Title : Oxyhydride perovskites: From characterization to reactivity study
Abstract:
Oxyhydride perovskites adapt to either conventional ABX3 or Ruddlesden-Popper A2 BX4 structures where both anions H- and O2- are accommodated in one frame work. In ABX3 , hydride anions can substitute O2- in any sites of the BO6 octahedron, while the figure for A2 BO4 is slightly different. Hydride partially occupies the axial positions of octahedral O2- sites only along b-direction of the BO2 planar square, which may result in the filling of anionic sites by H- , O2- or vacancies. The presence of hydride species in the structures result in intriguing characteristics: high Neel temperature observed in Crand Co-based oxyhydride perovskites; lability of hydrides in BaTi(OH)3 allows to synthesis oxynitrides at significantly milder conditions; hydride intercalation may alter crystallinity or unusual oxidation states of transition metals in the oxyhydride perovskites. Moreover, hydride mobility in the structures was evidenced, which leads to potential applications of oxyhydrides in catalysis. In the presentation, two oxyhydride perovskites LaSrCoO3.5-xHy (y-x £ 0.5) and BaTiO3-xHx bearing Ruddlesden- Popper A2 BX4 and ABX3 structures, respectively, will be discussed in term of their topochemical synthesis, perovskite structures and properties. Moreover, various techniques of oxyhydride perovskites characterizations will be deeply mentioned. For example, X-Ray diffraction, magnetic measurements, Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric mass spectroscopic (TGA-MS), X-ray photoelectron spectroscopy (XPS) and H2 -temperature programmed reduction (H2 -TPR). The work will also show different levels of thermal stability of these oxyhydride under oxidative/reducing conditions, which were studied by in situ XRD and H2 -TPR techniques. Interactions of hydrides with supports lead to questions about possible reactivity of oxyhydrides towards hydro-related reactions. Reactivity of the oxyhydrides LaSrCoO3.5-xHy and BaTiO3-xHx forwards to hydrogenation reactions will be also discussed. The work may open some the reactive potentiality of oxyhydrides for other reactions and applications.
