Hierarchical structure characterized by the decoration of few-layer graphene (FLG) surface with a dense network of carbon nanofibers (CNF) was synthesized by Chemical Vapor Deposition. This hierarchical composite was further used as host matrix for the dispersion of nanodiamonds (ND) to produce a metal-free catalyst for the direct dehydrogenation (DH) process of ethylbenzene (EB) to styrene. The as-synthesized three-dimension ND/CNF-FLG composite displays excellent dehydrogenation activity and stability, especially under severe reaction conditions similar to those in the industrial process. Up to 600 °C with EB concentration of 10 vol.%, the ND/CNF-FLG catalyst displays a significant high DH activity of along with 91.3% styrene selectivity. In addition, no deactivation is observed during more than 70 h of test. The outstanding catalytic performance and the superior stability of the hybrid ND/CNF-FLG composite compared to the conventional carbon-based and promoted iron industrial catalysts, render it among the most promising metal-free catalyst for industrial direct dehydrogenation process.