Preparation of ZnO/Al₂O₃ catalysts by using atomic layer deposition for plasma-assisted non-oxidative methane coupling

We prepared a ZnO/mesoporous Al₂O₃-shell/core structure by using atomic layer deposition (ALD) of ZnO on commercially-available mesoporous Al₂O₃. We used various analysis techniques such as scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-atomic emission spectroscopy, and surface area and pore size analyses based on nitrogen isotherm data. A 200 nm-thick slab of mesoporous Al₂O₃ particles was decorated by ZnO upon ALD deposition, whereas the inner part of the Al₂O₃ particle was free of ZnO. We evaluated the catalytic activity of the bare and the ZnO-covered Al₂O₃ for plasma-assisted nonoxidative coupling of methane. The catalytic behavior was shown to be sensitive to the amount of ZnO deposited. Particularly, 40-cycled ZnO/Al₂O₃ showed an enhanced selectivity to the olefin product with almost the same CH4 conversion as that of bare Al₂O₃. Preparation of the shell/core structure by using ALD can be an interesting strategy for finding highly-efficient catalysts in a plasma-assisted catalytic reaction.