Tuning the catalytic performance of carbon nanotubes by tuning the conjugation between the π orbitals of carbon nanotubes and the active oxygenic functional groups

Abstract

Periodic density functional theory calculations were used to systematically investigate the origin of the catalytic activity of carbon nanotubes (CNTs) and ways to improve the catalytic performance of CNTs for the oxidative dehydrogenation of propane. Detailed characterizations of the geometric and electronic structure of the active oxygenic functional groups (CO groups) were presented. The results reveal that the catalytic performance of CNTs can be tuned by tuning the conjugation between CNT π orbitals and the orbitals of the active CO groups. Through conjugation, CNTs act as an electron reservoir to donate or accept electrons from the CO group. We found that CO groups with a negative charge have higher C–H bond activation activity but lead to a more stable i -propoxide intermediate, which inhibits the formation of propene, while positively charged CO groups have the opposite effect. The balance between the activities of the two C–H activation steps can be obtained by tuning the charge of the CO group. This study increases the understanding of the origin of the activity of CNT catalysts at the microscopic scale and gives guidance for the preparation of high-performance CNT catalysts. The conjugation between CNT π orbitals and the orbitals of functional groups plays a key role in balancing the activity of the two C–H activation steps in the propane dehydrogenation reaction.