The synthesis of structured Pd/C hydrogenation catalysts by the chemical vapor deposition of Pd(allyl)Cp onto functionalized carbon nanotubes anchored to vapor grown carbon microfibers

Vapor grown carbon fibers (VGCF) were prepared by the iron-catalyzed decomposition of methane. The as-grown microfibers were treated by HNO3, and iron nanoparticles were deposited onto the fiber surface by impregnation. Carbon nanotubes (CNT) were grown homogeneously as branches on the microfiber surface by tuning the process parameters of the methane decomposition. A composite carbon nanotube-carbon microfiber (CNT-VGCF) system was thus obtained and used as support for palladium nanoparticles. Oxygen-containing functional groups were introduced into the CNT-VGCF system by plasma treatment in a fluidized-bed reactor. The Pd/C catalyst was prepared by chemical vapor deposition on the CNT-VGCF support using Pd(allyl)Cp as a precursor (MOCVD) in a fixed-bed reactor. The effects of the surface treatment and the deposition of palladium were investigated by X-ray photoelectron spectroscopy (XPS). Only traces of palladium were detected after deposition on as-grown fibers, whereas a significantly higher concentration was found on plasma-treated fibers. The catalytic activity of the Pd/C catalyst was evaluated by the hydrogenation of cyclooctene in a fixed-bed microreactor under plug-flow conditions. The CNT-VGCF system was found to be a suitable structured support for Pd nanoparticles.