Highly Selective Conversion of CH4 to High Value-Added C1 Oxygenates over Pd Loaded ZnTi-LDH

Abstract

The selective oxidation of methane to high value-added liquid oxygenated compounds under mild conditions is of great significance to promote the efficient utilization of the carbon source, but it also faces the dilemma of low activity and over-oxidation. Here, ZnTi-layered double hydroxides (LDH)-A200 photocatalysts with Pd loading are prepared to achieve efficient oxidation of methane, with O2 as an oxidant under ambient condition. The highest generation rate of C1 liquid products (methanol and formaldehyde) reaches 4924.47 µmol g−1 h−1 with a selectivity close to 100% over 0.5Pd-ZnTi-LDH-A200, which is 20 times higher than that of bare ZnTi-LDH-A200. The photochemical results show that the modified photocatalysts present much higher generation and separation efficiency of electron-hole pairs. In situ X–ray photoelectron spectroscopy indicates that Pd nanoparticles are the hole acceptor, which is beneficial to charge separation in the photocatalysis. Furthermore, electron spinresonance spectroscopy and temperature–programmed–desorption analysis prove that Pd loading is helpful to the adsorption of methane and oxygen on the surface of ZnTi-LDH-A200, promoting the production of reactive oxygen species and activation of methane. All these factors work together to promote the efficient conversion of CH4 to high value-added C1 oxygenates.