Abstract
Reaction network analysis of the oxidative dehydrogenation (ODH) reaction of isobutane over model carbon catalysts with tailored open-edge graphitic structure and uniform oxygenated functionalities was used to identify the selective pathways for the formation of isobutene. Carbon-based materials have been widely used in catalysis, but the active sites are not well-understood due to the complexity of the carbon structure. Correct identification of these sites is essential for learning how to manipulate material structure to achieve high catalytic yields of the desired products. In this study, we created model catalysts with controllable surface concentration of oxygenated functionalities based on graphitized mesoporous carbon (GMC). The concentration of the oxygenated functional groups on the surface of the GMCs was varied in a continuous manner through a simply control of the burn-off level. Our studies reveal that the ODH reaction of isobutane on carbon catalysts is a parallel-consecutive pathway with partial oxidative dehydrogenation for the formation of isobutene and deep oxidation pathway for the direct formation of CO and CO2 from isobutane. These two pathways show different dependence on the quinone-type oxygen sites: the rate constant leading to the desired partial oxidation product does not show a strong correlation to the density of oxygen sites, whereas the rate constant leading to the unselective COx products increases continuously with the density of oxygen sites. These results may give insight on the rational design of carbon catalysts for ODH reactions with desirable properties.
