Amino-functionalised metal–organic frameworks UiO-66 and -67 were post-synthetically modified with salicylaldehyde. A molybdenum complex was immobilised on the resulting materials. They were characterised by ¹³C-MAS-NMR, XPS and PXRD to confirm immobilisation and stability. The immobilised complex is an active and reusable catalyst for olefin epoxidation with tert-butyl hydroperoxide (TBHP) as an oxidant. It is shown that the effective pore size, probed with Brunauer–Emmett–Teller (BET) surface area analysis and the number of amino groups affect the diffusion of reactants and products, as well as catalyst recycling.