Cambridge researchers think they’ve figured out a way to improve the efficiency of ammonia synthesis process, research which could have wide-reaching implications in the agricultural and energy sector.
Ammonia is currently produced from natural gas via the Haber (or Haber-Bosch) process, but researchers from the University of Cambridge think they’ve devised a more efficient process using ultra high vacuum (uhv) conditions.
“The Haber-Bosch process was developed in the early twentieth century but little has changed since that time,” said Dr Steve Jenkins from the department of chemistry, “Clearly, given the massive scale of worldwide ammonia production, even a tiny improvement in the efficiency of the ammonia synthesis process can have massive implications, not only for the economics of fertiliser production, but also for global energy demand.”
“The surface science approach uses single-crystal iron samples of high purity, and typically involves experiments carried out under uhv conditions (i.e. pressures less than one millionth of a millionth of an atmosphere,” Jenkins continued, “We have conducted experiments that combine some of the attractive features of single-crystal uhv surface science with those of higher pressure techniques.”
Researchers exposed an iron sample to nitrogen to build up coverage of nitrogen atoms on the surface – one atom per two top-layer iron atoms at the surface. Under uhv conditions, they quantified nitrogen coverage using Auger Electron spectroscopy (AES) before exposing the sample to 0.6mbar H2 gas for several minutes – a much lower pressure than used in industrial processes which allows the reaction to proceed rapidly enough for researchers to take meaningful measurements over a timescale of minutes.
Researchers work episodically, exposing the sample to cycles of AES and uhv and measuring the drop in surface nitrogen and so the corresponding production of ammonia as a function of time and temperature.
“Our results suggest, that under certain conditions – namely when the ammonia pressure is kept low – the hydrogenation steps (from N to NH to NH2 to NH3) may actually be the most important,” said Professor Sir David King.
The Haber-Bosch process
The Haber process was developed by German chemist Fritz Haber in 1909 who sold the process to chemical company BASF. They assigned Carl Bosch to scale it up to an industrial process. Haber was awarded the Nobel Prize in 1918, with Bosch receiving one in 1931, for their work on overcoming the chemical and engineering problems posed by ammonia production.