Influence of Ni substitution on redox properties of In_(2(1-x)) Ni_(2x)TiO_(5-δ) oxides

摘要

The thermal behavior of mixed metal oxides with nominal compositions of In_(2(1-x))Ni_(2x)TiO_(5-δ) where 0.0 ≤ x ≤ 0.2, were investigated by recording their temperature programmed reduction (TPR). The samples were synthesized by ceramic route and analyzed for phase composition using powder X-ray diffraction. The TPR profile of pristine In _2TiO_5 indicated the reduction of In~(3+), which takes place predominantly over the other species Ti~(4+) in In _2TiO_5 sample. Ni substitution at In~(3+) site induced ease in reducibility as indicated by lowering of onset reduction temperature and T_(max). Moreover, it also facilitated the reduction of otherwise non reducible cation, Ti~(4+). Ni metal initially formed by reduction, dissociates and activates hydrogen which then reacts and reduces the oxide (even Ti~(4+)), a case of hydrogen spillover. The metallic Ni forms an alloy Ti_2Ni with reduced Ti metal and δIn _3Ni_2 alloy with the reduced In metal as evident by XRD and XPS results of the reduced residue of 20% Ni doped (In_(1.6)Ni _(0.4)TiO_(5-δ)) sample. Due to formation of new alloy phases of δIn_3Ni_2 and Ti_2Ni, the rate of hydrogen adsorption diminishes which slows down further hydrogen activation and consequent further Ti~(4+) reduction.