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Better Catalyst to Reduce NOx Emissions

A UConn team is developing a novel device aimed at improving the performance, durability and cost of automotive emission reduction equipment in both heavy- and light-duty vehicles. Dr. Gao, an assistant professor in the CMBE Department and the Institute of Materials Science specializing in nano-materials, leads the project team, which includes colleagues Drs. Pamir Alpay and Ramamurthy Ramprasad – who bring expertise in thin film and computational materials, and Dr. Christopher Brooks of the Honda Research Institute, a principal scientist and emissions control expert.

With $1.25 million in support from the U.S. Department of Energy/National Energy Technology Lab, the researchers intend to develop a new class of oxide-based three-dimensional (3D) composite nanocatalysts that may be used in nitrogen oxide (NOx) storage and reduction, hydrocarbon and carbon monoxide (CO) oxidation, and particulate matter filtering under lean burn conditions.

NOx, CO and hydrocarbons, which are regulated by the EPA, contribute to the formation of ground-level ozone and smog. They are also associated with global climate change and contribute to the formation of particulates, which may lead to breathing difficulties, especially in people with asthma.

According to an EPA report, in 2005 motor vehicles contributed an estimated 6.5 million tons of NOx in the U.S. alone. Non-road equipment and electricity generation contributed nearly 8 million tons of NOx the same year. The automotive and fuel industries are keenly interested in reducing NOx emissions. This year, for example, GE researchers – partnering with Tenneco Inc. and Umicore – developed a new catalyst for the after-treatment reduction of emissions from diesel engines.

The team intends to build a better catalytic converter.

Catalytic converters are located in an automobile’s exhaust system and process exhaust gases before they are vented through the tailpipe. Conventional converters, explained Dr. Gao, are efficient at oxidizing carbon monoxide (CO) and hydrocarbons (HC) into carbon dioxide and water when operating in so-called “lean” (oxygen-rich) conditions. However, while they are well suited for CO and HC reduction, lean conditions actually prevent current catalytic converters from also reducing NOx efficiently.

Another challenge for the researchers is to simplify and unify the current emission reduction technology – comprising an array of emission control devices laid out sequentially at different places within the converter – into a single unit. The single multi-functional, 3D nanostructured composite catalyst the team envisions will allow CO/HC oxidation, NOx reduction, and particulate filtering to take place within one unit.

Dr. Gao and his colleagues also aim to reduce the cost of materials and to enhance the durability of the catalyst, which is an ongoing challenge due to the harsh environment – characterized by high temperature, high-velocity exhaust gas flow, etc. – within the converter as it works to clean the exhaust. Current catalytic converters rely heavily on costly platinum and palladium; the researchers aim to either replace these precious metals with oxide-based composite nanomaterials or to reduce the amount needed in the nano-catalyst.

The team has carried out a range of synthesis, characterization, and modeling activities since the start of the project in October 2009. Three-dimensional oxide-based composite nano-architectures are being rationally designed and fabricated using a combination approach including vapor and solution phase deposition methods. In addition, the team is employing various metal doping/loading methodologies to form a new class of lean NOx emission control catalysts as either lean NOx catalysts or lean NOx trapping absorbents, with the intent to reduce the noble metal usage in the catalyst, therefore reducing the total unit cost.

“Our nanocatalyst technology sees beyond current technologies and will, we hope, offer the next generation of automotive catalysts used in the near future,” remarked Dr. Gao.