Ultrathin PdAu Nanowires with High Alloying Degree for the Direct Oxidation of Methane to C1 Oxygenates

Abstract

The direct oxidation of methane (CH₄) into high-valued C1 oxygenates production has garnered increased attention in effectively using vast CH₄ and alleviating the global energy crisis. However, due to the high cleavage energy of C—H bond and low polarity of CH₄ molecule, it is difficult to activate the first C—H bond. Furthermore, C1 oxygenates are readily inclined to be oxidized to CO₂, because their weaker C—H bond comparing with CH₄ molecule, resulting in poor selectivity. Herein, we designed ultrathin Pd_xAu_y alloy NWs supported on ZSM-5 (Z-5) to investigate the direct oxidation of CH₄ to high value-added oxygenate under mild conditions. By precisely adjusting the molar ratio of Pd/Au and alloying degree, Pd₉Au₁NWs/Z-5 showed an excellent yield of 11.57 mmol·g^–l·h^–1 and the outstanding selectivity of 95.1% for C1 oxygenates (CH₃OH, CH₃OOH and HCOOH). The in-situ spectroscopic and mechanism analysis proved that the enhanced catalytic performance of Pd₉Au₁NWs/Z-5 was ascribed to the stable one-dimensional nanostructure and the strong synergy effect with high alloying PdAu, which could increase the adsorption capacity of CH₄ molecules on Pd atoms to promote the CH₄ conversion. This work offers valuable insights into the design concept of high-efficient catalysts and the structure-activity relationship for the direct oxidation of CH₄.