Aerogel 5 - Development of catalytic chromia-based aerogels

Over one billion automobiles are in use around the world, the majority of which employ internal combustion engines. Catalytic converters are used to convert the toxic compounds found in car exhaust -- carbon monoxide, nitrogen oxides (NOx) and hydrocarbons -- to less harmful gases. The typical catalytic converter employs, as three-way catalysts, expensive raw materials such as platinum, palladium and/or rhodium. Aerogel materials have high surface area and thermal stability, properties that make them attractive for catalysis applications. Aerogels made with transition metal oxides (TMOs) are candidates to replace platinum in the catalytic converter. Chromium oxide (chromia) materials have demonstrated catalytic activity in other applications due to favorable redox chemistry, stability and selectivity. In this work, sol-gel synthesis techniques, using a 1:5 mole ratio of chromium(III) to aluminum, are adapted to a patented rapid supercritical extraction (RSCE) method to fabricate chromia-alumina catalytic aerogels. Physical characterization via several methods, including XRD and SEM, is performed on the chromia-alumina aerogels as prepared and following heat treatment. Catalytic performance of these promising materials is evaluated using an in-house-constructed testbed in which the aerogel materials are exposed to simulated automotive exhaust under temperature conditions that approximate those experienced in a catalytic converter. Initial tests demonstrate that chromia-alumina aerogels act as three-way catalysts.