Enhanced performance of chemical looping methane oxidative coupling by the synergistic effect of TiO2 doped Na2WO4/Mn2O3/SiO2 oxygen carriers

Chemical looping methane oxidative coupling is a promising method to directly convert methane to C 2 products but is limited by the trade-off between CH 4 conversion and C 2 selectivity. Here, we develop a series of TiO 2 doped Na 2 WO 4 /Mn 2 O 3 /SiO 2 for chemical looping methane oxidative coupling and investigate the underline mechanism for the enhanced performance. The results show that 5 wt% TiO 2 doped Na 2 WO 4 /Mn 2 O 3 /SiO 2 exhibited 31.2% CH 4 conversion, which is 1.68 times as large as that of Na 2 WO 4 /Mn 2 O 3 /SiO 2 , without significantly decreasing C 2 selectivity (~70.3%). Pulse experiments show that TiO 2 improves the bulk oxygen diffusion, providing more surface oxygen to convert methane, thus leading to enhanced CH 4 conversion. O 1 s spectra manifests that the active oxygen content on the surface was not significantly increased by TiO 2 dopant , thus TiO 2 dopant has little effect on C 2 selectivity. Therefore, 5 wt% TiO 2 doped Na 2 WO 4 /Mn 2 O 3 /SiO 2 shows high chemical looping methane oxidative coupling performance. The explored mechanism in this work can be extended to design more oxygen carriers to enhance the chemical looping reactions.