N.Vamsi Krishna Bore, M.T.; Pham, H. N.; Switzer, E. E.; Ward, T. L.; Fukuoka, A.; Datye, A. K. J. Phys. Chem. B 2005, 109, 2873. Introduction By using a suitable combination of active metal phase and support; catalyst can have high activity, selective and mechanical stability. The rate and extent of sintering of supported metals depend on temperature, atmosphere, support, promoter, and metal. To study explicitly the role of pore size on sintering of supported metal particles, it would be desirable to work with supports having pores of uniform size and shape, preferably well ordered. By depositing uniformly sized metal particles inside the pores of mesoporous silica, we study more clearly the role of pore size, pore structure, and connectivity and impact on the thermal sintering. One limitation of mesoporous silica for thermal sintering studies lies in its low hydrothermal stability at elevated temperatures. It is known that gold nanoparticles supported on oxide supports show high reactivity for CO oxidation at low temperature, but only when the Au particles are very small (