Determination of chromium and titanium in silica-based catalysts by ultraviolet/visible spectrophotometry

Abstract

Samples were prepared by different methods, for determination by ultraviolet/visible (UV/VIS) spectrophotometry, of chromium and titanium in silica-based catalysts prepared by saturating gas–solid reactions of titanium tetrachloride and tris(acetylacetone)chromium. Chromium was determined in basic solution as chromate and titanium in acidic solution as its peroxy complex. Chromium(III) was oxidized to chromium(VI) either in concentrated sodium hydroxide solution with hydrogen peroxide, or by heating in air at 400 °C. The latter method enabled the chromium to be leached with de-ionized water without decomposition of the silica. Depending on the reaction temperature used in the catalyst preparation, titanium was released either by decomposing the silica in concentrated sodium hydroxide solution or by leaching with dilute sulfuric acid. Comparison with chromium determinations by atomic absorption spectrometry, and titanium determinations by instrumental neutron activation analysis, demonstrated the quantitative nature of the determinations by UV/VIS spectrophotometry and confirmed the efficiency of concentrated sodium hydroxide solution in bringing titanium and chromium into solution. Because the exact history of the preparation of the catalyst was known, the determinations could be simplified and the chromium and titanium species on silica be characterized by means of different sample preparations.