Tuning of shape, defects, and disorder in lanthanum-doped ceria nanoparticles

Abstract

The instability of petroleum prices and the advancements in extraction technologies of natural gas has increased the interest in the direct conversion of methane to C2 products via oxidative coupling of methane (OCM) reactions. The design of catalysts by tailoring the structural defects and disorder has a significant impact on their performance. Within this context, in this work, the fine-tuning of oxygen defects in rod-like NPs was performed via La3+ doping (LaxCe1-xO2-1/2), x, in the 10-70 mol% range. The NPs characterization was performed by SEM, HRTEM, XRD, BET and Raman spectroscopy, and the OCM catalytic performance was evaluated at 750 °C. The relative concentration of reagents (CH4 and O2) and products H2, CO, CO2, C2H4, and C2H6 was measured by an online mass spectrometer. XRD and Raman analysis revealed that the CeO2 fluorite crystalline structure is essentially maintained in the doped nanorods, even for x = 0.7. The Raman spectra analysis indicates that La doping results in the formation of extrinsic and intrinsic oxygen defects, which increase proportionally to La concentration. The catalysts showed good performance for OCM with methane conversion up to 32% and C2 selectivity up to 44% for x=0.5. In addition, all catalysts showed high stability within 20h time on stream. The demonstrated structural defect control on La-doped CeO2 NPs can provide important insights to improve the performance of OCM reactions.