Abstract: LaOX (X = Cl, Br) nanoparticles with tetragonal crystal structure were successfully prepared via sol-gel approach with non-aqueous solvents. Characterizations by X-ray powder diffraction and scanning electronic microscopy show that the LaOX nanoparticles are regularly in shape and highly uniform in size with an average diameter of about 47 nm. For oxidative coupling of methane (OCM), the nanosize LaOX catalysts have higher methane conversion and C₂ selectivity than the LaOX catalysts with conventional size and show good stability in activity and selectivity during the catalyst life test at 650 °C. At conventional size, the methane conversion and C₂ selectivity for OCM over the LaOBr catalyst are higher than that over the LaOCl catalyst, and at nanosize, there is not so much difference in methane conversion between LaOBr and LaOCl. However, the C₂ selectivity for OCM reaction over LaOBr is significantly higher than that over LaOCl, especially at low temperature.

Key words: nanometer, lanthanum oxyhalide, oxidative coupling of methane, sol-gel, non-aqueous solvent, low temperature activation