The unusual physical properties of aerogels – including high surface area, low density and ability to withstand high temperatures – render these materials attractive for applications in heterogeneous catalysis. In this work, cerium-copper-silica (Ce-Cu-Si) and cerium-copper-alumina (Ce-Cu-Al) aerogels were prepared and characterized. Silica wet gels were prepared via a tetraethyl orthosilicate (TEOS) based recipe, using oxalic acid to catalyze hydrolysis and ammonia to catalyze gelation. Alumina wet gels were fabricated from aluminum chloride hexahydrate through an epoxide-assisted reaction. These silica and alumina gels were impregnated with cerium (III) and copper (II) during an ethanol solvent-exchange step, with molar ratios of 75:25, 50:50 and 25:75 Ce:Cu employed. The resulting mixed-metal gels were then placed in a contained mold held within the platens of a hydraulic hot press and processed via rapid supercritical extraction to yield aerogels. The aerogels were calcined at 800 C and characterized using a variety of physical and spectroscopic methods. Bulk densities are in the range 0.083 to 0.098 g/mL. Observed variations in color of the gels during processing and heat treatment are indicative of changes in ligand structure and speciation of Ce and Cu. The aerogels are predominantly amorphous; however, XRD identified microcrystalline regions within the aerogel matrices. Ce-Cu-Si aerogels include small peaks attributable to CuO and several peaks that indicate the presence of Ce(IV). XRD plots for Ce-Cu-Al aerogels demonstrate the presence of gamma-alumina and Ce(IV). The aerogels in this study were subjected to catalytic characterization using an in-house-constructed catalytic testbed. Aerogels were exposed to a mixture of propane, NO and CO and conversion was measured. Ce-Cu-Si and Ce-Cu-Al aerogels show promise as three-way catalysts.

Fabrication and characterization of cerium-copper-silica and cerium-copper-alumina catalytic aerogels

256th National Meeting (2018)

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