Described is a method of preparing transition metal nanoparticles on a graphene support, in which a tertiary graphite intercalation compound is provided with intercalated metal ions such that the tertiary graphite intercalation compound comprises a graphene sheet having a negative charge. The graphene sheet is contacted with a transition metal salt to cause reduction of the transition metal salt by the graphene sheet, and to form transition metal nanoparticles. Also described are products arising from the method, and uses of those products.