Defect-Enriched N,O-Codoped Nanodiamond/Carbon Nanotube Catalysts for Styrene Production via Dehydrogenation of Ethylbenzene

Abstract

Owing to the unique structure and enriched surface ketonic carbonyl group, nanodiamond (ND) shows excellent catalytic performance for dehydrogenation reaction. However, the agglomeration of predispersed ND aggregate by surface bonding force suppresses its catalytic activity. In this work, a nitrogen and oxygen codoped nanodiamond/carbon nanotube hybrid catalyst with the enriched structural defects (N,O-ND/CNT-d) has been fabricated by a facile two-step strategy including the hexamethylenetetramine (HTM)-assisted wet chemical approach and pyrolysis process, and the subsequent HNO3 treatment process. The prepared N,O-ND/CNT-d hybrid catalyst gives 16.8% styrene yield with 98.7%f selectivity and 5.2 mmol g(-1) h(-1) of steady-state styrene formation rate. It not only shows 4.7 and 1.9 times high steady-state styrene rate as compared to the parent oxidized carbon nanotube (CNT-o) and oxidized ND (ND-o), respectively, but also exhibits higher catalytic performance than the previously reported carbon-based catalysts. This is ascribed to the more accessible catalytic active sites from the isolating effect of CNT by the formation of a hybrid and the dual roles of HTM as dispersant in the wet chemical process and as nitrogen precursor in the pyrolysis process and also to the oxygen doping by HNO3 treatment, apart from the improved nucleophilicity of surface kenotic carbonyl groups and basic properties by the nitrogen doping. This work not only produces a novel and highly efficient metal-free catalyst with outstanding catalytic performance for clean and energy-efficient styrene synthesis through direct dehydrogenation of ethylbenzene under steam- and oxidant-free conditions but also presents a facile two-step strategy to fabricate other hybrids from dispersion-required carbon parents toward a variety of applications.