Anomalous diffusion during isopropanol decomposition on (ZrO2)1−x (CeO2)x catalysts Original Research Article

In this work the effect of composition of (ZrO2)1−x (CeO2)x catalysts on the ratio γ = Ec/Ed between the activation energies for the isopropanol decomposition, estimated in the chemical reaction (Ec) and the diffusion (Ed) controlled regimes, was studied. The solid catalysts with x = 0.0; 0.2; 0.5; 0.8 and 1.0 were prepared by heating the precursors at 400, 600 and 800 °C and characterized by N2 porosimetry, X-ray diffraction, SEM/EDS analysis and NH3/TPD. Their catalytic activity for the decomposition of isopropanol in the temperature range 200–400 °C was probed in a tubular flow reactor. The estimated Arrhenius plots showed a distinct and well-defined change of slopes corresponding to alternation from the chemical to the internal diffusion-controlled regime of the process. The ratio γ = Ec/Ed of the corresponding activation energies was found equal to γ ≈ 1 for x = 0.0, meaning total lack of diffusion limitations, and converges to γ ≈ 2 for x = 1.0, corresponding to classical internal diffusion control. For 0 < x < 1 the values of 1 < γ < 2 signify anomalous diffusion related linearly to some compositional property of the (ZrO2)1−x (CeO2)x catalysts. The origin of this phenomenon is discussed in relation to the variable binding strength and friction of movement of the isopropanol species on the more active ZrO2 and the less active CeO2 nanoparticles of the solid catalysts.