Determination of chromium in catalysts by ultraviolet/visible spectrophotometry

Abstract

Instrumental neutron-activation analysis (INAA), atomic absorption spectrometry (AAS) and ultraviolet/visible (UV/VIS) spectrophotometry were applied as independent methods to the determination of chromium in Phillips-type polymerization catalysts. Catalysts were prepared in the gas phase, using chromium oxychloride vapour as the adsorbate and silica as the support. From freshly prepared catalysts, chromium was quantitatively brought into solution with de-ionized water, enabling its rapid determination as chromate by UV/VIS spectrophotometry. The use of INAA and AAS in addition to UV/VIS spectrophotometry allowed the quantitative nature of the release of chromium from silica with de-ionized water to be verified, the accuracy of the chromium determination to be checked and the speciation of chromium between the oxidation states +3 and +6 to be determined.