The cyclopentanone and derivatives are a class of crucial fine chemicals for various industries and currently produced by conventional petrochemical synthetic routes. Here, we demonstrated a new synthetic approach to directly fabricate N-doped carbon nanotube (N-CNTs) networks with confined Co nanoparticles from Co²⁺-impregnated bulk g-C₃N₄ as high performance hydrogenation rearrangement (HR) catalyst to efficiently convert a wide spectrum of biomass-derived furanic aldehydes to the corresponding cyclopentanones in water under a record-low H₂ pressure of 0.5 MPa and mild temperature. We unveiled a Co-catalysed bulk g-C₃N₄ decomposition/carbonisation CNTs formation mechanism. A new HR pathway was also unveiled.