Identification of role of nitrogen dopants in nanocarbon catalysis

The influence of nitrogen dopants on the catalytic activity of carbon-based materials has been studied extensively, but the exact role of nitrogen species in these materials remains unclear. A challenge in understanding the role of nitrogen is that most nitrogen-doped nanocarbon (NC) materials are dominated by uncontrollable surface functional groups, and changes in nitrogen species often lead to variations in oxygen functional groups, which makes the specific role of nitrogen difficult to isolate. To address this issue, we developed a series of NCs containing variable types and contents of nitrogen (5–30 at.%) and a constant oxygen content of approximately 4 at.%. Results show that the different types of nitrogen in the NCs, namely, graphitic nitrogen and pyridinic nitrogen, serve as electron-donating and -withdrawing modulators, respectively, and can tailor the oxidative dehydrogenation activity of the NCs. Additionally, graphitic nitrogen plays a role in mediating frustrated Lewis pairs consisting of pyridinic nitrogen and neighboring carbon atoms. These pairs are responsible for the activation of hydrogen–hydrogen bonds, which is the rate-determining step in nitrobenzene hydrogenation.