Fractal dimension of zirconia nanopowders and their activity in the CO oxidation

We present a study of the CO oxidation on zirconia nanopowders consisted of nanoparticles with a size in a range of 3–7 nm. The fractal characteristics of zirconia nanopowders were studied both by nitrogen adsorption and small-angle X-ray scattering. The surface fractal dimension of zirconia is approximately constant and equals to 2 indicating that zirconia nanoparticles have a smooth surface in all solids. The mass fractal dimension is in the range between 2.1 and 2.5 showing a difference in nanoparticle aggregation depending on their size. Catalytic tests indicate that the activation energy of the CO oxidation on zirconia nanopowders (Ea) is constant. We associate this observation with constancy of the surface fractal dimension. The pre-exponential factor of the rate constant (ko) varies significantly decreasing with increasing the mass fractal dimension of solids. This finding is in a good agreement with theoretical approach developed in this communication.

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► The activation energy of the CO oxidation on zirconia nanopowders (Ea) is constant.
► The pre-exponential factor of the rate constant (ko) significantly varies.
► Changes of ko are associated with changes of the mass fractal dimension of catalysts.