Nitrogen-doped nanotubes-decorated activated carbon-based hybrid nanoarchitecture as a superior catalyst for direct dehydrogenation

Abstract

A novel N-doped activated carbon (AC) based nanostructure decorated with nanotubes (N-CNT-AC) has been successfully fabricated through a facile and scalable approach involving the mechanical milling and subsequent solid pyrolysis of the low-cost and commercially available AC and melamine. Various characterization techniques including high resolution transmission electron microscopy, X-ray diffraction, nitrogen adsorption, X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy were employed to reveal the relationship between catalyst features and catalytic performance in the oxidant- and steam-free direct dehydrogenation (DDH) of ethylbenzene to styrene. Although the as-synthesized AC-based hybrid nanostructure has a much lower surface area (397.0 cm² g⁻¹) and pore volume (0.17 cm³ g⁻¹) than the parent AC (777.1 cm² g⁻¹ surface area and 0.4 cm³ g⁻¹ pore volume), it demonstrates 1.74 and 3.67 times the steady-state styrene rate of the per gram parent AC and the industrially-used K–Fe catalyst, respectively, for the DDH reaction, which is ascribed to the promoting effect of the unique hybrid microstructure, the surface rich CO group and defect/edge feature, the increased basic properties through N-introduction into the hybrid nanostructure, the small size of the graphitic crystallite, as well as the inherent high surface and large porosity of the AC-based materials. The in situ Fourier transform infrared spectroscopy measurement suggests a lower activation energy over the developed novel N-doped AC-based hybrid nanostructure for the DDH reaction than over the parent AC. Interestingly, the developed hybrid nanocomposite exhibits a much superior selectivity for styrene production compared to the parent AC, which is ascribed to the N-doping into the AC-based matrix. The developed N-doped AC-based hybrid nanostructure catalyst could be a potential candidate for catalytic styrene production via steam- and oxidant-free direct dehydrogenation of ethylbenzene.