Coexistence of sulfonic and pyridinic sites on H2SO4 treated N-doped carbon nanotubes

Abstract

Three types of purified nitrogen doped CNTs were tested for isopropyl alcohol conversion under nitrogen or air atmosphere, and compared to undoped CNTs. The N-doped CNTs differ from their nitrogen content, from the presence or not of undoped section in their structure, and from their sulfur content. The isopropyl alcohol conversion leads to the formation of acetone as the sole product on catalysts presenting no nitrogen or low nitrogen and sulfur content, pointing to the presence of basic sites. At higher nitrogen and sulfur content, N-doped catalysts lead to the formation of acetone and propene, highlighting the presence of both basic and acidic sites on such material. XPS characterizations allow us to propose that the basic sites consist in pyridinic surface groups, and the acidic sites in sulfonic surface groups formed during the purification of these materials with sulfuric acid.