Correlation Between Oxygen Reduction Reaction and Oxidative Dehydrogenation Activities Over Nanostructured Carbon Catalysts

Abstract

Nitrogen containing nano-structured carbon catalysts were grown on Fe/Al2O3 and Ni/Al2O3 supports using acetonitrile pyrolysis. The post-pyrolysis samples were tested for activity in the oxygen reduction reaction (ORR) and oxidative dehydrogenation (ODH) reaction. Samples were characterized using BET, XPS and TEM. The samples grown over iron containing supports gave the highest activity in both reactions. There was a strong correlation between ODH and ORR activity suggesting the possibility of a common active site between reactions with the quinone/hydroquinone group being a possible candidate. XPS analysis supported this hypothesis showing that catalysts with a higher percentage of oxygen in the form of quinones tend to have the highest ORR and ODH activity. XPS analysis also demonstrated that samples with higher pyridinic nitrogen content, which is a marker for edge plane exposure and may be a part of the ORR active site, gave higher ORR and ODH activity. TEM images confirm that samples with high pyridinic nitrogen content tend to form structures with higher edge plane exposure. Because the active site, regardless of its identity, likely lies on the graphitic edge plane, this leaves the possibility that a common active site is not necessary to explain the correlation between ODH and ORR activity. Nitrogen containing, nano-structured carbon catalysts were shown to exhibit a correlation between the activities of oxidative dehydrogenation and electrocatalytic oxygen reduction reactions.