Scheme 1. Fabrication route for composites 1, 2 and 3. Impregnation of a mesoporous silica hard template with the carbon source sucrose and the Brønsted acid and metal oxide precursor [H₃PMo₁₂O₄₀] (PMo12) and subsequent carbonization and HF etching to remove the silica gives composite 1, a mesoporous carbon containing Mo^IVO₂ nanoparticles. Subsequent oxidative fragmentation using aqueous HNO₃ leads to the decoration of sub-nanometer [Mo-oxo]_n (n = 1–20) clusters on the carbon matrix of composite 2. Subsequent cyanamide impregnation and calcination leads to the N-doping of the carbon matrix while retaining the [Mo-oxo]_n clusters in composite 3.