ELECTRONIC-STRUCTURE, REACTIVITY AND SOLID-STATE CHEMISTRY OF LA2-XSRXNI1-YFEYO4+DELTA

Ceramic samples of La2-xSrxNi1-yFeyO4+delta, designed to model the ICI Hydecat catalyst, have been prepared via precipitation followed by hi gh temperature annealing. The samples are characterized by X-ray diffr action, EDAX and atomic absorption spectrometry. The small changes in electronic structure as a function of x and y have been probed using p hotoemission. This reveals a progressive shift of the valence-band edg e towards the Fermi level as a function of Sr-doping level, consistent with the approach to a metal to non-metal transition. Resonant photoe mission at the Fe and Ni 3p thresholds is used to identify the transit ion metal contributions to the valence band density of states, and con firms a valence state of greater than or equal to 3.0 for Fe. High res olution ESCA is used to quantify the surface composition of the sample s, revealing Sr segregation consistent with that found in related pero vskites and layered perovskites. Adsorption of CO onto the surfaces of these materials is seen to give rise to the ready production of a car bonate species. Water adsorption studies, which test the potential sta bility of the materials for possible applications in aqueous solution, are also presented.