NOVELTY - Preparing a noble metal-based alloy catalyst on a support material comprises preparing a solution of a first metal in a polyol solvent; adding a support material to the solvent to obtain a suspension; heating the suspension to 80-160degreesC and adding a solution of a second metal in a polyol solvent; and heating the suspension to the boiling point of the polyol solvent and maintaining the temperature for 30-120 minutes.    USE - For preparing a noble metal-based alloy catalyst on a support material, e.g. a supported platinum-ruthenium alloy catalyst or a supported platinum-cobalt alloy catalyst for use as an electrocatalyst for fuel cells or as a gas-phase catalyst for carbon monoxide (CO) oxidation or exhaust gas purification (claimed), wherein the fuel cell is e.g. polymer electrolyte membrane fuel cell (PEMFC) or direct methanol fuel cell (DMFC).    ADVANTAGE - The invention prepares catalysts supported on a carrier material and showing a high degree of alloying and a small crystallite size of less than 3 nm. It avoids expensive and time-consuming heat treatment and/or calcination processes for alloy generation. It avoids particle agglomeration, sintering and particle growth, commonly associated with heat treatment and/or calcination processes.    DETAILED DESCRIPTION - Preparing a noble metal-based alloy catalyst on a support material comprises preparing a solution of a first metal in a polyol solvent; adding a support material to the solvent to obtain a suspension; heating the suspension to 80-160degreesC and adding a solution of a second metal in a polyol solvent; heating the suspension to the boiling point of the polyol solvent and maintaining the temperature for 30-120 minutes; and cooling the suspension to room temperature and isolating the catalyst material. INDEPENDENT CLAIMS are also included for:    (1) a supported platinum-ruthenium alloy catalyst with the platinum-to-ruthenium (Pt:Ru) atomic ratio of 1:1, wherein the crystallite size is less than 3 nm and the lattice constant is lower than 0.3850 nm by X-ray diffraction (XRD);    (2) a supported platinum-cobalt alloy catalyst with the platinum-to-cobalt (Pt:Co) atomic ratio of 3:1, wherein the crystallite size is less than 3 nm and the lattice constant is lower than 0.3870 nm by XRD; and    (3) use of the catalyst.