Zirconia Aerogels and Catalysis

Kalies et al. [34] studied the hydrogenation of formate species on a Pt-zirconia aerogel catalyst. Zirconia was synthesized by the hydrolysis of a solution of zirconium isopropylate in isopropanol. The solvent was evacuated by SCD. Zirconia was further impregnated with a solution of hexachloroplatinic acid in isopropanol to obtain a 0.5 wt% loading of Pt. The Pt-impregnated zirconia was then dried under supercritical isopropanol 

Phosphate ions were also used to increase acidity on the surface of zirconia aerogel. Boyse et al. [40] prepared zirconia-phosphate aerogels by two methods a one-step sol-gel synthesis followed by SCD and an incipient wetness impregnation synthesis of a calcined zirconia aerogel. They reported that zirconia-phosphate aerogels possess Bronsted acid sites, and the phosphate species were claimed to be responsible of their generation. 

Studies focusing on the use of sulfated zirconia have shown that reaction taking place at the strong acid sites also needs the metallic phase such as platinum for buming-off coke produced over sulfated zirconia, stabilizing the reaction intermediates of the isomerization. 

Characterization by XF5 indicates that the loss of sulfur at higher temperature is easier for the xerogel. The ability of the aerogel AZS0.5H3 to retain sulfur at higher temperature explains its better stability and confers it good catalytic performances in the -hexane isomerization reaction (Table 6.1). 

TabIS 6.1. Activity (10 mol g s ) of AZS0.5H3 and XZS0.5H3 in n-hexane isomerization 

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