A method of preparing a catalytic structure the method including the steps of: providing a solution of a precursor compound in a solvent at ambient conditions; providing a suspension of a support material having a specific surface area of at least 1 m2/g in a solvent at ambient conditions; mixing the solution of the precursor compound and the suspension of the support material; providing a reactive solvent in a supercritical or subcritical state; admixing the mixture of the solution of the precursor compound and the suspension of the support material in the supercritical or subcritical reactive solvent to form a reaction solution; injecting the reaction solution into a reactor tube via an inlet; allowing a reaction of the precursor compound in the supercritical or subcritical reactive solvent in the reactor tube to form the catalyst nanoparticles on the support material to provide the catalytic structure.
