Microstructure of carbon nanofibers and their catalytic performance for oxidative dehydrogenation of propane

Carbon nanofibers (CNFs) with different microstructure were synthesized by chemical vapor deposition method and treated in argon at 1 700 degrees C for 12 h. The CNFs were used as catalysts for oxidative dehydrogenation of propane (ODP). The fish-bone CNF (F-CNF) had good performance for the reaction, showing propane conversion of 44.9% and propene selectivity of 33.0% at 550 degrees C. But, the catalytic performance over tubular CNF (T-CNF) was much lower than that over F-CNF. Raising the reaction temperature was favorable for achieving high propene yield. The TEM, XRD, N-2-adsorption and Boehm titration were carried out to characterize the structure and surface property of the CNFs. The most obvious structure difference was that the graphite layer of F-CNF had 5 degrees similar to 10 degrees angles to the axis, which would lead to different ratios of edge carbon atoms to basal carbon atoms. The carbon atoms at these two sites had different functions for ODP, especially for the process of oxygen transformation. F-CNF had more edge carbon atoms than T-CNF, which could combine with oxygen to form surface oxygen complexes. This could be confirmed by comparing the amounts of surface carbonyl groups. Temperature-programmed adsorption-desorption of propane over CNFs testified that the surface oxygen complexes played a key role in conversion of propane to propene. The structure stability of CNFs was characterized by TG in the reaction atmosphere.