Palladium supported on carbon nanofiber coated monoliths for three-phase nitrobenzene hydrogenation: Influence of reduction temperature and oxidation pre-treatment

Carbon nanofiber (CNF) coated monoliths with a homogeneous and consistent layer were prepared by catalytic decomposition of ethane on Ni particles, and the CNF coated monolith supports were oxidized using different agents to get different oxidation degrees. The as-prepared catalysts were characterized by SEM, TG, Raman spectra, FT-IR, TPD, TPR, CO pulsar and TEM, while the behavior of Pd supported on CNF coated monoliths were tested by liquid phase of nitrobenzene hydrogenation in a continuous flow reactor. For comparison Pd/Al2O3/cordierite was also prepared. It was found that the reduction temperature controlled Pd dispersion, which in turn was responsible for the catalytic activity. A good linear relationship between nitrobenzene conversion and Pd dispersion was observed. Furthermore, Pd/CNF/cordierite showed higher nitrobenzene conversion compared with Pd/Al2O3/cordierite, indicating CNF was a superior support. The aniline selectivity was related to the amount of surface oxygen groups (SOCs) formed during the oxidation pre-treatment. SOCs, especially carboxylic acid groups, increased as the degree of oxidation deepened, and more amounts of SOCs on CNF surface were responsible for the lower aniline selectivity.