Supported catalysts are manufactured from a pretreated porous support material and a nanocatalyst solution of catalyst nanoparticles. The porous support material is pre-treated with a gaseous solvent (e.g., steam or alcohol) to protect the support material from cracking during impregnation of the nanocatalyst solution. The supported catalysts have more uniform size, lower attrition of metals during manufacturing and use, and improved distributions of metal loading compared to catalysts manufactured using known techniques. Hydrogen peroxide manufactured from such catalysts is less likely to be contaminated with catalyst metal.