NiFe2O4 nanoparticles stabilized by porous silica shells (NiFe2O4@SiO2) were prepared using a one-pot synthesis and characterized for their physical and chemical stability in severe environments, representative of those encountered in industrial catalytic reactors. The SiO2 shell is porous, allowing transport of gases to and from the metal core. The shell also stabilizes NiFe2O4 at the nanoparticle surface: NiFe2O4@SiO2 annealed at temperatures through 973 K displays evidence of surface Ni, as verified by H-2 TPD analyses. At 1,173 K, hematite forms at the surface of the metallic cores of the NiFe2O4@SiO2 nanoparticles and surface Ni is no longer observed. Without the silica shell, however, even mild reduction (at 773 K) can draw Fe to the surface and eliminate surface Ni sites. Bright field TEM images of SiO2@NiFe2O4 nanoparticles packed to form nanospheres (A) or nanorods (B). The silica shell is 10-20 nm thick.