Carbon nanotube-supported Ru (Ru/CNT) catalysts were covered with silica layers to inhibit the aggregation of Ru particles as well as the detachment of Ru particles from the CNTs during catalytic reactions. Coverage of the Ru/CNT with silica was performed by the successive hydrolysis of 3- aminopropyltriethoxysilane and tetraethoxysilane in the presence of CNT-supported Ru metal precursors, followed by reduction with hydrogen at 623 K. The diameter of the Ru particles in the silica-coated Ru/CNT ranged from 1 to 3 nm. The Ru particles and the CNTs in the silica-coated catalysts were uniformly covered with silica layers a few nanometers thick. The size of the Ru particles in the silica-coated catalysts did not change appreciably after treatment at 873 K, while the metal particles in the Ru/CNT were seriously aggregated after treatment at 873 K. The silica-coated Ru/CNT catalyzed the CO hydrogenation and the 1-hexene hydrogenation, despite the coverage of Ru particles with silica. In addition, the silica-coated Ru catalysts showed high durability toward Ru detachment from the CNTs during the repeated hydrogenation of 1-hexene, whereas the catalysts without silica layers were deactivated because of Ru detachment. Therefore, coverage of the Ru/CNT catalysts with silica layers prevented the deactivation of the catalysts.
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