The activity of a catalyst towards the oxygen reduction reaction (ORR) is determined by its surface composition and structure. Although careful synthesis strategies have managed to improve the ORR activity of Pt by a factor of 40 in recent years, the long-term stability of supported catalysts still poses a challenge.^[1] One approach that can be used to supress degradation phenomena, such as particle migration and agglomeration, is incorporation of the active metal species in the pores of a conducting, porous graphitic matrix, in order to hinder the motion of the alloy particles. ^[2-4] Here, we describe the synthesis, characterization and stability of octahedral Pt₃NiMo nanoparticle catalysts supported in hollow graphitic spheres. By combining electrochemically active surface area (ECSA) measurements, identical location scanning transmission electron microscopy (STEM) and measurements performed using an in situ electrocatalytic scanning flow cell coupled to an inductively coupled plasma mass spectrometer (SFC-ICP-MS), we demonstrate the stabilizing effect of the hollow graphitic spheres on the PtNi octahedra. After 10800 cycles, the octahedra are found to have retained their shape, with only a small loss of ECSA. In summary, we demonstrate the successful incorporation of shaped bimetallic nanoparticles into a porous support. This design strategy can be used for other catalytic reactions and opens new ways for achieving space confinement of faceted Pt alloy particles. References: [1] P. Strasser, Science 2015, 349, pp 379-380. [2] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc. 2012, 134, pp 20457– 20465. [3] S. Mezzavilla, C. Baldizzone, A.-C. Swertz, N. Hodnik, E. Pizzutilo, G. Polymeros, G. P. Keeley, J. Knossalla, M. Heggen, K. J. J. Mayrhofer, F. Schüth, ACS Catal., 2016, 6 (12), pp 8058–8068. [4] E. Pizzutilo, J. Knossalla, S. Geiger, J. P. Grote, G. Polymeros, C. Baldizzone, S. Mezzavilla, M. Ledendecker, A. Mingers, S. Cherevko, F. Schuth, K. J. J. Mayrhofer, Adv. Energy. Mater. 2017, 7(20).