Iridium dispersion control in Ir/Al2O3–SiO2 catalysts by calcination temperature using chloroiridic acid as catalyst precursor

The pre‐treatment effect on the metallic accessibility on the Ir/modified-alumina by silica was evaluated. Catalysts were prepared by impregnation with H2IrCl6 as the Ir metal precursor. After ionic exchange, impregnated supports were calcined in oxygen flow at various temperatures followed by reduction in hydrogen flow. When the supported precursor was calcined and then reduced, Ir dispersion was not affected by the reduction temperature but depended heavily on the calcination temperature, ranging widely from 9 to 80%. A good correlation was observed between the particle size estimated from CO chemisorption and that seen with a transmission electron microscope. Furthermore, it was found that calcination at the temperature at which IrCl2 is stable gives the highest Ir dispersion. X‐ray fluorescence analysis of the calcined samples confirmed IrCl2 formula. High Ir accessibility after calcination at optimum temperature was also demonstrated with X‐ray diffraction analysis from the absence of sharp diffraction peaks. The results suggest that encouraging formation and redispersion of IrCl2 caused high Ir dispersion.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Ir dispersion of Ir/Al2O3–SiO2 depends profoundly on the calcination temperature. ► High dispersion of Ir catalysts obtained after calcination at 450 °C and reduction. ► Modified-alumina ensures higher Ir dispersion than alumina support.