The preparation of model bimetallic Pd-Au/HOPG catalysts has been investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques. Initially, model "core-shell" type Pd-Au/HOPG catalysts with similar particle size distribution (5-8 nm), but with different densities of particle locations on the HOPG surface and Pd/Au atomic ratios are prepared. Further, their thermal stability is studied within a temperature range of 50-500 degrees C at UHV conditions. It has been shown that annealing the model catalysts at a temperature range of 300-400 degrees C leads to formation of Pd-Au alloyed particles. Enhancement of heating temperature up to 500 degrees C results in sintering of bimetallic nanoparticles. Contribution of different parameters controlling the properties of Pd-Au alloyed particles has been discussed. (C) 2016 Elsevier B.V. All rights reserved.