Methane Conversion to Methanol Using Au/ZSM-5 is Promoted by Carbon
Jingxian Cao, Richard J. Lewis, Guodong Qi, Donald Bethell, Mark J. Howard, Brian Harrison, Bingqing Yao, Qian He, David Morgan, Fenglou Ni, Pankaj Sharma, Christopher J. Kiely, Xu Li, Feng Deng, Jun Xu, Graham J. Hutchings
Abstract
High Resolution Image Download MS PowerPoint Slide The oxidation of methane using molecular oxygen as the terminal oxidant, over a Au/ZSM-5 catalyst, has been previously shown to produce methanol and acetic acid as products. We now show that this reaction is significantly enhanced by the addition of a range of carbon additives. Isotopic 13 C-labeled studies and corresponding investigation into the activity of the carbon materials alone reveal that nearly all the methanol produced is derived from methane oxidation, with a negligible contribution attributed to the carbon additives, while further study identified carbon as the primary source of acetic acid, which was observed as a minor product. Gas phase CO is not observed as a product in the reaction of Au/ZSM-5 with CH 4 + O 2, and in reactions with added CO, not all the CO is converted. We, therefore, conclude that the effect observed with the carbon additive is not due to the in situ production of gas phase CO as a reaction intermediate. Rather, we postulate that the effect derives from the oxidation of the surface of the carbon in the aqueous reaction mixture and the interaction of the oxidized carbon surface with Au/ZSM-5. The reactivity of carbon in this reaction at 240 °C is unexpected, and the presence of water is required to observe the effect.