Structure-performance relationship of nanodiamonds @ nitrogen-doped mesoporous carbon in the direct dehydrogenation of ethylbenzene

Abstract

Nanocarbon materials have been reported as an alternative robust metal-free catalyst in the field of the catalytic dehydrogenation with improved catalytic performance as well as stability. In this study, the hybrid metal-free catalyst consisting of dispersed nanodiamonds within a nitrogen-doped mesoporous carbon (ND@NMC) phase was investigated. Such material with high effective surface area and porosity was prepared under different thermal treatment temperatures and further evaluated for the direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). The characterization techniques such as N2 adsorption-desorption, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopic analysis were used to investigate the surface properties and structures of the as-prepared ND@NMC composites. The ND@NMC-700 catalyst annealed at 700°C presented a ST specific reaction rate and a relative areal activity of 5.8mmolST gcatalyst−1h−1 and 0.28μmolST m−2h−1 with a ST selectivity of 99.6%, which is the highest DDH activity among the investigated nanocarbons including ND, carbon nanotubes, NMC and ND@MC (ND covered by mesoporous carbon) catalysts. The superior dehydrogenation performance could be attributed to the high dispersion of the metal-free nanodiamond centers within the NMC layer which provided a well surface contact with the reactant. It can also be confirmed that the rational contents of ketone (CO) functional groups, as well as the opened porous network in ND@NMC-700 catalyst resulted to the superior DDH activity and styrene selectivity. Moreover, the presented nitrogen groups are beneficial for construction of surface defects and porosity as well as the improvement of styrene selectivity.