Evaluation of functionality in Ni@stabilized ZrO₂ and NiO@NiO–Zn through X-ray diffraction technique

A mathematical model is developed for calculating X-ray penetration depth based on the theories of diffraction to quantitatively characterize the heterogeneous functional materials with core-shell morphology. Functional materials viz. Ni@stabilized ZrO₂ (SZ) and NiO@NiO–Zn are synthesized and penetration depth (ξ_Ni/ξ_NiO) is calculated. Ni@SZ and NiO@NiO–Zn function as effective catalyst for methane steam reformation and olefin epoxidation respectively. Functionality of the catalysts lies in the core-shell morphology with interconnection among the phases. The author's aim to optimize the shell thickness using the mathematical model and correlate with the catalyst activity. Sequential increase of Ni-content in Ni@SZ from 25 to 40 vol % results in reduction of penetration depth [~2.1 to 0.8 μm] relative to core (ξ_SZ-core) thereby restricting the SZ contribution and limiting the oxide ion percolation. Similarly, surface coverage of nano NiO onto NiO–Zn for olefine epoxidation requires the involvement of three zone region viz. NiO, Zn and pi electron cloud of the substrate. Effectivity of the catalytic activity of such NiO@NiO–Zn matrix is found optimum (4.3 μm w.r.t.ξ_NiO) with the penetration depth derived from mathematical modeling. Hence, such modeling reveals its significance towards finding the penetration depth for core-shell type functional materials for catalysis compared to disperse heterogeneous catalyst.