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Catalysts to Cut N2O Emissions
July 1, 2009   
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Nitrous oxide (N2O) can be a much more significant contributing factor to the greenhouse effect than carbon dioxide (CO2), and it can also damage the ozone layer which protects the earth from harmful UV rays. Polish scientists have developed a method to prevent the formation of N2O, which is an undesirable side effect of nitric acid production.

One way to reduce N2O emissions is to place a catalyst for high-temperature decomposition of N2O in an ammonia oxidation reactor, the scientists say. The catalyst has been invented by researchers from the Fertilizers Research Institute in Puławy southeast of Warsaw. Together with chemists from the Jagiellonian University in Cracow, the Puławy researchers have also developed a catalyst for low-temperature N2O decomposition.

Saving the ozone layer
Marcin Wilk, D.Sc., from the Fertilizers Research Institute, says N2O is produced along with other nitrogen oxides when ammonia is oxidized on meshes made of platinum alloys. The reaction occurs at a temperature of 800-940 degrees Celsius. Ammonia oxidation is the first phase of nitric acid production. N2O is harmless at ground level and in the troposphere, but it gradually diffuses to the stratosphere and becomes active there. It is a greenhouse gas that absorbs infrared rays 310 times faster than carbon dioxide (CO2). Although the total amount of N2O worldwide is not considerable, Wilk says, the gas produces a significant effect. Moreover, UV rays in the stratosphere break N2O down into nitric oxide (NO) and oxygen atoms which react with ozone. In this way, N2O contributes to the ozone hole.

In industry, N2O is mostly released from installations producing nitric acid. “Catalysts for N2O removal can be located in two places in such installations,” says Wilk. “First, the gas can be decomposed in the high-temperature zone (800-940ºC), which is the ammonia oxidation reactor. The other option is the low-temperature zone (200-450ºC) in the tail gas stream.”

The high-temperature catalyst in the ammonia oxidation reactor is used right below the catalytic mesh of platinum alloys. The catalyst contains iron (III) oxide (Fe2O3) as the base active component; aluminum oxide (Al2O3) as the binding and form-giving component; and admixtures to increase the catalyst’s activity and mechanical durability. The raw material used to produce the catalyst is iron sulfate, a by-product in the chemical industry and metallurgy. The use of the high-temperature catalyst in the ammonia oxidation reactor makes it possible to reduce N2O emissions by over 90 percent, while the amount of NO remains unchanged.

The low-temperature catalyst, in turn, is used in a special reactor through which hot tail gases flow before they are decompressed in an expansion turbine. The catalyst works in temperatures below 350 degrees Celsius. This catalyst is quite simple in its chemical composition, the scientists say; it contains no noble metals and is highly active and resistant to inhibitors (substances that decrease chemical activity) which the tail gases contain. It allows an N2O decomposition rate of over 90 percent. Raw materials to produce the low-temperature catalyst are cheap and easily available, the scientists say.


High and Low

The high-temperature catalyst was developed at the Fertilizers Research Institute in Puławy by Marcin Wilk; Janusz Kruk, Ph.D.; and Andrzej Gołębiowski, D.Sc. The low-temperature catalyst was built by a team made up of Prof. Zbigniew Sojka and Andrzej Kotarba, Ph.D., of the Faculty of Chemistry of the Jagiellonian University in Cracow; and Marcin Wilk and Marek Inger, M.Sc., from the Fertilizers Research Institute.

The high-temperature catalyst has been applied in two nitric acid installations in Poland. Work is also under way to use the low-temperature catalyst on an industrial scale.

The high-temperature catalyst won a silver medal at the 56th Brussels-Eureka World Exhibition of Innovation, Research and New Technology in 2007 and another silver at the IWIS 2007 First International Warsaw Invention Show.

The low-temperature catalyst won a gold medal at the IWIS 2008 Second International Warsaw Invention Show and a bronze medal at the Brussels-Eureka event.

Both catalysts also won gold medals at the 37th International Exhibition of Inventions, New Technology and Products in Geneva, Switzerland, in April this year.

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