High-loading silica-encapsulated PdPt catalysts (PdPt@SiO2, 4 wt.% Pd, 7 wt.% Pt) are synthesized using a Stdber-based method and are tested in lean methane combustion in the presence of water up to 550 degrees C. The as synthesized bimetallic core particles have an average size of 7 nm, are uniform alloys of Pd and Pt, and are well dispersed inside the oxide shells. The SiO2 shells are about 60 nm in diameter, with a specific surface area of 600 m(2)/g and a median pore diameter of 3.4 nm. The catalyst shows a stable methane conversion during a hydrothermal ageing (HTA) test which is two- and ten-fold higher than the conversion for the impregnated Al2O3 and SiO2-supported catalysts of the same metal loading, respectively. The surface area of the porous shell remains unaffected after HTA; however, the metal dispersion evaluated by CO chemisorption increases after the ageing and some changes in the morphology of the bimetallic PdPt nanoparticles occur.