Thermal methane conversion to formaldehyde promoted by single platinum atoms in PtAl₂O₄^- cluster anions

Identification and mechanistic study of thermal methane conversion mediated by gas-phase species is important for finding potentially useful routes for direct methane transformation under mild conditions. Negatively charged oxide species are usually inert with methane. This work reports an unexpected result that the bi-metallic oxide cluster anions PtAl₂O₄ ^- can transform methane into a stable organic compound, formaldehyde, with high selectivity. The clusters are prepared by laser ablation and reacted with CH₄ in an ion trap reactor. The reaction is characterized by mass spectrometry and density functional theory calculations. It is found that platinum rather than oxygen activates CH₄ at the beginning of the reaction. The Al₂O₄^- moiety serves as the support of Pt atom and plays important roles in the late stage of the reaction. A new mechanism for selective methane conversion is provided and new insights into the surface chemistry of single Pt atoms may be obtained from this study. One atom is enough: The negatively charged oxide cluster PtAl₂O ₄^- is an active species in thermal methane conversion. The single platinum atom activates methane and delivers two hydrogen atoms to the "oxide support" Al₂O₄^-. Methane is then transformed to formaldehyde with a high selectivity.