XPS AND EPR STUDY OF HIGH AND LOW SURFACE-AREA COO-MGO SOLID-SOLUTIONS - SURFACE-COMPOSITION AND CO2+ ION DISPERSION

Solid solutions CoO-MgO (MCo) of low and high surface area (LSA and HS A) have been studied by XPS and EPR analysis to evaluate the surface c omposition and the dispersion of cobalt ions in the systems. Different preparation routes were adopted: wet impregnation (I-w), dry impregna tion (I-d) and coprecipitation (C). LSA solid solutions (A(s) = 10-20 m(2) g(-1)) were obtained after treatment in air at 1173 K (1173 LSA) or at 1473 K (1473 LSA), HSA materials (A(s) = 200-300 m(2) g(-1)) aft er treatment under vacuum at 1173 (1173 HSA). XPS intensity ratios, I- Co/I-Mg vs. x(Co)/x(Mg) molar fraction showed no appreciable differenc es between the bulk and surface compositions of LSA and HSA solid solu tions from I-d and C precursors, calcined at 1173 and at 1473 K. MCo 1 173 LSA I-w samples had evident cobalt enrichment, due to Co3O4 segreg ation, whereas I-w HSA did not. NO2 or O-2 treatments led to the forma tion of Co-III. The Co2+ bulk dispersion in LSA and HSA was studied by EPR.