Detection and quantitative determination of the composition of bismuth molybdate phases by various spectroscopic techniques

Abstract

Mixtures of three bismuth molybdate phases α, β and γ have been prepared by mechanical mixing or impregnation procedures and studied by u.v.-vis, i.r. and Raman spectroscopies. A quantitative determination of the composition of such mixtures has ben established for the three techniques starting from mixtures of known composition. By extension the technique was used for unknown mixtures prepared either by impregnation and calcination or by solid state reaction with MoO₃ at 550 °C. The technique holds true for binary but not ternary mixtures as the samples are calcined in air at 480 °C prior to the analysis in order to avoid such side effects as ageing in air or partial reduction under catalytic reaction conditions. The detection limit was determined experimentally to equal ca. 3 % for α and β in the γ phase, for both i.r. and Raman spectroscopies. For impregnated γ phase samples at low additional Mo content the presence of some amount of β phase was postulated from u.v.-vis and i.r. data.