Sol–gel preparation of alumina stabilized rare earth areo- and xerogels and their use as oxidation catalysts

• We prepared mixed Ce/Al and Pr/Al hybrid oxide aero- and xerogels using cheap metal salt precursors.
• All hybrid gels were tested as oxidation catalysts in a tube reactor and in a microreactor.
• The catalytic properties of Ce/Al gels are in line with ceria nanodomains in a alumina matrix.
• Ce/Al aero- and xerogels show improved sinter stability in comparison to pure ceria.

A new sol–gel synthesis route for rare earth (Ce and Pr) alumina hybrid aero- and xerogels is presented which is based on the so-called epoxide addition method. The resulting materials are characterized by TEM, XRD and nitrogen adsorption. The results reveal a different crystallization behavior for the praseodymia/alumina and the ceria/alumina gel. Whereas the first remains amorphous until 875° C, small ceria domains form already after preparation in the second case which grow with increasing calcination temperature. The use of the calcined gels as CO oxidation catalysts was studied in a quartz tube (lab) reactor and in a (slit) microreactor and compared to reference catalysts consisting of the pure rare earth oxides. The Ce/Al hybrid gels exhibit a good catalytic activity and a thermal stability against sintering which was superior to the investigated reference catalyst. In contrast, the Pr/Al hybrid gels show lower CO oxidation activity which, due to the formation of PrAlO3, decreased with increasing calcination temperature.

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