room temperature

Abstract

• Multinuclear Ga-oxo clusters were formed by O 2 activation of Ga-CHA. • O 2 -treated Ga-CHA zeolites promoted the oxidation of CH 4 at room temperature. • Formaldehyde and formic acid were generated by the CH 4 partial oxidation. • The C–H bond cleavage on plausible Ga-oxo species were theoretically examined. • The Ga-oxo cluster is likely to promote C–H bond cleavage via a heterolytic pathway. A catalytic system for activation of CH 4 under mild conditions is in high demand. In this study, Ga-oxo clusters in CHA zeolites were prepared by reductive solid-state ion-exchange followed by O 2 treatment. Formation of the Ga-oxo clusters was demonstrated using X-ray absorption fine structure (XAFS) measurements. Plausible models of the cluster were developed by using an ab initio thermodynamic analysis. Importantly, the CHA zeolite-supported Ga-oxo clusters promote partial oxidation of CH 4 to yield adsorbed formaldehyde and formic acid. The results of density functional theory (DFT) calculations, designed to gain information about the mechanism of the process, show that the Z 2 [Ga 2 (O)(OH) 2 ] is likely the most active cluster for C–H bond activation of CH 4 . Observations made in this experimental and theoretical effort demonstrate that main-group metal-oxo clusters have the potential of serving as active species for transformations of CH 4 .