Researchers from the University of Strathclyde and the University of St. Andrews have demonstrated that ammonia can be synthesized directly from air (instead of N2) and H2O (instead of H2) under a mild condition (room temperature, one atmosphere) with supplied electricity which can be obtained from renewable resources such as solar, wind or marine. In addition to providing a less carbon-intensive pathway for ammonia, their process could also reduce the pressure on renewable energy storage, they note.
Their paper appears in Scientific Reports, the open access journal from the Nature Publishing Group.
Globally 131 million tons of ammonia were produced in 2010. The dominant ammonia production process is the Haber-Bosch process invented in 1904 which requires high temperature (~500°C) and high pressure (150-300 bar), in addition to efficient catalysts. Natural gas or coal is used as the energy source of the ammonia industry. 1.87 tons of CO2 is released per ton of ammonia produced. Globally 245 million tons of CO2 were released by the ammonia industry in 2010 equivalent to about 50% of the UK CO2 emissions (495.8 million tons) in that year. In the Haber-Bosch process, the presence of ppm level oxygen may poison the commonly used Fe-based catalysts. In industry, extensive purification of N2 and H2 is needed and this remarkably increases the overall cost of the process. Therefore researchers have been seeking a simpler way for synthesis of ammonia from nitrogen separated from air.
...It is well known that some higher plants can synthesize ammonia or its derivatives directly from air and water at room temperature. The ammonia produced by plants is normally directly used as fertilizer by the plants. To the best of our knowledge, there is no report on artificial synthesis of ammonia direct from air and water. It has been a dream for researchers who can imitate this natural process to synthesize ammonia under similar conditions.
...In most reports, H2 and N2 were commonly used as precursors for electrochemical synthesis of ammonia while H2 production and N2 separation are essential. H2 production can be bypassed if H2O was used as a precursor; however, the reaction between H2O and N2 to form ammonia is thermodynamically non-spontaneous under normally pressure; however, this can be achieved through electrochemical process because the applied voltage provides extra driving force.
-Lan et al.
In their study, they first fabricated an electrochemical cell for ammonia synthesis. H2 (or water) and N2 (or air) were passed through room temperature water first then filled into the chambers of the cell. The DC potential was applied by a Solartron 1470A electrochemical interface controlled by software for automatic data collection.
A maximum ammonia production rate of 1.14 √ó 10‚àí5 mol m‚àí2 s‚àí1 was achieved when a voltage of 1.6 V was applied. Potentially, this can provide an alternative route for the mass production of the basic chemical ammonia under mild conditions, they concluded.
Resources
Rong Lan, John T. S. Irvine & Shanwen Tao (2013) Synthesis of ammonia directly from air and water at ambient temperature and pressure. Scientific Reports 3, Article number: 1145 doi: 10.1038/srep01145
http://www.greencarcongress.com/2013/01/ammonia-20130130.htm
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