A facile and scalable approach for fabricating structural defect-rich nitrogen-doped carbon nanotubes (MCSA-CNTs) through explosive decomposition of melamine–cyanuric acid supramolecular assembly is presented. In comparison to pristine carbon nanotubes, MCSA-CNT exhibits significantly enhanced catalytic performance in oxidant- and steam-free direct dehydrogenation of ethylbenzene, demonstrating the potential for metal-free clean and energy-saving styrene production. This finding also opens a new horizon for preparing highly-efficient carbocatalysts rich in structural defect sites for diverse transformations.

Nitrogen-doped carbon nanotubes (CNTs) with defect- and CO-group-rich surface features were fabricated through a facile and scalable physical dry milling and subsequent pyrolysis approach of carbon nanotubes and melamine in the presence of guanidine nitrate. The catalytic performance of the as-prepared N-doped CNTs with diverse guanidine nitrate dosages and pyrolysis temperatures for direct dehydrogenation of ethylbenzene to styrene under oxidant- and steam-free conditions was measured. Various characterization techniques including high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen–adsorption and thermogravimetric analysis, and Raman spectroscopy were employed to investigate the structure and surface properties, as well as to explore the relationship between catalyst nature and catalytic performance. It is found that the addition of guanidine nitrate in the pyrolysis process of CNT with melamine significantly affects the structure, surface properties, and catalytic performance. The optimized N-doped CNTs demonstrate steady-state styrene production rates 1.56 and 1.60 times higher than those of the parent CNTs and the established nanodiamond, as well as 6.49 times the rate of commercially available K–Fe catalyst without compromising the selectivity to styrene. The much superior catalytic performance in metal-free catalytic direct dehydrogenation can be ascribed to the CO group- and defect-rich surface nature, the basic properties resulted from N-doping, the larger surface area and pore volume, and smaller graphitic carbon crystallites. The fabricated novel N-doped CNTs can be considered as a promising candidate for sustainable production of styrene through oxidant- and steam-free direct dehydrogenation of ethylbenzene with energy-saving and environmentally benign features. The developed defect-formation strategy in this work can be used for preparation of other metal-free carbocatalysts.

Owing to their unique structural features and surface properties, graphene and nanodiamond have attracted tremendous attention in diverse fields. However, restacking of graphene and reagglomeration of dispersed nanodiamond inevitably depress their catalytic properties. Herein, inspired by the historic discovery of “pillared clay”, we successfully realized the simultaneous inhibition of their restacking by fabricating a N-doped mesoporous graphene/nanodiamond (N-RGO/ND) nanocomposite by a facile wet-chemical approach. The electrocatalytic oxygen reduction reaction (ORR) and the thermocatalytic oxidant-free and steam-free direct dehydrogenation (DDH) of ethylbenzene were used to examine its catalytic properties. The nanocomposite showed synergistically improved catalytic DDH and electrocatalytic ORR activity relative to that of the individual components, which can be ascribed to synergy between graphene and nanodiamond and to the large surface area, well-ordered mesoporous structure, small crystalline size, and rich defect and CO surface features. Moreover, the developed synthetic strategy in this work can be extended to diverse N-doped nanocomposites from dispersion-required carbon precursors.