Methane Conversion to Methanol Using Au/ZSM-5 is Promoted by Carbon

The oxidation of methane using molecular oxygen as theterminaloxidant, over a Au/ZSM-5 catalyst, has been previously shown to producemethanol and acetic acid as products. We now show that this reactionis significantly enhanced by the addition of a range of carbon additives.Isotopic C-13-labeled studies and corresponding investigationinto the activity of the carbon materials alone reveal that nearlyall the methanol produced is derived from methane oxidation, witha negligible contribution attributed to the carbon additives, whilefurther study identified carbon as the primary source of acetic acid,which was observed as a minor product. Gas phase CO is not observedas a product in the reaction of Au/ZSM-5 with CH4 + O-2, and in reactions with added CO, not all the CO is converted.We, therefore, conclude that the effect observed with the carbon additiveis not due to the in situ production of gas phase CO as a reactionintermediate. Rather, we postulate that the effect derives from theoxidation of the surface of the carbon in the aqueous reaction mixtureand the interaction of the oxidized carbon surface with Au/ZSM-5.The reactivity of carbon in this reaction at 240 degrees C is unexpected,and the presence of water is required to observe the effect.